cppinit.c (remove_dup_dirs): Inform if a system include directory is being reordered.

	* cppinit.c (remove_dup_dirs): Inform if a system include
        directory is being reordered.
	* doc/invoke.texi (Directory Options): GCC warns if you hide a
	system include.
	* doc/cpp.texi (Search Paths): Likewise.
	* doc/gcc.texi (Interoperation): Remove information about
	-I/usr/include.

From-SVN: r43769

gcc/ChangeLog

 2001-07-04  Nathan Sidwell  <nathan@codesourcery.com>
 
+	* cppinit.c (remove_dup_dirs): Inform if a system include
+        directory is being reordered.
+	* doc/invoke.texi (Directory Options): GCC warns if you hide a
+	system include.
+	* doc/cpp.texi (Search Paths): Likewise.
+	* doc/gcc.texi (Interoperation): Remove information about
+	-I/usr/include.
+
+2001-07-04  Nathan Sidwell  <nathan@codesourcery.com>
+
 	* varray.h (VARRAY_TOP_GENERIC_PTR): Remove spurious parameter.
 	(VARRAY_TOP_CHAR_PTR): Likewise.
 

gcc/cppinit.c

@@ -297,6 +297,21 @@ remove_dup_dirs (pfile, head)
       for (other = head; other != cur; other = other->next)
         if (INO_T_EQ (cur->ino, other->ino) && cur->dev == other->dev)
 	  {
+	    if (cur->sysp)
+	      {
+		cpp_warning (pfile,
+			     "changing search order for system directory \"%s\"",
+			     cur->name);
+		if (strcmp (cur->name, other->name))
+		  cpp_warning (pfile, other->sysp
+			       ? "  as it is the same as system directory \"%s\""
+			       : "  as it is the same as non-system directory \"%s\"",
+			       other->name);
+		else
+		  cpp_warning (pfile, other->sysp
+			       ? "  as it has already been specified as a system directory"
+			       : "  as it has already been specified as a non-system directory");
+	      }
 	    cur = remove_dup_dir (pfile, prev);
 	    break;
 	  }

gcc/doc/cpp.texi

@@ -834,6 +834,12 @@ For example, if @file{/usr/include/sys/stat.h} contains
 @code{@w{#include "types.h"}}, GCC looks for @file{types.h} first in
 @file{/usr/include/sys}, then in its usual search path.
 
+If you name a search directory with @option{-I@var{dir}} that is also a
+system include directory, the @option{-I} wins; the directory will be
+searched according to the @option{-I} ordering, and it will not be
+treated as a system include directory. GCC will warn you when a system
+include directory is hidden in this way.
+
 @samp{#line} (@pxref{Line Control}) does not change GCC's idea of the
 directory containing the current file.
 
@@ -1067,7 +1073,7 @@ All directories named by @option{-isystem} are searched @emph{after} all
 directories named by @option{-I}, no matter what their order was on the
 command line.  If the same directory is named by both @option{-I} and
 @option{-isystem}, @option{-I} wins; it is as if the @option{-isystem} option
-had never been specified at all.
+had never been specified at all. GCC warns you when this happens.
 
 @findex #pragma GCC system_header
 There is also a directive, @code{@w{#pragma GCC system_header}}, which

gcc/doc/invoke.texi

@@ -4363,6 +4363,17 @@ system header files (use @option{-isystem} for that).  If you use more than
 one @option{-I} option, the directories are scanned in left-to-right
 order; the standard system directories come after.
 
+If a standard system include directory, or a directory specified with
+@option{-isystem}, is also specified with @option{-I}, it will be
+searched only in the position requested by @option{-I}.  Also, it will
+not be considered a system include directory.  If that directory really
+does contain system headers, there is a good chance that they will
+break.  For instance, if GCC's installation procedure edited the headers
+in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the
+original, buggy headers to be found instead of the corrected ones.  GCC
+will issue a warning when a system include directory is hidden in this
+way.
+
 @item -I-
 @opindex I-
 Any directories you specify with @option{-I} options before the @option{-I-}