From 33e72d94911c4dc0b43cc14cd8ab2c3a9c429b30 Mon Sep 17 00:00:00 2001
From: yeonjuan <yeonjuan93@naver.com>
Date: Tue, 26 Mar 2024 01:52:50 +0900
Subject: [PATCH 1/4] fix(eslint-plugin): [no-unnecessary-type-assertion]
 handle exactOptionalPropertyTypes compiler option

---
 .../rules/no-unnecessary-type-assertion.ts    | 32 ++++++-
 .../no-unnecessary-type-assertion.test.ts     | 86 +++++++++++++++++++
 2 files changed, 117 insertions(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
index fdb957b4602e..6984f54ecc7a 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
@@ -128,6 +128,36 @@ export default createRule<Options, MessageIds>({
       );
     }
 
+    function isTypeChanged(uncast: ts.Type, cast: ts.Type): boolean {
+      if (uncast === cast) {
+        return true;
+      } else if (
+        isTypeFlagSet(uncast, ts.TypeFlags.Undefined) &&
+        isTypeFlagSet(cast, ts.TypeFlags.Undefined) &&
+        tsutils.isCompilerOptionEnabled(
+          compilerOptions,
+          'exactOptionalPropertyTypes',
+        )
+      ) {
+        const uncastParts = tsutils
+          .unionTypeParts(uncast)
+          .filter(part => !isTypeFlagSet(part, ts.TypeFlags.Undefined));
+
+        const castParts = tsutils
+          .unionTypeParts(cast)
+          .filter(part => !isTypeFlagSet(part, ts.TypeFlags.Undefined));
+
+        if (uncastParts.length !== castParts.length) {
+          return false;
+        }
+
+        const castPartsSet = new Set(castParts);
+        uncastParts.forEach(part => castPartsSet.delete(part));
+        return castPartsSet.size === 0;
+      }
+      return false;
+    }
+
     return {
       TSNonNullExpression(node): void {
         if (
@@ -232,7 +262,7 @@ export default createRule<Options, MessageIds>({
 
         const castType = services.getTypeAtLocation(node);
         const uncastType = services.getTypeAtLocation(node.expression);
-        const typeIsUnchanged = uncastType === castType;
+        const typeIsUnchanged = isTypeChanged(uncastType, castType);
 
         const wouldSameTypeBeInferred = castType.isLiteral()
           ? isLiteralVariableDeclarationChangingTypeWithConst(node)
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
index a0dd0755239e..bc5cffee6d0d 100644
--- a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
@@ -19,6 +19,11 @@ const optionsWithOnUncheckedIndexedAccess = {
   project: './tsconfig.noUncheckedIndexedAccess.json',
 };
 
+const optionsWithExactOptionalPropertyTypes = {
+  tsconfigRootDir: rootDir,
+  project: './tsconfig.exactOptionalPropertyTypes.json',
+};
+
 ruleTester.run('no-unnecessary-type-assertion', rule, {
   valid: [
     `
@@ -287,6 +292,42 @@ const templateLiteral = \`\${myString}-somethingElse\` as const;
 const myString = 'foo';
 const templateLiteral = <const>\`\${myString}-somethingElse\`;
     `,
+    {
+      code: `
+declare const foo: {
+  a?: string;
+};
+const bar = foo.a as string;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
+    {
+      code: `
+declare const foo: {
+  a?: string | undefined;
+};
+const bar = foo.a as string;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
+    {
+      code: `
+declare const foo: {
+  a: string;
+};
+const bar = foo.a as string | undefined;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
+    {
+      code: `
+declare const foo: {
+  a: string | null | number;
+};
+const bar = foo.a as string | undefined;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
   ],
 
   invalid: [
@@ -934,5 +975,50 @@ function bar(items: string[]) {
         },
       ],
     },
+    // exactOptionalPropertyTypes = true
+    {
+      code: `
+declare const foo: {
+  a?: string;
+};
+const bar = foo.a as string | undefined;
+      `,
+      output: `
+declare const foo: {
+  a?: string;
+};
+const bar = foo.a;
+      `,
+      errors: [
+        {
+          messageId: 'unnecessaryAssertion',
+          line: 5,
+          column: 13,
+        },
+      ],
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
+    {
+      code: `
+declare const foo: {
+  a?: string | undefined;
+};
+const bar = foo.a as string | undefined;
+      `,
+      output: `
+declare const foo: {
+  a?: string | undefined;
+};
+const bar = foo.a;
+      `,
+      errors: [
+        {
+          messageId: 'unnecessaryAssertion',
+          line: 5,
+          column: 13,
+        },
+      ],
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
   ],
 });

