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

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

Index: sdk/lib/_internal/compiler/implementation/deferred_load.dart
diff --git a/sdk/lib/_internal/compiler/implementation/deferred_load.dart b/sdk/lib/_internal/compiler/implementation/deferred_load.dart
index ddf061c62e25b7dd1e5d0a46b67a12a20115803f..dffcbb9ecb23f56e47220ad002727de58ab19966 100644
--- a/sdk/lib/_internal/compiler/implementation/deferred_load.dart
+++ b/sdk/lib/_internal/compiler/implementation/deferred_load.dart
@@ -57,6 +57,8 @@ 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.
 ///
@@ -564,9 +566,21 @@ class DeferredLoadTask extends CompilerTask {
 
     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;
     }