Allow dart2dart to output one file per library.

sdk/lib/_internal/compiler/implementation/dart_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/dart_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/dart_backend/backend.dart
index c323fcf9d1b1d60f4e1ecaba59b454a757c2e426..d6a3cc77337b0bdf817d32b1a7a4be035fd5b41a 100644
--- a/sdk/lib/_internal/compiler/implementation/dart_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart_backend/backend.dart
@@ -25,6 +25,10 @@ class DartBackend extends Backend {
   final bool outputAst = false;
   final Map<ClassNode, List<Node>> memberNodes;
 
+  // Should the output go to one file per input library, or everything in one
+  // file.

[Johnni Winther, 2014/08/15 08:07:31]

Paraphrase to something like "If `true`, libraries are generated into separate
files." 

[sigurdm, 2014/08/15 13:31:42]

Done.

+  final bool multiFile;
+
   PlaceholderRenamer placeholderRenamer;
 
   // TODO(zarah) Maybe change this to a command-line option.
@@ -102,7 +106,7 @@ class DartBackend extends Backend {
     return true;
   }
 
-  DartBackend(Compiler compiler, List<String> strips)
+  DartBackend(Compiler compiler, List<String> strips, {this.multiFile})
       : tasks = <CompilerTask>[],
         memberNodes = new Map<ClassNode, List<Node>>(),
         forceStripTypes = strips.indexOf('types') != -1,
@@ -264,6 +268,9 @@ class DartBackend extends Backend {
       }
     }
 
+    List<LibraryElement> userLibraries =
+        compiler.libraryLoader.libraries.where(isUserLibrary).toList();
+
     Set<Element> topLevelElements = new Set<Element>();
     Map<ClassElement, Set<Element>> classMembers =
         new Map<ClassElement, Set<Element>>();
@@ -451,17 +458,65 @@ class DartBackend extends Backend {
                                topLevelNodes, collector);
     }
 
-    final unparser = new EmitterUnparser(placeholderRenamer.renames,
-                                         stripTypes: forceStripTypes,
-                                         minify: compiler.enableMinification);
-    for(LibraryElement library in placeholderRenamer.platformImports) {
-      if (library.isPlatformLibrary && !library.isInternalLibrary) {
-        unparser.unparseImportTag(library.canonicalUri.toString());
+    Map<LibraryElement, String> outputUris = new Map<LibraryElement, String>();
+    Map<LibraryElement, EmitterUnparser> unparsers =
+        new Map<LibraryElement, EmitterUnparser>();
+
+    // The single unparser used if we collect all the output in one file
+    EmitterUnparser mainUnparser = multiFile
+        ? null
+        : new EmitterUnparser(placeholderRenamer.renames,
+            stripTypes: forceStripTypes,
+            minify: compiler.enableMinification);
+
+    if (multiFile) {
+      Set<String> usedLibraryNames = new Set<String>();
+      for (LibraryElement library in userLibraries) {
+        List<String> names = library.canonicalUri.pathSegments.last.split(".");
+        if (names.last == "dart") {
+          names = names.sublist(0, names.length - 1);

[floitsch, 2014/08/15 11:59:36]

names is only used when the library is not the mainApp.
It looks like a
if (library == compiler.mainApp) {
...
} else {
...
}

would simplify the code.

[sigurdm, 2014/08/15 13:31:42]

Done.

+        }
+        String mainName = compiler.outputUri.path.split('/').last;

[jgruber1, 2014/08/15 06:20:53]

Does this work on windows?

[Johnni Winther, 2014/08/15 08:07:31]

Use [Uri.pathSegments] instead of `path.split('/')`.

[floitsch, 2014/08/15 11:59:36]

You should be able to compute the mainName/mmainBaseName outside the loop.

[sigurdm, 2014/08/15 13:31:42]

I think so - Uri's should normalize path segment seperators.

[sigurdm, 2014/08/15 13:31:42]

Thanks

[sigurdm, 2014/08/15 13:31:42]

Done.

+        String mainBaseName = mainName.endsWith(".dart")
+            ? mainName.substring(0, mainName.length - 5)
+            : mainName;
+        String uri = library == compiler.mainApp
+            ? mainBaseName
+            : "$mainBaseName.${makeUnique(names.join("."), usedLibraryNames)}";

[floitsch, 2014/08/15 11:59:36]

usedLibraryNames does not contain the "mainBaseName".

