Change execution root for external repositories to be ../repo

Some of the important aspect of this change:

* Remote repos in the execution root are under output_base/execroot/repo_name, so the prefix is ../repo_name (to escape the local workspace name).
* Package roots for external repos were previously "output_base/", they are now output_base/external/repo_name (which means source artifacts always have a relative path from their repository).
* Outputs are under bazel-bin/external/repo_name/ (or similarly under genfiles). Note that this is a bit of a change from how this was implemented in the previous cl.

Fixes #1262.

RELNOTES[INC]: Previously, an external repository would be symlinked into the
execution root at execroot/local_repo/external/remote_repo. This changes it to
be at execroot/remote_repo. This may break genrules/Skylark actions that
hardcode execution root paths. If this causes breakages for you, ensure that
genrules are using $(location :target) to access files and Skylark rules are
using http://bazel.io/docs/skylark/lib/File.html's path, dirname, etc.
functions.

Roll forward of bdfd58a.

--
MOS_MIGRATED_REVID=133606309

1 files changed, 4 insertions, 3 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/CompilationHelper.java b/src/main/java/com/google/devtools/build/lib/analysis/CompilationHelper.java
index 8a1fddc6ff..a3769e3e07 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/CompilationHelper.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/CompilationHelper.java
@@ -54,8 +54,8 @@ public final class CompilationHelper {
     }
     MiddlemanFactory factory = env.getMiddlemanFactory();
     return ImmutableList.of(factory.createMiddlemanAllowMultiple(
-        env, actionOwner, ruleContext.getPackageDirectory(), purpose, filesToBuild,
-        ruleContext.getConfiguration().getMiddlemanDirectory(
+        env, actionOwner, ruleContext.getRule().getLabel().getPackageIdentifier().getSourceRoot(),
+        purpose, filesToBuild, ruleContext.getConfiguration().getMiddlemanDirectory(
             ruleContext.getRule().getRepository())));
   }
 
@@ -87,7 +87,8 @@ public final class CompilationHelper {
     MiddlemanFactory factory = env.getMiddlemanFactory();
     Iterable<Artifact> artifacts = dep.getProvider(FileProvider.class).getFilesToBuild();
     return ImmutableList.of(
-        factory.createMiddlemanAllowMultiple(env, actionOwner, ruleContext.getPackageDirectory(),
+        factory.createMiddlemanAllowMultiple(env, actionOwner,
+            ruleContext.getRule().getLabel().getPackageIdentifier().getSourceRoot(),
             purpose, artifacts, ruleContext.getConfiguration().getMiddlemanDirectory(
                 ruleContext.getRule().getRepository())));
   }