From 5f821cf4855a65cef537d7b2edca055d261dc60f Mon Sep 17 00:00:00 2001
From: Michael Giambalvo <heathkit@google.com>
Date: Thu, 25 Jan 2018 14:37:37 -0800
Subject: [PATCH] Add isPromiseType.

Returns true if a type is a union type that includes Promise, or a type
that extends Promise.
---
 test/rules/promise-use/promise.ts.lint       | 42 ++++++++++++++++++++
 test/rules/promise-use/testPromiseUseRule.ts | 37 +++++++++++++++++
 test/rules/promise-use/tsconfig.json         | 26 ++++++++++++
 test/rules/promise-use/tslint.json           |  8 ++++
 util/type.ts                                 | 19 +++++++++
 5 files changed, 132 insertions(+)
 create mode 100644 test/rules/promise-use/promise.ts.lint
 create mode 100644 test/rules/promise-use/testPromiseUseRule.ts
 create mode 100644 test/rules/promise-use/tsconfig.json
 create mode 100644 test/rules/promise-use/tslint.json

diff --git a/test/rules/promise-use/promise.ts.lint b/test/rules/promise-use/promise.ts.lint
new file mode 100644
index 0000000..ded5521
--- /dev/null
+++ b/test/rules/promise-use/promise.ts.lint
@@ -0,0 +1,42 @@
+function returnsPromise() {
+    return Promise.resolve(true);
+}
+
+type Future = Promise<number>;
+function aliasedPromise(): Future {
+    return Promise.resolve(1);
+}
+
+class Extended extends Promise<number> {}
+function extendedPromise(): Extended {
+    return Promise.resolve(1);
+}
+
+class DoubleExtended extends Extended {}
+function doubleExtendedPromise(): Extended {
+    return Promise.resolve(1);
+}
+
+function maybePromise(): Promise<number>|number {
+    return 3;
+}
+
+async function returnLaterPromise() {
+    return () => Promise.resolve(1);
+}
+
+function unusedPromises() {
+    returnsPromise();
+    ~~~~~~~~~~~~~~~~  [Promise]
+    maybePromise();
+    ~~~~~~~~~~~~~~  [Promise]
+    aliasedPromise();
+    ~~~~~~~~~~~~~~~~  [Promise]
+    extendedPromise();
+    ~~~~~~~~~~~~~~~~~  [Promise]
+    doubleExtendedPromise();
+    ~~~~~~~~~~~~~~~~~~~~~~~  [Promise]
+    const later = await returnLaterPromise();
+    later();
+    ~~~~~~~  [Promise]
+}
diff --git a/test/rules/promise-use/testPromiseUseRule.ts b/test/rules/promise-use/testPromiseUseRule.ts
new file mode 100644
index 0000000..3a0101c
--- /dev/null
+++ b/test/rules/promise-use/testPromiseUseRule.ts
@@ -0,0 +1,37 @@
+import * as ts from 'typescript';
+import * as Lint from 'tslint';
+import { isCallExpression } from "../../../typeguard/node";
+import { isExpressionValueUsed } from "../../../util/util";
+import { isPromiseType } from '../../../util/type';
+
+export class Rule extends Lint.Rules.TypedRule {
+    applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, (ctx) => walk(ctx, program));
+    }
+}
+
+function walk(ctx: Lint.WalkContext<void>, program: ts.Program) {
+    const cb = (node: ts.Node): void => {
+        if (isCallExpression(node)) {
+            if (!isExpressionValueUsed(node) && isPromiseExpression(node, program)) {
+              ctx.addFailureAtNode(node, 'Promise');
+            }
+        }
+        return ts.forEachChild(node, cb);
+    };
+    return ts.forEachChild(ctx.sourceFile, cb);
+}
+
+function isPromiseExpression(node: ts.CallExpression, program: ts.Program) {
+    const checker = program.getTypeChecker();
+    const signature = checker.getResolvedSignature(node);
+    if (signature === undefined) {
+        return false;
+    }
+    const returnType = checker.getReturnTypeOfSignature(signature);
+    if (!!(returnType.flags & ts.TypeFlags.Void)) {
+        return false;
+    }
+
+    return isPromiseType(returnType);
+}
diff --git a/test/rules/promise-use/tsconfig.json b/test/rules/promise-use/tsconfig.json
new file mode 100644
index 0000000..5ce8453
--- /dev/null
+++ b/test/rules/promise-use/tsconfig.json
@@ -0,0 +1,26 @@
+{
+    "compilerOptions": {
+        "target": "es6",
+        "module": "commonjs",
+        "removeComments": true,
+        "inlineSourceMap": true,
+        "preserveConstEnums": true,
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "suppressImplicitAnyIndexErrors": true,
+        "strictFunctionTypes": true,
+        "noUnusedLocals": true,
+        "noUnusedParameters": true,
+        "strictNullChecks": true,
+        "stripInternal": true,
+        "lib": ["es2016"],
+        "skipLibCheck": true,
+        "declaration": true,
+        "importHelpers": true
+    },
+    "exclude": [
+    ],
+    "files": [
+        "../../type/promise.ts"
+    ]
+}
diff --git a/test/rules/promise-use/tslint.json b/test/rules/promise-use/tslint.json
new file mode 100644
index 0000000..253f80e
--- /dev/null
+++ b/test/rules/promise-use/tslint.json
@@ -0,0 +1,8 @@
+{
+    "rulesDirectory": [
+        "."
+    ],
+    "rules":{
+        "test-promise-use": true
+    }
+}
diff --git a/util/type.ts b/util/type.ts
index 47bb5d6..997dce5 100644
--- a/util/type.ts
+++ b/util/type.ts
@@ -67,6 +67,25 @@ function isTypeAssignableTo(checker: ts.TypeChecker, type: ts.Type, flags: ts.Ty
     })(type);
 }
 
+/**
+ * Returns true if the given type is a union type that includes Promise or a type that extends
+ * Promise.
+ */
+export function isPromiseType(type: ts.Type): boolean {
+    const isPromise = (t: ts.Type) => {
+        const sym = t.getSymbol();
+        if (sym !== undefined) return sym.name === 'Promise';
+        return false;
+    };
+
+    const baseTypes = type.getBaseTypes();
+    if (baseTypes && baseTypes.some(isPromise)) return true;
+
+    if (isUnionType(type) || isIntersectionType(type)) return type.types.some(isPromise);
+
+    return isPromise(type);
+}
+
 export function getCallSignaturesOfType(type: ts.Type): ts.Signature[] {
     if (isUnionType(type)) {
         const signatures = [];