fix(eslint-plugin): [no-unnecessary-type-assertion] avoid remove cons…

…t casting on template literals with expressions inside (typescript-eslint#8740)
yeonjuan · Mar 31, 2024 · 6d07f42 · 6d07f42
1 parent 69204a4
commit 6d07f42
Show file tree

Hide file tree

Showing 2 changed files with 33 additions and 5 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
@@ -108,10 +108,23 @@ export default createRule<Options, MessageIds>({
       );
     }
 
-    function isConstVariableDeclaration(node: TSESTree.Node): boolean {
+    function isLiteralVariableDeclarationChangingTypeWithConst(
+      node: TSESTree.TSAsExpression | TSESTree.TSTypeAssertion,
+    ): boolean {
+      /**
+       * If the type assertion is on a template literal WITH expressions we
+       * should keep the `const` casting
+       * @see https://github.com/typescript-eslint/typescript-eslint/issues/8737
+       */
+      if (node.expression.type === AST_NODE_TYPES.TemplateLiteral) {
+        return node.expression.expressions.length === 0;
+      }
+
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const maybeDeclarationNode = node.parent.parent!;
       return (
-        node.type === AST_NODE_TYPES.VariableDeclaration &&
-        node.kind === 'const'
+        maybeDeclarationNode.type === AST_NODE_TYPES.VariableDeclaration &&
+        maybeDeclarationNode.kind === 'const'
       );
     }
 
@@ -222,8 +235,7 @@ export default createRule<Options, MessageIds>({
         const typeIsUnchanged = uncastType === castType;
 
         const wouldSameTypeBeInferred = castType.isLiteral()
-          ? // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-            isConstVariableDeclaration(node.parent.parent!)
+          ? isLiteralVariableDeclarationChangingTypeWithConst(node)
           : !isConstAssertion(node.typeAnnotation);
 
         if (typeIsUnchanged && wouldSameTypeBeInferred) {

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
@@ -277,9 +277,25 @@ function bar(items: string[]) {
       `,
       parserOptions: optionsWithOnUncheckedIndexedAccess,
     },
+    // https://github.com/typescript-eslint/typescript-eslint/issues/8737
+    `
+const myString = 'foo';
+const templateLiteral = \`\${myString}-somethingElse\` as const;
+    `,
+    // https://github.com/typescript-eslint/typescript-eslint/issues/8737
+    `
+const myString = 'foo';
+const templateLiteral = <const>\`\${myString}-somethingElse\`;
+    `,
   ],
 
   invalid: [
+    // https://github.com/typescript-eslint/typescript-eslint/issues/8737
+    {
+      code: 'const a = `a` as const;',
+      output: 'const a = `a`;',
+      errors: [{ messageId: 'unnecessaryAssertion', line: 1 }],
+    },
     {
       code: "const a = 'a' as const;",
       output: "const a = 'a';",