PATCH: cpp include directory search order warning (mark 2)

["John David Anglin" <dave at hiauly1 dot hia dot nrc dot ca>]

> 3) Zack's (yet to be written) patch will give you a search order
> (that might be) different to what you asked for, but does fulfil the
> spirit, in that the directory will be searched.

Here is a crack at implementing Zack's suggestion.  I didn't implement
any warnings because, if the patch is correct, a -I option will never
reorder the system include chain or cause a system include directory to
be ignored.

I have also enclosed a revised version of the text for install.texi
which I think is somewhat clearer and incorporates previous suggestions.

The current version of that patch has survived bootstrap on hppa-linux
and hppa64-hp-hpux11.00.  Regression testing is in progress.  I didn't
see any regressions in previous versions.  I have manually observed
the effect of adding a system directory with -I to the include chain.
I have checked various alternatives at the quote-bracket boundary.
I have sucessfully built a number of packages which add GCC "system
include" directories to CPPFLAGS under hppa2.0w-hp-hpux11.00
with a previous of the patch.  This version does a simpler and more
efficient removal of non-system directories from the quote chain
after it is merged.

Are we getting any closer to a solution?

Dave
-- 
J. David Anglin                                  dave.anglin@nrc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)

2002-08-09  John David Anglin  <dave@hiauly1.hia.nrc.ca>

	* cppinit.c (remove_dup_dir): Add head_ptr argument to handle removal
	at head.
	(remove_dup_nonsys_dirs): New function.
	(remove_dup_dirs): Change argument head to head_ptr.  Remove warnings.
	(merge_include_chains): Remove non-system include directories from
	quote and bracket include chains when they duplicate equivalent system
	directories.
	* doc/install.texi (--with-local-prefix): Further document usage of
	this option.

Index: cppinit.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/cppinit.c,v
retrieving revision 1.251
diff -u -3 -p -r1.251 cppinit.c
--- cppinit.c	9 Aug 2002 06:19:08 -0000	1.251
+++ cppinit.c	9 Aug 2002 20:39:46 -0000
@@ -95,9 +95,13 @@ static void mark_named_operators	PARAMS 
 static void append_include_chain	PARAMS ((cpp_reader *,
 						 char *, int, int));
 static struct search_path * remove_dup_dir	PARAMS ((cpp_reader *,
+						 struct search_path *,
+						 struct search_path **));
+static struct search_path * remove_dup_nonsys_dirs PARAMS ((cpp_reader *,
+						 struct search_path **,
 						 struct search_path *));
 static struct search_path * remove_dup_dirs PARAMS ((cpp_reader *,
-						 struct search_path *));
+						 struct search_path **));
 static void merge_include_chains	PARAMS ((cpp_reader *));
 static bool push_include		PARAMS ((cpp_reader *,
 						 struct pending_option *));
@@ -260,55 +264,86 @@ append_include_chain (pfile, dir, path, 
 }
 
 /* Handle a duplicated include path.  PREV is the link in the chain
-   before the duplicate.  The duplicate is removed from the chain and
-   freed.  Returns PREV.  */
+   before the duplicate, or NULL if the duplicate is at the head of
+   the chain.  The duplicate is removed from the chain and freed.
+   Returns PREV.  */
 static struct search_path *
-remove_dup_dir (pfile, prev)
+remove_dup_dir (pfile, prev, head_ptr)
      cpp_reader *pfile;
      struct search_path *prev;
+     struct search_path **head_ptr;
 {
-  struct search_path *cur = prev->next;
+  struct search_path *cur;
+
+  if (prev != NULL)
+    {
+      cur = prev->next;
+      prev->next = cur->next;
+    }
+  else
+    {
+      cur = *head_ptr;
+      *head_ptr = cur->next;
+    }
 
   if (CPP_OPTION (pfile, verbose))
     fprintf (stderr, _("ignoring duplicate directory \"%s\"\n"), cur->name);
 
-  prev->next = cur->next;
   free ((PTR) cur->name);
   free (cur);
 
   return prev;
 }
 
+/* Remove duplicate non-system directories for which there is an equivalent
+   system directory latter in the chain.  The range for removal is between
+   *HEAD_PTR and END.  Returns the directory before END, or NULL if none.
+   This algorithm is quadratic in the number of -I switches, which is
+   acceptable since there aren't usually that many of them.  */
+static struct search_path *
+remove_dup_nonsys_dirs (pfile, head_ptr, end)
+     cpp_reader *pfile;
+     struct search_path **head_ptr;
+     struct search_path *end;
+{
+  struct search_path *prev = NULL, *cur, *other;
+
+  for (cur = *head_ptr; cur != end; cur = cur ? cur->next : *head_ptr)
+    {
+      if (!cur->sysp)
+	{
+	  for (other = cur->next; other; other = other->next)
+	    if (INO_T_EQ (cur->ino, other->ino)
+		&& cur->dev == other->dev
+		&& other->sysp)
+	      {
+		cur = remove_dup_dir (pfile, prev, head_ptr);
+		break;
+	      }
+	}
+      prev = cur;
+    }
+
+  return prev;
+}
+
 /* Remove duplicate directories from a chain.  Returns the tail of the
    chain, or NULL if the chain is empty.  This algorithm is quadratic
    in the number of -I switches, which is acceptable since there
    aren't usually that many of them.  */
 static struct search_path *
-remove_dup_dirs (pfile, head)
+remove_dup_dirs (pfile, head_ptr)
      cpp_reader *pfile;
-     struct search_path *head;
+     struct search_path **head_ptr;
 {
   struct search_path *prev = NULL, *cur, *other;
 
