feat: static variable analysis (#770)

* feat: static variable analysis

* Accept any iterable from `children`, `arguments`, etc.

* Test analysis of standard tags

* Use `TagToken.tokenizer` instead of creating a new one

* Test analysis of netsted tags

* Group variables by their root value

* Test analysis of nested globals and locals

* Analyze included and rendered templates WIP

* Use existing tokenizer when constructing `Hash`

* Improve test coverage

* Analyze variables from `layout` and `block` tags

* Test analysis of Jekyll style includes

* Handle variables that start with a nested variable

* Async analysis

* Test non-standard tag end to end

* Implement convenience analysis methods on the `Liquid` class

* More analysis convenience methods

* Accept string or template array

* Draft static analysis docs

* Deduplicate variables names

* Fix isolated scope global variable map

* Coerce variables to strings instead of extending String

* Private map instead of extending Map

* Fix e2e test

* Tentatively implement analysis of aliased variables

* Fix nested variable segments array

* Update docs sidebar

docs/source/_data/sidebar.yml

@@ -20,6 +20,7 @@ tutorials:
     operators: operators.html
     truth: truthy-and-falsy.html
     dos: dos.html
+    static_analysis: static-analysis.html
   miscellaneous:
     migration9: migrate-to-9.html
     changelog: changelog.html

docs/source/tutorials/static-analysis.md

@@ -0,0 +1,286 @@
+---
+title: Static Template Analysis
+---
+
+{% since %}v10.20.0{% endsince %}
+
+{% note info Sync and Async %}
+There are synchronous and asynchronous versions of each of the methods demonstrated on this page. See the [Liquid API](liquid-api) for a complete reference.
+{% endnote %}
+
+## Variables
+
+Retrieve the names of variables used in a template with `Liquid.variables(template)`. It returns an array of strings, one string for each distinct variable, without its properties.
+
+```javascript
+import { Liquid } from 'liquidjs'
+
+const engine = new Liquid()
+
+const template = engine.parse(`\
+<p>
+  {% assign title = user.title | capitalize %}
+  {{ title }} {{ user.first_name | default: user.name }} {{ user.last_name }}
+  {% if user.address %}
+    {{ user.address.line1 }}
+  {% else %}
+    {{ user.email_addresses[0] }}
+    {% for email in user.email_addresses %}
+       - {{ email }}
+    {% endfor %}
+  {% endif %}
+  {{ a[b.c].d }}
+<p>
+`)
+
+console.log(engine.variablesSync(template))
+```
+
+**Output**
+
+```javascript
+[ 'user', 'title', 'email', 'a', 'b' ]
+```
+
+Notice that variables from tag and filter arguments are included, as well as nested variables like `b` in the example. Alternatively, use `Liquid.fullVariables(template)` to get a list of variables including their properties as strings.
+
+```javascript
+// continued from above
+engine.fullVariables(template).then(console.log)
+```
+
+**Output**
+
+```javascript
+[
+  'user.title',
+  'user.first_name',
+  'user.name',
+  'user.last_name',
+  'user.address',
+  'user.address.line1',
+  'user.email_addresses[0]',
+  'user.email_addresses',
+  'title',
+  'email',
+  'a[b.c].d',
+  'b.c'
+]
+```
+
+Or use `Liquid.variableSegments(template)` to get an array of strings and numbers that make up each variable's path.
+
+```javascript
+// continued from above
+engine.variableSegments(template).then(console.log)
+```
+
+**Output**
+
+```javascript
+[
+  [ 'user', 'title' ],
+  [ 'user', 'first_name' ],
+  [ 'user', 'name' ],
+  [ 'user', 'last_name' ],
+  [ 'user', 'address' ],
+  [ 'user', 'address', 'line1' ],
+  [ 'user', 'email_addresses', 0 ],
+  [ 'user', 'email_addresses' ],
+  [ 'title' ],
+  [ 'email' ],
+  [ 'a', [ 'b', 'c' ], 'd' ],
+  [ 'b', 'c' ]
+]
+```
+
+### Global Variables
+
+Notice, in the examples above, that `title` and `email` are included in the results. Often you'll want to exclude names that are in scope from `{% assign %}` tags, and temporary variables like those introduced by a `{% for %}` tag.
+
+To get names that are expected to be _global_, that is, provided by application developers rather than template authors, use the `globalVariables`, `globalFullVariables` or `globalVariableSegments` methods (or their synchronous equivalents) of a `Liquid` class instance.
+
+```javascript
+// continued from above
+engine.globalVariableSegments(template).then(console.log)
+```
+
+**Output**
+
+```javascript
+[
+  [ 'user', 'title' ],
+  [ 'user', 'first_name' ],
+  [ 'user', 'name' ],
+  [ 'user', 'last_name' ],
+  [ 'user', 'address' ],
+  [ 'user', 'address', 'line1' ],
+  [ 'user', 'email_addresses', 0 ],
+  [ 'user', 'email_addresses' ],
+  [ 'a', [ 'b', 'c' ], 'd' ],
+  [ 'b', 'c' ]
+]
+```
+
+### Partial Templates
+
+By default, LiquidJS will try to load and analyze any included and rendered templates too.
+
+```javascript
+import { Liquid } from 'liquidjs'
+
+const footer = `\
+<footer>
+  <p>&copy; {{ "now" | date: "%Y" }} {{ site_name }}</p>
+  <p>{{ site_description }}</p>
+</footer>`
+
+const engine = new Liquid({ templates: { footer } })
+
+const template = engine.parse(`\
+<body>
+  <h1>Hi, {{ you | default: 'World' }}!</h1>
+  {% assign some = 'thing' %}
+  {% include 'footer' %}
+</body>
+`)
+
+engine.globalVariables(template).then(console.log)
+```
+
+**Output**
+
+```javascript
+[ 'you', 'site_name', 'site_description' ]
+```
+
+You can disable analysis of partial templates by setting the `partials` options to `false`.
+
+```javascript
+// continue from above
+engine.globalVariables(template, { partials: false }).then(console.log)
+```
+
+**Output**
+
+```javascript
+[ 'you' ]
+```
+
+If an `{% include %}` tag uses a dynamic template name (one that can't be determined without rendering the template) it will be ignored, even if `partials` is set to `true`.
+
+### Advanced Usage
+
+The examples so far all use convenience methods of the `Liquid` class, intended to cover the most common use cases. Instead, you can work with [analysis results](static-analysis-interface) directly, which expose the row, column and file name for every occurrence of each variable.
+
+This is an example of an object returned from `Liquid.analyze()`, passing it the template from the [Partial Template](#partial-templates) section above.
+
+```javascript
+{
+  variables: {
+    you: [
+      [String (Variable): 'you'] {
+        segments: [ 'you' ],
+        location: { row: 2, col: 14, file: undefined }
+      }
+    ],
+    site_name: [
+      [String (Variable): 'site_name'] {
+        segments: [ 'site_name' ],
+        location: { row: 2, col: 41, file: 'footer' }
+      }
+    ],
+    site_description: [
+      [String (Variable): 'site_description'] {
+        segments: [ 'site_description' ],
+        location: { row: 3, col: 9, file: 'footer' }
+      }
+    ]
+  },
+  globals: {
+    you: [
+      [String (Variable): 'you'] {
+        segments: [ 'you' ],
+        location: { row: 2, col: 14, file: undefined }
+      }
+    ],
+    site_name: [
+      [String (Variable): 'site_name'] {
+        segments: [ 'site_name' ],
+        location: { row: 2, col: 41, file: 'footer' }
+      }
+    ],
+    site_description: [
+      [String (Variable): 'site_description'] {
+        segments: [ 'site_description' ],
+        location: { row: 3, col: 9, file: 'footer' }
+      }
+    ]
+  },
+  locals: {
+    some: [
+      [String (Variable): 'some'] {
+        segments: [ 'some' ],
+        location: { row: 3, col: 13, file: undefined }
+      }
+    ]
+  }
+}
+```
+
+### Analyzing Custom Tags
+
+For static analysis to include results from custom tags, those tags must implement some additional methods defined on the [Template interface]( /api/interfaces/Template.html). LiquidJS will use the information returned from these methods to traverse the template and report variable usage.
+
+Not all methods are required, depending in the kind of tag. If it's a block with a start tag, end tag and any amount of Liquid markup in between, it will need to implement the [`children()`](/api/interfaces/Template.html#children) method. `children()` is defined as a generator, so that we can use it in synchronous and asynchronous contexts, just like `render()`. It should return HTML content, output statements and tags that are child nodes of the current tag.
+
+The [`blockScope()`](/api/interfaces/Template.html#blockScope) method is responsible for telling LiquidJS which names will be in scope for the duration of the tag's block. Some of these names could depend on the tag's arguments, and some will be fixed, like `forloop` from the `{% for %}` tag.
+
+Whether a tag is an inline tag or a block tag, if it accepts arguments it should implement [`arguments()`](/api/interfaces/Template.html#arguments), which is responsible for returning the tag's arguments as a sequence of [`Value`](/api/classes/Value.html) instances or tokens of type [`ValueToken`](/api/types/ValueToken.html).
+
+This example demonstrates these methods for a block tag. See LiquidJS's [built-in tags](built-in) for more examples.
+
+```javascript
+import { Liquid, Tag, Hash } from 'liquidjs'
+
+class ExampleTag extends Tag {
+  args
+  templates
+
+  constructor (token, remainTokens, liquid, parser) {
+    super(token, remainTokens, liquid)
+    this.args = new Hash(token.tokenizer)
+    this.templates = []
+
+    const stream = parser.parseStream(remainTokens)
+      .on('tag:endexample', () => { stream.stop() })
+      .on('template', (tpl) => this.templates.push(tpl))
+      .on('end', () => { throw new Error(`tag ${token.getText()} not closed`) })
+
+    stream.start()
+  }
+
+  * render (ctx, emitter) {
+    const scope = (yield this.args.render(ctx))
+    ctx.push(scope)
+    yield this.liquid.renderer.renderTemplates(this.templates, ctx, emitter)
+    ctx.pop()
+  }
+
+  * children () {
+    return this.templates
+  }
+
+  * arguments () {
+    yield * Object.values(this.args.hash).filter((el) => el !== undefined)
+  }
+
+  blockScope () {
+    return Object.keys(this.args.hash)
+  }
+}
+```
+
+[liquid-api]: /api/classes/Liquid.html
+[static-analysis-interface]: /api/interfaces/StaticAnalysis.html
+[built-in]: https://github.com/harttle/liquidjs/tree/master/src/tags