[sigurdm, 2014/08/15 13:31:42]

But this is only a suffix.
So we generate
mainBaseName.$a
where $a should make the whole thing unique. It can never clash with
mainBaseName

+        outputUris[library] = uri;
+        unparsers[library] = new EmitterUnparser(placeholderRenamer.renames,
+            stripTypes: forceStripTypes, minify: compiler.enableMinification);
+      }
+
+      for(LibraryElement outputLibrary in userLibraries) {

[jgruber1, 2014/08/15 06:20:53]

Can we merge this into the previous for loop? 

[Johnni Winther, 2014/08/15 08:07:31]

No. This loop requires [outputUris] to be fully computed.

[sigurdm, 2014/08/15 13:31:42]

Acknowledged.

[sigurdm, 2014/08/15 13:31:42]

We want to set up all the ouputUris before using them for emitting the imports.

But I think setting up the unparsers can be moved down

+        EmitterUnparser unparser = unparsers[outputLibrary];
+        for (LibraryTag tag in outputLibrary.tags) {
+          if (tag is! LibraryDependency) continue;
+          LibraryDependency dependency = tag;
+          LibraryElement libraryElement =
+              outputLibrary.getLibraryFromTag(dependency);
+          String uri = outputUris.containsKey(libraryElement)
+              ? outputUris[libraryElement] + ".dart"

[Johnni Winther, 2014/08/15 08:07:31]

Use '${outputUri[LibraryElement]}.dart' instead of +

[sigurdm, 2014/08/15 13:31:42]

Done.

+              : libraryElement.canonicalUri.toString();
+          if (dependency is Import) {
+            unparser.unparseImportTag('$uri');

[jgruber1, 2014/08/15 06:20:53]

unparseImportTag(uri)?

[sigurdm, 2014/08/15 13:31:42]

Done.

+          } else {
+            unparser.unparseExportTag('$uri');
+          }
+        }
+      }
+    } else {
+      for(LibraryElement library in placeholderRenamer.platformImports) {
+        if (library.isPlatformLibrary && !library.isInternalLibrary) {
+          mainUnparser.unparseImportTag(library.canonicalUri.toString());
+        }
       }
     }
+
     for (int i = 0; i < sortedTopLevels.length; i++) {
       Element element = sortedTopLevels[i];
       Node node = topLevelNodes[i];
+      Unparser unparser = multiFile ? unparsers[element.library] : mainUnparser;
       if (node is ClassNode) {
         // TODO(smok): Filter out default constructors here.
         unparser.unparseClassWithBody(node, memberNodes[node]);
@@ -471,13 +526,25 @@ class DartBackend extends Backend {
       unparser.newline();
     }
 
-    compiler.assembledCode = unparser.result;
-    compiler.outputProvider("", "dart")
-         ..add(compiler.assembledCode)
-         ..close();
-    // Output verbose info about size ratio of resulting bundle to all
-    // referenced non-platform sources.
-    logResultBundleSizeInfo(topLevelElements);
+    if (multiFile) {
+      for(LibraryElement outputLibrary in userLibraries) {
+        compiler.outputProvider(outputUris[outputLibrary], "dart")
+             ..add(unparsers[outputLibrary].result)

[Johnni Winther, 2014/08/15 08:07:31]

Add a TODO to enable direct output, i.e. avoid caching in `.result`.

[sigurdm, 2014/08/15 13:31:42]

Done.

+             ..close();
+      }
+      // TODO(sigurdm): What to do here? Probably we should get rid of
+      // compiler.assembledCode
+      compiler.assembledCode = "";
+    } else {
+      compiler.assembledCode = mainUnparser.result;
+      compiler.outputProvider("", "dart")
+           ..add(compiler.assembledCode)
+           ..close();
+
+      // Output verbose info about size ratio of resulting bundle to all
+      // referenced non-platform sources.
+      logResultBundleSizeInfo(topLevelElements);
+    }
   }
 
   void logResultBundleSizeInfo(Set<Element> topLevelElements) {