feat: Add no-async-subscribe rule.

package.json

@@ -59,7 +59,7 @@
     "test": "yarn run lint && yarn run test:build && yarn run test:mocha && yarn run test:tslint-v5 && yarn run test:tslint-v6 && yarn run test:tslint-v6-compat",
     "test:build": "yarn run test:clean && tsc -p tsconfig.json",
     "test:clean": "rimraf build",
-    "test:debug": "tslint --test ./test/v6/fixtures/no-exposed-subjects/**/tslint.json",
+    "test:debug": "tslint --test ./test/v6/fixtures/no-async-subscribe/**/tslint.json",
     "test:issues": "yarn run test:clean && tsc -p tsconfig.json && tslint --test ./test/v6/fixtures/issues/**/tslint.json",
     "test:mocha": "mocha build/**/*-spec.js",
     "test:tslint-v5": "yarn --cwd ./test/v5 install && yarn --cwd ./test/v5 upgrade && tslint --test ./test/v5/fixtures/**/tslint.json",

source/rules/rxjsNoAsyncSubscribeRule.ts

@@ -0,0 +1,65 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/rxjs-tslint-rules
+ */
+
+import * as Lint from "tslint";
+import * as ts from "typescript";
+import * as tsutils from "tsutils";
+import { tsquery } from "@phenomnomnominal/tsquery";
+import { couldBeType } from "../support/util";
+
+export class Rule extends Lint.Rules.TypedRule {
+
+    public static metadata: Lint.IRuleMetadata = {
+        description: "Disallows async functions to subscribe.",
+        options: null,
+        optionsDescription: "Not configurable.",
+        requiresTypeInfo: false,
+        ruleName: "rxjs-no-async-subscribe",
+        type: "functionality",
+        typescriptOnly: false
+    };
+
+    public static FAILURE_STRING = "Passing async functions to subscribe is forbidden";
+
+    public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+
+        const failures: Lint.RuleFailure[] = [];
+        const typeChecker = program.getTypeChecker();
+
+        const callExpressions = tsquery(
+            sourceFile,
+            `CallExpression[expression.name.text="subscribe"]`
+        );
+        callExpressions.forEach(node => {
+            const callExpression = node as ts.CallExpression;
+            if (tsutils.isPropertyAccessExpression(callExpression.expression)) {
+                const propertyAccessExpression = callExpression.expression;
+                const { arguments: args } = callExpression;
+                let observable: boolean | undefined = undefined;
+                args.forEach(arg => {
+                    if (tsutils.isArrowFunction(arg) || tsutils.isFunctionExpression(arg)) {
+                        const modifier = tsutils.getModifier(arg, ts.SyntaxKind.AsyncKeyword);
+                        if (modifier) {
+                            if (observable === undefined) {
+                                const type = typeChecker.getTypeAtLocation(propertyAccessExpression.expression);
+                                observable = couldBeType(type, "Observable");
+                            }
+                            if (observable) {
+                                failures.push(new Lint.RuleFailure(
+                                    sourceFile,
+                                    modifier.getStart(),
+                                    modifier.getStart() + modifier.getWidth(),
+                                    Rule.FAILURE_STRING,
+                                    this.ruleName
+                                ));
+                            }
+                        }
+                    }
+                });
+            }
+        });
+        return failures;
+    }
+}

test/v6/fixtures/no-async-subscribe/default/fixture.ts.lint

@@ -0,0 +1,9 @@
+import { of } from "rxjs";
+
+of("a").subscribe(async () => {
+                  ~~~~~             [no-async-subscribe]
+    return await "a";
+});
+of("b").subscribe(() => {});
+
+[no-async-subscribe]: Passing async functions to subscribe is forbidden

test/v6/fixtures/no-async-subscribe/default/tsconfig.json

@@ -0,0 +1,13 @@
+{
+  "compilerOptions": {
+    "baseUrl": ".",
+    "lib": ["es2015"],
+    "noEmit": true,
+    "paths": {
+      "rxjs": ["../../node_modules/rxjs"]
+    },
+    "skipLibCheck": true,
+    "target": "es5"
+  },
+  "include": ["fixture.ts"]
+}

test/v6/fixtures/no-async-subscribe/default/tslint.json

@@ -0,0 +1,8 @@
+{
+  "defaultSeverity": "error",
+  "jsRules": {},
+  "rules": {
+    "rxjs-no-async-subscribe": { "severity": "error" }
+  },
+  "rulesDirectory": "../../../../../build/rules"
+}