typescript-eslint · danvk · Mar 23, 2023 · Mar 23, 2023 · Mar 23, 2023 · Mar 23, 2023
diff --git a/packages/eslint-plugin/docs/rules/consistent-type-assertions.md b/packages/eslint-plugin/docs/rules/consistent-type-assertions.md
@@ -103,6 +103,34 @@ const foo = <Foo props={{ ... } as Bar}/>;
 
 <!--/tabs-->
 
+### `arrayLiteralTypeAssertions`
+
+Always prefer `const x: T[] = [ ... ];` to `const x = [ ... ] as T[];` (or similar with angle brackets). The rationale for this is exactly the same as for `objectLiteralTypeAssertions`.
+
+The const assertion `const x = [1, 2, 3] as const`, introduced in TypeScript 3.4, is considered beneficial and is ignored by this option.
+
+Assertions to `any` are also ignored by this option.
+
+Examples of code for `{ assertionStyle: 'as', arrayLiteralTypeAssertions: 'never' }`:
+
+<!--tabs-->
+
+#### ❌ Incorrect
+
+```ts
+const x = [] as string[];
+const y = ['a'] as string[];
+```
+
+#### ✅ Correct
+
+```ts
+const x: string[] = [];
+const y: string[] = ['a'];
+```
+
+<!--/tabs-->
+
 ## When Not To Use It
 
 If you do not want to enforce consistent type assertions.
diff --git a/packages/eslint-plugin/src/rules/consistent-type-assertions.ts b/packages/eslint-plugin/src/rules/consistent-type-assertions.ts
@@ -9,12 +9,16 @@ type MessageIds =
   | 'angle-bracket'
   | 'never'
   | 'unexpectedObjectTypeAssertion'
+  | 'unexpectedArrayTypeAssertion'
   | 'replaceObjectTypeAssertionWithAnnotation'
-  | 'replaceObjectTypeAssertionWithSatisfies';
+  | 'replaceObjectTypeAssertionWithSatisfies'
+  | 'replaceArrayTypeAssertionWithAnnotation'
+  | 'replaceArrayTypeAssertionWithSatisfies';
 type OptUnion =
   | {
       assertionStyle: 'as' | 'angle-bracket';
       objectLiteralTypeAssertions?: 'allow' | 'allow-as-parameter' | 'never';
+      arrayLiteralTypeAssertions?: 'allow' | 'never';
     }
   | {
       assertionStyle: 'never';
@@ -36,10 +40,15 @@ export default util.createRule<Options, MessageIds>({
       'angle-bracket': "Use '<{{cast}}>' instead of 'as {{cast}}'.",
       never: 'Do not use any type assertions.',
       unexpectedObjectTypeAssertion: 'Always prefer const x: T = { ... }.',
+      unexpectedArrayTypeAssertion: 'Always prefer const x: T[] = [ ... ].',
       replaceObjectTypeAssertionWithAnnotation:
         'Use const x: {{cast}} = { ... } instead.',
       replaceObjectTypeAssertionWithSatisfies:
         'Use const x = { ... } satisfies {{cast}} instead.',
+      replaceArrayTypeAssertionWithAnnotation:
+        'Use const x: [{cast}] = [ ... ] instead.',
+      replaceArrayTypeAssertionWithSatisfies:
+        'Use const x = [ ... ] satisfies [{cast}] instead.',
     },
     schema: [
       {
@@ -63,6 +72,9 @@ export default util.createRule<Options, MessageIds>({
               objectLiteralTypeAssertions: {
                 enum: ['allow', 'allow-as-parameter', 'never'],
               },
+              arrayLiteralTypeAssertions: {
+                enum: ['allow', 'never'],
+              },
             },
             additionalProperties: false,
             required: ['assertionStyle'],
@@ -75,6 +87,7 @@ export default util.createRule<Options, MessageIds>({
     {
       assertionStyle: 'as',
       objectLiteralTypeAssertions: 'allow',
+      arrayLiteralTypeAssertions: 'allow',
     },
   ],
   create(context, [options]) {
@@ -164,7 +177,46 @@ export default util.createRule<Options, MessageIds>({
       }
     }
 
