Grinder wrapper for doc generation.

BUG=
[email protected]

Review URL: https://codereview.chromium.org//2180083003 .

tool/doc.dart

@@ -24,23 +24,7 @@ void main([List<String> args]) {
   }
 
   var outDir = options['out'];
-
-  if (outDir != null) {
-    Directory d = new Directory(outDir);
-    if (!d.existsSync()) {
-      print("Directory '${d.path}' does not exist");
-      return;
-    }
-  }
-
-  // Generate index
-  new Indexer(ruleRegistry).generate(outDir);
-
-  // Generate rule files
-  rules.forEach((l) => new Generator(l).generate(outDir));
-
-  // Generate options samples.
-  new OptionsSample(rules).generate(outDir);
+  generateDocs(outDir);
 }
 
 const ruleFootMatter = '''
@@ -87,6 +71,25 @@ String get enumerateStyleRules => rules
 
 List<String> get sortedRules => rules.map((r) => r.name).toList()..sort();
 
+void generateDocs(String outDir) {
+  if (outDir != null) {
+    Directory d = new Directory(outDir);
+    if (!d.existsSync()) {
+      print("Directory '${d.path}' does not exist");
+      return;
+    }
+  }
+
+  // Generate index
+  new Indexer(ruleRegistry).generate(outDir);
+
+  // Generate rule files
+  rules.forEach((l) => new Generator(l).generate(outDir));
+
+  // Generate options samples.
+  new OptionsSample(rules).generate(outDir);
+}
+
 void printUsage(ArgParser parser, [String error]) {
   var message = 'Generates lint docs.';
   if (error != null) {

tool/grind.dart

@@ -7,19 +7,31 @@ import 'dart:io';
 import 'package:grinder/grinder.dart';
 import 'package:unscripted/unscripted.dart';
 
+import 'doc.dart';
 import 'rule.dart';
 
 main([List<String> args]) {
-  addTask(new GrinderTask('rule', taskFunction: () {
-    String ruleName = context.invocation.positionals.first;
-    _generate(ruleName);
-  },
+  _addTask('rule',
+      parser: (String name) =>
+          generateRule(name, outDir: Directory.current.path),
       description: 'Generate a lint rule stub.',
-      positionals: [new Positional(valueHelp: 'Name of rule to generate')]));
+      valueHelp: 'Name of rule to generate.');
+
+  _addTask('docs',
+      parser: (String outDir) => generateDocs(outDir),
+      description: 'Generate lint rule docs.',
+      valueHelp: 'Documentation `lints/` directory.');
 
   grind(args);
 }
 
-void _generate(String ruleName) {
-  generateRule(ruleName, outDir: Directory.current.path);
+_addTask(String name, {String description, Parser parser, String valueHelp}) {
+  addTask(new GrinderTask(name, taskFunction: () {
+    String value = context.invocation.positionals.first;
+    parser(value);
+  },
+      description: description,
+      positionals: [new Positional(valueHelp: valueHelp)]));
 }
+
+typedef String Parser(String);