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Fix crash in CFA when for loop initializer throws #63108

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Fix crash in CFA when for loop initializer throws #63108

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629847d
add tests
Andarist Feb 5, 2026
f0aeeeb
add reentry mitigation
Andarist Feb 5, 2026
aa5b116
update tests
Andarist Feb 5, 2026
1ed6890
target fix in the binder
Andarist Feb 5, 2026
805972d
improve comment
Andarist Feb 5, 2026
76f2f2f
add test
Andarist Feb 5, 2026
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13 changes: 12 additions & 1 deletion src/compiler/binder.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1539,11 +1539,22 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
}

function bindForStatement(node: ForStatement): void {
bind(node.initializer);
if (currentFlow === unreachableFlow) {
// Unlike while/do, the for-loop initializer is bound inside this function before the loop's
// flow graph is constructed. If it makes flow unreachable (e.g. a throwing IIFE), addAntecedent
// will filter out the unreachable entry to preLoopLabel, leaving only the back-edge from the
// incrementor. This creates a cycle with no exit that crashes isReachableFlowNodeWorker.
// Bail out early and just bind the remaining children with unreachable flow.
bind(node.condition);
bind(node.statement);
bind(node.incrementor);
return;
}
const preLoopLabel = setContinueTarget(node, createLoopLabel());
const preBodyLabel = createBranchLabel();
const preIncrementorLabel = createBranchLabel();
const postLoopLabel = createBranchLabel();
bind(node.initializer);
addAntecedent(preLoopLabel, currentFlow);
currentFlow = preLoopLabel;
bindCondition(node.condition, preBodyLabel, postLoopLabel);
Expand Down
21 changes: 21 additions & 0 deletions ...nes/reference/unreachableFlowAfterThrowingForHead1(allowunreachablecode=false).errors.txt
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@@ -0,0 +1,21 @@
unreachableFlowAfterThrowingForHead1.ts(7,9): error TS7027: Unreachable code detected.
unreachableFlowAfterThrowingForHead1.ts(11,2): error TS2304: Cannot find name 'as'.


==== unreachableFlowAfterThrowingForHead1.ts (2 errors) ====
try {
for (
(function () { throw "1"; })();
(function* () { throw "2"; })();
(function* () { throw "3"; })()
) {
console.log("1");
~~~~~~~~~~~~~~~~~
!!! error TS7027: Unreachable code detected.
}
}
catch (e) { }
as ;
~~
!!! error TS2304: Cannot find name 'as'.

20 changes: 20 additions & 0 deletions ...elines/reference/unreachableFlowAfterThrowingForHead1(allowunreachablecode=false).symbols
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@@ -0,0 +1,20 @@
//// [tests/cases/compiler/unreachableFlowAfterThrowingForHead1.ts] ////

=== unreachableFlowAfterThrowingForHead1.ts ===
try {
for (
(function () { throw "1"; })();
(function* () { throw "2"; })();
(function* () { throw "3"; })()
) {
console.log("1");
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
}
}
catch (e) { }
>e : Symbol(e, Decl(unreachableFlowAfterThrowingForHead1.ts, 9, 7))

as ;

57 changes: 57 additions & 0 deletions ...aselines/reference/unreachableFlowAfterThrowingForHead1(allowunreachablecode=false).types
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@@ -0,0 +1,57 @@
//// [tests/cases/compiler/unreachableFlowAfterThrowingForHead1.ts] ////

=== unreachableFlowAfterThrowingForHead1.ts ===
try {
for (
(function () { throw "1"; })();
>(function () { throw "1"; })() : never
> : ^^^^^
>(function () { throw "1"; }) : () => never
> : ^^^^^^^^^^^
>function () { throw "1"; } : () => never
> : ^^^^^^^^^^^
>"1" : "1"
> : ^^^

(function* () { throw "2"; })();
>(function* () { throw "2"; })() : Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>(function* () { throw "2"; }) : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>function* () { throw "2"; } : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>"2" : "2"
> : ^^^

(function* () { throw "3"; })()
>(function* () { throw "3"; })() : Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>(function* () { throw "3"; }) : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>function* () { throw "3"; } : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>"3" : "3"
> : ^^^

) {
console.log("1");
>console.log("1") : void
> : ^^^^
>console.log : (...data: any[]) => void
> : ^^^^ ^^ ^^^^^
>console : Console
> : ^^^^^^^
>log : (...data: any[]) => void
> : ^^^^ ^^ ^^^^^
>"1" : "1"
> : ^^^
}
}
catch (e) { }
>e : unknown
> : ^^^^^^^

as ;
>as : any
> : ^^^

18 changes: 18 additions & 0 deletions ...ines/reference/unreachableFlowAfterThrowingForHead1(allowunreachablecode=true).errors.txt
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@@ -0,0 +1,18 @@
unreachableFlowAfterThrowingForHead1.ts(11,2): error TS2304: Cannot find name 'as'.


==== unreachableFlowAfterThrowingForHead1.ts (1 errors) ====
try {
for (
(function () { throw "1"; })();
(function* () { throw "2"; })();
(function* () { throw "3"; })()
) {
console.log("1");
}
}
catch (e) { }
as ;
~~
!!! error TS2304: Cannot find name 'as'.

20 changes: 20 additions & 0 deletions ...selines/reference/unreachableFlowAfterThrowingForHead1(allowunreachablecode=true).symbols
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@@ -0,0 +1,20 @@
//// [tests/cases/compiler/unreachableFlowAfterThrowingForHead1.ts] ////

=== unreachableFlowAfterThrowingForHead1.ts ===
try {
for (
(function () { throw "1"; })();
(function* () { throw "2"; })();
(function* () { throw "3"; })()
) {
console.log("1");
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
}
}
catch (e) { }
>e : Symbol(e, Decl(unreachableFlowAfterThrowingForHead1.ts, 9, 7))

as ;

57 changes: 57 additions & 0 deletions ...baselines/reference/unreachableFlowAfterThrowingForHead1(allowunreachablecode=true).types
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@@ -0,0 +1,57 @@
//// [tests/cases/compiler/unreachableFlowAfterThrowingForHead1.ts] ////

=== unreachableFlowAfterThrowingForHead1.ts ===
try {
for (
(function () { throw "1"; })();
>(function () { throw "1"; })() : never
> : ^^^^^
>(function () { throw "1"; }) : () => never
> : ^^^^^^^^^^^
>function () { throw "1"; } : () => never
> : ^^^^^^^^^^^
>"1" : "1"
> : ^^^

(function* () { throw "2"; })();
>(function* () { throw "2"; })() : Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>(function* () { throw "2"; }) : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>function* () { throw "2"; } : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>"2" : "2"
> : ^^^

(function* () { throw "3"; })()
>(function* () { throw "3"; })() : Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>(function* () { throw "3"; }) : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>function* () { throw "3"; } : () => Generator<never, never, unknown>
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>"3" : "3"
> : ^^^

) {
console.log("1");
>console.log("1") : void
> : ^^^^
>console.log : (...data: any[]) => void
> : ^^^^ ^^ ^^^^^
>console : Console
> : ^^^^^^^
>log : (...data: any[]) => void
> : ^^^^ ^^ ^^^^^
>"1" : "1"
> : ^^^
}
}
catch (e) { }
>e : unknown
> : ^^^^^^^

as ;
>as : any
> : ^^^

36 changes: 36 additions & 0 deletions ...nes/reference/unreachableFlowAfterThrowingForHead2(allowunreachablecode=false).errors.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
unreachableFlowAfterThrowingForHead2.ts(9,5): error TS7027: Unreachable code detected.
unreachableFlowAfterThrowingForHead2.ts(22,7): error TS7027: Unreachable code detected.


==== unreachableFlowAfterThrowingForHead2.ts (2 errors) ====
function test1(v: 0 | 1 | 2) {
for (
(function () {
throw new Error("");
})();
v;
v++
) {
console.log("1");
~~~~~~~~~~~~~~~~~
!!! error TS7027: Unreachable code detected.
}
}