-    function checkExpression(
+    function getReplacementSuggestions(
+      node: TSESTree.TSTypeAssertion | TSESTree.TSAsExpression,
+      annotationMessageId: MessageIds,
+      satisfiesMessageId: MessageIds,
+    ): TSESLint.ReportSuggestionArray<MessageIds> {
+      const suggest: TSESLint.ReportSuggestionArray<MessageIds> = [];
+      if (
+        node.parent?.type === AST_NODE_TYPES.VariableDeclarator &&
+        !node.parent.id.typeAnnotation
+      ) {
+        const { parent } = node;
+        suggest.push({
+          messageId: annotationMessageId,
+          data: { cast: sourceCode.getText(node.typeAnnotation) },
+          fix: fixer => [
+            fixer.insertTextAfter(
+              parent.id,
+              `: ${sourceCode.getText(node.typeAnnotation)}`,
+            ),
+            fixer.replaceText(node, getTextWithParentheses(node.expression)),
+          ],
+        });
+      }
+      suggest.push({
+        messageId: satisfiesMessageId,
+        data: { cast: sourceCode.getText(node.typeAnnotation) },
+        fix: fixer => [
+          fixer.replaceText(node, getTextWithParentheses(node.expression)),
+          fixer.insertTextAfter(
+            node,
+            ` satisfies ${context
+              .getSourceCode()
+              .getText(node.typeAnnotation)}`,
+          ),
+        ],
+      });
+      return suggest;
+    }
+
+    function checkExpressionForObjectAssertion(
       node: TSESTree.TSTypeAssertion | TSESTree.TSAsExpression,
     ): void {
       if (
@@ -191,37 +243,11 @@ export default util.createRule<Options, MessageIds>({
         checkType(node.typeAnnotation) &&
         node.expression.type === AST_NODE_TYPES.ObjectExpression
       ) {
-        const suggest: TSESLint.ReportSuggestionArray<MessageIds> = [];
-        if (
-          node.parent?.type === AST_NODE_TYPES.VariableDeclarator &&
-          !node.parent.id.typeAnnotation
-        ) {
-          const { parent } = node;
-          suggest.push({
-            messageId: 'replaceObjectTypeAssertionWithAnnotation',
-            data: { cast: sourceCode.getText(node.typeAnnotation) },
-            fix: fixer => [
-              fixer.insertTextAfter(
-                parent.id,
-                `: ${sourceCode.getText(node.typeAnnotation)}`,
-              ),
-              fixer.replaceText(node, getTextWithParentheses(node.expression)),
-            ],
-          });
-        }
-        suggest.push({
-          messageId: 'replaceObjectTypeAssertionWithSatisfies',
-          data: { cast: sourceCode.getText(node.typeAnnotation) },
-          fix: fixer => [
-            fixer.replaceText(node, getTextWithParentheses(node.expression)),
-            fixer.insertTextAfter(
-              node,
-              ` satisfies ${context
-                .getSourceCode()
-                .getText(node.typeAnnotation)}`,
-            ),
-          ],
-        });
+        const suggest = getReplacementSuggestions(
+          node,
+          'replaceObjectTypeAssertionWithAnnotation',
+          'replaceObjectTypeAssertionWithSatisfies',
+        );
 
         context.report({
           node,
@@ -231,22 +257,53 @@ export default util.createRule<Options, MessageIds>({
       }
     }
 
+    function checkExpressionForArrayAssertion(
+      node: TSESTree.TSTypeAssertion | TSESTree.TSAsExpression,
+    ): void {
+      if (
+        options.assertionStyle === 'never' ||
+        options.arrayLiteralTypeAssertions === 'allow' ||
+        node.expression.type !== AST_NODE_TYPES.ArrayExpression
+      ) {
+        return;
+      }
+
+      if (
+        checkType(node.typeAnnotation) &&
+        node.expression.type === AST_NODE_TYPES.ArrayExpression
+      ) {
+        const suggest = getReplacementSuggestions(
+          node,
+          'replaceArrayTypeAssertionWithAnnotation',
+          'replaceArrayTypeAssertionWithSatisfies',
+        );
+
+        context.report({
+          node,
+          messageId: 'unexpectedArrayTypeAssertion',
+          suggest,
+        });
+      }
+    }
+
     return {
       TSTypeAssertion(node): void {
         if (options.assertionStyle !== 'angle-bracket') {
           reportIncorrectAssertionType(node);
           return;
         }
 
-        checkExpression(node);
+        checkExpressionForObjectAssertion(node);
+        checkExpressionForArrayAssertion(node);
       },
       TSAsExpression(node): void {
         if (options.assertionStyle !== 'as') {
           reportIncorrectAssertionType(node);
           return;
         }
 
-        checkExpression(node);
+        checkExpressionForObjectAssertion(node);
+        checkExpressionForArrayAssertion(node);
       },
     };
   },