Add codefix for 'Cannot find name' diagnostic

Author: rFlorian

src/compiler/diagnosticMessages.json

@@ -4799,5 +4799,13 @@
     "Add names to all parameters without names": {
         "category": "Message",
         "code": 95073
+    },
+    "Add const modifier to unresolved variable": {
+        "category": "Message",
+        "code": 95074
+    },
+    "Add const modifiers to all unresolved variables": {
+        "category": "Message",
+        "code": 95075
     }
 }

src/services/codefixes/addMissingConstInForLoop.ts

@@ -0,0 +1,23 @@
+/* @internal */
+namespace ts.codefix {
+    const fixId = "addMissingConstInForLoop";
+    const errorCodes = [Diagnostics.Cannot_find_name_0.code];
+    registerCodeFix({
+        errorCodes,
+        getCodeActions: (context) => {
+            const changes = textChanges.ChangeTracker.with(context, t => makeChange(t, context.sourceFile, context.span.start));
+            return [createCodeFixAction(fixId, changes, Diagnostics.Add_const_modifier_to_unresolved_variable, fixId, Diagnostics.Add_const_modifiers_to_all_unresolved_variables)];
+        },
+        fixIds: [fixId],
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => makeChange(changes, diag.file, diag.start)),
+    });
+
+    function makeChange(changeTracker: textChanges.ChangeTracker, sourceFile: SourceFile, pos: number) {
+        const token = getTokenAtPosition(sourceFile, pos);
+        // fails on 'for ([x, y] of [[1,2]]) {}' when called for y
+        // since findPrecedingMatchingToken does not return the open paren here after iterating over another identifier (x)
+        const openParenToken = <Node>findPrecedingMatchingToken(token, SyntaxKind.OpenParenToken, sourceFile);
+        Debug.assert(!!openParenToken, "openParenToken must be defined");
+        changeTracker.insertNodeAt(sourceFile, openParenToken.getEnd(), createToken(SyntaxKind.ConstKeyword), { suffix: " " });
+    }
+}

src/services/tsconfig.json

@@ -44,6 +44,7 @@
         "codeFixProvider.ts",
         "refactorProvider.ts",
         "codefixes/addConvertToUnknownForNonOverlappingTypes.ts",
+        "codefixes/addMissingConstInForLoop.ts",
         "codefixes/addMissingInvocationForDecorator.ts",
         "codefixes/addNameToNamelessParameter.ts",
         "codefixes/annotateWithTypeFromJSDoc.ts",

src/services/utilities.ts

@@ -936,7 +936,7 @@ namespace ts {
                 return undefined;
             }
             token = preceding;
-
+            
             if (token.kind === matchingTokenKind) {
                 if (remainingMatchingTokens === 0) {
                     return token;

tests/cases/fourslash/codeFixAddMissingConstInForLoop1.ts

@@ -0,0 +1,8 @@
+/// <reference path='fourslash.ts' />
+
+////[|for (x of []) {}|]
+
+verify.codeFix({
+    description: "Add const modifier to unresolved variable",
+    newRangeContent: "for (const x of []) {}"
+});

tests/cases/fourslash/codeFixAddMissingConstInForLoop2.ts

@@ -0,0 +1,12 @@
+/// <reference path='fourslash.ts' />
+
+////[|for (x of []) {}|]
+////[|for (y of []) {}|]
+
+verify.codeFixAll({
+    fixId: "addMissingConstInForLoop",
+    fixAllDescription: "Add const modifiers to all unresolved variables",
+    newFileContent: 
+`for (const x of []) {}
+for (const y of []) {}`
+});

tests/cases/fourslash/codeFixAddMissingConstInForLoop3.ts

@@ -0,0 +1,8 @@
+/// <reference path='fourslash.ts' />
+
+////[|for ([x] of [[1,2]]) {}|]
+
+verify.codeFix({
+    description: "Add const modifier to unresolved variable",
+    newRangeContent: "for (const [x] of [[1,2]]) {}"
+});

tests/cases/fourslash/codeFixAddMissingConstInForLoop4.ts

@@ -0,0 +1,8 @@
+/// <reference path='fourslash.ts' />
+
+////[|for ([x, y] of [[1,2]]) {}|]
+
+verify.codeFix({
+    description: "Add const modifier to unresolved variable",
+    newRangeContent: "for (const [x, y] of [[1,2]]) {}"
+});