docs/themes/navy/languages/en.yml

@@ -52,6 +52,7 @@ sidebar:
     operators: Operators
     truth: Truthy and Falsy
     dos: DoS
+    static_analysis: Static Analysis
 
     miscellaneous: Miscellaneous
     migration9: 'Migrate to LiquidJS 9'

src/index.ts

@@ -6,9 +6,9 @@ export { Drop } from './drop'
 export { Emitter } from './emitters'
 export { defaultOperators, Operators, evalToken, evalQuotedToken, Expression, isFalsy, isTruthy } from './render'
 export { Context, Scope } from './context'
-export { Value, Hash, Template, FilterImplOptions, Tag, Filter, Output } from './template'
+export { Value, Hash, Template, FilterImplOptions, Tag, Filter, Output, Variable, VariableLocation, VariableSegments, Variables, StaticAnalysis, StaticAnalysisOptions, analyze, analyzeSync, Arguments, PartialScope } from './template'
 export { Token, TopLevelToken, TagToken, ValueToken } from './tokens'
-export { TokenKind, Tokenizer, ParseStream } from './parser'
+export { TokenKind, Tokenizer, ParseStream, Parser } from './parser'
 export { filters } from './filters'
 export * from './tags'
 export { defaultOptions, LiquidOptions } from './liquid-options'

src/liquid.ts

@@ -1,6 +1,6 @@
 import { Context } from './context'
-import { toPromise, toValueSync, isFunction, forOwn } from './util'
-import { TagClass, createTagClass, TagImplOptions, FilterImplOptions, Template, Value } from './template'
+import { toPromise, toValueSync, isFunction, forOwn, isString, strictUniq } from './util'
+import { TagClass, createTagClass, TagImplOptions, FilterImplOptions, Template, Value, StaticAnalysisOptions, StaticAnalysis, analyze, analyzeSync, SegmentArray } from './template'
 import { LookupType } from './fs/loader'
 import { Render } from './render'
 import { Parser } from './parser'
@@ -122,4 +122,92 @@ export class Liquid {
       self.renderFile(filePath, ctx).then(html => callback(null, html) as any, callback as any)
     }
   }
+
+  public async analyze (template: Template[], options: StaticAnalysisOptions = {}): Promise<StaticAnalysis> {
+    return analyze(template, options)
+  }
+
+  public analyzeSync (template: Template[], options: StaticAnalysisOptions = {}): StaticAnalysis {
+    return analyzeSync(template, options)
+  }
+
+  public async parseAndAnalyze (html: string, filename?: string, options: StaticAnalysisOptions = {}): Promise<StaticAnalysis> {
+    return analyze(this.parse(html, filename), options)
+  }
+
+  public parseAndAnalyzeSync (html: string, filename?: string, options: StaticAnalysisOptions = {}): StaticAnalysis {
+    return analyzeSync(this.parse(html, filename), options)
+  }
+
+  /** Return an array of all variables without their properties. */
+  public async variables (template: string | Template[], options: StaticAnalysisOptions = {}): Promise<string[]> {
+    const analysis = await analyze(isString(template) ? this.parse(template) : template, options)
+    return Object.keys(analysis.variables)
+  }
+
+  /** Return an array of all variables without their properties. */
+  public variablesSync (template: string | Template[], options: StaticAnalysisOptions = {}): string[] {
+    const analysis = analyzeSync(isString(template) ? this.parse(template) : template, options)
+    return Object.keys(analysis.variables)
+  }
+
+  /** Return an array of all variables including their properties/paths. */
+  public async fullVariables (template: string | Template[], options: StaticAnalysisOptions = {}): Promise<string[]> {
+    const analysis = await analyze(isString(template) ? this.parse(template) : template, options)
+    return Array.from(new Set(Object.values(analysis.variables).flatMap((a) => a.map((v) => String(v)))))
+  }
+
+  /** Return an array of all variables including their properties/paths. */
+  public fullVariablesSync (template: string | Template[], options: StaticAnalysisOptions = {}): string[] {
+    const analysis = analyzeSync(isString(template) ? this.parse(template) : template, options)
+    return Array.from(new Set(Object.values(analysis.variables).flatMap((a) => a.map((v) => String(v)))))
+  }
+
+  /** Return an array of all variables, each as an array of properties/segments. */
+  public async variableSegments (template: string | Template[], options: StaticAnalysisOptions = {}): Promise<Array<SegmentArray>> {
+    const analysis = await analyze(isString(template) ? this.parse(template) : template, options)
+    return Array.from(strictUniq(Object.values(analysis.variables).flatMap((a) => a.map((v) => v.toArray()))))
+  }
+
+  /** Return an array of all variables, each as an array of properties/segments. */
+  public variableSegmentsSync (template: string | Template[], options: StaticAnalysisOptions = {}): Array<SegmentArray> {
+    const analysis = analyzeSync(isString(template) ? this.parse(template) : template, options)
+    return Array.from(strictUniq(Object.values(analysis.variables).flatMap((a) => a.map((v) => v.toArray()))))
+  }
+
+  /** Return an array of all expected context variables without their properties. */
+  public async globalVariables (template: string | Template[], options: StaticAnalysisOptions = {}): Promise<string[]> {
+    const analysis = await analyze(isString(template) ? this.parse(template) : template, options)
+    return Object.keys(analysis.globals)
+  }
+
+  /** Return an array of all expected context variables without their properties. */
+  public globalVariablesSync (template: string | Template[], options: StaticAnalysisOptions = {}): string[] {
+    const analysis = analyzeSync(isString(template) ? this.parse(template) : template, options)
+    return Object.keys(analysis.globals)
+  }
+
+  /** Return an array of all expected context variables including their properties/paths. */
+  public async globalFullVariables (template: string | Template[], options: StaticAnalysisOptions = {}): Promise<string[]> {
+    const analysis = await analyze(isString(template) ? this.parse(template) : template, options)
+    return Array.from(new Set(Object.values(analysis.globals).flatMap((a) => a.map((v) => String(v)))))
+  }
+
+  /** Return an array of all expected context variables including their properties/paths. */
+  public globalFullVariablesSync (template: string | Template[], options: StaticAnalysisOptions = {}): string[] {
+    const analysis = analyzeSync(isString(template) ? this.parse(template) : template, options)
+    return Array.from(new Set(Object.values(analysis.globals).flatMap((a) => a.map((v) => String(v)))))
+  }
+
+  /** Return an array of all expected context variables, each as an array of properties/segments. */
+  public async globalVariableSegments (template: string | Template[], options: StaticAnalysisOptions = {}): Promise<Array<SegmentArray>> {
+    const analysis = await analyze(isString(template) ? this.parse(template) : template, options)
+    return Array.from(strictUniq(Object.values(analysis.globals).flatMap((a) => a.map((v) => v.toArray()))))
+  }
+
+  /** Return an array of all expected context variables, each as an array of properties/segments. */
+  public globalVariableSegmentsSync (template: string | Template[], options: StaticAnalysisOptions = {}): Array<SegmentArray> {
+    const analysis = analyzeSync(isString(template) ? this.parse(template) : template, options)
+    return Array.from(strictUniq(Object.values(analysis.globals).flatMap((a) => a.map((v) => v.toArray()))))
+  }
 }

