Add codefix to make non-reassignable variables reassignable

src/compiler/diagnosticMessages.json

@@ -4683,5 +4683,13 @@
     "Generate types for all packages without types": {
         "category": "Message",
         "code": 95068
+    },
+    "Make all const or readonly expressions reassignable": {
+        "category": "Message",
+        "code": 95069
+    },
+    "Remove '{0}' modifier": {
+        "category": "Message",
+        "code": 95070
     }
 }

src/services/codefixes/fixConvertConstantVariableOrProperty.ts

@@ -0,0 +1,51 @@
+/* @internal */
+namespace ts.codefix {
+    const fixId = "fixConvertConstantVariableOrProperty";
+    const errorCodes = [
+        Diagnostics.Cannot_assign_to_0_because_it_is_a_constant_or_a_read_only_property.code
+    ];
+    registerCodeFix({
+        errorCodes,
+        getCodeActions(context) {
+            const { sourceFile, span, program } = context;
+            const declaration = getDeclaration(sourceFile, span.start, program.getTypeChecker());
+            if (!declaration) return undefined;
+            const changes = textChanges.ChangeTracker.with(context, t => doChange(t, sourceFile, declaration));
+            const type = declaration.kind === SyntaxKind.VariableDeclaration ? "const" : "readonly";
+            return [createCodeFixAction(fixId, changes, [Diagnostics.Remove_0_modifier, type], fixId, Diagnostics.Make_all_const_or_readonly_expressions_reassignable)];
+        },
+        fixIds: [fixId],
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
+            const declaration = getDeclaration(diag.file, diag.start, context.program.getTypeChecker());
+            if (declaration) doChange(changes, context.sourceFile, declaration);
+        }),
+    });
+    function getDeclaration(sourceFile: SourceFile, pos: number, checker: TypeChecker): Declaration | undefined {
+        const node = getTokenAtPosition(sourceFile, pos);
+        const symbol = checker.getSymbolAtLocation(node);
+        if (symbol) {
+            return symbol.valueDeclaration;
+        }
+    }
+
+    function doChange(changes: textChanges.ChangeTracker, sourceFile: SourceFile, node: Declaration) {
+        if (node.kind === SyntaxKind.VariableDeclaration) {
+            const oldDeclarationList = node.parent as VariableDeclarationList;
+            const declarationList = createVariableDeclarationList(oldDeclarationList.declarations, NodeFlags.Let);
+            changes.replaceNode(sourceFile, oldDeclarationList, declarationList);
+        }
+        else if (node.kind === SyntaxKind.PropertyDeclaration) {
+            const readonlyToken = findAnyChildOfKind(node, SyntaxKind.ReadonlyKeyword);
+            if (readonlyToken) {
+                changes.delete(sourceFile, readonlyToken);
+            }
+        }
+    }
+
+    function findAnyChildOfKind(node: Node, kind: SyntaxKind): Node | undefined {
+        return node.forEachChild(child => {
+            if (child.kind === kind) return child;
+            else findAnyChildOfKind(child, kind);
+        });
+    }
+}

src/services/tsconfig.json

@@ -57,6 +57,7 @@
         "codefixes/fixClassDoesntImplementInheritedAbstractMember.ts",
         "codefixes/fixClassSuperMustPrecedeThisAccess.ts",
         "codefixes/fixConstructorForDerivedNeedSuperCall.ts",
+        "codefixes/fixConvertConstantVariableOrProperty.ts",
         "codefixes/fixExtendsInterfaceBecomesImplements.ts",
         "codefixes/fixForgottenThisPropertyAccess.ts",
         "codefixes/fixUnusedIdentifier.ts",

tests/cases/fourslash/codeFixConvertConstantVariableOrProperty_const.tsx

@@ -0,0 +1,11 @@
+/// <reference path='fourslash.ts' />
+
+////const variable = 5;
+////variable = 4;
+
+verify.codeFix({
+    description: "Remove 'const' modifier",
+    newFileContent:
+`let variable = 5;
+variable = 4;`,
+});

tests/cases/fourslash/codeFixConvertConstantVariableOrProperty_readonly.tsx

@@ -0,0 +1,17 @@
+/// <reference path='fourslash.ts' />
+
+////class Test {
+////    readonly prop = 5;
+////}
+////let testInstance = new Test();
+////testInstance.prop = 3;
+
+verify.codeFix({
+    description: "Remove 'readonly' modifier",
+    newFileContent:
+`class Test {
+ prop = 5;
+}
+let testInstance = new Test();
+testInstance.prop = 3;`,
+});