function test2(v: 0 | 1 | 2) {
try {
for (
(function () {
throw new Error("");
})();
v;
v++
) {
console.log("1");
~~~~~~~~~~~~~~~~~
!!! error TS7027: Unreachable code detected.
}
} catch (e) {}
v;
}

57 changes: 57 additions & 0 deletions ...elines/reference/unreachableFlowAfterThrowingForHead2(allowunreachablecode=false).symbols
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@@ -0,0 +1,57 @@
//// [tests/cases/compiler/unreachableFlowAfterThrowingForHead2.ts] ////

=== unreachableFlowAfterThrowingForHead2.ts ===
function test1(v: 0 | 1 | 2) {
>test1 : Symbol(test1, Decl(unreachableFlowAfterThrowingForHead2.ts, 0, 0))
>v : Symbol(v, Decl(unreachableFlowAfterThrowingForHead2.ts, 0, 15))

for (
(function () {
throw new Error("");
>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2022.error.d.ts, --, --))

})();
v;
>v : Symbol(v, Decl(unreachableFlowAfterThrowingForHead2.ts, 0, 15))

v++
>v : Symbol(v, Decl(unreachableFlowAfterThrowingForHead2.ts, 0, 15))

) {
console.log("1");
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
}
}

function test2(v: 0 | 1 | 2) {
>test2 : Symbol(test2, Decl(unreachableFlowAfterThrowingForHead2.ts, 10, 1))
>v : Symbol(v, Decl(unreachableFlowAfterThrowingForHead2.ts, 12, 15))

try {
for (
(function () {
throw new Error("");
>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2022.error.d.ts, --, --))

})();
v;
>v : Symbol(v, Decl(unreachableFlowAfterThrowingForHead2.ts, 12, 15))

v++
>v : Symbol(v, Decl(unreachableFlowAfterThrowingForHead2.ts, 12, 15))

) {
console.log("1");
>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
}
} catch (e) {}
>e : Symbol(e, Decl(unreachableFlowAfterThrowingForHead2.ts, 23, 11))

v;
>v : Symbol(v, Decl(unreachableFlowAfterThrowingForHead2.ts, 12, 15))
}

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