From a92881ea7d15224970e6509dd7bd925c375e9373 Mon Sep 17 00:00:00 2001
From: mdm317 <dbswh1008@gmail.com>
Date: Thu, 24 Apr 2025 19:13:22 +0900
Subject: [PATCH 1/5] fix : Add parentheses to expressions that require them,
 even when they are missing in the original code

---
 .../src/rules/prefer-nullish-coalescing.ts    | 18 ++++-
 .../rules/prefer-nullish-coalescing.test.ts   | 79 +++++++++++++++++++
 2 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
index b05e43d0431e..977155cee41e 100644
--- a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
+++ b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
@@ -18,7 +18,9 @@ import {
   nullThrows,
   NullThrowsReasons,
   skipChainExpression,
+  isParenthesized,
 } from '../util';
+import { SourceCode } from '@typescript-eslint/utils/ts-eslint';
 
 const isMemberAccessLike = isNodeOfTypes([
   AST_NODE_TYPES.ChainExpression,
@@ -512,7 +514,7 @@ export default createRule<Options, MessageIds>({
                     `${getTextWithParentheses(
                       context.sourceCode,
                       nullishCoalescingParams.nullishCoalescingLeftNode,
-                    )} ?? ${getTextWithParentheses(
+                    )} ?? ${getTextWithEnsuredParentheses(
                       context.sourceCode,
                       getBranchNodes(node, operator).nullishBranch,
                     )}`,
@@ -932,3 +934,17 @@ function formatComments(
     )
     .join('');
 }
+
+function getTextWithEnsuredParentheses(
+  sourceCode: Readonly<SourceCode>,
+  node: TSESTree.Node,
+): string {
+  const replaceCode = getTextWithParentheses(sourceCode, node);
+  if (
+    node.type === AST_NODE_TYPES.ConditionalExpression &&
+    !isParenthesized(node, sourceCode)
+  ) {
+    return `(${replaceCode})`;
+  }
+  return replaceCode;
+}
diff --git a/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts b/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts
index 0926a839ee38..01834adde9e2 100644
--- a/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts
+++ b/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts
@@ -6248,5 +6248,84 @@ function weirdParens() {
       ],
       output: null,
     },
+    {
+      code: `
+let a: string | undefined
+let b: { message: string } | undefined
+
+const foo = a
+      ? a
+      : (b
+        ? 1 : 2)
+      `,
+      errors: [
+        {
+          messageId: 'preferNullishOverTernary',
+          suggestions: [
+            {
+              messageId: 'suggestNullish',
+              output: `
+let a: string | undefined
+let b: { message: string } | undefined
+
+const foo = a ?? (b
+        ? 1 : 2)
+      `,
+            },
+          ],
+        },
+      ],
+      output: null,
+    },
+    {
+      code: `
+let a: string | undefined
+let b: { message: string } | undefined
+
+const foo = a
+      ? a
+      : b
+        ? 1 : 2
+      `,
+      errors: [
+        {
+          messageId: 'preferNullishOverTernary',
+          suggestions: [
+            {
+              messageId: 'suggestNullish',
+              output: `
+let a: string | undefined
+let b: { message: string } | undefined
+
+const foo = a ?? (b
+        ? 1 : 2)
+      `,
+            },
+          ],
+        },
+      ],
+      output: null,
+    },
+    {
+      code: `
+declare const c: string | null;
+c !== null ? c :  c ? 1 : 2
+      `,
+      errors: [
+        {
+          messageId: 'preferNullishOverTernary',
+          suggestions: [
+            {
+              messageId: 'suggestNullish',
+              output: `
+declare const c: string | null;
+c ?? (c ? 1 : 2)
+      `,
+            },
+          ],
+        },
+      ],
+      output: null,
+    },
   ],
 });

From eb8ef5c8deea322f12de14def7498ee5f50f4885 Mon Sep 17 00:00:00 2001
From: mdm317 <dbswh1008@gmail.com>
Date: Thu, 24 Apr 2025 19:28:14 +0900
Subject: [PATCH 2/5] fix : format

