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Re: [PATCH] configure: warn if not using a separate build directory

From: BALATON Zoltan
Subject: Re: [PATCH] configure: warn if not using a separate build directory
Date: Tue, 31 Mar 2020 17:10:19 +0200 (CEST)
User-agent: Alpine 2.22 (BSF 395 2020-01-19)

On Tue, 31 Mar 2020, Eric Blake wrote:
On 3/31/20 5:37 AM, Daniel P. Berrangé wrote:
Running configure directly from the source directory is a build
configuration that will go away in future. It is also not currently
covered by any automated testing. Display a deprecation warning if
the user attempts to use an in-srcdir build setup, so that they are
aware that they're building QEMU in an undesirable manner.

Signed-off-by: Daniel P. Berrangé <address@hidden>
  configure | 30 ++++++++++++++++++++++++++++++
  1 file changed, 30 insertions(+)

It sounds like you already have a v2 coming up to address Phillipe's comments, but I'd be happy to see this concept make it into v5.0.

diff --git a/configure b/configure
index e225a1e3ff..1ab7492ab5 100755
--- a/configure
+++ b/configure
@@ -3,6 +3,19 @@
  # qemu configure script (c) 2003 Fabrice Bellard

Why fork out to 'pwd', when we can rely on $PWD for the same answer? Note that both $(pwd) and $PWD $BUILDDIR always give an absolute (but no necessarily canonical) path, which means...

+SRCDIR=$(dirname "$0")

...calling this ABS_BUILDDIR is a misnomer (it was already absolute). What it is really doing is chasing through symlinks to result in a canonical name, particularly since unless you have absolute names, using only string comparison to see if two filenames are equivalent will have false negatives (/tmp vs. /tmp/., for example).

+ABS_SRCDIR=$(realpath $SRCDIR)

Not robust if there are spaces in the directory names.  Safer would be
ABS_BUILDDIR=$(realpath -- "$BUILDDIR")
and similarly for ABS_SRCDIR.

+if [ "$ABS_SRCDIR" == "$ABS_BUILDDIR" ]

Bashism. You MUST spell this '=', not '==', since configure is run under /bin/sh which might be dash which does not understand ==.

+    in_srcdir=yes
  # Unset some variables known to interfere with behavior of common tools,
  # just as autoconf does.
@@ -6799,6 +6812,23 @@ if test "$supported_os" = "no"; then
      echo "us upstream at address@hidden."
  +if test "$in_srcdir" = "yes"; then
+    echo
+    echo
+    echo "Support for running the 'configure' script directly from the"
+    echo "source directory is deprecated and will go away in a future"
+    echo "release. In source dir builds are not covered by automated"
+    echo "testing and are liable to break without warning. Users are"
+    echo "strongly recommended to switch to a separate build directory:"
+    echo
+    echo "  $ mkdir build"
+    echo "  $ cd build"
+    echo "  $ ../configure"
+    echo "  $ make"
+    echo

You know, it WOULD be possible to further enhance this to actually create 'build' as well as a shim GNUmakefile that would auto-forward on to building directly in build, so that you maintain the illusion of an in-place build (other than all the build artifacts now living in a different location), and muscle memory for in-tree 'make' still works; I've posted elsewhere and will repeat here the contents of my GNUmakefile:

# Hack for redirecting while reminding myself to use distinct builddir
recurse: all
%: force
        @echo 'changing directory to build...'
        @sleep 2

Right, just drop all the 14 line warning above, this one line here should be enough to remind people (maybe reworded to say that build results are found there and move it after the $(MAKE) so it's printed last and drop the sleep 2 and this should work.


        @$(MAKE) -C build -f Makefile $(MAKECMDGOALS)
force: ;
.PHONY: force
GNUmakefile: ;

But we could do that as a patch on top of yours.

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