[ASTReader] Improve ReadASTBlock error message when module not available

Point to the PCM file that could not be found.

rdar://problem/30381981

llvm-svn: 294362

1 files changed, 4 insertions, 1 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 67c7e460997..1b65ecbe98a 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -2965,7 +2965,10 @@ ASTReader::ReadASTBlock(ModuleFile &F, unsigned ClientLoadCapabilities) {
         Data += Len;
         ModuleFile *OM = ModuleMgr.lookup(Name);
         if (!OM) {
-          Error("SourceLocation remap refers to unknown module");
+          std::string Msg =
+              "SourceLocation remap refers to unknown module, cannot find ";
+          Msg.append(Name);
+          Error(Msg);
           return Failure;
         }