Error on shadowed var declarations without initializers (#55228)

src/compiler/checker.ts

@@ -41020,12 +41020,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return;
         }
 
-        // skip variable declarations that don't have initializers
         // NOTE: in ES6 spec initializer is required in variable declarations where name is binding pattern
         // so we'll always treat binding elements as initialized
-        if (node.kind === SyntaxKind.VariableDeclaration && !node.initializer) {
-            return;
-        }
 
         const symbol = getSymbolOfDeclaration(node);
         if (symbol.flags & SymbolFlags.FunctionScopedVariable) {
@@ -41050,10 +41046,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                             container.kind === SyntaxKind.ModuleDeclaration ||
                             container.kind === SyntaxKind.SourceFile);
 
-                    // here we know that function scoped variable is shadowed by block scoped one
-                    // if they are defined in the same scope - binder has already reported redeclaration error
-                    // otherwise if variable has an initializer - show error that initialization will fail
-                    // since LHS will be block scoped name instead of function scoped
+                    // here we know that function scoped variable is "shadowed" by block scoped one
+                    // a var declatation can't hoist past a lexical declaration and it results in a SyntaxError at runtime
                     if (!namesShareScope) {
                         const name = symbolToString(localDeclarationSymbol);
                         error(node, Diagnostics.Cannot_initialize_outer_scoped_variable_0_in_the_same_scope_as_block_scoped_declaration_1, name, name);

tests/baselines/reference/for-of53.errors.txt

@@ -0,0 +1,9 @@
+for-of53.ts(2,9): error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+
+
+==== for-of53.ts (1 errors) ====
+    for (let v of []) {
+        var v;
+            ~
+!!! error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+    }

tests/baselines/reference/shadowedFunctionScopedVariablesByBlockScopedOnes.errors.txt

@@ -0,0 +1,48 @@
+shadowedFunctionScopedVariablesByBlockScopedOnes.ts(4,27): error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+shadowedFunctionScopedVariablesByBlockScopedOnes.ts(7,29): error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+shadowedFunctionScopedVariablesByBlockScopedOnes.ts(10,29): error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+shadowedFunctionScopedVariablesByBlockScopedOnes.ts(16,17): error TS2481: Cannot initialize outer scoped variable 'x' in the same scope as block scoped declaration 'x'.
+shadowedFunctionScopedVariablesByBlockScopedOnes.ts(23,17): error TS2481: Cannot initialize outer scoped variable 'x' in the same scope as block scoped declaration 'x'.
+
+
+==== shadowedFunctionScopedVariablesByBlockScopedOnes.ts (5 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/2185
+    
+    function test1() {
+        for (let v; ; ) { var v; }
+                              ~
+!!! error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+    }
+    function test2() {
+        for (let v in []) { var v; }
+                                ~
+!!! error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+    }
+    function test3() {
+        for (let v of []) { var v; }
+                                ~
+!!! error TS2481: Cannot initialize outer scoped variable 'v' in the same scope as block scoped declaration 'v'.
+    }
+    function test4() {
+        {
+            let x;
+            {
+                var x;
+                    ~
+!!! error TS2481: Cannot initialize outer scoped variable 'x' in the same scope as block scoped declaration 'x'.
+            }
+        }
+    }
+    function test5() {
+        {
+            {
+                var x;
+                    ~
+!!! error TS2481: Cannot initialize outer scoped variable 'x' in the same scope as block scoped declaration 'x'.
+            }
+            let x;
+        }
+    }
+    
+    
+    

tests/baselines/reference/shadowedFunctionScopedVariablesByBlockScopedOnes.symbols

@@ -0,0 +1,51 @@
+//// [tests/cases/compiler/shadowedFunctionScopedVariablesByBlockScopedOnes.ts] ////
+
+=== shadowedFunctionScopedVariablesByBlockScopedOnes.ts ===
+// https://github.com/microsoft/TypeScript/issues/2185
+
+function test1() {
+>test1 : Symbol(test1, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 0, 0))
+
+    for (let v; ; ) { var v; }
+>v : Symbol(v, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 3, 12))
+>v : Symbol(v, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 3, 25))
+}
+function test2() {
+>test2 : Symbol(test2, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 4, 1))
+
+    for (let v in []) { var v; }
+>v : Symbol(v, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 6, 12))
+>v : Symbol(v, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 6, 27))
+}
+function test3() {
+>test3 : Symbol(test3, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 7, 1))
+
+    for (let v of []) { var v; }
+>v : Symbol(v, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 9, 12))
+>v : Symbol(v, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 9, 27))
+}
+function test4() {
+>test4 : Symbol(test4, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 10, 1))
+    {
+        let x;
+>x : Symbol(x, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 13, 11))
+        {
+            var x;
+>x : Symbol(x, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 15, 15))
+        }
+    }
+}
+function test5() {
+>test5 : Symbol(test5, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 18, 1))
+    {
+        {
+            var x;
+>x : Symbol(x, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 22, 15))
+        }
+        let x;
+>x : Symbol(x, Decl(shadowedFunctionScopedVariablesByBlockScopedOnes.ts, 24, 11))
+    }
+}
+
+
+

tests/baselines/reference/shadowedFunctionScopedVariablesByBlockScopedOnes.types

@@ -0,0 +1,53 @@
+//// [tests/cases/compiler/shadowedFunctionScopedVariablesByBlockScopedOnes.ts] ////
+
+=== shadowedFunctionScopedVariablesByBlockScopedOnes.ts ===
+// https://github.com/microsoft/TypeScript/issues/2185
+
+function test1() {
+>test1 : () => void
+
+    for (let v; ; ) { var v; }
+>v : any
+>v : any
+}
+function test2() {
+>test2 : () => void
+
+    for (let v in []) { var v; }
+>v : string
+>[] : undefined[]
+>v : any
+}
+function test3() {
+>test3 : () => void
+
+    for (let v of []) { var v; }
+>v : any
+>[] : undefined[]
+>v : any
+}
+function test4() {
+>test4 : () => void
+    {
+        let x;
+>x : any
+        {
+            var x;
+>x : any
+        }
+    }
+}
+function test5() {
+>test5 : () => void
+    {
+        {
+            var x;
+>x : any
+        }
+        let x;
+>x : any
+    }
+}
+
+
+

tests/cases/compiler/shadowedFunctionScopedVariablesByBlockScopedOnes.ts

@@ -0,0 +1,31 @@
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/2185
+
+function test1() {
+    for (let v; ; ) { var v; }
+}
+function test2() {
+    for (let v in []) { var v; }
+}
+function test3() {
+    for (let v of []) { var v; }
+}
+function test4() {
+    {
+        let x;
+        {
+            var x;
+        }
+    }
+}
+function test5() {
+    {
+        {
+            var x;
+        }
+        let x;
+    }
+}
+
+