From e702eb7cbc89784233ba92cc060ba46728cb29ad Mon Sep 17 00:00:00 2001
From: yeonjuan <yeonjuan93@naver.com>
Date: Tue, 26 Mar 2024 02:23:58 +0900
Subject: [PATCH 2/4] rename function

---
 .../eslint-plugin/src/rules/no-unnecessary-type-assertion.ts  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
index 6984f54ecc7a..2d41e1df5879 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
@@ -128,7 +128,7 @@ export default createRule<Options, MessageIds>({
       );
     }
 
-    function isTypeChanged(uncast: ts.Type, cast: ts.Type): boolean {
+    function isTypeUnchanged(uncast: ts.Type, cast: ts.Type): boolean {
       if (uncast === cast) {
         return true;
       } else if (
@@ -262,7 +262,7 @@ export default createRule<Options, MessageIds>({
 
         const castType = services.getTypeAtLocation(node);
         const uncastType = services.getTypeAtLocation(node.expression);
-        const typeIsUnchanged = isTypeChanged(uncastType, castType);
+        const typeIsUnchanged = isTypeUnchanged(uncastType, castType);
 
         const wouldSameTypeBeInferred = castType.isLiteral()
           ? isLiteralVariableDeclarationChangingTypeWithConst(node)

From a48a580821f4282d31ce459ac5745c99f8525b41 Mon Sep 17 00:00:00 2001
From: yeonjuan <yeonjuan93@naver.com>
Date: Tue, 26 Mar 2024 02:44:40 +0900
Subject: [PATCH 3/4] edit tc

---
 .../tests/rules/no-unnecessary-type-assertion.test.ts           | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
index bc5cffee6d0d..bd65853c6d1c 100644
--- a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
@@ -322,7 +322,7 @@ const bar = foo.a as string | undefined;
     {
       code: `
 declare const foo: {
-  a: string | null | number;
+  a?: string | null | number;
 };
 const bar = foo.a as string | undefined;
       `,

From 72a9a55a04dab5e35829a9dcb504440b6b21a6bb Mon Sep 17 00:00:00 2001
From: yeonjuan <yeonjuan93@naver.com>
Date: Wed, 27 Mar 2024 00:02:17 +0900
Subject: [PATCH 4/4] apply review

---
 .../src/rules/no-unnecessary-type-assertion.ts         | 10 ++++++----
 .../tests/rules/no-unnecessary-type-assertion.test.ts  |  9 +++++++++
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
index 2d41e1df5879..a73962b9acbd 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
@@ -131,7 +131,9 @@ export default createRule<Options, MessageIds>({
     function isTypeUnchanged(uncast: ts.Type, cast: ts.Type): boolean {
       if (uncast === cast) {
         return true;
-      } else if (
+      }
+
+      if (
         isTypeFlagSet(uncast, ts.TypeFlags.Undefined) &&
         isTypeFlagSet(cast, ts.TypeFlags.Undefined) &&
         tsutils.isCompilerOptionEnabled(
@@ -151,10 +153,10 @@ export default createRule<Options, MessageIds>({
           return false;
         }
 
-        const castPartsSet = new Set(castParts);
-        uncastParts.forEach(part => castPartsSet.delete(part));
-        return castPartsSet.size === 0;
+        const uncastPartsSet = new Set(uncastParts);
+        return castParts.every(part => uncastPartsSet.has(part));
       }
+
       return false;
     }
 
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
index bd65853c6d1c..17efb3ff0baf 100644
--- a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
@@ -328,6 +328,15 @@ const bar = foo.a as string | undefined;
       `,
       parserOptions: optionsWithExactOptionalPropertyTypes,
     },
+    {
+      code: `
+declare const foo: {
+  a?: string | number;
+};
+const bar = foo.a as string | undefined | bigint;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
   ],
 
   invalid: [

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