[new-rule] add jsx-space-before-trailing-slash rule (#164)

Author: jkillian

README.md

@@ -100,6 +100,9 @@ The built-in configuration preset you get with `"extends": "tslint-react"` is se
   <div className="foo" />
   ```
   - Rule options: _none_
+- `jsx-space-before-trailing-slash`
+  - Checks that self-closing JSX elements have a space before the '/>' part.
+  - Rule options: _none_
 - `jsx-wrap-multiline` (since v2.1)
   - Enforces that multiline JSX expressions are wrapped with parentheses.
   - Opening parenthesis must be followed by a newline.

src/rules/jsxSpaceBeforeTrailingSlashRule.ts

@@ -0,0 +1,56 @@
+/**
+ * @license
+ * Copyright 2016 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 Lint from "tslint";
+import { isJsxSelfClosingElement } from "tsutils";
+import * as ts from "typescript";
+
+export class Rule extends Lint.Rules.AbstractRule {
+    /* tslint:disable:object-literal-sort-keys */
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "jsx-space-before-trailing-slash",
+        description: "Checks that self-closing JSX elements have a space before the '/>' part.",
+        options: null,
+        optionsDescription: "",
+        optionExamples: ["true"],
+        type: "style",
+        typescriptOnly: false,
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static FAILURE_STRING = "Self-closing JSX elements must have a space before the '/>' part";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, walk);
+    }
+}
+
+const closingLength = "/>".length;
+const isWhiteSpace = (char: string) => /\s/.test(char);
+const hasWhitespaceBeforeClosing = (nodeText: string) =>
+    isWhiteSpace(nodeText.charAt(nodeText.length - closingLength - 1));
+
+function walk(ctx: Lint.WalkContext<void>): void {
+    return ts.forEachChild(ctx.sourceFile, function cb(node: ts.Node): void {
+        if (isJsxSelfClosingElement(node)) {
+            if (!hasWhitespaceBeforeClosing(node.getText(ctx.sourceFile))) {
+                ctx.addFailureAtNode(node, Rule.FAILURE_STRING);
+            }
+        }
+        return ts.forEachChild(node, cb);
+    });
+}

test/rules/jsx-space-before-trailing-slash/test.tsx.lint

@@ -0,0 +1,17 @@
+<div>
+    Contents
+</div>
+
+<span/>
+~~~~~~~ [Self-closing JSX elements must have a space before the '/>' part]
+
+<button />
+
+<h2 class="colouring" contents="B"/>
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [Self-closing JSX elements must have a space before the '/>' part]
+
+<button onClick="run()" />
+
+<img
+    src="./foo/bar.png"
+/>

test/rules/jsx-space-before-trailing-slash/tslint.json

@@ -0,0 +1,5 @@
+{
+    "rules": {
+        "jsx-space-before-trailing-slash": true
+    }
+}