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Merged
Wesley Wigham (weswigham) merged 4 commits into from
Aug 19, 2026
Merged

Preserve comments when downleveling arrow expression bodies #4723

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de6d68f
Add arrow body comment emit regressions
jakebailey Aug 14, 2026
b0e85fb
Preserve comments on rewritten arrow bodies
jakebailey Aug 14, 2026
aca5f3b
Reuse function block converter
Copilot Aug 18, 2026
70c3165
Preserve async return origin
Copilot Aug 18, 2026
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22 changes: 20 additions & 2 deletions internal/printer/emitcontext.go
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Original file line number Diff line number Diff line change
Expand Up @@ -900,6 +900,19 @@ func (c *EmitContext) AddInitializationStatement(node *ast.Node) {
scope.initializationStatements = append(scope.initializationStatements, node)
}

func (c *EmitContext) ConvertToFunctionBlock(node *ast.Node, multiLine bool) *ast.Node {
if ast.IsBlock(node) {
return node
}
returnStatement := c.Factory.NewReturnStatement(node)
returnStatement.Loc = node.Loc
statements := c.Factory.NewNodeList([]*ast.Node{returnStatement})
statements.Loc = node.Loc
block := c.Factory.NewBlock(statements, multiLine)
block.Loc = node.Loc
return block
}

func (c *EmitContext) VisitFunctionBody(node *ast.BlockOrExpression, visitor *ast.NodeVisitor) *ast.BlockOrExpression {
// !!! c.resumeVariableEnvironment()
updated := visitor.VisitNode(node)
Expand All @@ -913,8 +926,13 @@ func (c *EmitContext) VisitFunctionBody(node *ast.BlockOrExpression, visitor *as
}

if !ast.IsBlock(updated) {
statements := c.MergeEnvironment([]*ast.Statement{c.Factory.NewReturnStatement(updated)}, declarations)
return c.Factory.NewBlock(c.Factory.NewNodeList(statements), false /*multiLine*/)
c.AddEmitFlags(updated, EFNoComments)
block := c.ConvertToFunctionBlock(updated, false /*multiLine*/)
return c.Factory.UpdateBlock(
block.AsBlock(),
c.MergeEnvironmentList(block.StatementList(), declarations),
block.AsBlock().MultiLine,
)
}

return c.Factory.UpdateBlock(
Expand Down
19 changes: 4 additions & 15 deletions internal/transformers/estransforms/async.go
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Original file line number Diff line number Diff line change
Expand Up @@ -841,7 +841,10 @@ func (tx *asyncTransformer) transformAsyncFunctionBody(node *ast.Node, outerPara
)

if captureLexicalArguments && tx.lexicalArguments.used {
block := tx.convertToFunctionBlock(result)
block := tx.EmitContext().ConvertToFunctionBlock(result, true /*multiLine*/)
if !ast.IsBlock(result) {
tx.EmitContext().SetOriginal(block.StatementList().Nodes[0], result)
}
result = tx.Factory().UpdateBlock(
block.AsBlock(),
tx.EmitContext().MergeEnvironmentList(block.StatementList(), []*ast.Node{tx.createCaptureArgumentsStatement()}),
Expand Down Expand Up @@ -889,20 +892,6 @@ func (tx *asyncTransformer) transformAsyncFunctionBodyWorker(body *ast.Node) *as
return block
}

func (tx *asyncTransformer) convertToFunctionBlock(node *ast.Node) *ast.Node {
if ast.IsBlock(node) {
return node
}
ret := tx.Factory().NewReturnStatement(node)
ret.Loc = node.Loc
tx.EmitContext().SetOriginal(ret, node)
list := tx.Factory().NewNodeList([]*ast.Node{ret})
list.Loc = node.Loc
block := tx.Factory().NewBlock(list, true)
block.Loc = node.Loc
return block
}

// assignmentTargetContainsSuperProperty checks top-down whether an assignment target
// expression contains a super property or element access (super.x or super[x]).
// This avoids relying on parent pointers (IsAssignmentTarget) which may not be set
Expand Down
40 changes: 40 additions & 0 deletions testdata/baselines/reference/compiler/optionalChainingArrowFunctionCommentEs2018.js
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@@ -0,0 +1,40 @@
//// [tests/cases/compiler/optionalChainingArrowFunctionCommentEs2018.ts] ////