src/render/expression.ts

@@ -5,7 +5,7 @@ import type { UnaryOperatorHandler } from '../render'
 import { Drop } from '../drop'
 
 export class Expression {
-  private postfix: Token[]
+  readonly postfix: Token[]
 
   public constructor (tokens: IterableIterator<Token>) {
     this.postfix = [...toPostfix(tokens)]

src/tags/assign.ts

@@ -1,11 +1,16 @@
 import { Value, Liquid, TopLevelToken, TagToken, Context, Tag } from '..'
+import { Arguments } from '../template'
+import { IdentifierToken } from '../tokens'
+
 export default class extends Tag {
   private key: string
   private value: Value
+  private identifier: IdentifierToken
 
   constructor (token: TagToken, remainTokens: TopLevelToken[], liquid: Liquid) {
     super(token, remainTokens, liquid)
-    this.key = this.tokenizer.readIdentifier().content
+    this.identifier = this.tokenizer.readIdentifier()
+    this.key = this.identifier.content
     this.tokenizer.assert(this.key, 'expected variable name')
 
     this.tokenizer.skipBlank()
@@ -17,4 +22,12 @@ export default class extends Tag {
   * render (ctx: Context): Generator<unknown, void, unknown> {
     ctx.bottom()[this.key] = yield this.value.value(ctx, this.liquid.options.lenientIf)
   }
+
+  public * arguments (): Arguments {
+    yield this.value
+  }
+
+  public * localScope (): Iterable<IdentifierToken> {
+    yield this.identifier
+  }
 }

src/tags/block.ts

@@ -42,4 +42,12 @@ export default class extends Tag {
       ? (superBlock: BlockDrop, emitter: Emitter) => renderChild(new BlockDrop(() => renderCurrent(superBlock, emitter)), emitter)
       : renderCurrent
   }
+
+  public * children (): Generator<unknown, Template[]> {
+    return this.templates
+  }
+
+  public blockScope (): Iterable<string> {
+    return ['block']
+  }
 }

src/tags/capture.ts

@@ -1,14 +1,16 @@
 import { Liquid, Tag, Template, Context, TagToken, TopLevelToken } from '..'
 import { Parser } from '../parser'
-import { evalQuotedToken } from '../render'
+import { IdentifierToken, QuotedToken } from '../tokens'
 import { isTagToken } from '../util'
 
 export default class extends Tag {
+  identifier: IdentifierToken | QuotedToken
   variable: string
   templates: Template[] = []
   constructor (tagToken: TagToken, remainTokens: TopLevelToken[], liquid: Liquid, parser: Parser) {
     super(tagToken, remainTokens, liquid)
-    this.variable = this.readVariableName()
+    this.identifier = this.readVariable()
+    this.variable = this.identifier.content
 
     while (remainTokens.length) {
       const token = remainTokens.shift()!
@@ -17,16 +19,26 @@ export default class extends Tag {
     }
     throw new Error(`tag ${tagToken.getText()} not closed`)
   }
+
+  private readVariable (): IdentifierToken | QuotedToken {
+    let ident: IdentifierToken | QuotedToken | undefined = this.tokenizer.readIdentifier()
+    if (ident.content) return ident
+    ident = this.tokenizer.readQuoted()
+    if (ident) return ident
+    throw this.tokenizer.error('invalid capture name')
+  }
+
   * render (ctx: Context): Generator<unknown, void, string> {
     const r = this.liquid.renderer
     const html = yield r.renderTemplates(this.templates, ctx)
     ctx.bottom()[this.variable] = html
   }
-  private readVariableName () {
-    const word = this.tokenizer.readIdentifier().content
-    if (word) return word
-    const quoted = this.tokenizer.readQuoted()
-    if (quoted) return evalQuotedToken(quoted)
-    throw this.tokenizer.error('invalid capture name')
+
+  public * children (): Generator<unknown, Template[]> {
+    return this.templates
+  }
+
+  public * localScope (): Iterable<string | IdentifierToken | QuotedToken> {
+    yield this.identifier
   }
 }

src/tags/case.ts

@@ -1,6 +1,7 @@
 import { ValueToken, Liquid, toValue, evalToken, Value, Emitter, TagToken, TopLevelToken, Context, Template, Tag, ParseStream } from '..'
 import { Parser } from '../parser'
 import { equals } from '../render'
+import { Arguments } from '../template'
 
 export default class extends Tag {
   value: Value
@@ -71,4 +72,17 @@ export default class extends Tag {
       yield r.renderTemplates(this.elseTemplates, ctx, emitter)
     }
   }
+
+  public * arguments (): Arguments {
+    yield this.value
+    yield * this.branches.flatMap(b => b.values)
+  }
+
+  public * children (): Generator<unknown, Template[]> {
+    const templates = this.branches.flatMap(b => b.templates)
+    if (this.elseTemplates) {
+      templates.push(...this.elseTemplates)
+    }
+    return templates
+  }
 }

src/tags/cycle.ts

@@ -1,4 +1,5 @@
 import { TopLevelToken, Liquid, ValueToken, evalToken, Emitter, TagToken, Context, Tag } from '..'
+import { Arguments } from '../template'
 
 export default class extends Tag {
   private candidates: ValueToken[] = []
@@ -38,4 +39,12 @@ export default class extends Tag {
     groups[fingerprint] = idx
     return yield evalToken(candidate, ctx)
   }
+
+  public * arguments (): Arguments {
+    yield * this.candidates
+
+    if (this.group) {
+      yield this.group
+    }
+  }
 }

src/tags/decrement.ts

@@ -1,11 +1,14 @@
 import { Tag, Liquid, TopLevelToken, Emitter, TagToken, Context } from '..'
+import { IdentifierToken } from '../tokens'
 import { isNumber, stringify } from '../util'
 
 export default class extends Tag {
+  private identifier: IdentifierToken
   private variable: string
   constructor (token: TagToken, remainTokens: TopLevelToken[], liquid: Liquid) {
     super(token, remainTokens, liquid)
-    this.variable = this.tokenizer.readIdentifier().content
+    this.identifier = this.tokenizer.readIdentifier()
+    this.variable = this.identifier.content
   }
   render (context: Context, emitter: Emitter) {
     const scope = context.environments
@@ -14,4 +17,8 @@ export default class extends Tag {
     }
     emitter.write(stringify(--scope[this.variable]))
   }
+
+  public * localScope (): Iterable<string | IdentifierToken> {
+    yield this.identifier
+  }
 }

src/tags/echo.ts

@@ -1,4 +1,5 @@
 import { Liquid, TopLevelToken, Emitter, Value, TagToken, Context, Tag } from '..'
+import { Arguments } from '../template'
 
 export default class extends Tag {
   private value?: Value
@@ -15,4 +16,10 @@ export default class extends Tag {
     const val = yield this.value.value(ctx, false)
     emitter.write(val)
   }
+
+  public * arguments (): Arguments {
+    if (this.value) {
+      yield this.value
+    }
+  }
 }

src/tags/for.ts

@@ -1,7 +1,8 @@
 import { Hash, ValueToken, Liquid, Tag, evalToken, Emitter, TagToken, TopLevelToken, Context, Template, ParseStream } from '..'
-import { assertEmpty, toEnumerable } from '../util'
+import { assertEmpty, isValueToken, toEnumerable } from '../util'
 import { ForloopDrop } from '../drop/forloop-drop'
 import { Parser } from '../parser'
+import { Arguments } from '../template'
 
 const MODIFIERS = ['offset', 'limit', 'reversed']
 
@@ -25,7 +26,7 @@ export default class extends Tag {
 
     this.variable = variable.content
     this.collection = collection
-    this.hash = new Hash(this.tokenizer.remaining(), liquid.options.keyValueSeparator)
+    this.hash = new Hash(this.tokenizer, liquid.options.keyValueSeparator)
     this.templates = []
     this.elseTemplates = []
 
