Re: Possible patch for autoconf?

[Akim Demaille]

>>>>> "Daniel" == Daniel Carroll <address@hidden> writes:

Daniel> After thinking about it some more, I believe that the outer
Daniel> _AC_PREPROC_IFELSE is going down the "else" codepath (which
Daniel> calls "m4_default([$2], :)"), because it considers the
Daniel> AC_LANG_SOURCE(address@hidden:@include <assert.h> Syntax error]])
Daniel> construct to have failed for "cc -E" (because $ac_cpp_err is
Daniel> set to "maybe").

Hm...  Indeed.  Then maybe (how this word sounds bad...) it simply
means the `maybe' assignment was badly placed?

Well, this code is too complex.  We struggle too much with it, let's
rewrite it completely.  What do you people think about this?

# _AC_PROG_PREPROC_WORKS_IFELSE(IF-WORKS, IF-NOT)
# -----------------------------------------------
# Check if $ac_cpp is a working preprocessor that can flag absent
# includes either by the exit status or by warnings.
# Set ac_cpp_err to a non-empty value if the preprocessor failed.
# This macro is for all languages, not only C.
AC_DEFUN([_AC_PROG_PREPROC_WORKS_IFELSE],
[ac_preproc_ok=false
for ac_[]_AC_LANG_ABBREV[]_preproc_warn_flag in '' yes
do
  # Use a header file that comes with gcc, so configuring glibc
  # with a fresh cross-compiler works.
  # On the NeXT, cc -E runs the code through the compiler's parser,
  # not just through cpp. "Syntax error" is here to catch this case.
  _AC_PREPROC_IFELSE([AC_LANG_SOURCE(address@hidden:@include <assert.h>
                     Syntax error]])],
                     [],
                     [# Broken: fails on valid input.
continue])

  # OK, works on sane cases.  Now check whether non-existent headers
  # can be detected and how.
  _AC_PREPROC_IFELSE([AC_LANG_SOURCE(address@hidden:@include 
<ac_nonexistent.h>]])],
                     [# Broken: success on invalid input.
continue],
                     [# Passes both tests.
ac_preproc_ok=:
break])

done
# Because of `break', _AC_PREPROC_IFELSE's cleaning code was skipped.
rm -f conftest.err conftest.$ac_ext
AS_IF([$ac_preproc_ok], [$1], [$2])])# _AC_PROG_PREPROC_WORKS_IFELSE




Index: aclang.m4
===================================================================
RCS file: /cvs/autoconf/aclang.m4,v
retrieving revision 1.127
diff -u -u -r1.127 aclang.m4
--- aclang.m4 2001/04/27 13:32:52 1.127
+++ aclang.m4 2001/05/10 17:18:01
@@ -832,30 +832,33 @@
 # Set ac_cpp_err to a non-empty value if the preprocessor failed.
 # This macro is for all languages, not only C.
 AC_DEFUN([_AC_PROG_PREPROC_WORKS_IFELSE],
-[# We don't know yet if stderr is the criterion (vs exit status).
-ac_[]_AC_LANG_ABBREV[]_preproc_warn_flag=maybe
+[ac_preproc_ok=false
+for ac_[]_AC_LANG_ABBREV[]_preproc_warn_flag in '' yes
+do
+  # Use a header file that comes with gcc, so configuring glibc
+  # with a fresh cross-compiler works.
+  # On the NeXT, cc -E runs the code through the compiler's parser,
+  # not just through cpp. "Syntax error" is here to catch this case.
+  _AC_PREPROC_IFELSE([AC_LANG_SOURCE(address@hidden:@include <assert.h>
+                     Syntax error]])],
+                     [],
+                     [# Broken: fails on valid input.
+continue])
+
+  # OK, works on sane cases.  Now check whether non-existent headers
+  # can be detected and how.
+  _AC_PREPROC_IFELSE([AC_LANG_SOURCE(address@hidden:@include 
<ac_nonexistent.h>]])],
+                     [# Broken: success on invalid input.
+continue],
+                     [# Passes both tests.
+ac_preproc_ok=:
+break])
+
+done
+# Because of `break', _AC_PREPROC_IFELSE's cleaning code was skipped.
+rm -f conftest.err conftest.$ac_ext
+AS_IF([$ac_preproc_ok], [$1], [$2])])# _AC_PROG_PREPROC_WORKS_IFELSE
 
