c++: header-unit build capability [PR 99023]

This defect really required building header-units and include translation
of pieces of the standard library.  This adds smarts to the modules
test harness to do that -- accept .X files as the source file, but
provide '-x c++-system-header $HDR' in the options.  The .X file will
be considered by the driver to be a linker script and ignored (with a
warning).

Using this we can add 2 tests that end up building list_initializer
and iostream, along with a test that iostream's build
include-translates list_initializer's #include.  That discovered a set
of issues with the -flang-info-include-translate=HDR handling, also
fixed and documented here.

	PR c++/99023
	gcc/cp/
	* module.cc (canonicalize_header_name): Use
	cpp_probe_header_unit.
	(maybe_translate_include): Fix note_includes comparison.
	(init_modules): Fix note_includes string termination.
	libcpp/
	* include/cpplib.h (cpp_find_header_unit): Rename to ...
	(cpp_probe_header_unit): ... this.
	* internal.h (_cp_find_header_unit): Declare.
	* files.c (cpp_find_header_unit): Break apart to ..
	(test_header_unit): ... this, and ...
	(_cpp_find_header_unit): ... and, or and ...
	(cpp_probe_header_unit): ... this.
	* macro.c (cpp_get_token_1): Call _cpp_find_header_unit.
	gcc/
	* doc/invoke.texi (flang-info-include-translate): Document header
	lookup behaviour.
	gcc/testsuite/
	* g++.dg/modules/modules.exp: Bail on cross-testing.  Add support
	for .X files.
	* g++.dg/modules/pr99023_a.X: New.
	* g++.dg/modules/pr99023_b.X: New.

4 files changed, 46 insertions, 21 deletions

diff --git a/libcpp/files.c b/libcpp/files.c
index 3a35f7c..6e20fc5 100644
--- a/libcpp/files.c
+++ b/libcpp/files.c
@@ -1108,31 +1108,54 @@ _cpp_stack_include (cpp_reader *pfile, const char *fname, int angle_brackets,
   return _cpp_stack_file (pfile, file, type, loc);
 }
 
-/* NAME is a header file name, find the path we'll use to open it.  */
+/* NAME is a header file name, find the _cpp_file, if any.  */
 
-const char *
-cpp_find_header_unit (cpp_reader *pfile, const char *name, bool angle,
-		      location_t loc)
+static _cpp_file *
+test_header_unit (cpp_reader *pfile, const char *name, bool angle,
+		  location_t loc)
 {
-  cpp_dir *dir = search_path_head (pfile, name, angle, IT_INCLUDE);
-  if (!dir)
-    return NULL;
+  if (cpp_dir *dir = search_path_head (pfile, name, angle, IT_INCLUDE))
+    return _cpp_find_file (pfile, name, dir, angle, _cpp_FFK_NORMAL, loc);
+
+  return nullptr;
+}
 
-  _cpp_file *file = _cpp_find_file (pfile, name, dir, angle,
-				    _cpp_FFK_NORMAL, loc);
-  if (!file)
-    return NULL;
+/* NAME is a header file name, find the path we'll use to open it and infer that
+   it is a header-unit.  */
 
-  if (file->fd > 0)
+const char *
+_cpp_find_header_unit (cpp_reader *pfile, const char *name, bool angle,
+		       location_t loc)
+{
+  if (_cpp_file *file = test_header_unit (pfile, name, angle, loc))
     {
-      /* Don't leave it open.  */
-      close (file->fd);
-      file->fd = 0;
+      if (file->fd > 0)
+	{
+	  /* Don't leave it open.  */
+	  close (file->fd);
+	  file->fd = 0;
+	}
+
+      file->header_unit = +1;
+      _cpp_mark_file_once_only (pfile, file);
+
+      return file->path;
     }
 
-  file->header_unit = +1;
-  _cpp_mark_file_once_only (pfile, file);
-  return file->path;
+  return nullptr;
+}
+
+/* NAME is a header file name, find the path we'll use to open it.  But do not
+   infer it is a header unit.  */
+
+const char *
+cpp_probe_header_unit (cpp_reader *pfile, const char *name, bool angle,
+		       location_t loc)
+{
+  if (_cpp_file *file = test_header_unit (pfile, name, angle, loc))
+    return file->path;
+
+  return nullptr;
 }
 
 /* Retrofit the just-entered main file asif it was an include.  This
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index 17feb64..41d75d9 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -1012,8 +1012,8 @@ extern cpp_callbacks *cpp_get_callbacks (cpp_reader *) ATTRIBUTE_PURE;
 extern void cpp_set_callbacks (cpp_reader *, cpp_callbacks *);
 extern class mkdeps *cpp_get_deps (cpp_reader *) ATTRIBUTE_PURE;
 
-extern const char *cpp_find_header_unit (cpp_reader *, const char *file,
-					 bool angle_p,  location_t);
+extern const char *cpp_probe_header_unit (cpp_reader *, const char *file,
+					  bool angle_p,  location_t);
 
 /* Call these to get name data about the various compile-time
    charsets.  */
diff --git a/libcpp/internal.h b/libcpp/internal.h
index 32f9f50..fd44de6 100644
--- a/libcpp/internal.h
+++ b/libcpp/internal.h
@@ -703,6 +703,8 @@ extern _cpp_file *_cpp_find_file (cpp_reader *, const char *, cpp_dir *,
 				  int angle, _cpp_find_file_kind, location_t);
 extern bool _cpp_find_failed (_cpp_file *);
 extern void _cpp_mark_file_once_only (cpp_reader *, struct _cpp_file *);
+extern const char *_cpp_find_header_unit (cpp_reader *, const char *file,
+					  bool angle_p,  location_t);
 extern void _cpp_fake_include (cpp_reader *, const char *);
 extern bool _cpp_stack_file (cpp_reader *, _cpp_file*, include_type, location_t);
 extern bool _cpp_stack_include (cpp_reader *, const char *, int,
diff --git a/libcpp/macro.c b/libcpp/macro.c
index fa6acff..dff7c98 100644
--- a/libcpp/macro.c
+++ b/libcpp/macro.c
@@ -3010,7 +3010,7 @@ cpp_get_token_1 (cpp_reader *pfile, location_t *location)
 
 	  if (need_search)
 	    {
-	      found = cpp_find_header_unit (pfile, fname, angle, tmp->src_loc);
+	      found = _cpp_find_header_unit (pfile, fname, angle, tmp->src_loc);
 	      if (!found)
 		found = "";
 	      len = strlen (found);