[Bug preprocessor/103026] Implement warning for Unicode bidi override characters [CVE-2021-42574]

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103026

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:1a7f2c0774129750fdf73e9f1b78f0ce983c9ab3

commit r12-5355-g1a7f2c0774129750fdf73e9f1b78f0ce983c9ab3
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Tue Nov 2 09:54:32 2021 -0400

    libcpp: escape non-ASCII source bytes in -Wbidi-chars= [PR103026]

    This flags rich_locations associated with -Wbidi-chars= so that
    non-ASCII bytes will be escaped when printing the source lines
    (using the diagnostics support I added in
    r12-4825-gbd5e882cf6e0def3dd1bc106075d59a303fe0d1e).

    In particular, this ensures that the printed source lines will
    be pure ASCII, and thus the visual ordering of the characters
    will be the same as the logical ordering.

    Before:

      Wbidi-chars-1.c: In function âmainâ:
      Wbidi-chars-1.c:6:43: warning: unpaired UTF-8 bidirectional control
character detected [-Wbidi-chars=]
          6 |     /*â® } â¦if (isAdmin)⩠⦠begin admins only */
            |                                           ^
      Wbidi-chars-1.c:9:28: warning: unpaired UTF-8 bidirectional control
character detected [-Wbidi-chars=]
          9 |     /* end admins only â® { â¦*/
            |                            ^

      Wbidi-chars-11.c:6:15: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
          6 | int LRE_âª_PDF_\u202c;
            |               ^
      Wbidi-chars-11.c:8:19: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
          8 | int LRE_\u202a_PDF_â¬_;
            |                   ^
      Wbidi-chars-11.c:10:28: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
         10 | const char *s1 = "LRE_âª_PDF_\u202c";
            |                            ^
      Wbidi-chars-11.c:12:33: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
         12 | const char *s2 = "LRE_\u202a_PDF_â¬";
            |                                 ^

    After:

      Wbidi-chars-1.c: In function âmainâ:
      Wbidi-chars-1.c:6:43: warning: unpaired UTF-8 bidirectional control
character detected [-Wbidi-chars=]
          6 |     /*<U+202E> } <U+2066>if (isAdmin)<U+2069> <U+2066> begin
admins only */
            |                                                                  
        ^
      Wbidi-chars-1.c:9:28: warning: unpaired UTF-8 bidirectional control
character detected [-Wbidi-chars=]
          9 |     /* end admins only <U+202E> { <U+2066>*/
            |                                            ^

      Wbidi-chars-11.c:6:15: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
          6 | int LRE_<U+202A>_PDF_\u202c;
            |                       ^
      Wbidi-chars-11.c:8:19: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
          8 | int LRE_\u202a_PDF_<U+202C>_;
            |                   ^
      Wbidi-chars-11.c:10:28: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
         10 | const char *s1 = "LRE_<U+202A>_PDF_\u202c";
            |                                    ^
      Wbidi-chars-11.c:12:33: warning: UTF-8 vs UCN mismatch when closing a
context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
         12 | const char *s2 = "LRE_\u202a_PDF_<U+202C>";
            |                                 ^

    libcpp/ChangeLog:
            PR preprocessor/103026
            * lex.c (maybe_warn_bidi_on_close): Use a rich_location
            and call set_escape_on_output (true) on it.
            (maybe_warn_bidi_on_char): Likewise.

    Signed-off-by: David Malcolm <dmalcolm@redhat.com>