fix(eslint-plugin): [require-await] improve performance (#1536)

packages/eslint-plugin/src/rules/require-await.ts

@@ -1,16 +1,28 @@
 import {
-  TSESTree,
   AST_NODE_TYPES,
+  TSESLint,
+  TSESTree,
 } from '@typescript-eslint/experimental-utils';
-import baseRule from 'eslint/lib/rules/require-await';
+import {
+  isArrowToken,
+  getFunctionNameWithKind,
+  isOpeningParenToken,
+} from 'eslint-utils';
 import * as tsutils from 'tsutils';
 import * as ts from 'typescript';
 import * as util from '../util';
 
-type Options = util.InferOptionsTypeFromRule<typeof baseRule>;
-type MessageIds = util.InferMessageIdsTypeFromRule<typeof baseRule>;
+interface ScopeInfo {
+  upper: ScopeInfo | null;
+  hasAwait: boolean;
+  hasAsync: boolean;
+}
+type FunctionNode =
+  | TSESTree.FunctionDeclaration
+  | TSESTree.FunctionExpression
+  | TSESTree.ArrowFunctionExpression;
 
-export default util.createRule<Options, MessageIds>({
+export default util.createRule({
   name: 'require-await',
   meta: {
     type: 'suggestion',
@@ -21,58 +33,172 @@ export default util.createRule<Options, MessageIds>({
       requiresTypeChecking: true,
       extendsBaseRule: true,
     },
-    schema: baseRule.meta.schema,
-    messages: baseRule.meta.messages,
+    schema: [],
+    messages: {
+      missingAwait: "{{name}} has no 'await' expression.",
+    },
   },
   defaultOptions: [],
   create(context) {
-    const rules = baseRule.create(context);
     const parserServices = util.getParserServices(context);
     const checker = parserServices.program.getTypeChecker();
 
+    const sourceCode = context.getSourceCode();
+    let scopeInfo: ScopeInfo | null = null;
+
+    /**
+     * Push the scope info object to the stack.
+     */
+    function enterFunction(node: FunctionNode): void {
+      scopeInfo = {
+        upper: scopeInfo,
+        hasAwait: false,
+        hasAsync: node.async,
+      };
+    }
+
+    /**
+     * Pop the top scope info object from the stack.
+     * Also, it reports the function if needed.
+     */
+    function exitFunction(node: FunctionNode): void {
+      /* istanbul ignore if */ if (!scopeInfo) {
+        // this shouldn't ever happen, as we have to exit a function after we enter it
+        return;
+      }
+
+      if (node.async && !scopeInfo.hasAwait && !isEmptyFunction(node)) {
+        context.report({
+          node,
+          loc: getFunctionHeadLoc(node, sourceCode),
+          messageId: 'missingAwait',
+          data: {
+            name: util.upperCaseFirst(getFunctionNameWithKind(node)),
+          },
+        });
+      }
+
+      scopeInfo = scopeInfo.upper;
+    }
+
     /**
      * Checks if the node returns a thenable type
-     *
-     * @param {ASTNode} node - The node to check
-     * @returns {boolean}
      */
     function isThenableType(node: ts.Node): boolean {
       const type = checker.getTypeAtLocation(node);
 
