feat(finnish): Add Finnish notation rule.

fixtures/finnish-with-$/fixture.ts

@@ -0,0 +1,28 @@
+import { Observable } from "rxjs";
+import "rxjs/add/observable/of";
+
+const someObservable$ = Observable.of(0);
+
+const someObject = { someKey$: someObservable$ };
+const { someKey$ } = someObject;
+const { someKey$: someRenamedKey$ } = someObject;
+
+const someArray: Observable<any>[] = [someConst$];
+const [someElement$] = someArray;
+someArray.forEach(function (element$: Observable<any>): void {});
+someArray.forEach((element$: Observable<any>) => {});
+
+function someFunction$(someParam$: Observable<any>): Observable<any> { return someParam$; }
+
+class SomeClass {
+    someProperty$: Observable<any>;
+    constructor (someParam$: Observable<any>) {}
+    get someGetter$(): Observable<any> { throw new Error("Some error."); }
+    set someSetter$(someParam$: Observable<any>) {}
+    someMethod$(someParam$: Observable<any>): Observable<any> { return someParam$; }
+}
+
+interface SomeInterface {
+    someProperty$: Observable<any>;
+    someMethod$(someParam$: Observable<any>): Observable<any>;
+}

fixtures/finnish-with-$/tsconfig.json

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

fixtures/finnish-with-$/tslint.json

@@ -0,0 +1,8 @@
+{
+  "defaultSeverity": "error",
+  "jsRules": {},
+  "rules": {
+    "rxjs-finnish": { "severity": "error" }
+  },
+  "rulesDirectory": "../../build/rules"
+}

fixtures/finnish-without-$/fixture.ts

@@ -0,0 +1,28 @@
+import { Observable } from "rxjs";
+import "rxjs/add/observable/of";
+
+const someObservable = Observable.of(0);
+
+const someObject = { someKey: someObservable };
+const { someKey } = someObject;
+const { someKey: someRenamedKey } = someObject;
+
+const someArray: Observable<any>[] = [someConst];
+const [someElement] = someArray;
+someArray.forEach(function (element: Observable<any>): void {});
+someArray.forEach((element: Observable<any>) => {});
+
+function someFunction(someParam: Observable<any>): Observable<any> { return someParam; }
+
+class SomeClass {
+    someProperty: Observable<any>;
+    constructor (someParam: Observable<any>) {}
+    get someGetter(): Observable<any> { throw new Error("Some error."); }
+    set someSetter(someParam: Observable<any>) {}
+    someMethod(someParam: Observable<any>): Observable<any> { return someParam; }
+}
+
+interface SomeInterface {
+    someProperty: Observable<any>;
+    someMethod(someParam: Observable<any>): Observable<any>;
+}

fixtures/finnish-without-$/tsconfig.json

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

fixtures/finnish-without-$/tslint.json

@@ -0,0 +1,8 @@
+{
+  "defaultSeverity": "error",
+  "jsRules": {},
+  "rules": {
+    "rxjs-finnish": { "severity": "error" }
+  },
+  "rulesDirectory": "../../build/rules"
+}

source/fixtures-spec.ts

@@ -67,6 +67,27 @@ describe("fixtures", function (): void {
             });
         });
 
+        describe("finnish-with-$", () => {
+
+            it("should effect no errors", () => {
+
+                const result = lint("finnish-with-$", "tslint.json");
+
+                expect(result).to.have.property("errorCount", 0);
+            });
+        });
+
+        describe("finnish-without-$", () => {
+
+            it("should effect 'rxjs-finnish' errors", () => {
+
+                const result = lint("finnish-without-$", "tslint.json");
+
+                expect(result).to.have.property("errorCount", 19);
+                result.failures.forEach(failure => expect(failure).to.have.property("ruleName", "rxjs-finnish"));
+            });
+        });
+
         describe("flat-map", () => {
 
             it("should effect no errors", () => {

source/rules/rxjsFinnishRule.ts

@@ -0,0 +1,116 @@
+/**
+ * @license Copyright © 2017 Nicholas Jamieson. All Rights Reserved.
+ * 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
+ */
+/*tslint:disable:no-use-before-declare*/
+
+import * as Lint from "tslint";
+import * as ts from "typescript";
+import * as tsutils from "tsutils";
+import { couldBeType } from "../support/util";
+
+export class Rule extends Lint.Rules.TypedRule {
+
+    public static metadata: Lint.IRuleMetadata = {
+        description: "Enforces the use of Finnish notation.",
+        options: null,
+        optionsDescription: "Not configurable.",
+        requiresTypeInfo: true,
+        ruleName: "rxjs-finnish",
+        type: "style",
+        typescriptOnly: true
+    };
+
+    public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+
+        return this.applyWithWalker(new Walker(sourceFile, this.getOptions(), program));
+    }
+}
+
+class Walker extends Lint.ProgramAwareRuleWalker {
+
+    protected visitFunctionDeclaration(node: ts.FunctionDeclaration): void {
+
+        this.validateNode(node, node.type);
+        super.visitFunctionDeclaration(node);
+    }
+
+    protected visitFunctionExpression(node: ts.FunctionExpression): void {
+
+        this.validateNode(node, node.type);
+        super.visitFunctionExpression(node);
+    }
+
+    protected visitGetAccessor(node: ts.AccessorDeclaration): void {
+
+        this.validateNode(node);
+        super.visitGetAccessor(node);
+    }
+
+    protected visitMethodDeclaration(node: ts.MethodDeclaration): void {
+
+        this.validateNode(node, node.type);
+        super.visitMethodDeclaration(node);
+    }
+
+    protected visitMethodSignature(node: ts.SignatureDeclaration): void {
+
+        this.validateNode(node, node.type);
+        super.visitMethodSignature(node);
+    }
+
+    protected visitObjectLiteralExpression(node: ts.ObjectLiteralExpression): void {
+
+        node.properties.forEach(property => {
+            if (property.name.kind !== ts.SyntaxKind.ComputedPropertyName) {
+                this.validateNode(property);
+            }
+        });
+        super.visitObjectLiteralExpression(node);
+    }
+
+    protected visitParameterDeclaration(node: ts.ParameterDeclaration): void {
+
+        this.validateNode(node);
+        super.visitParameterDeclaration(node);
+    }
+
+    protected visitPropertyDeclaration(node: ts.PropertyDeclaration): void {
+
+        this.validateNode(node);
+        super.visitPropertyDeclaration(node);
+    }
+
+    protected visitPropertySignature(node: ts.Node): void {
+
+        this.validateNode(node);
+        super.visitPropertySignature(node);
+    }
+
+    protected visitSetAccessor(node: ts.AccessorDeclaration): void {
+
+        this.validateNode(node);
+        super.visitSetAccessor(node);
+    }
+
+    protected visitVariableDeclarationList(node: ts.VariableDeclarationList): void {
+
+        tsutils.forEachDeclaredVariable(node, variable => {
+            this.validateNode(variable);
+        });
+        super.visitVariableDeclarationList(node);
+    }
+
+    private validateNode(node: ts.Node, typeNode?: ts.Node): void {
+
+        const { name } = node as any;
+        if (name) {
+            const text = name.getText();
+            const type = this.getTypeChecker().getTypeAtLocation(typeNode || node);
+            if (!/\$$/.test(text) && couldBeType(type, "Observable")) {
+                this.addFailureAtNode(node, `Finnish notation required for ${text}`);
+            }
+        }
+    }
+}