Fix TS2454 false positive for closed-over mutable variables

tsc/internal/checker/flow.go

@@ -2672,9 +2672,6 @@ func (c *Checker) isPastLastAssignment(symbol *ast.Symbol, location *ast.Node) b
 }
 
 func (c *Checker) ensureAssignmentsMarked(symbol *ast.Symbol) {
-	if c.markedAssignmentSymbolLinks.Get(symbol).lastAssignmentPos != 0 {
-		return
-	}
 	parent := ast.FindAncestor(symbol.ValueDeclaration, ast.IsFunctionOrSourceFile)
 	if parent == nil {
 		return

tsc/testdata/baselines/reference/compiler/definiteAssignmentOfClosedOverVariable.errors.txt

@@ -0,0 +1,42 @@
+definiteAssignmentOfClosedOverVariable.ts(32,9): error TS2454: Variable 'count3' is used before being assigned.
+
+
+==== definiteAssignmentOfClosedOverVariable.ts (1 errors) ====
+    // Repro for #63981
+
+    export {};
+
+    let count: number;
+
+    function makeCallback(p: string) {
+        return () => {
+            count += 1;
+            return p;
+        };
+    }
+
+    count = 0;
+    makeCallback('x')();
+
+    let count2: number;
+
+    function makeCallback2(p: string) {
+        const f = () => p;
+        return () => {
+            count2 += 1;
+        };
+    }
+
+    count2 = 0;
+
+    let count3: number;
+
+    function makeCallback3(p: string) {
+        return () => {
+            count3 += 1;
+            ~~~~~~
+!!! error TS2454: Variable 'count3' is used before being assigned.
+            return p;
+        };
+    }
+

tsc/testdata/baselines/reference/compiler/definiteAssignmentOfClosedOverVariable.symbols

@@ -0,0 +1,68 @@
+//// [tests/cases/compiler/definiteAssignmentOfClosedOverVariable.ts] ////
+
+=== definiteAssignmentOfClosedOverVariable.ts ===
+// Repro for #63981
+
+export {};
+
+let count: number;
+>count : Symbol(count, Decl(definiteAssignmentOfClosedOverVariable.ts, 4, 3))
+
+function makeCallback(p: string) {
+>makeCallback : Symbol(makeCallback, Decl(definiteAssignmentOfClosedOverVariable.ts, 4, 18))
+>p : Symbol(p, Decl(definiteAssignmentOfClosedOverVariable.ts, 6, 22))
+
+    return () => {
+        count += 1;
+>count : Symbol(count, Decl(definiteAssignmentOfClosedOverVariable.ts, 4, 3))
+
+        return p;
+>p : Symbol(p, Decl(definiteAssignmentOfClosedOverVariable.ts, 6, 22))
+
+    };
+}
+
+count = 0;
+>count : Symbol(count, Decl(definiteAssignmentOfClosedOverVariable.ts, 4, 3))
+
+makeCallback('x')();
+>makeCallback : Symbol(makeCallback, Decl(definiteAssignmentOfClosedOverVariable.ts, 4, 18))
+
+let count2: number;
+>count2 : Symbol(count2, Decl(definiteAssignmentOfClosedOverVariable.ts, 16, 3))
+
+function makeCallback2(p: string) {
+>makeCallback2 : Symbol(makeCallback2, Decl(definiteAssignmentOfClosedOverVariable.ts, 16, 19))
+>p : Symbol(p, Decl(definiteAssignmentOfClosedOverVariable.ts, 18, 23))
+
+    const f = () => p;
+>f : Symbol(f, Decl(definiteAssignmentOfClosedOverVariable.ts, 19, 9))
+>p : Symbol(p, Decl(definiteAssignmentOfClosedOverVariable.ts, 18, 23))
+
+    return () => {
+        count2 += 1;
+>count2 : Symbol(count2, Decl(definiteAssignmentOfClosedOverVariable.ts, 16, 3))
+
+    };
+}
+
+count2 = 0;
+>count2 : Symbol(count2, Decl(definiteAssignmentOfClosedOverVariable.ts, 16, 3))
+
+let count3: number;
+>count3 : Symbol(count3, Decl(definiteAssignmentOfClosedOverVariable.ts, 27, 3))
+
+function makeCallback3(p: string) {
+>makeCallback3 : Symbol(makeCallback3, Decl(definiteAssignmentOfClosedOverVariable.ts, 27, 19))
+>p : Symbol(p, Decl(definiteAssignmentOfClosedOverVariable.ts, 29, 23))
+
+    return () => {
+        count3 += 1;
+>count3 : Symbol(count3, Decl(definiteAssignmentOfClosedOverVariable.ts, 27, 3))
+
+        return p;
+>p : Symbol(p, Decl(definiteAssignmentOfClosedOverVariable.ts, 29, 23))
+
+    };
+}
+

tsc/testdata/baselines/reference/compiler/definiteAssignmentOfClosedOverVariable.types

@@ -0,0 +1,88 @@
+//// [tests/cases/compiler/definiteAssignmentOfClosedOverVariable.ts] ////
+
+=== definiteAssignmentOfClosedOverVariable.ts ===
+// Repro for #63981
+
+export {};
+
+let count: number;
+>count : number
+
+function makeCallback(p: string) {
+>makeCallback : (p: string) => () => string
+>p : string
+
+    return () => {
+>() => {        count += 1;        return p;    } : () => string
+
+        count += 1;
+>count += 1 : number
+>count : number
+>1 : 1
+
+        return p;
+>p : string
+
+    };
+}
+
+count = 0;
+>count = 0 : 0
+>count : number
+>0 : 0
+
+makeCallback('x')();
+>makeCallback('x')() : string
+>makeCallback('x') : () => string
+>makeCallback : (p: string) => () => string
+>'x' : "x"
+
+let count2: number;
+>count2 : number
+
+function makeCallback2(p: string) {
+>makeCallback2 : (p: string) => () => void
+>p : string
+
+    const f = () => p;
+>f : () => string
+>() => p : () => string
+>p : string
+
+    return () => {
+>() => {        count2 += 1;    } : () => void
+
+        count2 += 1;
+>count2 += 1 : number
+>count2 : number
+>1 : 1
+
+    };
+}
+
+count2 = 0;
+>count2 = 0 : 0
+>count2 : number
+>0 : 0
+
+let count3: number;
+>count3 : number
+
+function makeCallback3(p: string) {
+>makeCallback3 : (p: string) => () => string
+>p : string
+
+    return () => {
+>() => {        count3 += 1;        return p;    } : () => string
+
+        count3 += 1;
+>count3 += 1 : number
+>count3 : number
+>1 : 1
+
+        return p;
+>p : string
+
+    };
+}
+

tsc/testdata/tests/cases/compiler/definiteAssignmentOfClosedOverVariable.ts

@@ -0,0 +1,40 @@
+// @strict: true
+// @noEmit: true
+// @target: esnext
+// @module: esnext
+
+// Repro for #63981
+
+export {};
+
+let count: number;
+
+function makeCallback(p: string) {
+    return () => {
+        count += 1;
+        return p;
+    };
+}
+
+count = 0;
+makeCallback('x')();
+
+let count2: number;
+
+function makeCallback2(p: string) {
+    const f = () => p;
+    return () => {
+        count2 += 1;
+    };
+}
+
+count2 = 0;
+
+let count3: number;
+
+function makeCallback3(p: string) {
+    return () => {
+        count3 += 1;
+        return p;
+    };
+}