Add a configure option to disable system header canonicalizations (issue6495088)

[Ian Lance Taylor]

On Wed, Sep 5, 2012 at 6:56 AM, Simon Baldwin <simonb@google.com> wrote:
> Add a configure option to disable system header canonicalizations.

Why should this be a configure option rather than a command-line option?

Ian



> Libcpp may canonicalize system header paths with lrealpath() for diagnostics,
> dependency output, and similar.  If gcc is held in a symlink farm the
> canonicalized paths may be meaningless to users, and will also conflict with
> build frameworks that (for example) disallow absolute paths to header files.
>
> This change adds --[en/dis]able-canonical-system-headers, allowing configure
> to select whether or not to implement r186991.  See also PR c++/52974.
>
> Tested for regressions with bootstrap builds of C and C++, both with and
> without configure --disable-canonical-system-headers.
>
> Okay for trunk?
>
> libcpp/ChangeLog.google-integration
> 2012-09-05  Simon Baldwin  <simonb@google.com>
>
>         * files.c (maybe_shorter_path): Suppress function definition if
>         ENABLE_CANONICAL_SYSTEM_HEADERS is not defined.
>         * (find_file_in_dir): Call maybe_shorter_path() only if
>         ENABLE_CANONICAL_SYSTEM_HEADERS is defined.
>         * configure.ac: Add new --enable-canonical-system-headers.
>         * configure: Regenerate.
>         * config.in: Regenerate.
>
> gcc/ChangeLog.google-integration
> 2012-09-05  Simon Baldwin  <simonb@google.com>
>
>         * doc/install.texi: Document --enable-canonical-system-headers.
>
>
> Index: gcc/doc/install.texi
> ===================================================================
> --- gcc/doc/install.texi        (revision 190968)
> +++ gcc/doc/install.texi        (working copy)
> @@ -1710,6 +1710,14 @@ link time when @option{-fuse-linker-plug
>  This linker should have plugin support such as gold starting with
>  version 2.20 or GNU ld starting with version 2.21.
>  See @option{-fuse-linker-plugin} for details.
> +
> +@item --enable-canonical-system-headers
> +@itemx --disable-canonical-system-headers
> +Enable system header path canonicalization for @file{libcpp}.  This can
> +produce shorter header file paths in diagnostics and dependency output
> +files, but these changed header paths may conflict with some compilation
> +environments.  Enabled by default, and may be disabled using
> +@option{--disable-canonical-system-headers}.
>  @end table
>
>  @subheading Cross-Compiler-Specific Options
> Index: libcpp/configure
> ===================================================================
> --- libcpp/configure    (revision 190968)
> +++ libcpp/configure    (working copy)
> @@ -700,6 +700,7 @@ enable_rpath
>  with_libiconv_prefix
>  enable_maintainer_mode
>  enable_checking
> +enable_canonical_system_headers
>  '
>        ac_precious_vars='build_alias
>  host_alias
> @@ -1333,6 +1334,8 @@ Optional Features:
>    --disable-rpath         do not hardcode runtime library paths
>    --enable-maintainer-mode enable rules only needed by maintainers
>    --enable-checking      enable expensive run-time checks
> +  --enable-canonical-system-headers
> +                          enable or disable system headers canonicalization
>
>  Optional Packages:
>    --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
> @@ -7094,6 +7097,19 @@ $as_echo "#define ENABLE_CHECKING 1" >>c
>
>  fi
>
> +# Check whether --enable-canonical-system-headers was given.
> +if test "${enable_canonical_system_headers+set}" = set; then :
> +  enableval=$enable_canonical_system_headers;
> +else
> +  enable_canonical_system_headers=yes
> +fi
> +
> +if test $enable_canonical_system_headers != no; then
> +
> +$as_echo "#define ENABLE_CANONICAL_SYSTEM_HEADERS 1" >>confdefs.h
> +
> +fi
> +
>
>  case $target in
>         alpha*-*-* | \
> Index: libcpp/files.c
> ===================================================================
> --- libcpp/files.c      (revision 190968)
> +++ libcpp/files.c      (working copy)
> @@ -345,6 +345,7 @@ pch_open_file (cpp_reader *pfile, _cpp_f
>     shorter, otherwise return NULL.  This function does NOT free the
>     memory pointed by FILE.  */
>
> +#ifdef ENABLE_CANONICAL_SYSTEM_HEADERS
>  static char *
>  maybe_shorter_path (const char * file)
>  {
> @@ -359,6 +360,7 @@ maybe_shorter_path (const char * file)
>        return NULL;
>      }
>  }
> +#endif
>
>  /* Try to open the path FILE->name appended to FILE->dir.  This is
>     where remap and PCH intercept the file lookup process.  Return true
> @@ -384,6 +386,7 @@ find_file_in_dir (cpp_reader *pfile, _cp
>        char *copy;
>        void **pp;
>
> +#ifdef ENABLE_CANONICAL_SYSTEM_HEADERS
>        /* We try to canonicalize system headers.  */
>        if (file->dir->sysp)
>         {
> @@ -396,6 +399,7 @@ find_file_in_dir (cpp_reader *pfile, _cp
>               path = canonical_path;
>             }
>         }
> +#endif
>
>        hv = htab_hash_string (path);
>        if (htab_find_with_hash (pfile->nonexistent_file_hash, path, hv) != NULL)
> Index: libcpp/configure.ac
> ===================================================================
> --- libcpp/configure.ac (revision 190968)
> +++ libcpp/configure.ac (working copy)
> @@ -132,6 +132,16 @@ if test $enable_checking != no ; then
>  [Define if you want more run-time sanity checks.])
>  fi
>
> +AC_ARG_ENABLE(canonical-system-headers,
> +[  --enable-canonical-system-headers
> +                          enable or disable system headers canonicalization],
> +[],
> +enable_canonical_system_headers=yes)
> +if test $enable_canonical_system_headers != no; then
> +  AC_DEFINE(ENABLE_CANONICAL_SYSTEM_HEADERS,
> +            1, [Define to enable system headers canonicalization.])
> +fi
> +
>  m4_changequote(,)
>  case $target in
>         alpha*-*-* | \
> Index: libcpp/config.in
> ===================================================================
> --- libcpp/config.in    (revision 190968)
> +++ libcpp/config.in    (working copy)
> @@ -11,6 +11,9 @@
>  /* Define to 1 if using `alloca.c'. */
>  #undef C_ALLOCA
>
> +/* Define to enable system headers canonicalization. */
> +#undef ENABLE_CANONICAL_SYSTEM_HEADERS
> +
>  /* Define if you want more run-time sanity checks. */
>  #undef ENABLE_CHECKING
>
>
> --
> This patch is available for review at http://codereview.appspot.com/6495088