[RFA] make missing header a fatal error with -MMD

[Chris Demetriou <cgd at google dot com>]

This fixes a the long-open bug http://gcc.gnu.org/PR28435, in which
-MMD allows compilation to succeed even though a header was missing.
(.o file produced, and everything.  yuck.)

bootstrapped on x86_64-linux (Ubuntu Hardy) system @ rev 151627.

Tested:
Dropped the new tests into an existing source tree at the same rev.
bootstrapped, tested with make -j3 check -k
RUNTESTFLAGS="--target_board 'unix{-m32,-m64}'" from top-level.
Applied patch to a new tree, bootstrapped, ran the tests.

In the unmodified source tree, the new test
gcc.dg/cpp/missing-sysheader-MMD.c fails.  (The other new tests pass,
as expected).
In the modified source tree, all of the new tests pass.  All of the
other test results were identical.



chris
----
[libcpp/ChangeLog]
2009-09-10  Chris Demetriou  <cgd@google.com>

        PR preprocessor/28435:
        * include/cpplib.h (struct cpp_options): Add new member
        deps.need_preprocessor_output.
        * files.c (open_file_failed): If preprocessor output is needed
        always report an error.

[gcc/ChangeLog]
2009-09-10  Chris Demetriou  <cgd@google.com>

        PR preprocessor/28435:
        * c-opts.c (c_common_handle_option): For -MD and -MMD, indicate
        to cpplib that the preprocessor output is needed.

[gcc/testsuite/ChangeLog]
2009-09-10  Chris Demetriou  <cgd@google.com>

        PR preprocessor/28435:
        * gcc.dg/cpp/missing-header-MD.c: New test.
        * gcc.dg/cpp/missing-header-MMD.c: New test.
        * gcc.dg/cpp/missing-sysheader-MD.c: New test.
        * gcc.dg/cpp/missing-sysheader-MMD.c: New test.

[libcpp/ChangeLog]
2009-09-10  Chris Demetriou  <cgd@google.com>

	PR preprocessor/28435:
	* include/cpplib.h (struct cpp_options): Add new member
	deps.need_preprocessor_output.
	* files.c (open_file_failed): If preprocessor output is needed
	always report an error.

[gcc/ChangeLog]
2009-09-10  Chris Demetriou  <cgd@google.com>

	PR preprocessor/28435:
	* c-opts.c (c_common_handle_option): For -MD and -MMD, indicate
	to cpplib that the preprocessor output is needed.

[gcc/testsuite/ChangeLog]
2009-09-10  Chris Demetriou  <cgd@google.com>

	PR preprocessor/28435:
	* gcc.dg/cpp/missing-header-MD.c: New test.
	* gcc.dg/cpp/missing-header-MMD.c: New test.
	* gcc.dg/cpp/missing-sysheader-MD.c: New test.
	* gcc.dg/cpp/missing-sysheader-MMD.c: New test.