@@ -75,6 +76,28 @@ export default class extends Tag {
     }
     ctx.pop()
   }
+
+  public * children (): Generator<unknown, Template[]> {
+    const templates = this.templates.slice()
+    if (this.elseTemplates) {
+      templates.push(...this.elseTemplates)
+    }
+    return templates
+  }
+
+  public * arguments (): Arguments {
+    yield this.collection
+
+    for (const v of Object.values(this.hash.hash)) {
+      if (isValueToken(v)) {
+        yield v
+      }
+    }
+  }
+
+  public blockScope (): Iterable<string> {
+    return [this.variable, 'forloop']
+  }
 }
 
 function reversed<T> (arr: Array<T>) {

src/tags/if.ts

@@ -1,5 +1,6 @@
 import { Liquid, Tag, Value, Emitter, isTruthy, TagToken, TopLevelToken, Context, Template } from '..'
 import { Parser } from '../parser'
+import { Arguments } from '../template'
 import { assert, assertEmpty } from '../util'
 
 export default class extends Tag {
@@ -11,13 +12,13 @@ export default class extends Tag {
     let p: Template[] = []
     parser.parseStream(remainTokens)
       .on('start', () => this.branches.push({
-        value: new Value(tagToken.args, this.liquid),
+        value: new Value(tagToken.tokenizer.readFilteredValue(), this.liquid),
         templates: (p = [])
       }))
       .on('tag:elsif', (token: TagToken) => {
         assert(!this.elseTemplates, 'unexpected elsif after else')
         this.branches.push({
-          value: new Value(token.args, this.liquid),
+          value: new Value(token.tokenizer.readFilteredValue(), this.liquid),
           templates: (p = [])
         })
       })
@@ -44,4 +45,16 @@ export default class extends Tag {
     }
     yield r.renderTemplates(this.elseTemplates || [], ctx, emitter)
   }
+
+  public * children (): Generator<unknown, Template[]> {
+    const templates = this.branches.flatMap(b => b.templates)
+    if (this.elseTemplates) {
+      templates.push(...this.elseTemplates)
+    }
+    return templates
+  }
+
+  public arguments (): Arguments {
+    return this.branches.map(b => b.value)
+  }
 }

src/tags/include.ts

@@ -1,6 +1,8 @@
 import { Template, ValueToken, TopLevelToken, Liquid, Tag, assert, evalToken, Hash, Emitter, TagToken, Context } from '..'
 import { BlockMode, Scope } from '../context'
 import { Parser } from '../parser'
+import { Argument, Arguments, PartialScope } from '../template'
+import { isString, isValueToken } from '../util'
 import { parseFilePath, renderFilePath } from './render'
 
 export default class extends Tag {
@@ -21,7 +23,7 @@ export default class extends Tag {
       } else tokenizer.p = begin
     } else tokenizer.p = begin
 
-    this.hash = new Hash(tokenizer.remaining(), liquid.options.jekyllInclude || liquid.options.keyValueSeparator)
+    this.hash = new Hash(tokenizer, liquid.options.jekyllInclude || liquid.options.keyValueSeparator)
   }
   * render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> {
     const { liquid, hash, withVar } = this
@@ -40,4 +42,40 @@ export default class extends Tag {
     ctx.pop()
     ctx.restoreRegister(saved)
   }
+
+  public * children (partials: boolean, sync: boolean): Generator<unknown, Template[]> {
+    if (partials && isString(this['file'])) {
+      return (yield this.liquid._parsePartialFile(this['file'], sync, this['currentFile'])) as Template[]
+    }
+    return []
+  }
+
+  public partialScope (): PartialScope | undefined {
+    if (isString(this['file'])) {
+      let names: Array<string | [string, Argument]>
+
+      if (this.liquid.options.jekyllInclude) {
+        names = ['include']
+      } else {
+        names = Object.keys(this.hash.hash)
+        if (this.withVar) {
+          names.push([this['file'], this.withVar])
+        }
+      }
+
+      return { name: this['file'], isolated: false, scope: names }
+    }
+  }
+
+  public * arguments (): Arguments {
+    yield * Object.values(this.hash.hash).filter(isValueToken)
+
+    if (isValueToken(this['file'])) {
+      yield this['file']
+    }
+
+    if (isValueToken(this.withVar)) {
+      yield this.withVar
+    }
+  }
 }

src/tags/increment.ts

@@ -1,11 +1,14 @@
 import { isNumber, stringify } from '../util'
 import { Tag, Liquid, TopLevelToken, Emitter, TagToken, Context } from '..'
+import { IdentifierToken } from '../tokens'
 
 export default class extends Tag {
+  private identifier: IdentifierToken
   private variable: string
   constructor (token: TagToken, remainTokens: TopLevelToken[], liquid: Liquid) {
     super(token, remainTokens, liquid)
-    this.variable = this.tokenizer.readIdentifier().content
+    this.identifier = this.tokenizer.readIdentifier()
+    this.variable = this.identifier.content
   }
   render (context: Context, emitter: Emitter) {
     const scope = context.environments
@@ -16,4 +19,8 @@ export default class extends Tag {
     scope[this.variable]++
     emitter.write(stringify(val))
   }
+
+  public * localScope (): Iterable<string | IdentifierToken> {
+    yield this.identifier
+  }
 }

src/tags/layout.ts

@@ -3,6 +3,8 @@ import { BlockMode } from '../context'
 import { parseFilePath, renderFilePath, ParsedFileName } from './render'
 import { BlankDrop } from '../drop'
 import { Parser } from '../parser'
+import { Arguments, PartialScope } from '../template'
+import { isString, isValueToken } from '../util'
 
 export default class extends Tag {
   args: Hash
@@ -12,7 +14,7 @@ export default class extends Tag {
     super(token, remainTokens, liquid)
     this.file = parseFilePath(this.tokenizer, this.liquid, parser)
     this['currentFile'] = token.file
-    this.args = new Hash(this.tokenizer.remaining(), liquid.options.keyValueSeparator)
+    this.args = new Hash(this.tokenizer, liquid.options.keyValueSeparator)
     this.templates = parser.parseTokens(remainTokens)
   }
   * render (ctx: Context, emitter: Emitter): Generator<unknown, unknown, unknown> {
@@ -41,4 +43,32 @@ export default class extends Tag {
     yield renderer.renderTemplates(templates, ctx, emitter)
     ctx.pop()
   }
+
+  public * children (partials: boolean): Generator<unknown, Template[]> {
+    const templates = this.templates.slice()
+
+    if (partials && isString(this.file)) {
+      templates.push(...(yield this.liquid._parsePartialFile(this.file, true, this['currentFile'])) as Template[])
+    }
+
+    return templates
+  }
+
+  public * arguments (): Arguments {
+    for (const v of Object.values(this.args.hash)) {
+      if (isValueToken(v)) {
+        yield v
+      }
+    }
+
+    if (isValueToken(this.file)) {
+      yield this.file
+    }
+  }
+
+  public partialScope (): PartialScope | undefined {
+    if (isString(this.file)) {
+      return { name: this.file, isolated: false, scope: Object.keys(this.args.hash) }
+    }
+  }
 }

src/tags/liquid.ts

@@ -11,4 +11,8 @@ export default class extends Tag {
   * render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> {
     yield this.liquid.renderer.renderTemplates(this.templates, ctx, emitter)
   }
+
+  public * children (): Generator<unknown, Template[]> {
+    return this.templates
+  }
 }

src/tags/render.ts

@@ -1,8 +1,9 @@
 import { __assign } from 'tslib'
 import { ForloopDrop } from '../drop'
-import { toEnumerable } from '../util'
+import { isString, isValueToken, toEnumerable } from '../util'
 import { TopLevelToken, assert, Liquid, Token, Template, evalQuotedToken, TypeGuards, Tokenizer, evalToken, Hash, Emitter, TagToken, Context, Tag } from '..'
 import { Parser } from '../parser'
+import { Argument, Arguments, PartialScope } from '../template'
 
 export type ParsedFileName = Template[] | Token | string | undefined
 
@@ -45,7 +46,7 @@ export default class extends Tag {
       tokenizer.p = begin
       break
     }
-    this.hash = new Hash(tokenizer.remaining(), liquid.options.keyValueSeparator)
+    this.hash = new Hash(tokenizer, liquid.options.keyValueSeparator)
   }
   * render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> {
     const { liquid, hash } = this
@@ -75,6 +76,61 @@ export default class extends Tag {
       yield liquid.renderer.renderTemplates(templates, childCtx, emitter)
     }
   }
+
+  public * children (partials: boolean, sync: boolean): Generator<unknown, Template[]> {
+    if (partials && isString(this['file'])) {
+      return (yield this.liquid._parsePartialFile(this['file'], sync, this['currentFile'])) as Template[]
+    }
+    return []
+  }
+
+  public partialScope (): PartialScope | undefined {
+    if (isString(this['file'])) {
+      const names: Array<string | [string, Argument]> = Object.keys(this.hash.hash)
+
+      if (this['with']) {
+        const { value, alias } = this['with']
+        if (isString(alias)) {
+          names.push([alias, value])
+        } else if (isString(this.file)) {
+          names.push([this.file, value])
+        }
+      }
+
+      if (this['for']) {
+        const { value, alias } = this['for']
+        if (isString(alias)) {
+          names.push([alias, value])
+        } else if (isString(this.file)) {
+          names.push([this.file, value])
+        }
+      }
+
+      return { name: this['file'], isolated: true, scope: names }
+    }
+  }
+
+  public * arguments (): Arguments {
+    for (const v of Object.values(this.hash.hash)) {
+      if (isValueToken(v)) {
+        yield v
+      }
+    }
+
+    if (this['with']) {
+      const { value } = this['with']
+      if (isValueToken(value)) {
+        yield value
+      }
+    }
+
+    if (this['for']) {
+      const { value } = this['for']
+      if (isValueToken(value)) {
+        yield value
+      }
+    }
+  }
 }
 
