Add await-promise rule

src/rules/awaitPromiseRule.ts

@@ -0,0 +1,74 @@
+/**
+ * @license
+ * Copyright 2017 Palantir Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as ts from "typescript";
+import * as Lint from "../index";
+
+export class Rule extends Lint.Rules.TypedRule {
+    /* tslint:disable:object-literal-sort-keys */
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "strict-boolean-expressions",
+        description: "Warns for an awaited value that is not a Promise.",
+        optionsDescription: "Not configurable.",
+        options: null,
+        optionExamples: ["true"],
+        type: "functionality",
+        typescriptOnly: true,
+        requiresTypeInfo: true,
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static FAILURE_STRING = "'await' of non-Promise.";
+
+    public applyWithProgram(srcFile: ts.SourceFile, langSvc: ts.LanguageService): Lint.RuleFailure[] {
+        return this.applyWithWalker(new Walker(srcFile, this.getOptions(), langSvc.getProgram()));
+    }
+}
+
+class Walker extends Lint.ProgramAwareRuleWalker {
+    public visitNode(node: ts.Node) {
+        if (node.kind === ts.SyntaxKind.AwaitExpression &&
+            !couldBePromise(this.getTypeChecker().getTypeAtLocation((node as ts.AwaitExpression).expression))) {
+            this.addFailureAtNode(node, Rule.FAILURE_STRING);
+        }
+
+        super.visitNode(node);
+    }
+}
+
+function couldBePromise(type: ts.Type): boolean {
+    if (Lint.isTypeFlagSet(type, ts.TypeFlags.Any) || isPromiseType(type)) {
+        return true;
+    }
+
+    if (isUnionType(type)) {
+        return type.types.some(isPromiseType);
+    }
+
+    const bases = type.getBaseTypes();
+    return bases !== undefined && bases.some(couldBePromise);
+}
+
+function isPromiseType(type: ts.Type): boolean {
+    const { target } = type as ts.TypeReference;
+    const symbol = target && target.symbol;
+    return !!symbol && symbol.name === "Promise";
+}
+
+function isUnionType(type: ts.Type): type is ts.UnionType {
+    return Lint.isTypeFlagSet(type, ts.TypeFlags.Union);
+}

test/rules/await-promise/test.ts.lint

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+declare const num: Promise<number>;
+declare const isAny: any;
+
+async function f() {
+    await isAny;
+    await num;
+    await 0;
+    ~~~~~~~ [0]
+    await (Math.random() > 0.5 ? num : 0);
+    await (Math.random() > 0.5 ? "" : 0);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+
+    class MyPromise extends Promise<number> {}
+    const myPromise: MyPromise = MyPromise.resolve(2);
+    await myPromise;
+
+    class Foo extends MyPromise {}
+    const foo: Foo = Foo.resolve(2);
+    await foo;
+
+    class Bar extends Array {}
+    await new Bar();
+    ~~~~~~~~~~~~~~~ [0]
+}
+
+[0]: 'await' of non-Promise.

test/rules/await-promise/tsconfig.json

@@ -0,0 +1,5 @@
+{
+    "compilerOptions": {
+        "target": "es6"
+    }
+}

test/rules/await-promise/tslint.json

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+{
+  "linterOptions": {
+    "typeCheck": true
+  },
+  "rules": {
+    "await-promise": true
+  }
+}