[modules] Fix incorrect diagnostic mapping computation when a module changes

diagnostic settings using _Pragma within a macro.

The AST writer had previously been assuming that all diagnostic state
transitions would occur within a FileID corresponding to a file. When a
diagnostic state change occured within a macro, it was unable to form a
location for that state change and would instead corrupt the diagnostic state
of the "root" node (and thus that of the main compilation).

Also introduce a "#pragma clang __debug diag_mapping" debugging utility
that I added to track this issue down.

llvm-svn: 324695

2 files changed, 8 insertions, 2 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index b62c47c67f3..979ff0c2c62 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -5761,6 +5761,8 @@ void ASTReader::ReadPragmaDiagnosticMappings(DiagnosticsEngine &Diag) {
       Initial.ExtBehavior = (diag::Severity)Flags;
       FirstState = ReadDiagState(Initial, SourceLocation(), true);
 
+      assert(F.OriginalSourceFileID.isValid());
+
       // Set up the root buffer of the module to start with the initial
       // diagnostic state of the module itself, to cover files that contain no
       // explicit transitions (for which we did not serialize anything).
@@ -5781,6 +5783,7 @@ void ASTReader::ReadPragmaDiagnosticMappings(DiagnosticsEngine &Diag) {
              "Invalid data, missing pragma diagnostic states");
       SourceLocation Loc = ReadSourceLocation(F, Record[Idx++]);
       auto IDAndOffset = SourceMgr.getDecomposedLoc(Loc);
+      assert(IDAndOffset.first.isValid() && "invalid FileID for transition");
       assert(IDAndOffset.second == 0 && "not a start location for a FileID");
       unsigned Transitions = Record[Idx++];
 
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 50c60fe64c2..8c5863e28ae 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -3092,8 +3092,11 @@ void ASTWriter::WritePragmaDiagnosticMappings(const DiagnosticsEngine &Diag,
         !FileIDAndFile.second.HasLocalTransitions)
       continue;
     ++NumLocations;
-    AddSourceLocation(Diag.SourceMgr->getLocForStartOfFile(FileIDAndFile.first),
-                      Record);
+
+    SourceLocation Loc = Diag.SourceMgr->getComposedLoc(FileIDAndFile.first, 0);
+    assert(!Loc.isInvalid() && "start loc for valid FileID is invalid");
+    AddSourceLocation(Loc, Record);
+
     Record.push_back(FileIDAndFile.second.StateTransitions.size());
     for (auto &StatePoint : FileIDAndFile.second.StateTransitions) {
       Record.push_back(StatePoint.Offset);