 /**

src/tags/tablerow.ts

@@ -1,7 +1,8 @@
-import { toEnumerable } from '../util'
+import { isValueToken, toEnumerable } from '../util'
 import { ValueToken, Liquid, Tag, evalToken, Emitter, Hash, TagToken, TopLevelToken, Context, Template, ParseStream } from '..'
 import { TablerowloopDrop } from '../drop/tablerowloop-drop'
 import { Parser } from '../parser'
+import { Arguments } from '../template'
 
 export default class extends Tag {
   variable: string
@@ -21,7 +22,7 @@ export default class extends Tag {
 
     this.variable = variable.content
     this.collection = collectionToken
-    this.args = new Hash(this.tokenizer.remaining(), liquid.options.keyValueSeparator)
+    this.args = new Hash(this.tokenizer, liquid.options.keyValueSeparator)
     this.templates = []
 
     let p
@@ -63,4 +64,22 @@ export default class extends Tag {
     if (collection.length) emitter.write('</tr>')
     ctx.pop()
   }
+
+  public * children (): Generator<unknown, Template[]> {
+    return this.templates
+  }
+
+  public * arguments (): Arguments {
+    yield this.collection
+
+    for (const v of Object.values(this.args.hash)) {
+      if (isValueToken(v)) {
+        yield v
+      }
+    }
+  }
+
+  public blockScope (): string[] {
+    return [this.variable, 'tablerowloop']
+  }
 }

src/tags/unless.ts

@@ -1,5 +1,6 @@
 import { Liquid, Tag, Value, TopLevelToken, Template, Emitter, isTruthy, isFalsy, Context, TagToken } from '..'
 import { Parser } from '../parser'
+import { Arguments } from '../template'
 
 export default class extends Tag {
   branches: { value: Value, test: (val: any, ctx: Context) => boolean, templates: Template[] }[] = []
@@ -10,7 +11,7 @@ export default class extends Tag {
     let elseCount = 0
     parser.parseStream(remainTokens)
       .on('start', () => this.branches.push({
-        value: new Value(tagToken.args, this.liquid),
+        value: new Value(tagToken.tokenizer.readFilteredValue(), this.liquid),
         test: isFalsy,
         templates: (p = [])
       }))
@@ -20,7 +21,7 @@ export default class extends Tag {
           return
         }
         this.branches.push({
-          value: new Value(token.args, this.liquid),
+          value: new Value(token.tokenizer.readFilteredValue(), this.liquid),
           test: isTruthy,
           templates: (p = [])
         })
@@ -52,4 +53,16 @@ export default class extends Tag {
 
     yield r.renderTemplates(this.elseTemplates, ctx, emitter)
   }
+
+  public * children (): Generator<unknown, Template[]> {
+    const children = this.branches.flatMap(b => b.templates)
+    if (this.elseTemplates) {
+      children.push(...this.elseTemplates)
+    }
+    return children
+  }
+
+  public arguments (): Arguments {
+    return this.branches.map(b => b.value)
+  }
 }

src/template/analysis.spec.ts

@@ -0,0 +1,51 @@
+import { Variable, VariableMap } from './analysis'
+
+describe('Analysis variable', () => {
+  const mockLocation = { row: 1, col: 1, file: undefined }
+
+  it('should coerce to a string', () => {
+    const v = new Variable(['foo', 'bar'], mockLocation)
+    expect(String(v)).toBe('foo.bar')
+  })
+
+  it('should represent nested variables', () => {
+    const nested = new Variable(['bar', 1], mockLocation)
+    const v = new Variable(['foo', nested], mockLocation)
+    expect(`${v}`).toBe('foo[bar[1]]')
+  })
+
+  it('should represent bracketed segments', () => {
+    const v = new Variable(['foo', 'bar baz'], mockLocation)
+    expect(`${v}`).toBe("foo['bar baz']")
+  })
+
+  it('should represent bracketed root', () => {
+    const v = new Variable(['foo bar'], mockLocation)
+    expect(`${v}`).toBe("['foo bar']")
+  })
+
+  it('should have a segments property', () => {
+    const v = new Variable(['foo', 'bar'], mockLocation)
+    expect(v.segments).toStrictEqual(['foo', 'bar'])
+  })
+
+  it('should have a location property', () => {
+    const v = new Variable(['foo', 'bar'], mockLocation)
+    expect(v.location).toStrictEqual(mockLocation)
+  })
+})
+
+describe('Variable map', () => {
+  it('should coerce variables to their string representation', () => {
+    const v = new Variable(['foo', 'bar'], { row: 1, col: 1, file: undefined })
+    const mapping = new VariableMap()
+    mapping.push(v)
+    expect(mapping.has(v)).toBe(true)
+  })
+
+  it('should return an empty array if a variable is not in the map', () => {
+    const v = new Variable(['foo', 'bar'], { row: 1, col: 1, file: undefined })
+    const mapping = new VariableMap()
+    expect(mapping.get(v)).toStrictEqual([])
+  })
+})