       return tsutils.isThenableType(checker, node, type);
     }
 
+    /**
+     * Marks the current scope as having an await
+     */
+    function markAsHasAwait(): void {
+      if (!scopeInfo) {
+        return;
+      }
+
+      scopeInfo.hasAwait = true;
+    }
+
     return {
-      FunctionDeclaration: rules.FunctionDeclaration,
-      FunctionExpression: rules.FunctionExpression,
-      ArrowFunctionExpression: rules.ArrowFunctionExpression,
-      'ArrowFunctionExpression[async = true]'(
-        node: TSESTree.ArrowFunctionExpression,
+      FunctionDeclaration: enterFunction,
+      FunctionExpression: enterFunction,
+      ArrowFunctionExpression: enterFunction,
+      'FunctionDeclaration:exit': exitFunction,
+      'FunctionExpression:exit': exitFunction,
+      'ArrowFunctionExpression:exit': exitFunction,
+
+      AwaitExpression: markAsHasAwait,
+      'ForOfStatement[await = true]': markAsHasAwait,
+
+      // check body-less async arrow function.
+      // ignore `async () => await foo` because it's obviously correct
+      'ArrowFunctionExpression[async = true] > :not(BlockStatement, AwaitExpression)'(
+        node: Exclude<
+          TSESTree.Node,
+          TSESTree.BlockStatement | TSESTree.AwaitExpression
+        >,
       ): void {
-        // If body type is not BlockStatement, we need to check the return type here
-        if (node.body.type !== AST_NODE_TYPES.BlockStatement) {
-          const expression = parserServices.esTreeNodeToTSNodeMap.get(
-            node.body,
-          );
-          if (expression && isThenableType(expression)) {
-            // tell the base rule to mark the scope as having an await so it ignores it
-            rules.AwaitExpression();
-          }
+        const expression = parserServices.esTreeNodeToTSNodeMap.get(node);
+        if (expression && isThenableType(expression)) {
+          markAsHasAwait();
         }
       },
-      'FunctionDeclaration:exit': rules['FunctionDeclaration:exit'],
-      'FunctionExpression:exit': rules['FunctionExpression:exit'],
-      'ArrowFunctionExpression:exit': rules['ArrowFunctionExpression:exit'],
-      AwaitExpression: rules.AwaitExpression,
-      ForOfStatement: rules.ForOfStatement,
-
       ReturnStatement(node): void {
+        // short circuit early to avoid unnecessary type checks
+        if (!scopeInfo || scopeInfo.hasAwait || !scopeInfo.hasAsync) {
+          return;
+        }
+
         const { expression } = parserServices.esTreeNodeToTSNodeMap.get(node);
         if (expression && isThenableType(expression)) {
-          // tell the base rule to mark the scope as having an await so it ignores it
-          rules.AwaitExpression();
+          markAsHasAwait();
         }
       },
     };
   },
 });
+
+function isEmptyFunction(node: FunctionNode): boolean {
+  return (
+    node.body?.type === AST_NODE_TYPES.BlockStatement &&
+    node.body.body.length === 0
+  );
+}
+
+// https://github.com/eslint/eslint/blob/03a69dbe86d5b5768a310105416ae726822e3c1c/lib/rules/utils/ast-utils.js#L382-L392
+/**
+ * Gets the `(` token of the given function node.
+ */
+function getOpeningParenOfParams(
+  node: FunctionNode,
+  sourceCode: TSESLint.SourceCode,
+): TSESTree.Token {
+  return util.nullThrows(
+    node.id
+      ? sourceCode.getTokenAfter(node.id, isOpeningParenToken)
+      : sourceCode.getFirstToken(node, isOpeningParenToken),
+    util.NullThrowsReasons.MissingToken('(', node.type),
+  );
+}
+
+// https://github.com/eslint/eslint/blob/03a69dbe86d5b5768a310105416ae726822e3c1c/lib/rules/utils/ast-utils.js#L1220-L1242
+/**
+ * Gets the location of the given function node for reporting.
+ */
+function getFunctionHeadLoc(
+  node: FunctionNode,
+  sourceCode: TSESLint.SourceCode,
+): TSESTree.SourceLocation {
+  const parent = util.nullThrows(
+    node.parent,
+    util.NullThrowsReasons.MissingParent,
+  );
+  let start = null;
+  let end = null;
+
+  if (node.type === AST_NODE_TYPES.ArrowFunctionExpression) {
+    const arrowToken = util.nullThrows(
+      sourceCode.getTokenBefore(node.body, isArrowToken),
+      util.NullThrowsReasons.MissingToken('=>', node.type),
+    );
+
+    start = arrowToken.loc.start;
+    end = arrowToken.loc.end;
+  } else if (
+    parent.type === AST_NODE_TYPES.Property ||
+    parent.type === AST_NODE_TYPES.MethodDefinition
+  ) {
+    start = parent.loc.start;
+    end = getOpeningParenOfParams(node, sourceCode).loc.start;
+  } else {
+    start = node.loc.start;
+    end = getOpeningParenOfParams(node, sourceCode).loc.start;
+  }
+
+  return {
+    start,
+    end,
+  };
+}