Dart2js Avoid file-names of deferred .part-files from getting too long.

sdk/lib/_internal/compiler/implementation/deferred_load.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library deferred_load;
 
 import 'dart2jslib.dart' show
     Backend,
     Compiler,
     CompilerTask,
@@ skipping 39 matching lines @@
     LibraryDependency,
     LiteralString,
     LiteralDartString;
 
 import 'tree/tree.dart' as ast;
 
 import 'resolution/resolution.dart' show
     TreeElements,
     AnalyzableElementX;
 
+import "dart:math" show min;
+
 /// A "hunk" of the program that will be loaded whenever one of its [imports]
 /// are loaded.
 ///
 /// Elements that are only used in one deferred import, is in an OutputUnit with
 /// the deferred import as single element in the [imports] set.
 ///
 /// Whenever a deferred Element is shared between several deferred imports it is
 /// in an output unit with those imports in the [imports] Set.
 ///
 /// OutputUnits are equal if their [imports] are equal.
@@ skipping 487 matching lines @@
       }
       assert(result != null);
       importDeferName[import] = makeUnique(result, usedImportNames);;
     }
 
     Set<String> usedOutputUnitNames = new Set<String>();
     Map<OutputUnit, String> generatedNames = new Map<OutputUnit, String>();
 
     void computeOutputUnitName(OutputUnit outputUnit) {
       if (generatedNames[outputUnit] != null) return;
-      String suggestedName = outputUnit.imports.map((import) {
+      Iterable<String> importNames = outputUnit.imports.map((import) {
         return importDeferName[import];
-      }).join('_');
+      });
+      String suggestedName = importNames.join('_');

[Alan Knight, 2014/07/07 20:08:07]

Is this going to run into potential problems with non-uniqueness. e.g. suppose I
have 100 deferred libraries all named
    deferred_locale_datetime_data_<locale>.dart
and another 100 named
    deferred_locale_number_data_<locale>.dart
and there is shared code between these two groups. 

Or is there only ever one file with the shared code? It seems like it might be
desirable to have multiples, but that's more of a nice-to-have.

[sigurdm, 2014/07/08 07:19:58]

We take care of the uniqueness a few lines further down.

outputUnit.name = makeUnique(suggestedName, usedOutputUnitNames);

+      // Avoid the name getting too long.
+      // Try to abbreviate the prefix-names
+      if (suggestedName.length > 15) {
+        suggestedName = importNames.map((name) {
+          return name.substring(0, min(2, name.length));
+        }).join('_');
+      }
+      // If this is still too long, truncate the whole name.
+      if (suggestedName.length > 15) {
+        suggestedName = suggestedName.substring(0, 15);
+      }
       outputUnit.name = makeUnique(suggestedName, usedOutputUnitNames);
       generatedNames[outputUnit] = outputUnit.name;
     }
 
     for (Import import in _allDeferredImports.keys) {
       computeImportDeferName(import);
     }
 
     for (OutputUnit outputUnit in allOutputUnits) {
       computeOutputUnitName(outputUnit);
@@ skipping 216 matching lines @@
     Element maybePrefix = elements[identifier];
     if (maybePrefix != null && maybePrefix.isPrefix) {
       PrefixElement prefixElement = maybePrefix;
       if (prefixElement.isDeferred) {
         return prefixElement;
       }
     }
     return null;
   }
 }