Add a feature to require explicitly passing module maps.

Currently, module maps contain both "use <module>" entries that specify which
modules the current module map depends on, and "extern module" entries that
provide paths where to load the dependent module maps from.

This change adds a feature "module_map_without_extern_module", which instructs
blaze to not write the "extern module" entries into the module map. Instead,
the crosstool needs to add -fmodule-file flags for each dependent module file
where needed for the compile via the new build variable
"dependent_module_map_files".

Note that the feature is phrased negatively ("_without_") in order to simplify
the roll-out of this feature: as long as crosstools do not specify any
features, they still want the old behavior.
We cannot make the feature positive and add it to the legacy configuration, as
we currently cannot remove features that have already been set in the crosstool
file.

--
MOS_MIGRATED_REVID=104757413

1 files changed, 2 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java b/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
index 6ba0442d15..1c92409383 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
@@ -675,7 +675,8 @@ public final class CompilationSupport {
             ImmutableList.<PathFragment>of(),
             /*compiledModule=*/ true,
             /*moduleMapHomeIsCwd=*/ false,
-            /*generateSubModules=*/ false));
+            /*generateSubModules=*/ false,
+            /*externDependencies=*/ true));
   }
 
   private void registerLinkAction(ObjcProvider objcProvider, ExtraLinkArgs extraLinkArgs,