Add codefix.

packages/typespec-azure-resource-manager/src/rules/arm-resource-name-pattern.ts

@@ -1,7 +1,46 @@
-import { Program, createRule, getPattern } from "@typespec/compiler";
+import {
+  DiagnosticTarget,
+  Program,
+  SourceLocation,
+  createRule,
+  defineCodeFix,
+  getPattern,
+  getSourceLocation,
+} from "@typespec/compiler";
 
+import { isWhiteSpace } from "../../../../core/packages/compiler/src/core/charcode.js";
 import { getArmResources } from "../resource.js";
 
+// TODO: Replace this with a reusable implementation from the compiler package when implemented.
+// Issue: https://github.com/microsoft/typespec/issues/3044
+function createPatternCodeFix(diagnosticTarget: DiagnosticTarget) {
+  return defineCodeFix({
+    id: "add-pattern-decorator",
+    label: "Add `@pattern` decorator to the resource name property with the default ARM pattern.",
+    fix: (context) => {
+      const location = getSourceLocation(diagnosticTarget);
+      const { lineStart, indent } = findLineStartAndIndent(location);
+      const updatedLocation = { ...location, pos: lineStart };
+      return context.prependText(updatedLocation, `${indent}@pattern(/^[a-zA-Z0-9-]+$/)\n`);
+    },
+  });
+}
+
+function findLineStartAndIndent(location: SourceLocation): { lineStart: number; indent: string } {
+  const text = location.file.text;
+  let pos = location.pos;
+  let indent = 0;
+  while (pos > 0 && text[pos - 1] !== "\n") {
+    if (isWhiteSpace(text.charCodeAt(pos - 1))) {
+      indent++;
+    } else {
+      indent = 0;
+    }
+    pos--;
+  }
+  return { lineStart: pos, indent: location.file.text.slice(pos, pos + indent) };
+}
+
 /**
  * Verify that a delete operation only
  */
@@ -25,6 +64,7 @@ export const armResourceNamePatternRule = createRule({
             if (pattern === undefined) {
               context.reportDiagnostic({
                 target: nameProperty,
+                codefixes: [createPatternCodeFix(nameProperty)],
               });
             }
           }