fixUnusedIdentifier: Don't remove setter parameter (microsoft#22488)

Author: Andy

src/services/codefixes/fixUnusedIdentifier.ts

@@ -142,6 +142,11 @@ namespace ts.codefix {
 
             case SyntaxKind.Parameter:
                 const oldFunction = parent.parent;
+                if (isSetAccessor(oldFunction)) {
+                    // Setter must have a parameter
+                    break;
+                }
+
                 if (isArrowFunction(oldFunction) && oldFunction.parameters.length === 1) {
                     // Lambdas with exactly one parameter are special because, after removal, there
                     // must be an empty parameter list (i.e. `()`) and this won't necessarily be the

tests/cases/fourslash/codeFixUnusedIdentifier_set.ts

@@ -0,0 +1,19 @@
+/// <reference path='fourslash.ts' />
+
+// @noUnusedLocals: true
+// @noUnusedParameters: true
+
+////class C {
+////    set x(value: number) {}
+////}
+
+// No codefix to remove parameter, since setter must have a parameter
+verify.codeFixAvailable([{ description: "Prefix 'value' with an underscore" }]);
+
+verify.codeFix({
+    description: "Prefix 'value' with an underscore",
+    newFileContent:
+`class C {
+    set x(_value: number) {}
+}`,
+});