c++/modules: Fix include translation for already-seen headers [PR99243]

After importing a header unit we learn about and setup any header
modules that we transitively depend on.  However, this causes
'set_filename' to fail an assertion if we then come across this header
as an #include and attempt to translate it into a module.  We still need
to do this translation so that libcpp learns that this is a header unit,
but we shouldn't error just because we've already seen it as an import.

Instead this patch merely checks and errors to handle the case of a
broken mapper implementation which supplies a different CMI path from
the one we already got.

As a drive-by fix, also make failing to find the CMI for a module be a
fatal error: any further errors in the TU are unlikely to be helpful.

	PR c++/99243

gcc/cp/ChangeLog:

	* module.cc (module_state::set_filename): Handle repeated calls
	to 'set_filename' as long as the CMI path matches.
	(maybe_translate_include): Adjust comment.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/map-2.C: Prune additional fatal error message.
	* g++.dg/modules/inc-xlate-4_a.H: New test.
	* g++.dg/modules/inc-xlate-4_b.H: New test.
	* g++.dg/modules/inc-xlate-4_c.H: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 4cd7e1c..95c2405 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -20086,14 +20086,21 @@ canonicalize_header_name (cpp_reader *reader, location_t loc, bool unquoted,
 
 void module_state::set_filename (const Cody::Packet &packet)
 {
-  gcc_checking_assert (!filename);
   if (packet.GetCode () == Cody::Client::PC_PATHNAME)
-    filename = xstrdup (packet.GetString ().c_str ());
+    {
+      /* If we've seen this import before we better have the same CMI.  */
+      const std::string &path = packet.GetString ();
+      if (!filename)
+	filename = xstrdup (packet.GetString ().c_str ());
+      else if (filename != path)
+	error_at (loc, "mismatching compiled module interface: "
+		  "had %qs, got %qs", filename, path.c_str ());
+    }
   else
     {
       gcc_checking_assert (packet.GetCode () == Cody::Client::PC_ERROR);
-      error_at (loc, "unknown Compiled Module Interface: %s",
-		packet.GetString ().c_str ());
+      fatal_error (loc, "unknown compiled module interface: %s",
+		   packet.GetString ().c_str ());
     }
 }
 
@@ -20127,7 +20134,8 @@ maybe_translate_include (cpp_reader *reader, line_maps *lmaps, location_t loc,
     translate = packet.GetInteger () ? xlate_kind::text : xlate_kind::unknown;
   else if (packet.GetCode () == Cody::Client::PC_PATHNAME)
     {
-      /* Record the CMI name for when we do the import.  */
+      /* Record the CMI name for when we do the import.
+	 We may already know about this import, but libcpp doesn't yet.  */
       module_state *import = get_module (build_string (len, path));
       import->set_filename (packet);
       translate = xlate_kind::import;