feat: await promises returned by Drop.valueOf() (#948) (#953) (#959)

* feat: WIP async Drop valueOf resolution (#948)

Incomplete/abandoned implementation of async Drop.valueOf() awaited across the render pipeline. Kept for reference only; known to be inconsistent and not production-ready.

Co-authored-by: Cursor <[email protected]>

* feat!: resolve async Drop.valueOf() for filters and tags

Co-authored-by: Cursor <[email protected]>

* fix: keep Drops on filter and tag inputs

Filters and tag arguments still receive the Drop. Await valueOf() at output, conditions, and operators, and restore the existing render/include Drop tests.

Co-authored-by: Cursor <[email protected]>

---------

Co-authored-by: Cursor <[email protected]>

docs/source/tutorials/parse-parameters.md

@@ -38,7 +38,7 @@ The following modified template also contains 3 values to random from, but they'
 It can be tricky to parse all these cases manually, but there's a [Tokenizer][Tokenizer] class in LiquidJS you can make use of.
 
 ```javascript
-const { Liquid, Tokenizer, evalToken } = require('liquidjs')
+const { Liquid, Tokenizer, evalTokenValue } = require('liquidjs')
 engine.registerTag('random', {
   parse(tagToken) {
     const tokenizer = new Tokenizer(tagToken.args)
@@ -52,7 +52,7 @@ engine.registerTag('random', {
     const index = Math.floor(this.items.length * Math.random())
     const token = this.items[index]
     // in LiquidJS, we use yield to wait for async call
-    const value = yield evalToken(token, context)
+    const value = yield evalTokenValue(token, context)
     emitter.write(value)
   }
 })

src/drop/blank-drop.ts

@@ -2,11 +2,11 @@ import { isNil, isString, toValue } from '../util'
 import { EmptyDrop } from '../drop'
 
 export class BlankDrop extends EmptyDrop {
-  public equals (value: any) {
+  public * equals (value: any): Generator<unknown, boolean, any> {
     if (value === false) return true
-    if (isNil(toValue(value))) return true
+    if (isNil(yield toValue(value))) return true
     if (isString(value)) return /^\s*$/.test(value)
-    return super.equals(value)
+    return yield super.equals(value)
   }
   static is (value: unknown) {
     return value instanceof BlankDrop

src/drop/comparable.ts

@@ -1,11 +1,18 @@
 import { isFunction } from '../util'
 
+/**
+ * Comparison methods may return a boolean, a promise, or a generator.
+ * Operators yield the result, so sync implementations stay valid and async
+ * `valueOf()` can be awaited with `yield`.
+ */
+export type ComparableResult = boolean | Promise<boolean> | Generator<unknown, boolean, any>
+
 export interface Comparable {
-  equals: (rhs: any) => boolean;
-  gt: (rhs: any) => boolean;
-  geq: (rhs: any) => boolean;
-  lt: (rhs: any) => boolean;
-  leq: (rhs: any) => boolean;
+  equals: (rhs: any) => ComparableResult;
+  gt: (rhs: any) => ComparableResult;
+  geq: (rhs: any) => ComparableResult;
+  lt: (rhs: any) => ComparableResult;
+  leq: (rhs: any) => ComparableResult;
 }
 
 export function isComparable (arg: any): arg is Comparable {

src/drop/empty-drop.ts

@@ -3,9 +3,9 @@ import { Comparable } from './comparable'
 import { isObject, isString, isArray, toValue } from '../util'
 
 export class EmptyDrop extends Drop implements Comparable {
-  public equals (value: any) {
+  public * equals (value: any): Generator<unknown, boolean, any> {
     if (value instanceof EmptyDrop) return false
-    value = toValue(value)
+    value = yield toValue(value)
     if (isString(value) || isArray(value)) return value.length === 0
     if (isObject(value)) return Object.keys(value).length === 0
     return false

src/drop/null-drop.ts

@@ -3,8 +3,8 @@ import { Comparable } from './comparable'
 import { isNil, toValue } from '../util'
 
 export class NullDrop extends Drop implements Comparable {
-  public equals (value: any) {
-    return isNil(toValue(value))
+  public * equals (value: any): Generator<unknown, boolean, any> {
+    return isNil(yield toValue(value))
   }
   public gt () {
     return false

src/filters/array.ts

@@ -121,26 +121,26 @@ export function slice<T> (this: FilterImpl, v: T[] | string, begin: number, leng