src/template/analysis.ts

@@ -0,0 +1,448 @@
+import { Argument, Template, Value } from '.'
+import { isKeyValuePair } from '../parser/filter-arg'
+import { PropertyAccessToken, ValueToken } from '../tokens'
+import {
+  isNumberToken,
+  isPropertyAccessToken,
+  isQuotedToken,
+  isRangeToken,
+  isString,
+  isValueToken,
+  isWordToken,
+  toPromise,
+  toValueSync
+} from '../util'
+
+/**
+ * Row, column and file name where a variable was found.
+ */
+export interface VariableLocation {
+  row: number;
+  col: number;
+  file?: string;
+}
+
+/**
+ * A variable's segments as an array, possibly with nested arrays of segments.
+ */
+export type SegmentArray = Array<string | number | SegmentArray>
+
+/**
+ * A variable's segments and location, which can be coerced to a string.
+ */
+export class Variable {
+  constructor (
+    readonly segments: Array<string | number | Variable>,
+    readonly location: VariableLocation
+  ) {}
+
+  public toString (): string {
+    return segmentsString(this.segments, true)
+  }
+
+  /** Return this variable's segments as an array, possibly with nested arrays for nested paths. */
+  public toArray (): SegmentArray {
+    function * _visit (...segments: Array<string | number | Variable>): Generator<string | number | SegmentArray> {
+      for (const segment of segments) {
+        if (segment instanceof Variable) {
+          yield Array.from(_visit(...segment.segments))
+        } else {
+          yield segment
+        }
+      }
+    }
+    return Array.from(_visit(...this.segments))
+  }
+}
+
+/**
+ * Property names and array indexes that make up a path to a variable.
+ */
+export type VariableSegments = Array<string | number | Variable>;
+
+/**
+ * A mapping of variable names to an array of locations at which the variable was found.
+ */
+export type Variables = { [key: string]: Variable[] };
+
+/**
+ * Group variables by the string representation of their root segment.
+ */
+export class VariableMap {
+  private map: Map<string, Variable[]>
+
+  constructor () {
+    this.map = new Map()
+  }
+
+  public get (key: Variable): Variable[] {
+    const k = segmentsString([key.segments[0]])
+    if (!this.map.has(k)) {
+      this.map.set(k, [])
+    }
+    return this.map.get(k) as Variable[]
+  }
+
+  public has (key: Variable): boolean {
+    return this.map.has(segmentsString([key.segments[0]]))
+  }
+
+  public push (variable: Variable): void {
+    this.get(variable).push(variable)
+  }
+
+  public asObject (): Variables {
+    return Object.fromEntries(this.map)
+  }
+}
+
+/**
+ * The result of calling `analyze()` or `analyzeSync()`.
+ */
+export interface StaticAnalysis {
+  /**
+   * All variables, whether they are in scope or not. Including references to names
+   * such as `forloop` from the `for` tag.
+   */
+  variables: Variables;
+
+  /**
+   * Variables that are not in scope. These could be a "global" variables that are
+   * expected to be provided by the application developer, or possible mistakes
+   * from the template author.
+   *
+   * If a variable is referenced before and after assignment, you should expect
+   * that variable to be included in `globals`, `variables` and `locals`, each with
+   * a different location.
+   */
+  globals: Variables;
+
+  /**
+   * Template variables that are added to the template local scope using tags like
+   * `assign`, `capture` or `increment`.
+   */
+  locals: Variables;
+}
+
+export interface StaticAnalysisOptions {
+  /**
+   * When `true` (the default), try to load partial templates and analyze them too.
+   */
+  partials?: boolean;
+}
+
+export const defaultStaticAnalysisOptions: StaticAnalysisOptions = {
+  partials: true
+}
+
+function * _analyze (templates: Template[], partials: boolean, sync: boolean): Generator<unknown, StaticAnalysis> {
+  const variables = new VariableMap()
+  const globals = new VariableMap()
+  const locals = new VariableMap()
+
+  const rootScope = new DummyScope(new Set())
+
+  // Names of partial templates that we've already analyzed.
+  const seen: Set<string | undefined> = new Set()
+
+  function updateVariables (variable: Variable, scope: DummyScope) {
+    variables.push(variable)
+    const aliased = scope.alias(variable)
+
+    if (aliased !== undefined) {
+      const root = aliased.segments[0]
+      // TODO: What if a a template renders a rendered template? Do we need scope.parent?
+      if (isString(root) && !rootScope.has(root)) {
+        globals.push(aliased)
+      }
+    } else {
+      const root = variable.segments[0]
+      if (isString(root) && !scope.has(root)) {
+        globals.push(variable)
+      }
+    }
+
+    // Recurse for nested Variables
+    for (const segment of variable.segments) {
+      if (segment instanceof Variable) {
+        updateVariables(segment, scope)
+      }
+    }
+  }
+
+  function * visit (template: Template, scope: DummyScope): Generator<unknown, void> {
+    if (template.arguments) {
+      for (const arg of template.arguments()) {
+        for (const variable of extractVariables(arg)) {
+          updateVariables(variable, scope)
+        }
+      }
+    }
+
+    if (template.localScope) {
+      for (const ident of template.localScope()) {
+        scope.add(ident.content)
+        scope.deleteAlias(ident.content)
+        const [row, col] = ident.getPosition()
+        locals.push(new Variable([ident.content], { row, col, file: ident.file }))
+      }
+    }
+
+    if (template.children) {
+      if (template.partialScope) {
+        const partial = template.partialScope()
+
+        if (partial === undefined) {
+          // Layouts, for example, can have children that are not partials.
+          for (const child of (yield template.children(partials, sync)) as Template[]) {
+            yield visit(child, scope)
+          }
+          return
+        }
+
+        if (seen.has(partial.name)) return
+
+        const partialScopeNames: Set<string> = new Set()
+        const partialScope = partial.isolated
+          ? new DummyScope(partialScopeNames)
+          : scope.push(partialScopeNames)
+
+        for (const name of partial.scope) {
+          if (isString(name)) {
+            partialScopeNames.add(name)
+          } else {
+            const [alias, argument] = name
+            partialScopeNames.add(alias)
+            const variables = Array.from(extractVariables(argument))
+            if (variables.length) {
+              partialScope.setAlias(alias, variables[0].segments)
+            }
+          }
+        }
+
+        for (const child of (yield template.children(partials, sync)) as Template[]) {
+          yield visit(child, partialScope)
+          seen.add(partial.name)
+        }
+
+        partialScope.pop()
+      } else {
+        if (template.blockScope) {
+          scope.push(new Set(template.blockScope()))
+        }
+
+        for (const child of (yield template.children(partials, sync)) as Template[]) {
+          yield visit(child, scope)
+        }
+
+        if (template.blockScope) {
+          scope.pop()
+        }
+      }
+    }
+  }
+
+  for (const template of templates) {
+    yield visit(template, rootScope)
+  }
+
+  return {
+    variables: variables.asObject(),
+    globals: globals.asObject(),
+    locals: locals.asObject()
+  }
+}
+
+/**
+ * Statically analyze a template and report variable usage.
+ */
+export function analyze (template: Template[], options: StaticAnalysisOptions = {}): Promise<StaticAnalysis> {
+  const opts = { ...defaultStaticAnalysisOptions, ...options } as Required<StaticAnalysisOptions>
+  return toPromise(_analyze(template, opts.partials, false))
+}
+
+/**
+ * Statically analyze a template and report variable usage.
+ */
+export function analyzeSync (template: Template[], options: StaticAnalysisOptions = {}): StaticAnalysis {
+  const opts = { ...defaultStaticAnalysisOptions, ...options } as Required<StaticAnalysisOptions>
+  return toValueSync(_analyze(template, opts.partials, true))
+}
+
+interface ScopeStackItem {
+  names: Set<string>;
+  aliases: Map<string, VariableSegments>;
+}
+
+/**
+ * A stack to manage scopes while traversing templates during static analysis.
+ */
+class DummyScope {
+  private stack: Array<ScopeStackItem>
+
+  constructor (globals: Set<string>) {
+    this.stack = [{ names: globals, aliases: new Map() }]
+  }
+
+  /** Return true if `name` is in scope.  */
+  public has (name: string): boolean {
+    for (const scope of this.stack) {
+      if (scope.names.has(name)) {
+        return true
+      }
+    }
+    return false
+  }
+
+  public push (scope: Set<string>): DummyScope {
+    this.stack.push({ names: scope, aliases: new Map() })
+    return this
+  }
+
+  public pop (): Set<string> | undefined {
+    return this.stack.pop()?.names
+  }
+
+  // Add a name to the template scope.
+  public add (name: string): void {
+    this.stack[0].names.add(name)
+  }
+
+  /** Return the variable that `variable` aliases, or `variable` if it doesn't alias anything. */
+  public alias (variable: Variable): Variable | undefined {
+    const root = variable.segments[0]
+    if (!isString(root)) return undefined
+    const alias = this.getAlias(root)
+    if (alias === undefined) return undefined
+    return new Variable([...alias, ...variable.segments.slice(1)], variable.location)
+  }
+
+  // TODO: `from` could be a path with multiple segments, like `include.x`.
+  public setAlias (from: string, to: VariableSegments): void {
+    this.stack[this.stack.length - 1].aliases.set(from, to)
+  }
+
+  public deleteAlias (name: string): void {
+    this.stack[this.stack.length - 1].aliases.delete(name)
+  }
+
+  private getAlias (name: string): VariableSegments | undefined {
+    for (const scope of this.stack) {
+      if (scope.aliases.has(name)) {
+        return scope.aliases.get(name)
+      }
+
+      // If a scope has defined `name`, then it masks aliases in parent scopes.
+      if (scope.names.has(name)) {
+        return undefined
+      }
+    }
+    return undefined
+  }
+}
+
+function * extractVariables (value: Argument): Generator<Variable> {
+  if (isValueToken(value)) {
+    yield * extractValueTokenVariables(value)
+  } else if (value instanceof Value) {
+    yield * extractFilteredValueVariables(value)
+  }
+}
+
+function * extractFilteredValueVariables (value: Value): Generator<Variable> {
+  for (const token of value.initial.postfix) {
+    if (isValueToken(token)) {
+      yield * extractValueTokenVariables(token)
+    }
+  }
+
+  for (const filter of value.filters) {
+    for (const arg of filter.args) {
+      if (isKeyValuePair(arg) && arg[1]) {
+        yield * extractValueTokenVariables(arg[1])
+      } else if (isValueToken(arg)) {
+        yield * extractValueTokenVariables(arg)
+      }
+    }
+  }
+}
+
+function * extractValueTokenVariables (token: ValueToken): Generator<Variable> {
+  if (isRangeToken(token)) {
+    yield * extractValueTokenVariables(token.lhs)
+    yield * extractValueTokenVariables(token.rhs)
+  } else if (isPropertyAccessToken(token)) {
+    yield extractPropertyAccessVariable(token)
+  }
+}
+
+function extractPropertyAccessVariable (token: PropertyAccessToken): Variable {
+  const segments: VariableSegments = []
+
+  // token is not guaranteed to have `file` set. We'll try to get it from a prop if not.
+  let file: string | undefined = token.file
+
+  // Here we're flattening the first segment of a path if it is a nested path.
+  const root = token.props[0]
+  file = file || root.file
+  if (isQuotedToken(root) || isNumberToken(root) || isWordToken(root)) {
+    segments.push(root.content)
+  } else if (isPropertyAccessToken(root)) {
+    // Flatten paths that start with a nested path.
+    segments.push(...extractPropertyAccessVariable(root).segments)
+  }
+
+  for (const prop of token.props.slice(1)) {
+    file = file || prop.file
+    if (isQuotedToken(prop) || isNumberToken(prop) || isWordToken(prop)) {
+      segments.push(prop.content)
+    } else if (isPropertyAccessToken(prop)) {
+      segments.push(extractPropertyAccessVariable(prop))
+    }
+  }
+
+  const [row, col] = token.getPosition()
+  return new Variable(segments, {
+    row,
+    col,
+    file
+  })
+}
+
+// This is used to detect segments that can be represented with dot notation
+// when creating a string representation of VariableSegments.
+const RE_PROPERTY = /^[\u0080-\uFFFFa-zA-Z_][\u0080-\uFFFFa-zA-Z0-9_-]*$/
+
+/**
+ * Return a string representation of segments using dot notation where possible.
+ * @param segments - The property names and array indices that make up a path to a variable.
+ * @param bracketedRoot - If false (the default), don't surround the root segment with square brackets.
+ */
+function segmentsString (segments: VariableSegments, bracketedRoot = false): string {
+  const buf: string[] = []
+
+  const root = segments[0]
+  if (isString(root)) {
+    if (!bracketedRoot || root.match(RE_PROPERTY)) {
+      buf.push(`${root}`)
+    } else {
+      buf.push(`['${root}']`)
+    }
+  }
+
+  for (const segment of segments.slice(1)) {
+    if (segment instanceof Variable) {
+      buf.push(`[${segmentsString(segment.segments)}]`)
+    } else if (isString(segment)) {
+      if (segment.match(RE_PROPERTY)) {
+        buf.push(`.${segment}`)
+      } else {
+        buf.push(`['${segment}']`)
+      }
+    } else {
+      buf.push(`[${segment}]`)
+    }
+  }
+
+  return buf.join('')
+}