//// [optionalChainingArrowFunctionCommentEs2018.ts]
const thing = { nested: { condition: true } };

const wat = () =>
// explanatory comment
thing?.nested?.condition ? "pass" : "fail";

const watInline = () => /* inline explanatory comment */ thing?.nested?.condition ? "pass" : "fail";

const watInlineMultiline = () => /* inline
explanatory comment */ thing?.nested?.condition ? "pass" : "fail";

const watInlineThenLeading = () => /* inline explanatory comment */
// leading explanatory comment
thing?.nested?.condition ? "pass" : "fail";

declare const o: { a?: number[] };

export const f = () =>
// comment
o.a?.length;


//// [optionalChainingArrowFunctionCommentEs2018.js]
const thing = { nested: { condition: true } };
const wat = () => { var _a;
// explanatory comment
return ((_a = thing === null || thing === void 0 ? void 0 : thing.nested) === null || _a === void 0 ? void 0 : _a.condition) ? "pass" : "fail"; };
const watInline = () => /* inline explanatory comment */ { var _a; /* inline explanatory comment */ return ((_a = thing === null || thing === void 0 ? void 0 : thing.nested) === null || _a === void 0 ? void 0 : _a.condition) ? "pass" : "fail"; };
const watInlineMultiline = () => /* inline
explanatory comment */ { var _a; /* inline
explanatory comment */ return ((_a = thing === null || thing === void 0 ? void 0 : thing.nested) === null || _a === void 0 ? void 0 : _a.condition) ? "pass" : "fail"; };
const watInlineThenLeading = () => /* inline explanatory comment */ { var _a; /* inline explanatory comment */
// leading explanatory comment
return ((_a = thing === null || thing === void 0 ? void 0 : thing.nested) === null || _a === void 0 ? void 0 : _a.condition) ? "pass" : "fail"; };
export const f = () => { var _a;
// comment
return (_a = o.a) === null || _a === void 0 ? void 0 : _a.length; };
63 changes: 63 additions & 0 deletions testdata/baselines/reference/compiler/optionalChainingArrowFunctionCommentEs2018.symbols
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@@ -0,0 +1,63 @@
//// [tests/cases/compiler/optionalChainingArrowFunctionCommentEs2018.ts] ////

=== optionalChainingArrowFunctionCommentEs2018.ts ===
const thing = { nested: { condition: true } };
>thing : Symbol(thing, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 5))
>nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))

const wat = () =>
>wat : Symbol(wat, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 2, 5))

// explanatory comment
thing?.nested?.condition ? "pass" : "fail";
>thing?.nested?.condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))
>thing?.nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>thing : Symbol(thing, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 5))
>nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))

const watInline = () => /* inline explanatory comment */ thing?.nested?.condition ? "pass" : "fail";
>watInline : Symbol(watInline, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 6, 5))
>thing?.nested?.condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))
>thing?.nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>thing : Symbol(thing, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 5))
>nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))

const watInlineMultiline = () => /* inline
>watInlineMultiline : Symbol(watInlineMultiline, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 8, 5))

explanatory comment */ thing?.nested?.condition ? "pass" : "fail";
>thing?.nested?.condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))
>thing?.nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>thing : Symbol(thing, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 5))
>nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))

const watInlineThenLeading = () => /* inline explanatory comment */
>watInlineThenLeading : Symbol(watInlineThenLeading, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 11, 5))

// leading explanatory comment
thing?.nested?.condition ? "pass" : "fail";
>thing?.nested?.condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))
>thing?.nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>thing : Symbol(thing, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 5))
>nested : Symbol(nested, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 15))
>condition : Symbol(condition, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 0, 25))

declare const o: { a?: number[] };
>o : Symbol(o, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 15, 13))
>a : Symbol(a, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 15, 18))

export const f = () =>
>f : Symbol(f, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 17, 12))

// comment
o.a?.length;
>o.a?.length : Symbol(Array.length, Decl(lib.es5.d.ts, --, --))
>o.a : Symbol(a, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 15, 18))
>o : Symbol(o, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 15, 13))
>a : Symbol(a, Decl(optionalChainingArrowFunctionCommentEs2018.ts, 15, 18))
>length : Symbol(Array.length, Decl(lib.es5.d.ts, --, --))