     : String.prototype.slice.call(v, begin, begin + length)
 }
 
-function expectedMatcher (this: FilterImpl, expected: any): (v: any) => boolean {
+function * matches (this: FilterImpl, value: unknown, expected: unknown): Generator<unknown, boolean, any> {
   if (this.context.opts.jekyllWhere) {
-    return (v: any) => EmptyDrop.is(expected) ? equals(v, expected) : (isArray(v) ? arrayIncludes(v, expected) : equals(v, expected))
-  } else if (expected === undefined) {
-    return (v: any) => isTruthy(v, this.context)
-  } else {
-    return (v: any) => equals(v, expected)
+    if (EmptyDrop.is(expected)) return yield equals(value, expected)
+    if (isArray(value)) return yield arrayIncludes(value, expected)
+    return yield equals(value, expected)
   }
+  if (expected === undefined) return isTruthy(value, this.context)
+  return yield equals(value, expected)
 }
 
 function * filter<T extends object> (this: FilterImpl, include: boolean, arr: T[], property: string, expected: any): IterableIterator<unknown> {
-  const values: unknown[] = []
   arr = toArray(arr)
   this.context.memoryLimit.use(arr.length)
   const token = new Tokenizer(stringify(property)).readScopeValue()
+  const result: T[] = []
   for (const item of arr) {
-    values.push(yield evalToken(token, this.context.spawn(item)))
+    const value = yield evalToken(token, this.context.spawn(item))
+    if ((yield matches.call(this, value, expected)) === include) result.push(item)
   }
-  const matcher = expectedMatcher.call(this, expected)
-  return Array.prototype.filter.call(arr, (_, i) => matcher(values[i]) === include)
+  return result
 }
 
 function * filter_exp<T extends object> (this: FilterImpl, include: boolean, arr: T[], itemName: string, exp: string): IterableIterator<unknown> {
@@ -204,10 +204,9 @@ export function * group_by_exp<T extends object> (this: FilterImpl, arr: T[], it
 function * search<T extends object> (this: FilterImpl, arr: T[], property: string, expected: string): IterableIterator<unknown> {
   const token = new Tokenizer(stringify(property)).readScopeValue()
   const array = toArray(arr)
-  const matcher = expectedMatcher.call(this, expected)
   for (let index = 0; index < array.length; index++) {
     const value = yield evalToken(token, this.context.spawn(array[index]))
-    if (matcher(value)) return [index, array[index]]
+    if (yield matches.call(this, value, expected)) return [index, array[index]]
   }
 }
 

src/index.ts

@@ -4,9 +4,9 @@ export * as TypeGuards from './util/type-guards'
 export { toValue, createTrie, Trie, toPromise, toValueSync, assert, LiquidError, ParseError, RenderError, UndefinedVariableError, TokenizationError, AssertionError } from './util'
 export type { LiquidErrors } from './util/error'
 export { Drop } from './drop'
-export type { Comparable } from './drop'
+export type { Comparable, ComparableResult } from './drop'
 export { Emitter } from './emitters'
-export { defaultOperators, Operators, evalToken, evalQuotedToken, Expression, isFalsy, isTruthy } from './render'
+export { defaultOperators, Operators, evalToken, evalTokenValue, evalQuotedToken, Expression, isFalsy, isTruthy } from './render'
 export { Context, Scope } from './context'
 export { Value, Hash, Template, FilterImplOptions, Tag, Filter, Output, Variable, VariableLocation, VariableSegments, Variables, StaticAnalysis, StaticAnalysisOptions, analyze, analyzeSync, Arguments, PartialScope } from './template'
 export type { TagRenderReturn } from './template'

src/render/expression.ts

@@ -1,5 +1,5 @@
 import { QuotedToken, RangeToken, OperatorToken, Token, PropertyAccessToken, OperatorType, operatorTypes, FilteredValueToken } from '../tokens'
-import { isRangeToken, isPropertyAccessToken, isFilteredValueToken, UndefinedVariableError, range, isOperatorToken, assert } from '../util'
+import { isRangeToken, isPropertyAccessToken, isFilteredValueToken, UndefinedVariableError, range, isOperatorToken, assert, toValue } from '../util'
 import type { Context } from '../context'
 import type { UnaryOperatorHandler } from '../render'
 import { Drop } from '../drop'
@@ -36,6 +36,11 @@ export class Expression {
   }
 }
 
+/**
+ * Evaluate `token`, preserving Drops.