---
 .../rules/prefer-nullish-coalescing.test.ts   | 38 ++++++++-----------
 1 file changed, 15 insertions(+), 23 deletions(-)

diff --git a/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts b/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts
index 01834adde9e2..618d1c244414 100644
--- a/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts
+++ b/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts
@@ -6250,13 +6250,10 @@ function weirdParens() {
     },
     {
       code: `
-let a: string | undefined
-let b: { message: string } | undefined
+let a: string | undefined;
+let b: { message: string } | undefined;
 
-const foo = a
-      ? a
-      : (b
-        ? 1 : 2)
+const foo = a ? a : b ? 1 : 2;
       `,
       errors: [
         {
@@ -6265,11 +6262,10 @@ const foo = a
             {
               messageId: 'suggestNullish',
               output: `
-let a: string | undefined
-let b: { message: string } | undefined
+let a: string | undefined;
+let b: { message: string } | undefined;
 
-const foo = a ?? (b
-        ? 1 : 2)
+const foo = a ?? (b ? 1 : 2);
       `,
             },
           ],
@@ -6278,14 +6274,11 @@ const foo = a ?? (b
       output: null,
     },
     {
-      code: `
-let a: string | undefined
-let b: { message: string } | undefined
+      code: noFormat`
+let a: string | undefined;
+let b: { message: string } | undefined;
 
-const foo = a
-      ? a
-      : b
-        ? 1 : 2
+const foo = a ? a : (b ? 1 : 2);
       `,
       errors: [
         {
@@ -6294,11 +6287,10 @@ const foo = a
             {
               messageId: 'suggestNullish',
               output: `
-let a: string | undefined
-let b: { message: string } | undefined
+let a: string | undefined;
+let b: { message: string } | undefined;
 
-const foo = a ?? (b
-        ? 1 : 2)
+const foo = a ?? (b ? 1 : 2);
       `,
             },
           ],
@@ -6309,7 +6301,7 @@ const foo = a ?? (b
     {
       code: `
 declare const c: string | null;
-c !== null ? c :  c ? 1 : 2
+c !== null ? c : c ? 1 : 2;
       `,
       errors: [
         {
@@ -6319,7 +6311,7 @@ c !== null ? c :  c ? 1 : 2
               messageId: 'suggestNullish',
               output: `
 declare const c: string | null;
-c ?? (c ? 1 : 2)
+c ?? (c ? 1 : 2);
       `,
             },
           ],

From ed97c64b6652e7235d8d4b096a980e23a221879e Mon Sep 17 00:00:00 2001
From: mdm317 <dbswh1008@gmail.com>
Date: Thu, 24 Apr 2025 21:46:14 +0900
Subject: [PATCH 3/5] fix : lint err

---
 packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
index 977155cee41e..4e3a76bc0aba 100644
--- a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
+++ b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
@@ -1,4 +1,5 @@
 import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
+import type { SourceCode } from '@typescript-eslint/utils/ts-eslint';
 
 import { AST_NODE_TYPES, AST_TOKEN_TYPES } from '@typescript-eslint/utils';
 import * as tsutils from 'ts-api-utils';
@@ -20,7 +21,6 @@ import {
   skipChainExpression,
   isParenthesized,
 } from '../util';
-import { SourceCode } from '@typescript-eslint/utils/ts-eslint';
 
 const isMemberAccessLike = isNodeOfTypes([
   AST_NODE_TYPES.ChainExpression,

From 07a6d712498a0f6077e5c132b93885640fd21d94 Mon Sep 17 00:00:00 2001
From: mdm317 <dbswh1008@gmail.com>
Date: Tue, 29 Apr 2025 00:46:38 +0900
Subject: [PATCH 4/5] fix: leverage existing infrastructure

---
 .../src/rules/prefer-nullish-coalescing.ts    | 39 ++++++++++---------
 1 file changed, 20 insertions(+), 19 deletions(-)

diff --git a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
index 4e3a76bc0aba..8b34c6d3d0cd 100644
--- a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
+++ b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
@@ -1,5 +1,4 @@
 import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
-import type { SourceCode } from '@typescript-eslint/utils/ts-eslint';
 
 import { AST_NODE_TYPES, AST_TOKEN_TYPES } from '@typescript-eslint/utils';
 import * as tsutils from 'ts-api-utils';
@@ -20,7 +19,10 @@ import {
   NullThrowsReasons,
   skipChainExpression,
   isParenthesized,
+  getOperatorPrecedenceForNode,
+  OperatorPrecedence,
 } from '../util';
+import { getWrappedCode } from '../util/getWrappedCode';
 