83 changes: 83 additions & 0 deletions testdata/baselines/reference/compiler/optionalChainingArrowFunctionCommentEs2018.types
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@@ -0,0 +1,83 @@
//// [tests/cases/compiler/optionalChainingArrowFunctionCommentEs2018.ts] ////

=== optionalChainingArrowFunctionCommentEs2018.ts ===
const thing = { nested: { condition: true } };
>thing : { nested: { condition: boolean; }; }
>{ nested: { condition: true } } : { nested: { condition: boolean; }; }
>nested : { condition: boolean; }
>{ condition: true } : { condition: boolean; }
>condition : boolean
>true : true

const wat = () =>
>wat : () => "fail" | "pass"
>() => // explanatory comment thing?.nested?.condition ? "pass" : "fail" : () => "fail" | "pass"

// explanatory comment
thing?.nested?.condition ? "pass" : "fail";
>thing?.nested?.condition ? "pass" : "fail" : "fail" | "pass"
>thing?.nested?.condition : boolean
>thing?.nested : { condition: boolean; }
>thing : { nested: { condition: boolean; }; }
>nested : { condition: boolean; }
>condition : boolean
>"pass" : "pass"
>"fail" : "fail"

const watInline = () => /* inline explanatory comment */ thing?.nested?.condition ? "pass" : "fail";
>watInline : () => "fail" | "pass"
>() => /* inline explanatory comment */ thing?.nested?.condition ? "pass" : "fail" : () => "fail" | "pass"
>thing?.nested?.condition ? "pass" : "fail" : "fail" | "pass"
>thing?.nested?.condition : boolean
>thing?.nested : { condition: boolean; }
>thing : { nested: { condition: boolean; }; }
>nested : { condition: boolean; }
>condition : boolean
>"pass" : "pass"
>"fail" : "fail"

const watInlineMultiline = () => /* inline
>watInlineMultiline : () => "fail" | "pass"
>() => /* inlineexplanatory comment */ thing?.nested?.condition ? "pass" : "fail" : () => "fail" | "pass"

explanatory comment */ thing?.nested?.condition ? "pass" : "fail";
>thing?.nested?.condition ? "pass" : "fail" : "fail" | "pass"
>thing?.nested?.condition : boolean
>thing?.nested : { condition: boolean; }
>thing : { nested: { condition: boolean; }; }
>nested : { condition: boolean; }
>condition : boolean
>"pass" : "pass"
>"fail" : "fail"

const watInlineThenLeading = () => /* inline explanatory comment */
>watInlineThenLeading : () => "fail" | "pass"
>() => /* inline explanatory comment */ // leading explanatory comment thing?.nested?.condition ? "pass" : "fail" : () => "fail" | "pass"

// leading explanatory comment
thing?.nested?.condition ? "pass" : "fail";
>thing?.nested?.condition ? "pass" : "fail" : "fail" | "pass"
>thing?.nested?.condition : boolean
>thing?.nested : { condition: boolean; }
>thing : { nested: { condition: boolean; }; }
>nested : { condition: boolean; }
>condition : boolean
>"pass" : "pass"
>"fail" : "fail"

declare const o: { a?: number[] };
>o : { a?: number[]; }
>a : number[] | undefined

export const f = () =>
>f : () => number | undefined
>() => // comment o.a?.length : () => number | undefined

// comment
o.a?.length;
>o.a?.length : number | undefined
>o.a : number[] | undefined
>o : { a?: number[]; }
>a : number[] | undefined
>length : number | undefined

22 changes: 22 additions & 0 deletions testdata/tests/cases/compiler/optionalChainingArrowFunctionCommentEs2018.ts
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@@ -0,0 +1,22 @@
// @target: es2018

const thing = { nested: { condition: true } };

const wat = () =>
// explanatory comment
thing?.nested?.condition ? "pass" : "fail";

const watInline = () => /* inline explanatory comment */ thing?.nested?.condition ? "pass" : "fail";

const watInlineMultiline = () => /* inline
explanatory comment */ thing?.nested?.condition ? "pass" : "fail";

const watInlineThenLeading = () => /* inline explanatory comment */
// leading explanatory comment
thing?.nested?.condition ? "pass" : "fail";

declare const o: { a?: number[] };

export const f = () =>
// comment
o.a?.length;