+ * Operators use this so `Comparable` drops (`empty`, `nil`, `blank`) and custom drops
+ * are compared as drops rather than as their `valueOf()` result.
+ */
 export function * evalToken (token: Token | undefined, ctx: Context, lenient = false): IterableIterator<unknown> {
   if (!token) return
   if ('content' in token) return token.content
@@ -59,10 +64,18 @@ function * evalFilteredValueToken (token: FilteredValueToken, ctx: Context, leni
   return val
 }
 
+/**
+ * Evaluate `token` to the value filters and tags consume.
+ * Awaits a promise returned by `Drop.valueOf()`.
+ */
+export function * evalTokenValue (token: Token | undefined, ctx: Context, lenient = false): IterableIterator<unknown> {
+  return yield toValue(yield evalToken(token, ctx, lenient))
+}
+
 function * evalPropertyAccessToken (token: PropertyAccessToken, ctx: Context, lenient: boolean): IterableIterator<unknown> {
   const props: (string | number | Drop)[] = []
   for (const prop of token.props) {
-    props.push((yield evalToken(prop, ctx, false)) as unknown as string | number | Drop)
+    props.push((yield evalTokenValue(prop, ctx, false)) as unknown as string | number | Drop)
   }
   try {
     if (token.variable) {
@@ -81,9 +94,9 @@ export function evalQuotedToken (token: QuotedToken) {
   return token.content
 }
 
-function * evalRangeToken (token: RangeToken, ctx: Context) {
-  const low: number = yield evalToken(token.lhs, ctx)
-  const high: number = yield evalToken(token.rhs, ctx)
+function * evalRangeToken (token: RangeToken, ctx: Context): IterableIterator<unknown> {
+  const low = (yield evalTokenValue(token.lhs, ctx)) as unknown as number
+  const high = (yield evalTokenValue(token.rhs, ctx)) as unknown as number
   ctx.memoryLimit.use(high - low + 1)
   return range(+low, +high + 1)
 }

src/render/operator.ts

@@ -4,61 +4,74 @@ import { toValue } from '../util'
 import { isFalsy, isTruthy } from '../render/boolean'
 import { isArray, isFunction } from '../util/underscore'
 
-export type UnaryOperatorHandler = (operand: any, ctx: Context) => boolean;
-export type BinaryOperatorHandler = (lhs: any, rhs: any, ctx: Context) => boolean;
+/**
+ * A handler may return a `boolean` (legacy interface), a `Promise`, or a generator
+ * that `yield`s to await async values. The render driver resolves all three, so
+ * operators written against the legacy `=> boolean` signature keep working.