Index: gcc/testsuite/gcc.dg/cpp/missing-header-MD.c
===================================================================
--- gcc/testsuite/gcc.dg/cpp/missing-header-MD.c	(revision 0)
+++ gcc/testsuite/gcc.dg/cpp/missing-header-MD.c	(revision 0)
@@ -0,0 +1,6 @@
+/* Test that missing user headers are fatal errors with -MD.  */
+/* { dg-do compile } */
+/* { dg-options "-MD" } */
+
+#include "nonexistent.h" /* { dg-error "nonexistent.h" } */
+/* { dg-message "terminated" "" { target *-*-* } 0 } */
Index: gcc/testsuite/gcc.dg/cpp/missing-header-MMD.c
===================================================================
--- gcc/testsuite/gcc.dg/cpp/missing-header-MMD.c	(revision 0)
+++ gcc/testsuite/gcc.dg/cpp/missing-header-MMD.c	(revision 0)
@@ -0,0 +1,6 @@
+/* Test that missing user headers are fatal errors with -MMD.  */
+/* { dg-do compile } */
+/* { dg-options "-MMD" } */
+
+#include "nonexistent.h" /* { dg-error "nonexistent.h" } */
+/* { dg-message "terminated" "" { target *-*-* } 0 } */
Index: gcc/testsuite/gcc.dg/cpp/missing-sysheader-MD.c
===================================================================
--- gcc/testsuite/gcc.dg/cpp/missing-sysheader-MD.c	(revision 0)
+++ gcc/testsuite/gcc.dg/cpp/missing-sysheader-MD.c	(revision 0)
@@ -0,0 +1,6 @@
+/* Test that missing system headers are fatal errors with -MD.  */
+/* { dg-do compile } */
+/* { dg-options "-MD" } */
+
+#include <nonexistent.h> /* { dg-error "nonexistent.h" } */
+/* { dg-message "terminated" "" { target *-*-* } 0 } */
Index: gcc/testsuite/gcc.dg/cpp/missing-sysheader-MMD.c
===================================================================
--- gcc/testsuite/gcc.dg/cpp/missing-sysheader-MMD.c	(revision 0)
+++ gcc/testsuite/gcc.dg/cpp/missing-sysheader-MMD.c	(revision 0)
@@ -0,0 +1,6 @@
+/* Test that missing system headers are fatal errors with -MMD.  */
+/* { dg-do compile } */
+/* { dg-options "-MMD" } */
+
+#include <nonexistent.h> /* { dg-error "nonexistent.h" } */
+/* { dg-message "terminated" "" { target *-*-* } 0 } */
Index: gcc/c-opts.c
===================================================================
--- gcc/c-opts.c	(revision 151627)
+++ gcc/c-opts.c	(working copy)
@@ -343,6 +343,7 @@ c_common_handle_option (size_t scode, const char *
     case OPT_MD:
     case OPT_MMD:
       cpp_opts->deps.style = (code == OPT_MD ? DEPS_SYSTEM: DEPS_USER);
+      cpp_opts->deps.need_preprocessor_output = true;
       deps_file = arg;
       break;
 
Index: libcpp/files.c
===================================================================
--- libcpp/files.c	(revision 151627)
+++ libcpp/files.c	(working copy)
@@ -935,15 +935,28 @@ open_file_failed (cpp_reader *pfile, _cpp_file *fi
 
   errno = file->err_no;
   if (print_dep && CPP_OPTION (pfile, deps.missing_files) && errno == ENOENT)
-    deps_add_dep (pfile->deps, file->name);
+    {
+      deps_add_dep (pfile->deps, file->name);
+      /* If the preprocessor output (other than dependency information) is
+         being used, we must also flag an error.  */
+      if (CPP_OPTION (pfile, deps.need_preprocessor_output))
+	cpp_errno (pfile, CPP_DL_FATAL, file->path);
+    }
   else
     {
-      /* If we are outputting dependencies but not for this file then
-	 don't error because we can still produce correct output.  */
-      if (CPP_OPTION (pfile, deps.style) && ! print_dep)
+      /* If we are not outputting dependencies, or if we are and dependencies
+         were requested for this file, or if preprocessor output is needed
+         in addition to dependency information, this is an error.
+
+         Otherwise (outputting dependencies but not for this file, and not
+         using the preprocessor output), we can still produce correct output
+         so it's only a warning.  */
+      if (CPP_OPTION (pfile, deps.style) == DEPS_NONE
+          || print_dep
+          || CPP_OPTION (pfile, deps.need_preprocessor_output))
+	cpp_errno (pfile, CPP_DL_FATAL, file->path);
+      else
 	cpp_errno (pfile, CPP_DL_WARNING, file->path);
-      else
-	cpp_errno (pfile, CPP_DL_FATAL, file->path);
     }
 }
 
Index: libcpp/include/cpplib.h
===================================================================
--- libcpp/include/cpplib.h	(revision 151627)
+++ libcpp/include/cpplib.h	(working copy)
@@ -433,6 +433,10 @@ struct cpp_options
 
     /* If true, no dependency is generated on the main file.  */
     bool ignore_main_file;
+
+    /* If true, intend to use the preprocessor output (e.g., for compilation)
+       in addition to the dependency info.  */
+    bool need_preprocessor_output;
   } deps;
 
   /* Target-specific features set by the front end or client.  */