[Index/IndexStore] Preserve the canonical output file path

Additionally, make sure we don't accidentally convert the output file
path to the local equivalent when computing the unit name in IndexStore,
as that will accidentally treat it as a different unit.

Author: DavidGoldman

clang/lib/Index/IndexUnitReader.cpp

@@ -212,7 +212,11 @@ class IndexUnitBitstreamVisitor : public BitstreamVisitor<IndexUnitBitstreamVisi
       case UNIT_PATH_BUFFER:
         Reader.PathsBuffer = Blob;
         Reader.WorkingDir = Reader.getAndRemapPathFromBuffer(WorkDirOffset, WorkDirSize);
-        Reader.OutputFile = Reader.getAndRemapPathFromBuffer(OutputFileOffset, OutputFileSize);
+        // We intentionally do -not- remap the output file and instead leave it
+        // in the canonical form. This is because the output file need not be an
+        // actual real file path and this allows clients to provide the same
+        // canonical output path e.g. in the explicit output files list.
+        Reader.OutputFile = Reader.getPathFromBuffer(OutputFileOffset, OutputFileSize).str();
         Reader.SysrootPath = Reader.getAndRemapPathFromBuffer(SysrootOffset, SysrootSize);
 
         // now we can populate the main file's path

clang/test/Index/Store/print-unit-roundtrip-remapping.c

@@ -14,8 +14,7 @@ void foo(int i);
 // CHECK-NOT: main-path: SRC_ROOT{{/|\\}}print-unit-roundtrip-remapping.c
 // CHECK: main-path: {{.*}}{{/|\\}}print-unit-roundtrip-remapping.c
 // CHECK-NOT: work-dir: BUILD_ROOT
-// CHECK-NOT: out-file: SRC_ROOT{{/|\\}}print-unit-roundtrip-remapping.c.o
-// CHECK: out-file: {{.*}}{{/|\\}}print-unit-roundtrip-remapping.c.o
+// CHECK: out-file: SRC_ROOT{{/|\\}}print-unit-roundtrip-remapping.c.o
 // CHECK: target: x86_64-apple-macosx10.8
 // CHECK: is-debug: 1
 // CHECK: DEPEND START

clang/tools/IndexStore/IndexStore.cpp

@@ -613,7 +613,10 @@ indexstore_store_get_unit_name_from_output_path(indexstore_t c_store,
                                                 size_t buf_size) {
   IndexDataStore *store = static_cast<IndexDataStore*>(c_store);
   SmallString<256> unitName;
-  auto remapper = store->getPathRemapper();
+  // We intentionally don't use the index store's path remapper since it
+  // maps from canonical -> local instead of local -> canonical. This means that
+  // callers must gives us the canonical `output_path`, not the local one.
+  PathRemapper remapper;
   IndexUnitWriter::getUnitNameForAbsoluteOutputFile(output_path, unitName,
                                                     remapper);
   size_t nameLen = unitName.size();