+ */
+export type OperatorGenerator = Generator<unknown, boolean, any>
+export type OperatorResult = boolean | Promise<boolean> | OperatorGenerator
+export type UnaryOperatorHandler = (operand: any, ctx: Context) => OperatorResult;
+export type BinaryOperatorHandler = (lhs: any, rhs: any, ctx: Context) => OperatorResult;
 export type OperatorHandler = UnaryOperatorHandler | BinaryOperatorHandler;
 export type Operators = Record<string, OperatorHandler>
 
 export const defaultOperators: Operators = {
-  '==': equals,
-  '!=': (l: any, r: any) => !equals(l, r),
-  '>': (l: any, r: any) => {
-    if (isComparable(l)) return l.gt(r)
-    if (isComparable(r)) return r.lt(l)
-    return toValue(l) > toValue(r)
+  '==': function * (l: any, r: any): OperatorGenerator { return yield equals(l, r) },
+  '!=': function * (l: any, r: any): OperatorGenerator { return !(yield equals(l, r)) },
+  '>': function * (l: any, r: any): OperatorGenerator {
+    if (isComparable(l)) return yield l.gt(r)
+    if (isComparable(r)) return yield r.lt(l)
+    return (yield toValue(l)) > (yield toValue(r))
   },
-  '<': (l: any, r: any) => {
-    if (isComparable(l)) return l.lt(r)
-    if (isComparable(r)) return r.gt(l)
-    return toValue(l) < toValue(r)
+  '<': function * (l: any, r: any): OperatorGenerator {
+    if (isComparable(l)) return yield l.lt(r)
+    if (isComparable(r)) return yield r.gt(l)
+    return (yield toValue(l)) < (yield toValue(r))
   },
-  '>=': (l: any, r: any) => {
-    if (isComparable(l)) return l.geq(r)
-    if (isComparable(r)) return r.leq(l)
-    return toValue(l) >= toValue(r)
+  '>=': function * (l: any, r: any): OperatorGenerator {
+    if (isComparable(l)) return yield l.geq(r)
+    if (isComparable(r)) return yield r.leq(l)
+    return (yield toValue(l)) >= (yield toValue(r))
   },
-  '<=': (l: any, r: any) => {
-    if (isComparable(l)) return l.leq(r)
-    if (isComparable(r)) return r.geq(l)
-    return toValue(l) <= toValue(r)
+  '<=': function * (l: any, r: any): OperatorGenerator {
+    if (isComparable(l)) return yield l.leq(r)
+    if (isComparable(r)) return yield r.geq(l)
+    return (yield toValue(l)) <= (yield toValue(r))
   },
-  'contains': (l: any, r: any) => {
-    l = toValue(l)
-    if (isArray(l)) return l.some((i) => equals(i, r))
-    if (isFunction(l?.indexOf)) return l.indexOf(toValue(r)) > -1
+  'contains': function * (l: any, r: any): OperatorGenerator {
+    l = yield toValue(l)
+    if (isArray(l)) return yield arrayIncludes(l, r)
+    if (isFunction(l?.indexOf)) return l.indexOf(yield toValue(r)) > -1
     return false
   },
-  'not': (v: any, ctx: Context) => isFalsy(toValue(v), ctx),
-  'and': (l: any, r: any, ctx: Context) => isTruthy(toValue(l), ctx) && isTruthy(toValue(r), ctx),
-  'or': (l: any, r: any, ctx: Context) => isTruthy(toValue(l), ctx) || isTruthy(toValue(r), ctx)
+  'not': function * (v: any, ctx: Context): OperatorGenerator { return isFalsy(yield toValue(v), ctx) },
+  'and': function * (l: any, r: any, ctx: Context): OperatorGenerator { return isTruthy(yield toValue(l), ctx) && isTruthy(yield toValue(r), ctx) },
+  'or': function * (l: any, r: any, ctx: Context): OperatorGenerator { return isTruthy(yield toValue(l), ctx) || isTruthy(yield toValue(r), ctx) }
 }
 
-export function equals (lhs: any, rhs: any): boolean {
-  if (isComparable(lhs)) return lhs.equals(rhs)
-  if (isComparable(rhs)) return rhs.equals(lhs)
