feat(no-nested-subscribe): Add 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/prefer-async-pipe/**/tslint.json",
+    "test:debug": "tslint --test ./test/v6/fixtures/no-nested-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/rxjsNoNestedSubscribeRule.ts

@@ -0,0 +1,63 @@
+/**
+ * @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 the calling of `subscribe` within a `subscribe` callback.",
+        options: null,
+        optionsDescription: "Not configurable.",
+        requiresTypeInfo: true,
+        ruleName: "rxjs-no-nested-subscribe",
+        type: "style",
+        typescriptOnly: true
+    };
+
+    public static FAILURE_STRING = "Nested subscribe calls are forbidden";
+
+    public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+
+        const failures: Lint.RuleFailure[] = [];
+        const typeChecker = program.getTypeChecker();
+
+        const subscribeQuery = `CallExpression PropertyAccessExpression[name.name="subscribe"]`;
+        const propertyAccessExpressions = tsquery(sourceFile, subscribeQuery);
+        propertyAccessExpressions.forEach(propertyAccessExpression => {
+            const { parent: callExpression } = propertyAccessExpression;
+            if (tsutils.isCallExpression(callExpression)) {
+                if (tsutils.isPropertyAccessExpression(propertyAccessExpression)) {
+                    const type = typeChecker.getTypeAtLocation(propertyAccessExpression.expression);
+                    if (couldBeType(type, "Observable")) {
+                        callExpression.arguments.forEach(arg => {
+                            const propertyAccessExpressions = tsquery(arg, subscribeQuery);
+                            propertyAccessExpressions.forEach(propertyAccessExpression => {
+                                if (tsutils.isPropertyAccessExpression(propertyAccessExpression)) {
+                                    const type = typeChecker.getTypeAtLocation(propertyAccessExpression.expression);
+                                    if (couldBeType(type, "Observable")) {
+                                        const { name } = propertyAccessExpression;
+                                        failures.push(new Lint.RuleFailure(
+                                            sourceFile,
+                                            name.getStart(),
+                                            name.getStart() + name.getWidth(),
+                                            Rule.FAILURE_STRING,
+                                            this.ruleName
+                                        ));
+                                    }
+                                }
+                            });
+                        });
+                    }
+                }
+            }
+        });
+        return failures;
+    }
+}

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

@@ -0,0 +1,45 @@
+import { of } from "rxjs";
+
+of("foo").subscribe(
+    value => of("bar").subscribe()
+                       ~~~~~~~~~                [no-nested-subscribe]
+);
+of("foo").subscribe({
+    next: value => of("bar").subscribe()
+                             ~~~~~~~~~          [no-nested-subscribe]
+});
+of("foo").subscribe({
+    next(value) { of("bar").subscribe(); }
+                            ~~~~~~~~~           [no-nested-subscribe]
+});
+
+of("foo").subscribe(
+    undefined,
+    error => of("bar").subscribe()
+                       ~~~~~~~~~                [no-nested-subscribe]
+);
+of("foo").subscribe({
+    error: error => of("bar").subscribe()
+                              ~~~~~~~~~         [no-nested-subscribe]
+});
+of("foo").subscribe({
+    error(error) { of("bar").subscribe(); }
+                             ~~~~~~~~~          [no-nested-subscribe]
+});
+
+of("foo").subscribe(
+    undefined,
+    undefined,
+    () => of("bar").subscribe()
+                    ~~~~~~~~~                   [no-nested-subscribe]
+);
+of("foo").subscribe({
+    complete: () => of("bar").subscribe()
+                              ~~~~~~~~~         [no-nested-subscribe]
+});
+of("foo").subscribe({
+    complete() { of("bar").subscribe(); }
+                           ~~~~~~~~~            [no-nested-subscribe]
+});
+
+[no-nested-subscribe]: Nested subscribe calls are forbidden

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

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