[gcc r14-9464] libcpp: Fix __has_include_next ICE in the last directory of the path [PR80755]

[gcc r14-9464] libcpp: Fix __has_include_next ICE in the last directory of the path [PR80755]

[Lewis Hyatt]

https://gcc.gnu.org/g:6c166e55b15894ceb07dcc7b55f900e50e24ec5b

commit r14-9464-g6c166e55b15894ceb07dcc7b55f900e50e24ec5b
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Wed Dec 20 16:27:42 2023 -0500

    libcpp: Fix __has_include_next ICE in the last directory of the path [PR80755]
    
    In libcpp/files.cc, the function _cpp_has_header(), which implements
    __has_include and __has_include_next, does not check for a NULL return value
    from search_path_head(), leading to an ICE tripping an assert when
    _cpp_find_file() tries to use it. Fix it by checking for that case and
    silently returning false instead.
    
    As suggested by the PR author, it is easiest to make a testcase by using
    the -idirafter option. To enable that, also modify the dg-additional-options
    testsuite procedure to make the global $srcdir available, since -idirafter
    requires the full path.
    
    libcpp/ChangeLog:
    
            PR preprocessor/80755
            * files.cc (search_path_head): Add SUPPRESS_DIAGNOSTIC argument
            defaulting to false.
            (_cpp_has_header): Silently return false if the search path has been
            exhausted, rather than issuing a diagnostic and then hitting an
            assert.
    
    gcc/testsuite/ChangeLog:
    
            * lib/gcc-defs.exp (dg-additional-options): Make $srcdir usable in a
            dg-additional-options directive.
            * c-c++-common/cpp/has-include-next-2-dir/has-include-next-2.h: New test.
            * c-c++-common/cpp/has-include-next-2.c: New test.

Diff:
---
 .../cpp/has-include-next-2-dir/has-include-next-2.h          |  3 +++
 gcc/testsuite/c-c++-common/cpp/has-include-next-2.c          |  4 ++++
 gcc/testsuite/lib/gcc-defs.exp                               |  1 +
 libcpp/files.cc                                              | 12 ++++++++----
 4 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/gcc/testsuite/c-c++-common/cpp/has-include-next-2-dir/has-include-next-2.h b/gcc/testsuite/c-c++-common/cpp/has-include-next-2-dir/has-include-next-2.h
new file mode 100644
index 00000000000..1e4be6ce7a3
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/cpp/has-include-next-2-dir/has-include-next-2.h
@@ -0,0 +1,3 @@
+#if __has_include_next(<whatever>)
+/* This formerly led to an ICE when the current directory was the last one in the path.  */
+#endif
diff --git a/gcc/testsuite/c-c++-common/cpp/has-include-next-2.c b/gcc/testsuite/c-c++-common/cpp/has-include-next-2.c
new file mode 100644
index 00000000000..4928d3e992c
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/cpp/has-include-next-2.c
@@ -0,0 +1,4 @@
+/* PR preprocessor/80755 */
+/* { dg-do preprocess } */
+/* { dg-additional-options "-idirafter $srcdir/c-c++-common/cpp/has-include-next-2-dir" } */
+#include <has-include-next-2.h>
diff --git a/gcc/testsuite/lib/gcc-defs.exp b/gcc/testsuite/lib/gcc-defs.exp
index 56851f4a082..70215ed4905 100644
--- a/gcc/testsuite/lib/gcc-defs.exp
+++ b/gcc/testsuite/lib/gcc-defs.exp
@@ -280,6 +280,7 @@ if { [info exists env(GCC_RUNTEST_PARALLELIZE_DIR)] \
 
 proc dg-additional-options { args } {
     upvar dg-extra-tool-flags extra-tool-flags
+    global srcdir
 
     if { [llength $args] > 3 } {
 	error "[lindex $args 0]: too many arguments"
diff --git a/libcpp/files.cc b/libcpp/files.cc
index e66eef46534..c61df339e20 100644
--- a/libcpp/files.cc
+++ b/libcpp/files.cc
@@ -181,7 +181,8 @@ static bool read_file_guts (cpp_reader *pfile, _cpp_file *file,
 static bool read_file (cpp_reader *pfile, _cpp_file *file,
 		       location_t loc);
 static struct cpp_dir *search_path_head (cpp_reader *, const char *fname,
-				 int angle_brackets, enum include_type);
+					 int angle_brackets, enum include_type,
+					 bool suppress_diagnostic = false);
 static const char *dir_name_of_file (_cpp_file *file);
 static void open_file_failed (cpp_reader *pfile, _cpp_file *file, int,
 			      location_t);
@@ -1041,7 +1042,7 @@ _cpp_mark_file_once_only (cpp_reader *pfile, _cpp_file *file)
    nothing left in the path, returns NULL.  */
 static struct cpp_dir *
 search_path_head (cpp_reader *pfile, const char *fname, int angle_brackets,
-		  enum include_type type)
+		  enum include_type type, bool suppress_diagnostic)
 {
   cpp_dir *dir;
   _cpp_file *file;
@@ -1070,7 +1071,7 @@ search_path_head (cpp_reader *pfile, const char *fname, int angle_brackets,
     return make_cpp_dir (pfile, dir_name_of_file (file),
 			 pfile->buffer ? pfile->buffer->sysp : 0);
 
-  if (dir == NULL)
+  if (dir == NULL && !suppress_diagnostic)
     cpp_error (pfile, CPP_DL_ERROR,
 	       "no include path in which to search for %s", fname);
 
@@ -2164,7 +2165,10 @@ bool
 _cpp_has_header (cpp_reader *pfile, const char *fname, int angle_brackets,
 		 enum include_type type)
 {
-  cpp_dir *start_dir = search_path_head (pfile, fname, angle_brackets, type);
+  cpp_dir *start_dir = search_path_head (pfile, fname, angle_brackets, type,
+					 /* suppress_diagnostic = */ true);
+  if (!start_dir)
+    return false;
   _cpp_file *file = _cpp_find_file (pfile, fname, start_dir, angle_brackets,
 				    _cpp_FFK_HAS_INCLUDE, 0);
   return file->err_no != ENOENT;