-  lhs = toValue(lhs)
-  rhs = toValue(rhs)
+export function * equals (lhs: any, rhs: any): Generator<unknown, boolean, any> {
+  if (isComparable(lhs)) return yield lhs.equals(rhs)
+  if (isComparable(rhs)) return yield rhs.equals(lhs)
+  lhs = yield toValue(lhs)
+  rhs = yield toValue(rhs)
   if (isArray(lhs)) {
-    return isArray(rhs) && arrayEquals(lhs, rhs)
+    return isArray(rhs) && (yield arrayEquals(lhs, rhs))
   }
   return lhs === rhs
 }
 
-function arrayEquals (lhs: any[], rhs: any[]): boolean {
+function * arrayEquals (lhs: any[], rhs: any[]): Generator<unknown, boolean, any> {
   if (lhs.length !== rhs.length) return false
-  return !lhs.some((value, i) => !equals(value, rhs[i]))
+  for (let i = 0; i < lhs.length; i++) {
+    if (!(yield equals(lhs[i], rhs[i]))) return false
+  }
+  return true
 }
 
-export function arrayIncludes (arr: any[], item: any): boolean {
-  return arr.some(value => equals(value, item))
+export function * arrayIncludes (arr: any[], item: any): Generator<unknown, boolean, any> {
+  for (const value of arr) {
+    if (yield equals(value, item)) return true
+  }
+  return false
 }

src/tags/case.ts

@@ -56,12 +56,12 @@ export default class extends Tag {
 
   * render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> {
     const r = this.liquid.renderer
-    const target = toValue(yield this.value.value(ctx, ctx.opts.lenientIf))
+    const target = yield toValue(yield this.value.value(ctx, ctx.opts.lenientIf))
     let branchHit = false
     for (const branch of this.branches) {
       for (const valueToken of branch.values) {
         const value = yield evalToken(valueToken, ctx, ctx.opts.lenientIf)
-        if (equals(target, value)) {
+        if (yield equals(target, value)) {
           yield r.renderTemplates(branch.templates, ctx, emitter)
           branchHit = true
           break

src/tags/echo.ts

@@ -1,5 +1,6 @@
 import { Liquid, TopLevelToken, Emitter, Value, TagToken, Context, Tag } from '..'
 import { Arguments } from '../template'
+import { toValue } from '../util'
 
 export default class extends Tag {
   private value?: Value
@@ -13,7 +14,7 @@ export default class extends Tag {
   }
   * render (ctx: Context, emitter: Emitter): Generator<unknown, void, unknown> {
     if (!this.value) return
-    const val = yield this.value.value(ctx, false)
+    const val = yield toValue(yield this.value.value(ctx, false))
     emitter.write(val)
   }
 

src/tags/if.ts

@@ -1,7 +1,7 @@
 import { Liquid, Tag, Value, Emitter, isTruthy, TagToken, TopLevelToken, Context, Template } from '..'
 import { Parser } from '../parser'
 import { Arguments } from '../template'
-import { assert, assertEmpty } from '../util'
+import { assert, assertEmpty, toValue } from '../util'
 
 export default class extends Tag {
   branches: { value: Value, templates: Template[] }[] = []
@@ -37,7 +37,7 @@ export default class extends Tag {
     const r = this.liquid.renderer
 
     for (const { value, templates } of this.branches) {
-      const v = yield value.value(ctx, ctx.opts.lenientIf)
+      const v = yield toValue(yield value.value(ctx, ctx.opts.lenientIf))
       if (isTruthy(v, ctx)) {
         yield r.renderTemplates(templates, ctx, emitter)
         return

src/tags/unless.ts

@@ -1,6 +1,7 @@
 import { Liquid, Tag, Value, TopLevelToken, Template, Emitter, isTruthy, isFalsy, Context, TagToken } from '..'
