Merge pull request #5898 from Microsoft/fix3475_let

Disallow let in let/const declaration regardless of target

Author: yuit

src/compiler/checker.ts

@@ -15965,13 +15965,27 @@ namespace ts {
             if (forInOrOfStatement.initializer.kind === SyntaxKind.VariableDeclarationList) {
                 const variableList = <VariableDeclarationList>forInOrOfStatement.initializer;
                 if (!checkGrammarVariableDeclarationList(variableList)) {
-                    if (variableList.declarations.length > 1) {
+                    const declarations = variableList.declarations;
+
+                    // declarations.length can be zero if there is an error in variable declaration in for-of or for-in
+                    // See http://www.ecma-international.org/ecma-262/6.0/#sec-for-in-and-for-of-statements for details
+                    // For example:
+                    //      var let = 10;
+                    //      for (let of [1,2,3]) {} // this is invalid ES6 syntax
+                    //      for (let in [1,2,3]) {} // this is invalid ES6 syntax
+                    // We will then want to skip on grammar checking on variableList declaration
+                    if (!declarations.length) {
+                        return false;
+                    }
+
+                    if (declarations.length > 1) {
                         const diagnostic = forInOrOfStatement.kind === SyntaxKind.ForInStatement
                             ? Diagnostics.Only_a_single_variable_declaration_is_allowed_in_a_for_in_statement
                             : Diagnostics.Only_a_single_variable_declaration_is_allowed_in_a_for_of_statement;
                         return grammarErrorOnFirstToken(variableList.declarations[1], diagnostic);
                     }
-                    const firstDeclaration = variableList.declarations[0];
+                    const firstDeclaration = declarations[0];
+
                     if (firstDeclaration.initializer) {
                         const diagnostic = forInOrOfStatement.kind === SyntaxKind.ForInStatement
                             ? Diagnostics.The_variable_declaration_of_a_for_in_statement_cannot_have_an_initializer
@@ -16170,7 +16184,7 @@ namespace ts {
                 }
             }
 
-            const checkLetConstNames = languageVersion >= ScriptTarget.ES6 && (isLet(node) || isConst(node));
+            const checkLetConstNames = (isLet(node) || isConst(node));
 
             // 1. LexicalDeclaration : LetOrConst BindingList ;
             // It is a Syntax Error if the BoundNames of BindingList contains "let".
@@ -16184,7 +16198,7 @@ namespace ts {
 
         function checkGrammarNameInLetOrConstDeclarations(name: Identifier | BindingPattern): boolean {
             if (name.kind === SyntaxKind.Identifier) {
-                if ((<Identifier>name).text === "let") {
+                if ((<Identifier>name).originalKeywordKind === SyntaxKind.LetKeyword) {
                     return grammarErrorOnNode(name, Diagnostics.let_is_not_allowed_to_be_used_as_a_name_in_let_or_const_declarations);
                 }
             }

