Add code fix to remove unreachable code

Author: Andy Hanson

src/compiler/diagnosticMessages.json

@@ -4245,5 +4245,13 @@
     "Convert all 'require' to 'import'": {
         "category": "Message",
         "code": 95048
+    },
+    "Remove unreachable code": {
+        "category": "Message",
+        "code": 95049
+    },
+    "Remove all unreachable code": {
+        "category": "Message",
+        "code": 95050
     }
 }

src/harness/tsconfig.json

@@ -105,6 +105,7 @@
         "../services/codefixes/fixExtendsInterfaceBecomesImplements.ts",
         "../services/codefixes/fixForgottenThisPropertyAccess.ts",
         "../services/codefixes/fixUnusedIdentifier.ts",
+        "../services/codefixes/fixUnreachableCode.ts",
         "../services/codefixes/fixJSDocTypes.ts",
         "../services/codefixes/fixAwaitInSyncFunction.ts",
         "../services/codefixes/disableJsDiagnostics.ts",

src/server/tsconfig.json

@@ -101,6 +101,7 @@
         "../services/codefixes/fixExtendsInterfaceBecomesImplements.ts",
         "../services/codefixes/fixForgottenThisPropertyAccess.ts",
         "../services/codefixes/fixUnusedIdentifier.ts",
+        "../services/codefixes/fixUnreachableCode.ts",
         "../services/codefixes/fixJSDocTypes.ts",
         "../services/codefixes/fixAwaitInSyncFunction.ts",
         "../services/codefixes/disableJsDiagnostics.ts",

src/server/tsconfig.library.json

@@ -107,6 +107,7 @@
         "../services/codefixes/fixExtendsInterfaceBecomesImplements.ts",
         "../services/codefixes/fixForgottenThisPropertyAccess.ts",
         "../services/codefixes/fixUnusedIdentifier.ts",
+        "../services/codefixes/fixUnreachableCode.ts",
         "../services/codefixes/fixJSDocTypes.ts",
         "../services/codefixes/fixAwaitInSyncFunction.ts",
         "../services/codefixes/disableJsDiagnostics.ts",

src/services/codefixes/fixUnreachableCode.ts

@@ -0,0 +1,33 @@
+/* @internal */
+namespace ts.codefix {
+    const fixId = "fixUnreachableCode";
+    const errorCodes = [Diagnostics.Unreachable_code_detected.code];
+    registerCodeFix({
+        errorCodes,
+        getCodeActions: context => {
+            const { sourceFile, span } = context;
+            const changes = textChanges.ChangeTracker.with(context, t => t.deleteNode(sourceFile, getStatement(sourceFile, span.start)));
+            return [createCodeFixAction(fixId, changes, Diagnostics.Remove_unreachable_code, fixId, Diagnostics.Remove_all_unreachable_code)];
+        },
+        fixIds: [fixId],
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
+            changes.deleteNode(diag.file, getStatement(diag.file, diag.start));
+        }),
+    });
+
+    function getStatement(sourceFile: SourceFile, start: number): Statement {
+        const token = getTokenAtPosition(sourceFile, start, /*includeJsDocComment*/ false);
+        let statement = findAncestor(token, isStatement);
+        Debug.assert(statement.getStart(sourceFile) === token.getStart(sourceFile));
+        if (isBlock(statement.parent)) statement = statement.parent;
+        switch (statement.parent.kind) {
+            case SyntaxKind.IfStatement:
+                return (statement.parent as IfStatement).elseStatement ? statement : statement.parent as IfStatement;
+            case SyntaxKind.WhileStatement:
+            case SyntaxKind.ForStatement:
+                return statement.parent as WhileStatement | ForStatement;
+            default:
+                return statement;
+        }
+    }
+}

src/services/tsconfig.json

@@ -98,6 +98,7 @@
         "codefixes/fixExtendsInterfaceBecomesImplements.ts",
         "codefixes/fixForgottenThisPropertyAccess.ts",
         "codefixes/fixUnusedIdentifier.ts",
+        "codefixes/fixUnreachableCode.ts",
         "codefixes/fixJSDocTypes.ts",
         "codefixes/fixAwaitInSyncFunction.ts",
         "codefixes/disableJsDiagnostics.ts",

tests/cases/fourslash/codeFixUnreachableCode.ts

@@ -0,0 +1,14 @@
+/// <reference path='fourslash.ts' />
+
+////function f() {
+////    return 0;
+////    return 1;
+////}
+
+verify.codeFix({
+    description: "Remove unreachable code",
+    newFileContent:
+`function f() {
+    return 0;
+}`,
+});

tests/cases/fourslash/codeFixUnreachableCode_if.ts

@@ -0,0 +1,37 @@
+/// <reference path='fourslash.ts' />
+
+////if (false) a;
+////if (false) {
+////    a;
+////}
+////
+////// No good way to delete just the 'if' part
+////if (false) {
+////    a;
+////} else {
+////    b;
+////}
+////
+////while (false) a;
+////while (false) {
+////    a;
+////}
+////
+////for (let x = 0; false; ++x) a;
+////for (let x = 0; false; ++x) {
+////    a;
+////}
+
+verify.codeFixAll({
+    fixId: "fixUnreachableCode",
+    fixAllDescription: "Remove all unreachable code",
+    newFileContent:
+`
+// No good way to delete just the 'if' part
+if (false) else {
+    b;
+}
+
+
+`,
+});