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Fix panic in the optional-chain transform when a chain ends in a tagged template #63968

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Fix panic in the optional-chain transform when a chain ends in a tagged template #63968

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f7dbced
Fix optional-chain transform panic on tagged templates
bigboateng Aug 23, 2026
6840ebb
Merge branch 'main' into fix-63965
bigboateng Aug 24, 2026
b4863a0
Rename regression test and cover the untransformed target
bigboateng Aug 24, 2026
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15 changes: 15 additions & 0 deletions tsc/internal/transformers/estransforms/optionalchain.go
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Original file line number Diff line number Diff line change
Expand Up @@ -140,6 +140,10 @@ func flattenChain(chain *ast.Node) flattenResult {
debug.Assert(!isNonNullChain(chain))
links = append([]*ast.Node{chain}, links...)
}
if ast.IsTaggedTemplateExpression(chain) {
// A tagged template has no expression; its tag is the base of the chain.
return flattenResult{chain.AsTaggedTemplateExpression().Tag, links}
}
return flattenResult{chain.Expression(), links}
}

Expand Down Expand Up @@ -204,6 +208,17 @@ func (ch *optionalChainTransformer) visitOptionalExpression(node *ast.Node, capt
ast.NodeFlagsNone,
)
}
case ast.KindTaggedTemplateExpression:
// A tagged template can only be the head of the chain (flattenChain
// stops walking at it); re-tag its template onto the checked base.
t := segment.AsTaggedTemplateExpression()
rightExpression = ch.Factory().NewTaggedTemplateExpression(
rightExpression,
nil, /*questionDotToken*/
t.TypeArguments,
ch.Visitor().VisitNode(t.Template),
ast.NodeFlagsNone,
)
}
ch.EmitContext().SetOriginal(rightExpression, segment)
}
Expand Down
26 changes: 26 additions & 0 deletions ...stdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2017).errors.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
repro.ts(1,1): error TS2304: Cannot find name 'e'.
repro.ts(2,1): error TS1005: ')' expected.
siblings.ts(2,5): error TS1358: Tagged template expressions are not permitted in an optional chain.
siblings.ts(3,5): error TS1358: Tagged template expressions are not permitted in an optional chain.
siblings.ts(4,4): error TS1358: Tagged template expressions are not permitted in an optional chain.


==== repro.ts (2 errors) ====
e?.``(
~
!!! error TS2304: Cannot find name 'e'.


!!! error TS1005: ')' expected.
==== siblings.ts (3 errors) ====
declare var a: any;
a?.b`c`;
~~~
!!! error TS1358: Tagged template expressions are not permitted in an optional chain.
a?.b`c`();
~~~
!!! error TS1358: Tagged template expressions are not permitted in an optional chain.
a?.``.x;
~~
!!! error TS1358: Tagged template expressions are not permitted in an optional chain.

21 changes: 21 additions & 0 deletions tsc/testdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2017).js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,21 @@
//// [tests/cases/compiler/optionalChainTaggedTemplate.ts] ////

//// [repro.ts]
e?.``(

//// [siblings.ts]
declare var a: any;
a?.b`c`;
a?.b`c`();
a?.``.x;


//// [repro.js]
"use strict";
e === null || e === void 0 ? void 0 : e ``();
//// [siblings.js]
"use strict";
var _a;
(a === null || a === void 0 ? void 0 : a.b) `c`;
(_a = a === null || a === void 0 ? void 0 : a.b) === null || _a === void 0 ? void 0 : _a `c`();
a === null || a === void 0 ? void 0 : a ``.x;
19 changes: 19 additions & 0 deletions tsc/testdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2017).symbols
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@@ -0,0 +1,19 @@
//// [tests/cases/compiler/optionalChainTaggedTemplate.ts] ////

=== repro.ts ===

e?.``(

=== siblings.ts ===
declare var a: any;
>a : Symbol(a, Decl(siblings.ts, 0, 11))

a?.b`c`;
>a : Symbol(a, Decl(siblings.ts, 0, 11))

a?.b`c`();
>a : Symbol(a, Decl(siblings.ts, 0, 11))

a?.``.x;
>a : Symbol(a, Decl(siblings.ts, 0, 11))

