Fixed an issue causing spurious "used before being assigned" errors in for of/in loops

src/compiler/checker.ts

@@ -30452,7 +30452,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // We only look for uninitialized variables in strict null checking mode, and only when we can analyze
         // the entire control flow graph from the variable's declaration (i.e. when the flow container and
         // declaration container are the same).
-        const isNeverInitialized = immediateDeclaration && isVariableDeclaration(immediateDeclaration) && !immediateDeclaration.initializer && !immediateDeclaration.exclamationToken && isMutableLocalVariableDeclaration(immediateDeclaration) && !isSymbolAssignedDefinitely(symbol);
+        const isNeverInitialized = immediateDeclaration && isVariableDeclaration(immediateDeclaration) && !isForInOrOfStatement(immediateDeclaration.parent.parent) && !immediateDeclaration.initializer && !immediateDeclaration.exclamationToken && isMutableLocalVariableDeclaration(immediateDeclaration) && !isSymbolAssignedDefinitely(symbol);
         const assumeInitialized = isParameter || isAlias ||
             (isOuterVariable && !isNeverInitialized) ||
             isSpreadDestructuringAssignmentTarget || isModuleExports || isSameScopedBindingElement(node, declaration) ||

tests/baselines/reference/unusedLocalsInForInOrOf1.errors.txt

@@ -0,0 +1,84 @@
+unusedLocalsInForInOrOf1.ts(2,12): error TS6133: 'f' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(8,7): error TS6133: 'f' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(14,12): error TS6133: 'g' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(20,12): error TS6133: 'f2' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(26,7): error TS6133: 'f2' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(32,12): error TS6133: 'g2' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(38,12): error TS6133: 'f3' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(44,7): error TS6133: 'f3' is declared but its value is never read.
+unusedLocalsInForInOrOf1.ts(50,12): error TS6133: 'g3' is declared but its value is never read.
+
+
+==== unusedLocalsInForInOrOf1.ts (9 errors) ====
+    for (let x of [1, 2]) {
+      function f() {
+               ~
+!!! error TS6133: 'f' is declared but its value is never read.
+        x;
+      }
+    }
+
+    for (let x of [1, 2]) {
+      let f = () => {
+          ~
+!!! error TS6133: 'f' is declared but its value is never read.
+        x;
+      };
+    }
+
+    for (const x of [1, 2]) {
+      function g() {
+               ~
+!!! error TS6133: 'g' is declared but its value is never read.
+        x;
+      }
+    }
+
+    for (let x in { a: 1, b: 2 }) {
+      function f2() {
+               ~~
+!!! error TS6133: 'f2' is declared but its value is never read.
+        x;
+      }
+    }
+
+    for (let x in { a: 1, b: 2 }) {
+      let f2 = () => {
+          ~~
+!!! error TS6133: 'f2' is declared but its value is never read.
+        x;
+      };
+    }
+
+    for (const x in { a: 1, b: 2 }) {
+      function g2() {
+               ~~
+!!! error TS6133: 'g2' is declared but its value is never read.
+        x;
+      }
+    }
+
+    for (let { x } of [{ x: 1 }, { x: 2 }]) {
+      function f3() {
+               ~~
+!!! error TS6133: 'f3' is declared but its value is never read.
+        x;
+      }
+    }
+
+    for (let { x } of [{ x: 1 }, { x: 2 }]) {
+      let f3 = () => {
+          ~~
+!!! error TS6133: 'f3' is declared but its value is never read.
+        x;
+      };
+    }
+
+    for (const { x } of [{ x: 1 }, { x: 2 }]) {
+      function g3() {
+               ~~
+!!! error TS6133: 'g3' is declared but its value is never read.
+        x;
+      }
+    }
+

tests/baselines/reference/unusedLocalsInForInOrOf1.symbols

@@ -0,0 +1,117 @@
+//// [tests/cases/compiler/unusedLocalsInForInOrOf1.ts] ////
+
+=== unusedLocalsInForInOrOf1.ts ===
+for (let x of [1, 2]) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 0, 8))
+
+  function f() {
+>f : Symbol(f, Decl(unusedLocalsInForInOrOf1.ts, 0, 23))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 0, 8))
+  }
+}
+
+for (let x of [1, 2]) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 6, 8))
+
+  let f = () => {
+>f : Symbol(f, Decl(unusedLocalsInForInOrOf1.ts, 7, 5))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 6, 8))
+
+  };
+}
+
+for (const x of [1, 2]) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 12, 10))
+
+  function g() {
+>g : Symbol(g, Decl(unusedLocalsInForInOrOf1.ts, 12, 25))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 12, 10))
+  }
+}
+
+for (let x in { a: 1, b: 2 }) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 18, 8))
+>a : Symbol(a, Decl(unusedLocalsInForInOrOf1.ts, 18, 15))
+>b : Symbol(b, Decl(unusedLocalsInForInOrOf1.ts, 18, 21))
+
+  function f2() {
+>f2 : Symbol(f2, Decl(unusedLocalsInForInOrOf1.ts, 18, 31))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 18, 8))
+  }
+}
+
+for (let x in { a: 1, b: 2 }) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 24, 8))
+>a : Symbol(a, Decl(unusedLocalsInForInOrOf1.ts, 24, 15))
+>b : Symbol(b, Decl(unusedLocalsInForInOrOf1.ts, 24, 21))
+
+  let f2 = () => {
+>f2 : Symbol(f2, Decl(unusedLocalsInForInOrOf1.ts, 25, 5))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 24, 8))
+
+  };
+}
+
+for (const x in { a: 1, b: 2 }) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 30, 10))
+>a : Symbol(a, Decl(unusedLocalsInForInOrOf1.ts, 30, 17))
+>b : Symbol(b, Decl(unusedLocalsInForInOrOf1.ts, 30, 23))
+
+  function g2() {
+>g2 : Symbol(g2, Decl(unusedLocalsInForInOrOf1.ts, 30, 33))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 30, 10))
+  }
+}
+
+for (let { x } of [{ x: 1 }, { x: 2 }]) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 36, 10))
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 36, 20))
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 36, 30))
+
+  function f3() {
+>f3 : Symbol(f3, Decl(unusedLocalsInForInOrOf1.ts, 36, 41))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 36, 10))
+  }
+}
+
+for (let { x } of [{ x: 1 }, { x: 2 }]) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 42, 10))
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 42, 20))
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 42, 30))
+
+  let f3 = () => {
+>f3 : Symbol(f3, Decl(unusedLocalsInForInOrOf1.ts, 43, 5))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 42, 10))
+
+  };
+}
+
+for (const { x } of [{ x: 1 }, { x: 2 }]) {
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 48, 12))
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 48, 22))
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 48, 32))
+
+  function g3() {
+>g3 : Symbol(g3, Decl(unusedLocalsInForInOrOf1.ts, 48, 43))
+
+    x;
+>x : Symbol(x, Decl(unusedLocalsInForInOrOf1.ts, 48, 12))
+  }
+}
+