Qualify library names in packages

Partially addresses #504.  This is WIP, but wanted your thoughts.

Comment / questions:
- The current js_ast ImportDeclaration assumes a legal identifier I think.
  E.g., this gets lowered:
  import { src$interfaces } from "matcher"

- Should we thread package root through ModuleCompiler to let it packagify urls?

- How should we handle non-package urls?  Pass in an explicit root dir
  and go relative?

R=jmesserly@google.com

Review URL: https://codereview.chromium.org/1917863005 .

pkg/dev_compiler/lib/src/compiler/code_generator.dart

@@ -113,6 +113,8 @@ class CodeGenerator extends GeneralizingAstVisitor
 
   BuildUnit _buildUnit;
 
+  String _buildRoot;
+
   CodeGenerator(AnalysisContext c, this.options, this._extensionTypes)
       : context = c,
         types = c.typeProvider,
@@ -131,6 +133,10 @@ class CodeGenerator extends GeneralizingAstVisitor
   JSModuleFile compile(BuildUnit unit, List<CompilationUnit> compilationUnits,
       List<String> errors) {
     _buildUnit = unit;
+    _buildRoot = _buildUnit.buildRoot;
+    if (!_buildRoot.endsWith('/')) {
+      _buildRoot = '$_buildRoot/';
+    }
 
     var jsTree = _emitModule(compilationUnits);
     var codeAndSourceMap = _writeJSText(unit, jsTree);
@@ -190,7 +196,7 @@ class CodeGenerator extends GeneralizingAstVisitor
 
       var libraryTemp = _isDartRuntime(library)
           ? _runtimeLibVar
-          : new JS.TemporaryId(jsLibraryName(library));
+          : new JS.TemporaryId(jsLibraryName(_buildRoot, library));
       _libraries[library] = libraryTemp;
       items.add(new JS.ExportDeclaration(
           js.call('const # = Object.create(null)', [libraryTemp])));
@@ -3760,8 +3766,8 @@ class CodeGenerator extends GeneralizingAstVisitor
   JS.Identifier emitLibraryName(LibraryElement library) {
     // It's either one of the libraries in this module, or it's an import.
     return _libraries[library] ??
-        _imports.putIfAbsent(
-            library, () => new JS.TemporaryId(jsLibraryName(library)));
+        _imports.putIfAbsent(library,
+            () => new JS.TemporaryId(jsLibraryName(_buildRoot, library)));
   }
 
   JS.Node annotate(JS.Node node, AstNode original, [Element element]) {
@@ -3837,8 +3843,27 @@ class CodeGenerator extends GeneralizingAstVisitor
 /// Choose a canonical name from the library element.
 /// This never uses the library's name (the identifier in the `library`
 /// declaration) as it doesn't have any meaningful rules enforced.
-String jsLibraryName(LibraryElement library) {
-  return pathToJSIdentifier(library.source.uri.pathSegments.last);
+String jsLibraryName(String buildRoot, LibraryElement library) {
+  var uri = library.source.uri;
+  if (uri.scheme == 'dart') {
+    return uri.path;
+  }
+  // TODO(vsm): This is not necessarily unique if '__' appears in a file name.
+  var separator = '__';
+  String qualifiedPath;
+  if (uri.scheme == 'package') {
+    // Strip the package name.
+    // TODO(vsm): This is not unique if an escaped '/'appears in a filename.
+    // E.g., "foo/bar.dart" and "foo$47bar.dart" would collide.
+    qualifiedPath = uri.pathSegments.skip(1).join(separator);
+  } else if (uri.path.startsWith(buildRoot)) {
+    qualifiedPath =
+        uri.path.substring(buildRoot.length).replaceAll('/', separator);
+  } else {
+    // We don't have a unique name.
+    throw 'Invalid build root.  $buildRoot does not contain ${uri.path}';
+  }
+  return pathToJSIdentifier(qualifiedPath);
 }
 
 /// Shorthand for identifier-like property names.

pkg/dev_compiler/lib/src/compiler/command.dart

@@ -24,6 +24,10 @@ class CompileCommand extends Command {
   CompileCommand({MessageHandler messageHandler})
       : this.messageHandler = messageHandler ?? print {
     argParser.addOption('out', abbr: 'o', help: 'Output file (required)');
+    argParser.addOption('build-root',
+        help: '''
+Root of source files.  Generated library names are relative to this root.
+''');
     CompilerOptions.addArguments(argParser);
     AnalyzerOptions.addArguments(argParser);
   }
@@ -39,7 +43,14 @@ class CompileCommand extends Command {
       usageException('Please include the output file location. For example:\n'
           '    -o PATH/TO/OUTPUT_FILE.js');
     }
-    var unit = new BuildUnit(path.basenameWithoutExtension(outPath),
+
+    var buildRoot = argResults['build-root'] as String;
+    if (buildRoot != null) {
+      buildRoot = path.absolute(buildRoot);
+    } else {
+      buildRoot = Directory.current.path;
+    }
+    var unit = new BuildUnit(path.basenameWithoutExtension(outPath), buildRoot,
         argResults.rest, _moduleForLibrary);
 
     JSModuleFile module = compiler.compile(unit, compilerOptions);

pkg/dev_compiler/lib/src/compiler/compiler.dart

@@ -196,6 +196,9 @@ class BuildUnit {
   /// The name of this module.
   final String name;
 
+  /// Build root.  All library names are relative to this path/prefix.
+  final String buildRoot;
+
   /// The list of sources in this module.
   ///
   /// The set of Dart files can be arbitrarily large, but it must contain
@@ -209,7 +212,7 @@ class BuildUnit {
   // build units.
   final Func1<Source, String> libraryToModule;
 
-  BuildUnit(this.name, this.sources, this.libraryToModule);
+  BuildUnit(this.name, this.buildRoot, this.sources, this.libraryToModule);
 }
 
 /// The output of Dart->JS compilation.