35 changes: 35 additions & 0 deletions tsc/testdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2017).types
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Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
//// [tests/cases/compiler/optionalChainTaggedTemplate.ts] ////

=== repro.ts ===
e?.``(
>e?.``( : any
>e?.`` : any
>e : any
>`` : ""

=== siblings.ts ===
declare var a: any;
>a : any

a?.b`c`;
>a?.b`c` : any
>a?.b : any
>a : any
>b : any
>`c` : "c"

a?.b`c`();
>a?.b`c`() : any
>a?.b`c` : any
>a?.b : any
>a : any
>b : any
>`c` : "c"

a?.``.x;
>a?.``.x : any
>a?.`` : any
>a : any
>`` : ""
>x : any

26 changes: 26 additions & 0 deletions ...stdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2024).errors.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
repro.ts(1,1): error TS2304: Cannot find name 'e'.
repro.ts(2,1): error TS1005: ')' expected.
siblings.ts(2,5): error TS1358: Tagged template expressions are not permitted in an optional chain.
siblings.ts(3,5): error TS1358: Tagged template expressions are not permitted in an optional chain.
siblings.ts(4,4): error TS1358: Tagged template expressions are not permitted in an optional chain.


==== repro.ts (2 errors) ====
e?.``(
~
!!! error TS2304: Cannot find name 'e'.


!!! error TS1005: ')' expected.
==== siblings.ts (3 errors) ====
declare var a: any;
a?.b`c`;
~~~
!!! error TS1358: Tagged template expressions are not permitted in an optional chain.
a?.b`c`();
~~~
!!! error TS1358: Tagged template expressions are not permitted in an optional chain.
a?.``.x;
~~
!!! error TS1358: Tagged template expressions are not permitted in an optional chain.

20 changes: 20 additions & 0 deletions tsc/testdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2024).js
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@@ -0,0 +1,20 @@
//// [tests/cases/compiler/optionalChainTaggedTemplate.ts] ////

//// [repro.ts]
e?.``(

//// [siblings.ts]
declare var a: any;
a?.b`c`;
a?.b`c`();
a?.``.x;


//// [repro.js]
"use strict";
e ``();
//// [siblings.js]
"use strict";
(a?.b) `c`;
(a?.b) `c`();
a ``.x;
19 changes: 19 additions & 0 deletions tsc/testdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2024).symbols
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
//// [tests/cases/compiler/optionalChainTaggedTemplate.ts] ////

=== repro.ts ===

e?.``(

=== siblings.ts ===
declare var a: any;
>a : Symbol(a, Decl(siblings.ts, 0, 11))

a?.b`c`;
>a : Symbol(a, Decl(siblings.ts, 0, 11))

a?.b`c`();
>a : Symbol(a, Decl(siblings.ts, 0, 11))

a?.``.x;
>a : Symbol(a, Decl(siblings.ts, 0, 11))

35 changes: 35 additions & 0 deletions tsc/testdata/baselines/reference/compiler/optionalChainTaggedTemplate(target=es2024).types
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Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
//// [tests/cases/compiler/optionalChainTaggedTemplate.ts] ////

=== repro.ts ===
e?.``(
>e?.``( : any
>e?.`` : any
>e : any
>`` : ""

=== siblings.ts ===
declare var a: any;
>a : any

a?.b`c`;
>a?.b`c` : any
>a?.b : any
>a : any
>b : any
>`c` : "c"

a?.b`c`();
>a?.b`c`() : any
>a?.b`c` : any
>a?.b : any
>a : any
>b : any
>`c` : "c"

a?.``.x;
>a?.``.x : any
>a?.`` : any
>a : any
>`` : ""
>x : any

10 changes: 10 additions & 0 deletions tsc/testdata/tests/cases/compiler/optionalChainTaggedTemplate.ts
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@DanielRosenwasser Daniel Rosenwasser (DanielRosenwasser) Aug 24, 2026

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Nit: can we rename this to something that doesn't say "no crash"?

@bigboateng bigboateng Aug 24, 2026

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Renamed to optionalChainTaggedTemplate.ts.

Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
// @target: es2017, es2024

// @filename: repro.ts
e?.``(

// @filename: siblings.ts
declare var a: any;
a?.b`c`;
a?.b`c`();
a?.``.x;