[gcc r11-10188] c: Fix location for _Pragma tokens [PR97498]

[gcc r11-10188] c: Fix location for _Pragma tokens [PR97498]

[Lewis Hyatt]

https://gcc.gnu.org/g:d431d48c4e503c3ff17ccd51e504877f3fc9ce0e

commit r11-10188-gd431d48c4e503c3ff17ccd51e504877f3fc9ce0e
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Sat Jul 9 16:12:21 2022 -0400

    c: Fix location for _Pragma tokens [PR97498]
    
    The handling of #pragma GCC diagnostic uses input_location, which is not always
    as precise as needed; in particular the relative location of some tokens and a
    _Pragma directive will crucially determine whether a given diagnostic is enabled
    or suppressed in the desired way. PR97498 shows how the C frontend ends up with
    input_location pointing to the beginning of the line containing a _Pragma()
    directive, resulting in the wrong behavior if the diagnostic to be modified
    pertains to some tokens found earlier on the same line. This patch fixes that by
    addressing two issues:
    
        a) libcpp was not assigning a valid location to the CPP_PRAGMA token
        generated by the _Pragma directive.
        b) C frontend was not setting input_location to something reasonable.
    
    With this change, the C frontend is able to change input_location to point to
    the _Pragma token as needed.
    
    This is just a two-line fix (one for each of a) and b)), the testsuite changes
    were needed only because the location on the tested warnings has been somewhat
    improved, so the tests need to look for the new locations.
    
    gcc/c/ChangeLog:
    
            PR preprocessor/97498
            * c-parser.c (c_parser_pragma): Set input_location to the
            location of the pragma, rather than the start of the line.
    
    libcpp/ChangeLog:
    
            PR preprocessor/97498
            * directives.c (destringize_and_run): Override the location of
            the CPP_PRAGMA token from a _Pragma directive to the location of
            the expansion point, as is done for the tokens lexed from it.
    
    gcc/testsuite/ChangeLog:
    
            PR preprocessor/97498
            * c-c++-common/pr97498.c: New test.
            * gcc.dg/pragma-message.c: Adapt for improved warning locations.
    
    (cherry picked from commit 0587cef3d7962a8b0f44779589ba2920dd3d71e5)

Diff:
---
 gcc/c/c-parser.c                      | 1 +
 gcc/testsuite/c-c++-common/pr97498.c  | 4 ++++
 gcc/testsuite/gcc.dg/pragma-message.c | 8 +++++---
 libcpp/directives.c                   | 1 +
 4 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 7690977f6b8..407c22afa6f 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -12289,6 +12289,7 @@ c_parser_pragma (c_parser *parser, enum pragma_context context, bool *if_p)
   unsigned int id;
   const char *construct = NULL;
 
+  input_location = c_parser_peek_token (parser)->location;
   id = c_parser_peek_token (parser)->pragma_kind;
   gcc_assert (id != PRAGMA_NONE);
 
diff --git a/gcc/testsuite/c-c++-common/pr97498.c b/gcc/testsuite/c-c++-common/pr97498.c
new file mode 100644
index 00000000000..f5fa420415b
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr97498.c
@@ -0,0 +1,4 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-Wunused-function" } */
+#pragma GCC diagnostic ignored "-Wunused-function"
+static void f() {} _Pragma("GCC diagnostic error \"-Wunused-function\"") /* { dg-bogus "-Wunused-function" } */
diff --git a/gcc/testsuite/gcc.dg/pragma-message.c b/gcc/testsuite/gcc.dg/pragma-message.c
index 2f44b617710..1b7cf09de0a 100644
--- a/gcc/testsuite/gcc.dg/pragma-message.c
+++ b/gcc/testsuite/gcc.dg/pragma-message.c
@@ -42,9 +42,11 @@
 #pragma message ("Okay " THREE)  /* { dg-message "Okay 3" } */
 
 /* Create a TODO() that prints a message on compilation.  */
-#define DO_PRAGMA(x) _Pragma (#x)
-#define TODO(x) DO_PRAGMA(message ("TODO - " #x))
-TODO(Okay 4)                     /* { dg-message "TODO - Okay 4" } */
+#define DO_PRAGMA(x) _Pragma (#x) /* { dg-line pragma_loc1 } */
+#define TODO(x) DO_PRAGMA(message ("TODO - " #x)) /* { dg-line pragma_loc2 } */
+TODO(Okay 4) /* { dg-message "in expansion of macro 'TODO'" } */
+/* { dg-message "TODO - Okay 4" "test4.1" { target *-*-* } pragma_loc1 } */
+/* { dg-message "in expansion of macro 'DO_PRAGMA'" "test4.2" { target *-*-* } pragma_loc2 } */
 
 #if 0
 #pragma message ("Not printed")
diff --git a/libcpp/directives.c b/libcpp/directives.c
index 347ddb8b1e1..d764ddfa38e 100644
--- a/libcpp/directives.c
+++ b/libcpp/directives.c
@@ -1905,6 +1905,7 @@ destringize_and_run (cpp_reader *pfile, const cpp_string *in,
       maxcount = 50;
       toks = XNEWVEC (cpp_token, maxcount);
       toks[0] = pfile->directive_result;
+      toks[0].src_loc = expansion_loc;
 
       do
 	{