 import { Parser } from '../parser'
 import { Arguments } from '../template'
+import { toValue } from '../util'
 
 export default class extends Tag {
   branches: { value: Value, test: (val: any, ctx: Context) => boolean, templates: Template[] }[] = []
@@ -44,7 +45,7 @@ export default class extends Tag {
     const r = this.liquid.renderer
 
     for (const { value, test, templates } of this.branches) {
-      const v = yield value.value(ctx, ctx.opts.lenientIf)
+      const v = yield toValue(yield value.value(ctx, ctx.opts.lenientIf))
       if (test(v, ctx)) {
         yield r.renderTemplates(templates, ctx, emitter)
         return

src/template/output.ts

@@ -7,6 +7,7 @@ import { Tokenizer } from '../parser'
 import { Liquid } from '../liquid'
 import { Filter } from './filter'
 import { FilterToken } from '../tokens'
+import { toValue } from '../util'
 
 export class Output extends TemplateImpl<OutputToken> implements Template {
   value: Value
@@ -22,7 +23,7 @@ export class Output extends TemplateImpl<OutputToken> implements Template {
     }
   }
   public * render (ctx: Context, emitter: Emitter): IterableIterator<unknown> {
-    const val = yield this.value.value(ctx, false)
+    const val = yield toValue(yield this.value.value(ctx, false))
     emitter.write(val)
   }
 

test/integration/drop/drop.spec.ts

@@ -1,4 +1,5 @@
 import { Liquid, Drop } from '../../../src'
+import { mock, restore } from '../../stub/mockfs'
 
 describe('drop/drop', function () {
   let liquid: Liquid
@@ -71,6 +72,19 @@ describe('drop/drop', function () {
     const html = await liquid.parseAndRender(tpl, { drop: new CustomDrop() })
     expect(html).toBe('foobar: foo;bar;')
   })
+  it('should support promise returned by valueOf', async () => {
+    class AsyncValueOfDrop extends Drop {
+      id = '42'
+      async valueOf () {
+        return 'serialized'
+      }
+    }
+    const html = await liquid.parseAndRender(
+      `{{o.id}}:{{o}}:{% if o %}yes{% endif %}:{% unless o %}no{% endunless %}`,
+      { o: new AsyncValueOfDrop() }
+    )
+    expect(html).toBe('42:serialized:yes:')
+  })
   it('should support valueOf in == expression', async () => {
     class AddressDrop extends Drop {
       valueOf () {
@@ -119,4 +133,192 @@ describe('drop/drop', function () {
     const html = await liquid.parseAndRender(`{{obj.number}} {{obj.string}} {{obj.boolean}} {{obj.array | first}} {{obj.object.foo}} {{obj.drop.getName}}`, { obj: new DynamicTypeDrop() })
     expect(html).toBe('42 foo true 1 bar GET NAME')
   })
+
+  describe('async valueOf', function () {
+    beforeEach(() => {
+      liquid = new Liquid({ root: '/', extname: '.html' })
+    })
+    afterEach(restore)
+
+    class AsyncStringDrop extends Drop {
+      constructor (private value: string) { super() }
+      async valueOf () {
+        return this.value
+      }
+    }
+
+    class AsyncFalsyDrop extends Drop {
+      async valueOf () {
+        return false
+      }
+    }
+
+    class AsyncArrayDrop extends Drop {
+      constructor (private value: string[]) { super() }
+      async valueOf () {
+        return this.value
+      }
+    }
+
+    class AsyncNumberDrop extends Drop {
+      constructor (private value: number) { super() }
+      async valueOf () {
+        return this.value
+      }
+    }
+
+    describe('output & filters', function () {
+      it('output {{ drop }}', async function () {
+        const html = await liquid.parseAndRender(`{{a}}`, { a: new AsyncStringDrop('x') })
+        expect(html).toBe('x')
+      })
+      it('where_exp resolves async properties', async function () {
+        const items = [{ v: new AsyncStringDrop('x'), id: '1' }, { v: new AsyncStringDrop('y'), id: '2' }]
+        const html = await liquid.parseAndRender(`{% assign r = items | where_exp: 'item', 'item.v == "y"' %}{{ r[0].id }}`, { items })
+        expect(html).toBe('2')
+      })
+      it('where by async property', async function () {
+        const items = [{ v: new AsyncStringDrop('x'), id: '1' }, { v: new AsyncStringDrop('y'), id: '2' }]
+        const html = await liquid.parseAndRender(`{% assign r = items | where: 'v', 'y' %}{{ r[0].id }}`, { items })
+        expect(html).toBe('2')
+      })
+      it('find by async property', async function () {
