fix(eslint-plugin): [no-unnecessary-type-assertion] handle exactOptio…

…nalPropertyTypes compiler option (#8770) * fix(eslint-plugin): [no-unnecessary-type-assertion] handle exactOptionalPropertyTypes compiler option * rename function * edit tc * apply review
typescript-eslint · Apr 1, 2024 · f0b1c4f · f0b1c4f
1 parent 7f9fcca
commit f0b1c4f
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diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
@@ -128,6 +128,38 @@ export default createRule<Options, MessageIds>({
       );
     }
 
+    function isTypeUnchanged(uncast: ts.Type, cast: ts.Type): boolean {
+      if (uncast === cast) {
+        return true;
+      }
+
+      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 uncastPartsSet = new Set(uncastParts);
+        return castParts.every(part => uncastPartsSet.has(part));
+      }
+
+      return false;
+    }
+
     return {
       TSNonNullExpression(node): void {
         if (
@@ -232,7 +264,7 @@ export default createRule<Options, MessageIds>({
 
         const castType = services.getTypeAtLocation(node);
         const uncastType = services.getTypeAtLocation(node.expression);
-        const typeIsUnchanged = uncastType === castType;
+        const typeIsUnchanged = isTypeUnchanged(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
@@ -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 +292,51 @@ 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,
+    },
+    {
+      code: `
+declare const foo: {
+  a?: string | number;
+};
+const bar = foo.a as string | undefined | bigint;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
   ],
 
   invalid: [
@@ -934,5 +984,50 @@ 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,
+    },
   ],
 });