fix(eslint-plugin): [no-unused-vars] highlight last write reference (#5267)

Author: armano2

packages/eslint-plugin/src/rules/no-unused-vars.ts

@@ -422,10 +422,15 @@ export default util.createRule<Options, MessageIds>({
         for (const unusedVar of unusedVars) {
           // Report the first declaration.
           if (unusedVar.defs.length > 0) {
+            const writeReferences = unusedVar.references.filter(
+              ref =>
+                ref.isWrite() &&
+                ref.from.variableScope === unusedVar.scope.variableScope,
+            );
+
             context.report({
-              node: unusedVar.references.length
-                ? unusedVar.references[unusedVar.references.length - 1]
-                    .identifier
+              node: writeReferences.length
+                ? writeReferences[writeReferences.length - 1].identifier
                 : unusedVar.identifiers[0],
               messageId: 'unusedVar',
               data: unusedVar.references.some(ref => ref.isWrite())

packages/eslint-plugin/tests/rules/no-unused-vars/no-unused-vars-eslint.test.ts

@@ -1753,8 +1753,8 @@ foo.forEach(item => {
         },
         {
           ...assignedError('b'),
-          line: 4,
-          column: 7,
+          line: 2,
+          column: 9,
         },
       ],
     },
@@ -2601,7 +2601,7 @@ myArray = myArray.filter(x => x == 1);
         {
           ...assignedError('myArray'),
           line: 3,
-          column: 11,
+          column: 1,
         },
       ],
     },
@@ -2628,8 +2628,8 @@ var a = function () {
       errors: [
         {
           ...assignedError('a'),
-          line: 3,
-          column: 3,
+          line: 2,
+          column: 5,
         },
       ],
     },
@@ -2644,7 +2644,7 @@ var a = function () {
       errors: [
         {
           ...assignedError('a'),
-          line: 4,
+          line: 2,
           column: 5,
         },
       ],
@@ -2659,8 +2659,8 @@ const a = () => {
       errors: [
         {
           ...assignedError('a'),
-          line: 3,
-          column: 3,
+          line: 2,
+          column: 7,
         },
       ],
     },
@@ -2674,11 +2674,18 @@ const a = () => () => {
       errors: [
         {
           ...assignedError('a'),
-          line: 3,
-          column: 3,
+          line: 2,
+          column: 7,
         },
       ],
     },
+
+    // https://github.com/eslint/eslint/issues/14324
+    {
+      code: 'let x = [];\nx = x.concat(x);',
+      parserOptions: { ecmaVersion: 2015 },
+      errors: [{ ...assignedError('x'), line: 2, column: 1 }],
+    },
     {
       code: `
 let a = 'a';
@@ -2692,20 +2699,42 @@ function foo() {
       `,
       parserOptions: { ecmaVersion: 2020 },
       errors: [
+        {
+          ...assignedError('a'),
+          line: 3,
+          column: 1,
+        },
         {
           ...definedError('foo'),
           line: 4,
           column: 10,
         },
-        {
-          ...assignedError('a'),
-          line: 7,
-          column: 5,
-        },
       ],
     },
     {
       code: `
+let foo;
+init();
+foo = foo + 2;
+function init() {
+  foo = 1;
+}
+      `,
+      parserOptions: { ecmaVersion: 2020 },
+      errors: [{ ...assignedError('foo'), line: 4, column: 1 }],
+    },
+    {
+      code: `
+function foo(n) {
+  if (n < 2) return 1;
+  return n * foo(n - 1);
+}
+      `,
+      parserOptions: { ecmaVersion: 2020 },
+      errors: [{ ...definedError('foo'), line: 2, column: 10 }],
+    },
+    {
+      code: `
 let c = 'c';
 c = 10;
 function foo1() {

packages/eslint-plugin/tests/rules/no-unused-vars/no-unused-vars.test.ts

@@ -1458,8 +1458,8 @@ namespace Foo {
             action: 'defined',
             additional: '',
           },
-          line: 4,
-          column: 15,
+          line: 2,
+          column: 11,
         },
       ],
     },
@@ -1490,8 +1490,8 @@ namespace Foo {
             action: 'defined',
             additional: '',
           },
-          line: 5,
-          column: 17,
+          line: 3,
+          column: 13,
         },
       ],
     },
@@ -1506,7 +1506,8 @@ interface Foo {
       errors: [
         {
           messageId: 'unusedVar',
-          line: 4,
+          line: 2,
+          column: 11,
           data: {
             varName: 'Foo',
             action: 'defined',
@@ -1523,6 +1524,7 @@ type Foo = Array<Foo>;
         {
           messageId: 'unusedVar',
           line: 2,
+          column: 6,
           data: {
             varName: 'Foo',
             action: 'defined',
@@ -1550,6 +1552,7 @@ export const ComponentFoo = () => {
         {
           messageId: 'unusedVar',
           line: 3,
+          column: 10,
           data: {
             varName: 'Fragment',
             action: 'defined',
@@ -1577,6 +1580,7 @@ export const ComponentFoo = () => {
         {
           messageId: 'unusedVar',
           line: 2,
+          column: 8,
           data: {
             varName: 'React',
             action: 'defined',
@@ -1604,6 +1608,7 @@ export const ComponentFoo = () => {
         {
           messageId: 'unusedVar',
           line: 2,
+          column: 8,
           data: {
             varName: 'React',
             action: 'defined',
@@ -1624,6 +1629,7 @@ declare module 'foo' {
         {
           messageId: 'unusedVar',
           line: 3,
+          column: 8,
           data: {
             varName: 'Test',
             action: 'defined',
@@ -1649,6 +1655,7 @@ export namespace Foo {
         {
           messageId: 'unusedVar',
           line: 4,
+          column: 13,
           data: {
             varName: 'Bar',
             action: 'defined',
@@ -1658,6 +1665,7 @@ export namespace Foo {
         {
           messageId: 'unusedVar',
           line: 5,
+          column: 15,
           data: {
             varName: 'Baz',
             action: 'defined',
@@ -1667,6 +1675,7 @@ export namespace Foo {
         {
           messageId: 'unusedVar',
           line: 6,
+          column: 17,
           data: {
             varName: 'Bam',
             action: 'defined',
@@ -1676,6 +1685,7 @@ export namespace Foo {
         {
           messageId: 'unusedVar',
           line: 7,
+          column: 15,
           data: {
             varName: 'x',
             action: 'assigned a value',
@@ -1696,7 +1706,8 @@ interface Foo {
       errors: [
         {
           messageId: 'unusedVar',
-          line: 6,
+          line: 2,
+          column: 11,
           data: {
             varName: 'Foo',
             action: 'defined',
@@ -1705,5 +1716,23 @@ interface Foo {
         },
       ],
     },
+    {
+      code: `
+let x = null;
+x = foo(x);
+      `,
+      errors: [
+        {
+          messageId: 'unusedVar',
+          line: 3,
+          column: 1,
+          data: {
+            varName: 'x',
+            action: 'assigned a value',
+            additional: '',
+          },
+        },
+      ],
+    },
   ],
 });