+        const items = [{ v: new AsyncStringDrop('x'), id: '1' }, { v: new AsyncStringDrop('y'), id: '2' }]
+        const html = await liquid.parseAndRender(`{% assign f = items | find: 'v', 'y' %}{{ f.id }}`, { items })
+        expect(html).toBe('2')
+      })
+    })
+
+    describe('branch conditions', function () {
+      it('if truthy', async function () {
+        const html = await liquid.parseAndRender(`{% if a %}yes{% else %}no{% endif %}`, { a: new AsyncStringDrop('x') })
+        expect(html).toBe('yes')
+      })
+      it('if falsy', async function () {
+        const html = await liquid.parseAndRender(`{% if a %}yes{% else %}no{% endif %}`, { a: new AsyncFalsyDrop() })
+        expect(html).toBe('no')
+      })
+      it('unless', async function () {
+        const html = await liquid.parseAndRender(`{% unless a %}yes{% else %}no{% endunless %}`, { a: new AsyncFalsyDrop() })
+        expect(html).toBe('yes')
+      })
+      it('elsif', async function () {
+        const html = await liquid.parseAndRender(
+          `{% if false %}a{% elsif b %}b{% else %}c{% endif %}`,
+          { b: new AsyncStringDrop('x') }
+        )
+        expect(html).toBe('b')
+      })
+      it('case/when', async function () {
+        const html = await liquid.parseAndRender(
+          `{% case a %}{% when "x" %}X{% when "y" %}Y{% else %}Z{% endcase %}`,
+          { a: new AsyncStringDrop('y') }
+        )
+        expect(html).toBe('Y')
+      })
+      it('case when empty uses Comparable on the resolved value', async function () {
+        const html = await liquid.parseAndRender(
+          `{% case a %}{% when empty %}E{% else %}X{% endcase %}`,
+          { a: new AsyncArrayDrop([]) }
+        )
+        expect(html).toBe('E')
+      })
+    })
+
+    describe('operators', function () {
+      it('== / !=', async function () {
+        const html = await liquid.parseAndRender(
+          `{% if a == b %}eq{% endif %}/{% if a != c %}ne{% endif %}`,
+          { a: new AsyncStringDrop('t'), b: new AsyncStringDrop('t'), c: new AsyncStringDrop('u') }
+        )
+        expect(html).toBe('eq/ne')
+      })
+      it('< / >', async function () {
+        const html = await liquid.parseAndRender(
+          `{% if a < b %}lt{% endif %}/{% if b > a %}gt{% endif %}`,
+          { a: new AsyncNumberDrop(1), b: new AsyncNumberDrop(2) }
+        )
+        expect(html).toBe('lt/gt')
+      })
+      it('contains', async function () {
+        const html = await liquid.parseAndRender(
+          `{% if a contains "od" %}yes{% endif %}`,
+          { a: new AsyncStringDrop('product') }
+        )
+        expect(html).toBe('yes')
+      })
+      it('and / or', async function () {
+        const html = await liquid.parseAndRender(
+          `{% if a and b %}both{% endif %}/{% if f or a %}either{% endif %}`,
+          { a: new AsyncStringDrop('x'), b: new AsyncStringDrop('y'), f: new AsyncFalsyDrop() }
+        )
+        expect(html).toBe('both/either')
+      })
+      it('not (unless)', async function () {
+        const html = await liquid.parseAndRender(
+          `{% unless a %}yes{% else %}no{% endunless %}`,
+          { a: new AsyncFalsyDrop() }
+        )
+        expect(html).toBe('yes')
+      })
+    })
+
+    describe('pass-through tags', function () {
+      it('assign then output', async function () {
+        const html = await liquid.parseAndRender(`{% assign b = a %}{{ b }}`, { a: new AsyncStringDrop('z') })
+        expect(html).toBe('z')
+      })
+      it('assign keeps the drop so properties stay readable', async function () {
+        class NamedDrop extends Drop {
+          id = '42'
+          async valueOf () { return 'serialized' }
+        }
+        const html = await liquid.parseAndRender(`{% assign b = a %}{{ b.id }}:{{ b }}`, { a: new NamedDrop() })
+        expect(html).toBe('42:serialized')
+      })
+      it('supports async Comparable.equals', async function () {
+        class EqDrop extends Drop {
+          constructor (private n: string) { super() }
+          async equals (rhs: unknown) {
+            const other = rhs instanceof Drop ? await rhs.valueOf() : rhs
+            return (await this.valueOf()) === other
+          }
+          async valueOf () { return this.n }
+          gt () { return false }