src/template/hash.spec.ts

@@ -1,6 +1,7 @@
 import { toPromise } from '../util'
 import { Hash } from './hash'
 import { Context } from '../context'
+import { Tokenizer } from '../parser'
 
 describe('Hash', function () {
   it('should parse "reverse"', async function () {
@@ -43,4 +44,10 @@ describe('Hash', function () {
     const hash = await toPromise(new Hash('num=2.3', '=').render(new Context()))
     expect(hash.num).toBe(2.3)
   })
+  it('should accept an existing tokenizer', async function () {
+    const tokenizer = new Tokenizer('a:1, b:2')
+    const hash = await toPromise(new Hash(tokenizer).render(new Context()))
+    expect(hash.a).toBe(1)
+    expect(hash.b).toBe(2)
+  })
 })

src/template/hash.ts

@@ -15,12 +15,14 @@ type HashValueTokens = Record<string, Token | undefined>
  */
 export class Hash {
   hash: HashValueTokens = {}
-  constructor (markup: string, jekyllStyle?: boolean | string) {
-    const tokenizer = new Tokenizer(markup, {})
+
+  constructor (input: string | Tokenizer, jekyllStyle?: boolean | string) {
+    const tokenizer = input instanceof Tokenizer ? input : new Tokenizer(input, {})
     for (const hash of tokenizer.readHashes(jekyllStyle)) {
       this.hash[hash.name.content] = hash.value
     }
   }
+
   * render (ctx: Context): Generator<unknown, Record<string, any>, unknown> {
     const hash = {}
     for (const key of Object.keys(this.hash)) {

src/template/index.ts

@@ -8,3 +8,4 @@ export * from './hash'
 export * from './value'
 export * from './output'
 export * from './html'
+export * from './analysis'

src/template/output.ts

@@ -1,5 +1,5 @@
 import { Value } from './value'
-import { Template, TemplateImpl } from '../template'
+import { Arguments, Template, TemplateImpl } from '../template'
 import { Context } from '../context/context'
 import { Emitter } from '../emitters/emitter'
 import { OutputToken } from '../tokens/output-token'
@@ -25,4 +25,8 @@ export class Output extends TemplateImpl<OutputToken> implements Template {
     const val = yield this.value.value(ctx, false)
     emitter.write(val)
   }
+
+  public * arguments (): Arguments {
+    yield this.value
+  }
 }

src/template/template.ts

@@ -1,8 +1,41 @@
 import { Context } from '../context/context'
 import { Token } from '../tokens/token'
 import { Emitter } from '../emitters/emitter'
+import { IdentifierToken, QuotedToken, ValueToken } from '../tokens'
+import { Value } from './value'
+
+export type Argument = Value | ValueToken
+export type Arguments = Iterable<Argument>
+
+/** Scope information used when analyzing partial templates. */
+export interface PartialScope {
+  /**
+   * The name of the partial template. We need this to make sure we only analyze
+   * each template once.
+   * */
+  name: string;
+
+  /**
+   * If `true`, names in `scope` will be added to a new, isolated scope before
+   * analyzing any child templates, without access to the parent template's scope.
+   */
+  isolated: boolean;
+
+  /**
+   * A list of names that will be in scope for the child template.
+   *
+   * If an item is a [string, Argument] tuple, the string is considered an alias
+   * for the argument.
+   */
+  scope: Iterable<string | [string, Argument]>;
+}
 
 export interface Template {
   token: Token;
   render(ctx: Context, emitter: Emitter): any;
+  children?(partials: boolean, sync: boolean): Generator<unknown, Template[]> ;
+  arguments?(): Arguments;
+  blockScope?(): Iterable<string>;
+  localScope?(): Iterable<IdentifierToken | QuotedToken>;
+  partialScope?(): PartialScope | undefined;
 }

src/template/value.ts

@@ -20,6 +20,7 @@ export class Value {
     this.initial = token.initial
     this.filters = token.filters.map(token => new Filter(token, this.getFilter(liquid, token.name), liquid))
   }
+
   public * value (ctx: Context, lenient?: boolean): Generator<unknown, unknown, unknown> {
     lenient = lenient || (ctx.opts.lenientIf && this.filters.length > 0 && this.filters[0].name === 'default')
     let val = yield this.initial.evaluate(ctx, lenient)
@@ -29,6 +30,7 @@ export class Value {
     }
     return val
   }
+
   private getFilter (liquid: Liquid, name: string) {
     const impl = liquid.filters[name]
     assert(impl || !liquid.options.strictFilters, () => `undefined filter: ${name}`)

src/tokens/liquid-tag-token.ts

@@ -7,7 +7,6 @@ import { Tokenizer, TokenKind } from '../parser'
  */
 export class LiquidTagToken extends DelimitedToken {
   public name: string
-  public args: string
   public tokenizer: Tokenizer
   public constructor (
     input: string,
@@ -17,12 +16,13 @@ export class LiquidTagToken extends DelimitedToken {
     file?: string
   ) {
     super(TokenKind.Tag, [begin, end], input, begin, end, false, false, file)
-
     this.tokenizer = new Tokenizer(input, options.operators, file, this.contentRange)
     this.name = this.tokenizer.readTagName()
     this.tokenizer.assert(this.name, 'illegal liquid tag syntax')
-
     this.tokenizer.skipBlank()
-    this.args = this.tokenizer.remaining()
+  }
+
+  get args (): string {
+    return this.tokenizer.input.slice(this.tokenizer.p, this.contentRange[1])
   }
 }

src/tokens/tag-token.ts

@@ -21,6 +21,7 @@ export class TagToken extends DelimitedToken {
     this.tokenizer.assert(this.name, `illegal tag syntax, tag name expected`)
     this.tokenizer.skipBlank()
   }
+
   get args (): string {
     return this.tokenizer.input.slice(this.tokenizer.p, this.contentRange[1])
   }

src/util/type-guards.ts

@@ -1,4 +1,4 @@
-import { RangeToken, NumberToken, QuotedToken, LiteralToken, PropertyAccessToken, OutputToken, HTMLToken, TagToken, IdentifierToken, DelimitedToken, OperatorToken } from '../tokens'
+import { RangeToken, NumberToken, QuotedToken, LiteralToken, PropertyAccessToken, OutputToken, HTMLToken, TagToken, IdentifierToken, DelimitedToken, OperatorToken, ValueToken } from '../tokens'
 import { TokenKind } from '../parser'
 
 export function isDelimitedToken (val: any): val is DelimitedToken {
@@ -45,6 +45,11 @@ export function isRangeToken (val: any): val is RangeToken {
   return getKind(val) === TokenKind.Range
 }
 
+export function isValueToken (val: any): val is ValueToken {
+  // valueTokenBitMask = TokenKind.Number | TokenKind.Literal | TokenKind.Quoted | TokenKind.PropertyAccess | TokenKind.Range
+  return (getKind(val) & 1667) > 0
+}
+
 function getKind (val: any) {
   return val ? val.kind : -1
 }

src/util/underscore.ts

@@ -194,3 +194,16 @@ export function argumentsToValue<F extends (...args: any) => any, T> (fn: F) {
 export function escapeRegExp (text: string) {
   return text.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, '\\$&')
 }
+
+/** Return an array containing unique elements from _array_. Works with nested arrays and objects. */
+export function * strictUniq<T> (array: Array<T>): Generator<T> {
+  const seen = new Set()
+
+  for (const element of array) {
+    const key = JSON.stringify(element)
+    if (!seen.has(key)) {
+      seen.add(key)
+      yield element
+    }
+  }
+}