-# Use a header file that comes with gcc, so configuring glibc
-# with a fresh cross-compiler works.
-# On the NeXT, cc -E runs the code through the compiler's parser,
-# not just through cpp. "Syntax error" is here to catch this case.
-_AC_PREPROC_IFELSE([AC_LANG_SOURCE(address@hidden:@include <assert.h>
-Syntax error]])],
-[# OK, works on sane cases.  Now check whether non-existent headers can
-# be detected and how.
-_AC_PREPROC_IFELSE([AC_LANG_SOURCE(address@hidden:@include 
<ac_nonexistent.h>]])],
-[# Broken: cannot detect missing includes.
-m4_default([$2], :)],
-[# OK, detects failures.  How?
-if test "x$ac_cpp_err" = xmaybe; then
-   ac_[]_AC_LANG_ABBREV[]_preproc_warn_flag=yes
-else
-   ac_[]_AC_LANG_ABBREV[]_preproc_warn_flag=
-fi
-$1])],
-                  [# Broken: fails on valid input.
-m4_default([$2], :)])])# _AC_PROG_PREPROC_WORKS_IFELSE
-
 
 # AC_PROG_CPP
 # -----------
@@ -878,7 +881,8 @@
     # Double quotes because CPP needs to be expanded
     for CPP in "$CC -E" "$CC -E -traditional-cpp" "/lib/cpp"
     do
-      _AC_PROG_PREPROC_WORKS_IFELSE([break])
+      # break 2 since there is a loop in there.
+      _AC_PROG_PREPROC_WORKS_IFELSE([break 2])
     done
     ac_cv_prog_CPP=$CPP
   ])dnl
@@ -1085,7 +1089,8 @@
     # Double quotes because CXXCPP needs to be expanded
     for CXXCPP in "$CXX -E" "/lib/cpp"
     do
-      _AC_PROG_PREPROC_WORKS_IFELSE([break])
+      # break 2 since there is a loop in there.
+      _AC_PROG_PREPROC_WORKS_IFELSE([break 2])
     done
     ac_cv_prog_CXXCPP=$CXXCPP
   ])dnl
Index: tests/compile.at
===================================================================
RCS file: /cvs/autoconf/tests/compile.at,v
retrieving revision 1.19
diff -u -u -r1.19 compile.at
--- tests/compile.at 2001/05/10 15:41:18 1.19
+++ tests/compile.at 2001/05/10 17:18:02
@@ -171,6 +171,7 @@
 # Ignore if /lib/cpp doesn't work
 AT_CHECK([/lib/cpp </dev/null || exit 77], [], [ignore], [ignore])
 
+# A cpp which exit status is meaningless.
 AT_DATA([mycpp],
 [[#! /bin/sh
 /lib/cpp ${1+"$@"}
@@ -212,30 +213,27 @@
 echo "Annoying copyright message" >&2
 if test "$1" != "-E"; then
   exec cc $*
+elif test "$2" = "-traditional-cpp"; then
+  exec cc $*
 else
-  if test "$2" = "-traditional-cpp"; then
-    exec cc $*
-  else
-    exec /lib/cpp ${1+"$@"}
-  fi
+  exec /lib/cpp ${1+"$@"}
 fi
 ]])
 
 chmod +x mycc
 
+# We go through the following contortions, in order to have the
+# configure script go down the same codepaths as it would during a
+# normal CPP selection check.  If we explicitly set CPP, it goes down
+# a different codepath.
 _AT_CHECK_AC_MACRO(
-[[# We go through the following contortions, in order to
-#   have the configure script go down the same codepaths
-#   as it would during a normal CPP selection check.  If
-#   we explicitly set CPP, it goes down a different codepath.
-CC=mycc
+[[CC=./mycc
 AC_PROG_CPP
 # The test $CC compiler should have been selected.
-test "$CPP" != "mycc -E" &&
+test "$CPP" != "$CC -E" &&
   AC_MSG_ERROR([error messages on stderr cause the preprocessor selection to 
fail])
-# If the preprocessor is not strict, just ignore
-test "x$ac_c_preproc_warn_flag" = xyes &&
-  AC_MSG_ERROR([preprocessor has no warning option], 77)
+
+# Exercise CPP.
 AC_CHECK_HEADERS(stdio.h autoconf_io.h)]])
 
 AT_CHECK_DEFINES(







Note there is still a problem with the test suite itself: we should
_not_ run cc like this.  At least we should AC_PROG_CC to find the $CC
to pass to mycc, just as for the CPP test.  Left as an exercise :)