tests/baselines/reference/invalidLetInForOfAndForIn_ES5.errors.txt

@@ -0,0 +1,22 @@
+tests/cases/compiler/invalidLetInForOfAndForIn_ES5.ts(5,13): error TS1005: '=' expected.
+tests/cases/compiler/invalidLetInForOfAndForIn_ES5.ts(5,20): error TS1005: ',' expected.
+tests/cases/compiler/invalidLetInForOfAndForIn_ES5.ts(7,1): error TS1005: ';' expected.
+
+
+==== tests/cases/compiler/invalidLetInForOfAndForIn_ES5.ts (3 errors) ====
+    // This should be an error
+    // More details: http://www.ecma-international.org/ecma-262/6.0/#sec-iteration-statements
+    
+    var let = 10;
+    for (let of [1,2,3]) {}
+                ~
+!!! error TS1005: '=' expected.
+                       ~
+!!! error TS1005: ',' expected.
+    
+    for (let in [1,2,3]) {}
+    ~~~
+!!! error TS1005: ';' expected.
+     
+    
+    

tests/baselines/reference/invalidLetInForOfAndForIn_ES5.js

@@ -0,0 +1,18 @@
+//// [invalidLetInForOfAndForIn_ES5.ts]
+// This should be an error
+// More details: http://www.ecma-international.org/ecma-262/6.0/#sec-iteration-statements
+
+var let = 10;
+for (let of [1,2,3]) {}
+
+for (let in [1,2,3]) {}
+ 
+
+
+
+//// [invalidLetInForOfAndForIn_ES5.js]
+// This should be an error
+// More details: http://www.ecma-international.org/ecma-262/6.0/#sec-iteration-statements
+var let = 10;
+for (let of = [1, 2, 3], {  }; ; )
+    for ( in [1, 2, 3]) { }

tests/baselines/reference/invalidLetInForOfAndForIn_ES6.errors.txt

@@ -0,0 +1,22 @@
+tests/cases/compiler/invalidLetInForOfAndForIn_ES6.ts(5,13): error TS1005: '=' expected.
+tests/cases/compiler/invalidLetInForOfAndForIn_ES6.ts(5,20): error TS1005: ',' expected.
+tests/cases/compiler/invalidLetInForOfAndForIn_ES6.ts(7,1): error TS1005: ';' expected.
+
+
+==== tests/cases/compiler/invalidLetInForOfAndForIn_ES6.ts (3 errors) ====
+    // This should be an error
+    // More details: http://www.ecma-international.org/ecma-262/6.0/#sec-iteration-statements
+    
+    var let = 10;
+    for (let of [1,2,3]) {}
+                ~
+!!! error TS1005: '=' expected.
+                       ~
+!!! error TS1005: ',' expected.
+    
+    for (let in [1,2,3]) {}
+    ~~~
+!!! error TS1005: ';' expected.
+     
+    
+    

tests/baselines/reference/invalidLetInForOfAndForIn_ES6.js

@@ -0,0 +1,18 @@
+//// [invalidLetInForOfAndForIn_ES6.ts]
+// This should be an error
+// More details: http://www.ecma-international.org/ecma-262/6.0/#sec-iteration-statements
+
+var let = 10;
+for (let of [1,2,3]) {}
+
+for (let in [1,2,3]) {}
+ 
+
+
+
+//// [invalidLetInForOfAndForIn_ES6.js]
+// This should be an error
+// More details: http://www.ecma-international.org/ecma-262/6.0/#sec-iteration-statements
+var let = 10;
+for (let of = [1, 2, 3], {  }; ; )
+    for ( in [1, 2, 3]) { }

tests/baselines/reference/letAsIdentifier2.js

@@ -0,0 +1,6 @@
+//// [letAsIdentifier2.ts]
+
+function let() {}
+
+//// [letAsIdentifier2.js]
+function let() { }

tests/baselines/reference/letAsIdentifier2.symbols

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/letAsIdentifier2.ts ===
+
+function let() {}
+>let : Symbol(let, Decl(letAsIdentifier2.ts, 0, 0))
+

tests/baselines/reference/letAsIdentifier2.types

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/letAsIdentifier2.ts ===
+
+function let() {}
+>let : () => void
+

tests/baselines/reference/letInConstDeclarations_ES5.errors.txt

@@ -0,0 +1,16 @@
+tests/cases/compiler/letInConstDeclarations_ES5.ts(3,15): error TS2480: 'let' is not allowed to be used as a name in 'let' or 'const' declarations.
+tests/cases/compiler/letInConstDeclarations_ES5.ts(6,19): error TS2480: 'let' is not allowed to be used as a name in 'let' or 'const' declarations.
+
+
+==== tests/cases/compiler/letInConstDeclarations_ES5.ts (2 errors) ====
+    
+    // All use of let in const declaration should be an error
+    const x = 50, let = 5;
+                  ~~~
+!!! error TS2480: 'let' is not allowed to be used as a name in 'let' or 'const' declarations.
+    
+    {
+        const x = 10, let = 20;
+                      ~~~
+!!! error TS2480: 'let' is not allowed to be used as a name in 'let' or 'const' declarations.
+    }

tests/baselines/reference/letInConstDeclarations_ES5.js

@@ -0,0 +1,15 @@
+//// [letInConstDeclarations_ES5.ts]
+
+// All use of let in const declaration should be an error
+const x = 50, let = 5;
+
+{
+    const x = 10, let = 20;
+}
+
+//// [letInConstDeclarations_ES5.js]
+// All use of let in const declaration should be an error
+var x = 50, let = 5;
+{
+    var x_1 = 10, let_1 = 20;
+}