-  for (cur = head; cur; cur = cur->next)
+  for (cur = *head_ptr; cur; cur = cur->next)
     {
-      for (other = head; other != cur; other = other->next)
+      for (other = *head_ptr; other != cur; other = other->next)
 	if (INO_T_EQ (cur->ino, other->ino) && cur->dev == other->dev)
 	  {
-	    if (cur->sysp && !other->sysp)
-	      {
-		cpp_error (pfile, DL_WARNING,
-			   "changing search order for system directory \"%s\"",
-			   cur->name);
-		if (strcmp (cur->name, other->name))
-		  cpp_error (pfile, DL_WARNING,
-			     "  as it is the same as non-system directory \"%s\"",
-			     other->name);
-		else
-		  cpp_error (pfile, DL_WARNING,
-			     "  as it has already been specified as a non-system directory");
-	      }
-	    cur = remove_dup_dir (pfile, prev);
+	    cur = remove_dup_dir (pfile, prev, head_ptr);
 	    break;
 	  }
       prev = cur;
@@ -346,28 +381,33 @@ merge_include_chains (pfile)
   else
     brack = systm;
 
-  /* This is a bit tricky.  First we drop dupes from the quote-include
-     list.  Then we drop dupes from the bracket-include list.
-     Finally, if qtail and brack are the same directory, we cut out
-     brack and move brack up to point to qtail.
+  /* This is a bit tricky.  First we drop non-system dupes of system
+     directories from the merged bracket-include list.  Next we drop
+     dupes from the bracket and quote include lists.  Then we drop
+     non-system dupes from the merged quote-include list.  Finally,
+     if qtail and brack are the same directory, we cut out brack and
+     move brack up to point to qtail.
 
      We can't just merge the lists and then uniquify them because
      then we may lose directories from the <> search path that should
-     be there; consider -Ifoo -Ibar -I- -Ifoo -Iquux. It is however
+     be there; consider -Ifoo -Ibar -I- -Ifoo -Iquux.  It is however
      safe to treat -Ibar -Ifoo -I- -Ifoo -Iquux as if written
      -Ibar -I- -Ifoo -Iquux.  */
 
-  remove_dup_dirs (pfile, brack);
-  qtail = remove_dup_dirs (pfile, quote);
+  remove_dup_nonsys_dirs (pfile, &brack, NULL);
+  remove_dup_dirs (pfile, &brack);
 
   if (quote)
     {
+      qtail = remove_dup_dirs (pfile, &quote);
       qtail->next = brack;
 
+      qtail = remove_dup_nonsys_dirs (pfile, &quote, brack);
+
       /* If brack == qtail, remove brack as it's simpler.  */
-      if (brack && INO_T_EQ (qtail->ino, brack->ino)
+      if (qtail && brack && INO_T_EQ (qtail->ino, brack->ino)
 	  && qtail->dev == brack->dev)
-	brack = remove_dup_dir (pfile, qtail);
+	brack = remove_dup_dir (pfile, qtail, &quote);
     }
   else
     quote = brack;
Index: doc/install.texi
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/doc/install.texi,v
retrieving revision 1.131
diff -u -3 -p -r1.131 install.texi
--- doc/install.texi	8 Aug 2002 09:10:39 -0000	1.131
+++ doc/install.texi	9 Aug 2002 20:39:47 -0000
@@ -467,6 +467,43 @@ any in that directory---are not part of 
 programs---perhaps many others.  (GCC installs its own header files in
 another directory which is based on the @option{--prefix} value.)
 
+Both the local-prefix include directory and the GCC-prefix include
+directory are part of GCC's "system include" directories.  Although these
+two directories are not fixed, they need to be searched in the proper
+order for the correct processing of the include_next directive.  The
+local-prefix include directory is searched before the GCC-prefix
+include directory.  Another characteristic of system include directories
+is that pedantic warnings are turned off for headers in these directories.
+
+Some autoconf macros add @option{-I @var{directory}} options to the
+compiler command line, to ensure that directories containing installed
+packages' headers are searched.  When @var{directory} is one of GCC's
+system include directories, GCC will ignore the option so that system
+directories are continued to be processed in the correct order.  This
+may result in a search order different from what was specified but the
+directory will still be searched.
+
+GCC automatically searches for ordinary libraries using
+@env{GCC_EXEC_PREFIX}.  Thus, when the same installation prefix is
+used for both GCC and packages, GCC will automatically search for
+both headers and libraries.  This provides a configuration that is
+easy to use.  GCC behaves in a manner similar to that when it is
+installed as a system compiler in @file{/usr}.
+
+Sites that need to install multiple versions of GCC may not want to
+use the above simple configuration.  It is possible to use the
+@option{--program-prefix}, @option{--program-suffix} and
+@option{--program-transform-name} options to install multiple versions
+into a single directory, but it may be simpler to use different prefixes
+and the @option{--with-local-prefix} option to specify the location of the
+site-specific files for each version.  It will then be necessary for
+users to specify explicitly the location of local site libraries
+(e.g., with @env{LIBRARY_PATH}).
+
+The same value can be used for both @option{--with-local-prefix} and
+@option{--prefix} provided it is not @file{/usr}.  This can be used
+to avoid the default search of @file{/usr/local/include}.
+
 @strong{Do not} specify @file{/usr} as the @option{--with-local-prefix}!
 The directory you use for @option{--with-local-prefix} @strong{must not}
 contain any of the system's standard header files.  If it did contain