Don't count self-reference when setting isReferenced (#17495)

* Don't count self-reference when setting `isReferenced`

* Improve comment

Author: Andy

src/compiler/checker.ts

@@ -1086,7 +1086,10 @@ namespace ts {
                 location = location.parent;
             }
 
-            if (result && nameNotFoundMessage && noUnusedIdentifiers) {
+            // We just climbed up parents looking for the name, meaning that we started in a descendant node of `lastLocation`.
+            // If `result === lastLocation.symbol`, that means that we are somewhere inside `lastLocation` looking up a name, and resolving to `lastLocation` itself.
+            // That means that this is a self-reference of `lastLocation`, and shouldn't count this when considering whether `lastLocation` is used.
+            if (result && nameNotFoundMessage && noUnusedIdentifiers && result !== lastLocation.symbol) {
                 result.isReferenced = true;
             }
 
@@ -10800,17 +10803,6 @@ namespace ts {
             return undefined;
         }
 
-        function getLeftmostIdentifierOrThis(node: Node): Node {
-            switch (node.kind) {
-                case SyntaxKind.Identifier:
-                case SyntaxKind.ThisKeyword:
-                    return node;
-                case SyntaxKind.PropertyAccessExpression:
-                    return getLeftmostIdentifierOrThis((<PropertyAccessExpression>node).expression);
-            }
-            return undefined;
-        }
-
         function getBindingElementNameText(element: BindingElement): string | undefined {
             if (element.parent.kind === SyntaxKind.ObjectBindingPattern) {
                 const name = element.propertyName || element.name;
@@ -18520,15 +18512,6 @@ namespace ts {
                 return forEachChild(n, containsSuperCall);
             }
 
-            function markThisReferencesAsErrors(n: Node): void {
-                if (n.kind === SyntaxKind.ThisKeyword) {
-                    error(n, Diagnostics.this_cannot_be_referenced_in_current_location);
-                }
-                else if (n.kind !== SyntaxKind.FunctionExpression && n.kind !== SyntaxKind.FunctionDeclaration) {
-                    forEachChild(n, markThisReferencesAsErrors);
-                }
-            }
-
             function isInstancePropertyWithInitializer(n: Node): boolean {
                 return n.kind === SyntaxKind.PropertyDeclaration &&
                     !(getModifierFlags(n) & ModifierFlags.Static) &&

tests/baselines/reference/noUnusedLocals_selfReference.errors.txt

@@ -0,0 +1,28 @@
+tests/cases/compiler/noUnusedLocals_selfReference.ts(3,10): error TS6133: 'f' is declared but never used.
+tests/cases/compiler/noUnusedLocals_selfReference.ts(4,7): error TS6133: 'C' is declared but never used.
+tests/cases/compiler/noUnusedLocals_selfReference.ts(7,6): error TS6133: 'E' is declared but never used.
+
+
+==== tests/cases/compiler/noUnusedLocals_selfReference.ts (3 errors) ====
+    export {}; // Make this a module scope, so these are local variables.
+    
+    function f() { f; }
+             ~
+!!! error TS6133: 'f' is declared but never used.
+    class C {
+          ~
+!!! error TS6133: 'C' is declared but never used.
+        m() { C; }
+    }
+    enum E { A = 0, B = E.A }
+         ~
+!!! error TS6133: 'E' is declared but never used.
+    
+    // Does not detect mutual recursion.
+    function g() { D; }
+    class D { m() { g; } }
+    
+    // Does not work on private methods.
+    class P { private m() { this.m; } }
+    P;
+    

tests/baselines/reference/noUnusedLocals_selfReference.js

@@ -0,0 +1,49 @@
+//// [noUnusedLocals_selfReference.ts]
+export {}; // Make this a module scope, so these are local variables.
+
+function f() { f; }
+class C {
+    m() { C; }
+}
+enum E { A = 0, B = E.A }
+
+// Does not detect mutual recursion.
+function g() { D; }
+class D { m() { g; } }
+
+// Does not work on private methods.
+class P { private m() { this.m; } }
+P;
+
+
+//// [noUnusedLocals_selfReference.js]
+"use strict";
+exports.__esModule = true;
+function f() { f; }
+var C = (function () {
+    function C() {
+    }
+    C.prototype.m = function () { C; };
+    return C;
+}());
+var E;
+(function (E) {
+    E[E["A"] = 0] = "A";
+    E[E["B"] = 0] = "B";
+})(E || (E = {}));
+// Does not detect mutual recursion.
+function g() { D; }
+var D = (function () {
+    function D() {
+    }
+    D.prototype.m = function () { g; };
+    return D;
+}());
+// Does not work on private methods.
+var P = (function () {
+    function P() {
+    }
+    P.prototype.m = function () { this.m; };
+    return P;
+}());
+P;

tests/baselines/reference/unusedLocalsAndParametersTypeAliases2.errors.txt

@@ -1,15 +1,18 @@
 tests/cases/compiler/unusedLocalsAndParametersTypeAliases2.ts(2,6): error TS6133: 'handler1' is declared but never used.
+tests/cases/compiler/unusedLocalsAndParametersTypeAliases2.ts(5,10): error TS6133: 'foo' is declared but never used.
 tests/cases/compiler/unusedLocalsAndParametersTypeAliases2.ts(6,10): error TS6133: 'handler2' is declared but never used.
 
 
-==== tests/cases/compiler/unusedLocalsAndParametersTypeAliases2.ts (2 errors) ====
+==== tests/cases/compiler/unusedLocalsAndParametersTypeAliases2.ts (3 errors) ====
     // unused
     type handler1 = () => void;
          ~~~~~~~~
 !!! error TS6133: 'handler1' is declared but never used.
 
 
     function foo() {
+             ~~~
+!!! error TS6133: 'foo' is declared but never used.
         type handler2 = () => void;
              ~~~~~~~~
 !!! error TS6133: 'handler2' is declared but never used.

tests/cases/compiler/noUnusedLocals_selfReference.ts

@@ -0,0 +1,17 @@
+// @noUnusedLocals: true
+
+export {}; // Make this a module scope, so these are local variables.
+
+function f() { f; }
+class C {
+    m() { C; }
+}
+enum E { A = 0, B = E.A }
+
+// Does not detect mutual recursion.
+function g() { D; }
+class D { m() { g; } }
+
+// Does not work on private methods.
+class P { private m() { this.m; } }
+P;

tests/webTestServer.ts

@@ -125,22 +125,6 @@ function dir(dirPath: string, spec?: string, options?: any) {
     }
 }
 
-// fs.rmdirSync won't delete directories with files in it
-function deleteFolderRecursive(dirPath: string) {
-    if (fs.existsSync(dirPath)) {
-        fs.readdirSync(dirPath).forEach((file) => {
-            const curPath = path.join(dirPath, file);
-            if (fs.statSync(curPath).isDirectory()) { // recurse
-                deleteFolderRecursive(curPath);
-            }
-            else { // delete file
-                fs.unlinkSync(curPath);
-            }
-        });
-        fs.rmdirSync(dirPath);
-    }
-};
-
 function writeFile(path: string, data: any) {
     ensureDirectoriesExist(getDirectoryPath(path));
     fs.writeFileSync(path, data);