[RFA/gdb-9-branch] Abort configure immediately if building GDB in tree

[Joel Brobecker <brobecker@adacore.com>]

Hello,

Following the discussions on the gdb@ mailing-list regarding
the fact that GDB 9 is not buildable when configured in tree,
I propose the following patch for the gdb-9-branch. Ideally,
I would have liked to propose it for both master and gdb-9-branch,
but I think toplevel configure is supposed to be coordinated
between GCC and ourselves. Looking at this patch, I don't think
it's necessary, since we hope to lift that limitation at some
point.

---------------------------------------------------------------------------

The move of gnulib to the toplevel directory is causing the GDB build
to break if configured in tree. We hope to lift that limitation at
some point but, in the meantime, this commit allows us to abort
the initial configure right away with a clear error message should
the user attempt to build in tree.

ChangeLog:

        * configure.ac: Abort the build with an error if trying to build
        GDB in tree.
        * configure: Regenerate.

Tested by running the configure script with no argument, --enable-gdb,
and --disable-gdb; from both the toplevel source directory as well
as from other directories.

OK to push to gdb-9-branch?

Thanks,
-- 
Joel

---
 configure    | 9 +++++++++
 configure.ac | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/configure b/configure
index 6a9719f6091..6273a6a4055 100755
--- a/configure
+++ b/configure
@@ -2279,6 +2279,15 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+if test x"${enable_gdb}" != x"no"; then
+  # For this branch, we do not support building GDB in-tree.
+  # Try to detect whether we are in this situation or not by
+  # searching for a couple of known files in the source directory.
+  if test -f gnulib/update-gnulib.sh -a -f gdb/ChangeLog; then
+    as_fn_error $? "GDB must be configured and built in a directory separate from its sources" "$LINENO" 5
+  fi
+fi
+
 progname=$0
 # if PWD already has a value, it is probably wrong.
 if test -n "$PWD" ; then PWD=`${PWDCMD-pwd}`; fi
diff --git a/configure.ac b/configure.ac
index 7433badc217..25b3392da9a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -33,6 +33,15 @@ m4_include([config/isl.m4])
 AC_INIT(move-if-change)
 AC_DISABLE_OPTION_CHECKING
 
+if test x"${enable_gdb}" != x"no"; then
+  # For this branch, we do not support building GDB in-tree.
+  # Try to detect whether we are in this situation or not by
+  # searching for a couple of known files in the source directory.
+  if test -f gnulib/update-gnulib.sh -a -f gdb/ChangeLog; then
+    AC_MSG_ERROR([GDB must be configured and built in a directory separate from its sources])
+  fi
+fi
+
 progname=$0
 # if PWD already has a value, it is probably wrong.
 if test -n "$PWD" ; then PWD=`${PWDCMD-pwd}`; fi
-- 
2.17.1