test/e2e/parse-and-analyze.spec.ts

@@ -0,0 +1,70 @@
+import { Context, Emitter, Hash, Liquid, Scope, Tag, TagToken, Template, TopLevelToken, ParseStream, Parser, Arguments, analyzeSync, Variable, StaticAnalysisOptions, StaticAnalysis } from '../..'
+
+class MockTag extends Tag {
+  private args: Hash
+  private templates: Template[]
+
+  constructor (token: TagToken, remainTokens: TopLevelToken[], liquid: Liquid, parser: Parser) {
+    super(token, remainTokens, liquid)
+    this.args = new Hash(token.tokenizer)
+    this.templates = []
+
+    const stream: ParseStream = parser.parseStream(remainTokens)
+      .on<TagToken>('tag:endmock', () => { stream.stop() })
+      .on('template', (tpl: Template) => this.templates.push(tpl))
+      .on('end', () => { throw new Error(`tag ${token.getText()} not closed`) })
+
+    stream.start()
+  }
+
+  public * render (ctx: Context, emitter: Emitter): Generator<unknown, void, string> {
+    const scope = (yield this.args.render(ctx)) as unknown as Scope
+    ctx.push(scope)
+    yield this.liquid.renderer.renderTemplates(this.templates, ctx, emitter)
+    ctx.pop()
+  }
+
+  public * children (): Generator<unknown, Template[]> {
+    return this.templates
+  }
+
+  public * arguments (): Arguments {
+    // XXX: tokens and type guards are not exported
+    yield * Object.values(this.args.hash).filter((el) => el !== undefined) as Arguments
+  }
+
+  public blockScope (): Iterable<string> {
+    return Object.keys(this.args.hash)
+  }
+}
+
+describe('Static analysis', () => {
+  it('should report variables from non-standard tags', () => {
+    const engine = new Liquid()
+    engine.registerTag('mock', MockTag)
+
+    const template = engine.parse('{% mock a:b x:y %}{{ x }}{{ z }}{% endmock %}')
+    const analysis = analyzeSync(template)
+
+    const b = [new Variable(['b'], { row: 1, col: 11, file: undefined })]
+    const x = [new Variable(['x'], { row: 1, col: 22, file: undefined })]
+    const y = [new Variable(['y'], { row: 1, col: 15, file: undefined })]
+    const z = [new Variable(['z'], { row: 1, col: 29, file: undefined })]
+
+    expect(analysis).toStrictEqual({
+      variables: { b, x, y, z },
+      globals: { b, y, z },
+      locals: { }
+    })
+  })
+
+  it('should export analysis interfaces', () => {
+    const engine = new Liquid()
+    const template = engine.parse('{% include nothing %}')
+    const options: StaticAnalysisOptions = { partials: false }
+    const analysis: StaticAnalysis = analyzeSync(template, options)
+    const vars: Variable[] = analysis.variables['nothing'] || []
+    const v: Variable = vars[0]
+    expect(String(v)).toBe('nothing')
+  })
+})

test/integration/liquid/liquid.spec.ts

@@ -229,4 +229,113 @@ describe('Liquid', function () {
       expect(drainStream(stream)).rejects.toThrow(/intended render error/)
     })
   })
+  describe('#analyze', () => {
+    const engine = new Liquid()
+    it('should analyze templates asynchronously', () => {
+      const template = engine.parse('{{ a }}{{ b }}')
+      expect(engine.analyze(template).then((a) => Object.keys(a.variables))).resolves.toStrictEqual(['a', 'b'])
+    })
+  })
+  describe('#analyzeSync', () => {
+    const engine = new Liquid()
+    it('should analyze templates synchronously', () => {
+      const template = engine.parse('{{ a }}{{ b }}')
+      expect(Object.keys(engine.analyzeSync(template).variables)).toStrictEqual(['a', 'b'])
+    })
+  })
+  describe('#parseAndAnalyze', () => {
+    const engine = new Liquid()
+    it('should parse and analyze templates asynchronously', () => {
+      expect(engine.parseAndAnalyze('{{ a }}{{ b }}').then((a) => Object.keys(a.variables))).resolves.toStrictEqual(['a', 'b'])
+    })
+  })
+  describe('#parseAndAnalyzeSync', () => {
+    const engine = new Liquid()
+    it('should analyze templates synchronously', () => {
+      expect(Object.keys(engine.parseAndAnalyzeSync('{{ a }}{{ b }}').variables)).toStrictEqual(['a', 'b'])
+    })
+  })
+  describe('Convenience analysis', () => {
+    const engine = new Liquid()
+
+    it('should list all variables without their properties', () => {
+      expect(engine.variables('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).resolves.toStrictEqual(['a', 'c'])
+      expect(engine.variables(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).resolves.toStrictEqual(['a', 'c'])
+    })
+
+    it('should list all variables without their properties synchronously', () => {
+      expect(engine.variablesSync('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).toStrictEqual(['a', 'c'])
+      expect(engine.variablesSync(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).toStrictEqual(['a', 'c'])
+    })
+
+    it('should list global variables without their properties', () => {
+      expect(engine.globalVariables('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).resolves.toStrictEqual(['a'])
+      expect(engine.globalVariables(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).resolves.toStrictEqual(['a'])
+    })
+
+    it('should list global variables without their properties synchronously', () => {
+      expect(engine.globalVariablesSync('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).toStrictEqual(['a'])
+      expect(engine.globalVariablesSync(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).toStrictEqual(['a'])
+    })
+
+    it('should list all variables with their properties', () => {
+      expect(engine.fullVariables('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).resolves.toStrictEqual(['a.b', 'c'])
+      expect(engine.fullVariables(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).resolves.toStrictEqual(['a.b', 'c'])
+    })
+
+    it('should list all variables with their properties synchronously', () => {
+      expect(engine.fullVariablesSync('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).toStrictEqual(['a.b', 'c'])
+      expect(engine.fullVariablesSync(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).toStrictEqual(['a.b', 'c'])
+    })
+
+    it('should list global variables with their properties', () => {
+      expect(engine.globalFullVariables('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).resolves.toStrictEqual(['a.b'])
+      expect(engine.globalFullVariables(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).resolves.toStrictEqual(['a.b'])
+    })
+
+    it('should list global variables with their properties synchronously', () => {
+      expect(engine.globalFullVariablesSync('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).toStrictEqual(['a.b'])
+      expect(engine.globalFullVariablesSync(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).toStrictEqual(['a.b'])
+    })
+
+    it('should list all variables as an array of segments', () => {
+      expect(engine.variableSegments('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).resolves.toStrictEqual([['a', 'b'], ['c']])
+      expect(engine.variableSegments(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).resolves.toStrictEqual([['a', 'b'], ['c']])
+    })
+
+    it('should list all variables as an array of segments synchronously', () => {
+      expect(engine.variableSegmentsSync('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).toStrictEqual([['a', 'b'], ['c']])
+      expect(engine.variableSegmentsSync(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).toStrictEqual([['a', 'b'], ['c']])
+    })
+
+    it('should list all variables as an array of segments with nested variables as arrays', () => {
+      expect(engine.variableSegments('{{ a[b.c].d }}')).resolves.toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+      expect(engine.variableSegments(engine.parse('{{ a[b.c].d }}'))).resolves.toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+    })
+
+    it('should list all variables synchronously as an array of segments with nested variables as arrays', () => {
+      expect(engine.variableSegmentsSync('{{ a[b.c].d }}')).toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+      expect(engine.variableSegmentsSync(engine.parse('{{ a[b.c].d }}'))).toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+    })
+
+    it('should list global variables as an array of segments', () => {
+      expect(engine.globalVariableSegments('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).resolves.toStrictEqual([['a', 'b']])
+      expect(engine.globalVariableSegments(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).resolves.toStrictEqual([['a', 'b']])
+    })
+
+    it('should list global variables as an array of segments synchronously', () => {
+      expect(engine.globalVariableSegmentsSync('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}')).toStrictEqual([['a', 'b']])
+      expect(engine.globalVariableSegmentsSync(engine.parse('{% assign c = 1 %}{{ a.b }}{{ c }}{{ c }}'))).toStrictEqual([['a', 'b']])
+    })
+
+    it('should list global variables as an array of segments with nested variables as arrays', () => {
+      expect(engine.globalVariableSegments('{{ a[b.c].d }}')).resolves.toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+      expect(engine.globalVariableSegments(engine.parse('{{ a[b.c].d }}'))).resolves.toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+    })
+
+    it('should list global variables synchronously as an array of segments with nested variables as arrays', () => {
+      expect(engine.globalVariableSegmentsSync('{{ a[b.c].d }}')).toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+      expect(engine.globalVariableSegmentsSync(engine.parse('{{ a[b.c].d }}'))).toStrictEqual([['a', ['b', 'c'], 'd'], ['b', 'c']])
+    })
+  })
 })

test/integration/util/error.spec.ts

@@ -264,7 +264,7 @@ describe('error', function () {
     it('should throw ParseError when tag value not specified', async function () {
       await expect(engine.parseAndRender('{% if %}{% endif %}')).rejects.toMatchObject({
         name: 'TokenizationError',
-        message: 'invalid value expression: "", line:1, col:1'
+        message: 'invalid value expression: "", line:1, col:6'
       })
     })
     it('should throw ParseError when tag parse throws', async function () {