feat: add option to use external css rewriter in template_cache_generator.

The provided rewriter will be used to transform every css read by the
TemplateCache, the original css is provided on stdin, and result is read
from the stdout of provided binary.

TESTING:

The test uses a simple sed script to exercise the integration.

The test runs only if sed is present on the running system.  The test
uses CSS with simple rules that are being translated for RTL locales.

Closes #1052

Author: rkj

lib/tools/template_cache_generator.dart

@@ -9,6 +9,7 @@ import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:args/args.dart';
 import 'package:di/generator.dart';
+import 'dart:convert';
 
 const String PACKAGE_PREFIX = 'package:';
 const String DART_PACKAGE_PREFIX = 'dart:';
@@ -56,7 +57,8 @@ main(List arguments) {
     sink = f.openWrite();
   }
   return printTemplateCache(
-      templates, options.urlRewrites, options.outputLibrary, sink)
+      templates, options.urlRewrites, options.outputLibrary, sink,
+          options.cssRewriter)
       .then((_) => sink.flush());
 }
 
@@ -70,6 +72,7 @@ class Options {
   Map<RegExp, String> urlRewrites;
   Set<String> skippedClasses;
   bool verbose;
+  String cssRewriter;
 }
 
 Options parseArgs(List arguments) {
@@ -89,6 +92,9 @@ Options parseArgs(List arguments) {
                 'patternUrl,rewriteTo')
       ..addOption('skip-classes', abbr: 'b',
           help: 'comma-separated list of classes to skip templating')
+      ..addOption('css-rewriter', defaultsTo: null,
+          help: 'application used to rewrite css. Each css file will be passed '
+                'to stdin and rewriten one is expected on stdout.')
       ..addFlag('verbose', abbr: 'v', help: 'verbose output')
       ..addFlag('help', abbr: 'h', negatable: false, help: 'show this help');
 
@@ -142,31 +148,48 @@ Options parseArgs(List arguments) {
   if (args.rest.length != 2) {
     fail('unexpected arguments: ${args.rest.join(' ')}');
   }
+  options.cssRewriter = args['css-rewriter'];
   options.entryPoint = args.rest[0];
   options.outputLibrary = args.rest[1];
   return options;
 }
 
 printTemplateCache(Map<String, String> templateKeyMap,
-                        Map<RegExp, String> urlRewriters,
-                        String outputLibrary,
-                        IOSink outSink) {
+                   Map<RegExp, String> urlRewriters,
+                   String outputLibrary,
+                   IOSink outSink,
+                   String cssRewriter) {
 
   outSink.write(fileHeader(outputLibrary));
 
   Future future = new Future.value(0);
   List uris = templateKeyMap.keys.toList()..sort()..forEach((uri) {
     var templateFile = templateKeyMap[uri];
+    String resultUri = uri;
+    urlRewriters.forEach((regexp, replacement) {
+      resultUri = resultUri.replaceFirst(regexp, replacement);
+    });
+    var putToCache = (String content) {
+      var out = content.replaceAll('"""', r'\"\"\"');
+      outSink.write(
+        'tc.put("$resultUri", new HttpResponse(200, r"""$out"""));\n');
+    };
     future = future.then((_) {
-      return new File(templateFile).readAsString().then((fileStr) {
-        fileStr = fileStr.replaceAll('"""', r'\"\"\"');
-        String resultUri = uri;
-        urlRewriters.forEach((regexp, replacement) {
-          resultUri = resultUri.replaceFirst(regexp, replacement);
+      var fileContentFuture = new File(templateFile).readAsString();
+      if (templateFile.endsWith(".css") && cssRewriter != null) {
+        return fileContentFuture.then((fileStr) {
+          return Process.start(cssRewriter, []).then((process) {
+            process.stdin.write(fileStr);
+            process.stdin.close();
+            return process.stdout
+                          .transform(UTF8.decoder)
+                          .join("")
+                          .then(putToCache);
+          });
         });
-        outSink.write(
-            'tc.put("$resultUri", new HttpResponse(200, r"""$fileStr"""));\n');
-      });
+      } else {
+        return fileContentFuture.then(putToCache);
+      }
     });
   });
 

test/io/template_cache_generator_spec.dart

@@ -70,6 +70,45 @@ void main() {
       });
     });
 
+    if (new File("/bin/sed").existsSync()) {
+      it('should correctly use simple sed rewritter to fake css mirroring', () {
+        var tmpDir = Directory.systemTemp.createTempSync();
+        Future flush;
+        try {
+          flush = generator.main([
+              '--out=${tmpDir.path}/generated.dart',
+              '--url-rewrites=/test/io/test_files,rewritten',
+              '--css-rewriter=test/io/test_files/rewritter.sh',
+              'test/io/test_files/cssUrls/main.dart',
+              'generated']);
+        } catch(_) {
+          tmpDir.deleteSync(recursive: true);
+          rethrow;
+        }
+        return flush.then((_) {
+          expect(new File('${tmpDir.path}/generated.dart').readAsStringSync(),
+'''// GENERATED, DO NOT EDIT!
+library generated;
 
+import 'package:angular/angular.dart';
+
+primeTemplateCache(TemplateCache tc) {
+tc.put("rewritten/cssUrls/four.css", new HttpResponse(200, r""".float-right {
+  float: right;
+}
+.right-margin {
+  margin-right: 20px;
+}
+
+"""));
+tc.put("rewritten/cssUrls/one.css", new HttpResponse(200, r"""body {}"""));
+tc.put("rewritten/cssUrls/three.css", new HttpResponse(200, r"""body {}"""));
+tc.put("rewritten/cssUrls/two.css", new HttpResponse(200, r"""body {}"""));
+}''');
+        }).whenComplete(() {
+          tmpDir.deleteSync(recursive: true);
+        });
+      });
+    }
   });
 }

test/io/test_files/cssUrls/four.css

@@ -0,0 +1,7 @@
+.float-left {
+  float: left;
+}
+.left-margin {
+  margin-left: 20px;
+}
+

test/io/test_files/rewritter.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+/bin/sed 's/left/right/g'