+          geq () { return false }
+          lt () { return false }
+          leq () { return false }
+        }
+        const html = await liquid.parseAndRender(
+          `{% if a == b %}eq{% endif %}/{% if a == c %}bad{% else %}ne{% endif %}`,
+          { a: new EqDrop('t'), b: new EqDrop('t'), c: new EqDrop('u') }
+        )
+        expect(html).toBe('eq/ne')
+      })
+      it('echo', async function () {
+        const html = await liquid.parseAndRender(`{% echo a %}`, { a: new AsyncStringDrop('z') })
+        expect(html).toBe('z')
+      })
+      it('render with', async function () {
+        mock({
+          '/c.html': '{{ color }}'
+        })
+        const html = await liquid.parseAndRender(
+          `{% render "c" with a as color %}`,
+          { a: new AsyncStringDrop('red') }
+        )
+        expect(html).toBe('red')
+      })
+      it('include with', async function () {
+        mock({
+          '/color.html': '{{ color }}'
+        })
+        const html = await liquid.parseAndRender(
+          `{% include "color" with a %}`,
+          { a: new AsyncStringDrop('red') }
+        )
+        expect(html).toBe('red')
+      })
+    })
+  })
 })

test/integration/tags/if.spec.ts

@@ -65,6 +65,16 @@ describe('tags/if', function () {
       const html = await liquid.parseAndRender(src, scope)
       return expect(html).toBe('yes')
     })
+    it('should keep comparable operands uncoerced', async function () {
+      const src = '{% if empty == empty %}yes{%else%}no{%endif%}'
+      const html = await liquid.parseAndRender(src, scope)
+      return expect(html).toBe('no')
+    })
+    it('should keep comparable operands uncoerced in elsif', async function () {
+      const src = '{% if false %}a{% elsif empty == empty %}b{% else %}c{% endif %}'
+      const html = await liquid.parseAndRender(src, scope)
+      return expect(html).toBe('c')
+    })
     it('should support value and expression', async function () {
       const src = `X{%if version and version != '' %}x{{version}}y{%endif%}Y`
       const scope = { 'version': '' }

test/integration/tags/include.spec.ts

@@ -142,6 +142,21 @@ describe('tags/include', function () {
     const html = await liquid.renderFile('with.html', { color: new ColorDrop() })
     expect(html).toBe('ColorDrop')
   })
+  it('should await async valueOf when the included Drop is output', async function () {
+    class ColorDrop extends Drop {
+      label = 'blue'
+      public async valueOf () {
+        return 'red!'
+      }
+    }
+    liquid.registerFilter('name', x => x.constructor.name)
+    mock({
+      '/with.html': '{% include "color" with color %}',
+      '/color.html': '{{color.label}}:{{color}}:{{color | name}}'
+    })
+    const html = await liquid.renderFile('with.html', { color: new ColorDrop() })
+    expect(html).toBe('blue:red!:ColorDrop')
+  })
 
   it('should support nested includes', async function () {
     mock({

test/integration/tags/render.spec.ts

@@ -226,6 +226,21 @@ describe('tags/render', function () {
     const html = await liquid.renderFile('with.html', { color: new ColorDrop() })
     expect(html).toBe('ColorDrop')
   })
+  it('should await async valueOf when the rendered Drop is output', async function () {
+    class ColorDrop extends Drop {
+      label = 'blue'
+      public async valueOf () {
+        return 'red!'
+      }
+    }
+    liquid.registerFilter('name', x => x.constructor.name)
+    mock({
+      '/with.html': '{% render "color" with color %}',
+      '/color.html': '{{color.label}}:{{color}}:{{color | name}}'
+    })
+    const html = await liquid.renderFile('with.html', { color: new ColorDrop() })
+    expect(html).toBe('blue:red!:ColorDrop')
+  })
 
   it('should support nested renders', async function () {
     mock({

test/integration/tags/unless.spec.ts

@@ -35,6 +35,11 @@ describe('tags/unless', function () {
     const html = await liquid.parseAndRender(src)
     return expect(html).toBe('')
   })
+  it('should keep comparable operands uncoerced', async function () {
+    const src = '{% unless empty == empty %}yes{%else%}no{%endunless%}'
+    const html = await liquid.parseAndRender(src)
+    return expect(html).toBe('yes')
+  })
 
   it('should output unless contents in order', async function () {
     const src = `