 const isMemberAccessLike = isNodeOfTypes([
   AST_NODE_TYPES.ChainExpression,
@@ -514,10 +516,23 @@ export default createRule<Options, MessageIds>({
                     `${getTextWithParentheses(
                       context.sourceCode,
                       nullishCoalescingParams.nullishCoalescingLeftNode,
-                    )} ?? ${getTextWithEnsuredParentheses(
-                      context.sourceCode,
-                      getBranchNodes(node, operator).nullishBranch,
-                    )}`,
+                    )} ?? ${(() => {
+                      const branch = getBranchNodes(
+                        node,
+                        operator,
+                      ).nullishBranch;
+                      if (isParenthesized(branch, context.sourceCode)) {
+                        return getTextWithParentheses(
+                          context.sourceCode,
+                          branch,
+                        );
+                      }
+                      return getWrappedCode(
+                        getTextWithParentheses(context.sourceCode, branch),
+                        getOperatorPrecedenceForNode(branch),
+                        OperatorPrecedence.Coalesce,
+                      );
+                    })()}`,
                   );
                 },
               },
@@ -934,17 +949,3 @@ function formatComments(
     )
     .join('');
 }
-
-function getTextWithEnsuredParentheses(
-  sourceCode: Readonly<SourceCode>,
-  node: TSESTree.Node,
-): string {
-  const replaceCode = getTextWithParentheses(sourceCode, node);
-  if (
-    node.type === AST_NODE_TYPES.ConditionalExpression &&
-    !isParenthesized(node, sourceCode)
-  ) {
-    return `(${replaceCode})`;
-  }
-  return replaceCode;
-}

From dd690c4a03808da9f040028452da44ce84e885b0 Mon Sep 17 00:00:00 2001
From: Kirk Waiblinger <53019676+kirkwaiblinger@users.noreply.github.com>
Date: Thu, 1 May 2025 08:01:01 -0600
Subject: [PATCH 5/5] simplify syntax

---
 .../src/rules/prefer-nullish-coalescing.ts    | 40 ++++++++++---------
 1 file changed, 22 insertions(+), 18 deletions(-)

diff --git a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
index 8b34c6d3d0cd..8f4cffd98ffc 100644
--- a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
+++ b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
@@ -493,9 +493,14 @@ export default createRule<Options, MessageIds>({
           return;
         }
 
+        const { nonNullishBranch, nullishBranch } = getBranchNodes(
+          node,
+          operator,
+        );
+
         const nullishCoalescingParams = getNullishCoalescingParams(
           node,
-          getBranchNodes(node, operator).nonNullishBranch,
+          nonNullishBranch,
           nodesInsideTestExpression,
           operator,
         );
@@ -511,28 +516,27 @@ export default createRule<Options, MessageIds>({
                 messageId: 'suggestNullish',
                 data: { equals: '' },
                 fix(fixer: TSESLint.RuleFixer): TSESLint.RuleFix {
+                  const nullishBranchText = getTextWithParentheses(
+                    context.sourceCode,
+                    nullishBranch,
+                  );
+                  const rightOperandReplacement = isParenthesized(
+                    nullishBranch,
+                    context.sourceCode,
+                  )
+                    ? nullishBranchText
+                    : getWrappedCode(
+                        nullishBranchText,
+                        getOperatorPrecedenceForNode(nullishBranch),
+                        OperatorPrecedence.Coalesce,
+                      );
+
                   return fixer.replaceText(
                     node,
                     `${getTextWithParentheses(
                       context.sourceCode,
                       nullishCoalescingParams.nullishCoalescingLeftNode,
-                    )} ?? ${(() => {
-                      const branch = getBranchNodes(
-                        node,
-                        operator,
-                      ).nullishBranch;
-                      if (isParenthesized(branch, context.sourceCode)) {
-                        return getTextWithParentheses(
-                          context.sourceCode,
-                          branch,
-                        );
-                      }
-                      return getWrappedCode(
-                        getTextWithParentheses(context.sourceCode, branch),
-                        getOperatorPrecedenceForNode(branch),
-                        OperatorPrecedence.Coalesce,
-                      );
-                    })()}`,
+                    )} ?? ${rightOperandReplacement}`,
                   );
                 },
               },

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