[gimp] m4macros, configure: add and use AM_PYTHON_CHECK_PYGOBJECT() macro.

[Jehan <jehanp src gnome org>]

commit b1662443afbaa0ff6a9d200d346945087eefdf80
Author: Jehan <jehan girinstud io>
Date:   Fri Aug 9 18:05:09 2019 +0200

    m4macros, configure: add and use AM_PYTHON_CHECK_PYGOBJECT() macro.
    
    Rather than looking for pygobject-3.0 with pkg-config, run an actual
    test in python, loading the 'gi' module.
    I also added a version parameter making it possible to even check for a
    required version of PyGObject, though it is currently unused (as I have
    no idea if we have a minimum requirement for our plug-ins to work well).
    
    This is an improvement of commit 8e938e0960 as I realized that we don't
    need any development files, therefore I don't think that searching with
    pkg-config was the right idea in our case.

 configure.ac           | 26 ++++++++++++++------------
 m4macros/python3dev.m4 | 14 ++++++++++++++
 2 files changed, 28 insertions(+), 12 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 410bd86455..2263abd16f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2267,14 +2267,15 @@ elif test "x$with_python" = xforce; then
   with_python="yes"
   warning_python=
   AM_PATH_PYTHON3(python3_required_version, ,
-                  warning_python="Python python3_required_version or newer not found
-")
-  PKG_CHECK_MODULES(PYGOBJECT, pygobject-3.0, ,
-                    warning_python="PyGObject 3.0 not found
-$warning_python")
+                  warning_python="Python python3_required_version or newer not found")
+  if test "x$warning_python" = "x"; then
+    AM_PYTHON_CHECK_PYGOBJECT("$PYTHON", , ,
+                              warning_python="PyGObject 3.0 not found")
+  fi
   if test "x$warning_python" != "x"; then
     warning_python="
-WARNING: ${warning_python}         Python plug-ins will be installed anyway but you should make
+WARNING: ${warning_python}
+         Python plug-ins will be installed anyway but you should make
          sure that a compatible Python interpreter and PyGObject are
          available at installation, otherwise installed plug-ins won't
          be usable."
@@ -2284,14 +2285,15 @@ else
   with_python="yes"
   error_python=
   AM_PATH_PYTHON3(python3_required_version,,
-                  error_python="- Python python3_required_version or newer not found
-")
-  PKG_CHECK_MODULES(PYGOBJECT, pygobject-3.0, ,
-                    error_python="- PyGObject 3.0 not found
-$error_python")
+                  error_python="- Python python3_required_version or newer not found")
+  if test "x$error_python" = "x"; then
+    AM_PYTHON_CHECK_PYGOBJECT("$PYTHON", , ,
+                              error_python="PyGObject 3.0 not found")
+  fi
   if test "x$error_python" != "x"; then
     required_deps="$required_deps
-    $error_python        *** Please install Python 3 and PyGObject 3.
+    $error_python
+        *** Please install Python 3 and PyGObject 3.
         *** Note that you may install the Python plug-ins even if you have
         *** no Python interpreter at build-time by passing the configure
         *** option --with-python=force.
diff --git a/m4macros/python3dev.m4 b/m4macros/python3dev.m4
index bec231b166..44e0aff9cc 100644
--- a/m4macros/python3dev.m4
+++ b/m4macros/python3dev.m4
@@ -181,6 +181,20 @@ AC_DEFUN([AM_PATH_PYTHON3],
 ])
 
 
+# AM_PYTHON_CHECK_PYGOBJECT(PROG, VERSION, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
+# ---------------------------------------------------------------------------
+# Run ACTION-IF-TRUE if PyGObject is present and at least VERSION.
+# Run ACTION-IF-FALSE otherwise.
+# This supports any version of Python.
+AC_DEFUN([AM_PYTHON_CHECK_PYGOBJECT],
+ [prog="import sys, gi
+version = '3.0'
+if '$2' != '':
+  version = '$2'
+sys.exit(gi.check_version(version))"
+  AS_IF([AM_RUN_LOG([$1 -c "$prog"])], [$3], [$4])])
+
+
 # AM_PYTHON3_CHECK_VERSION(PROG, VERSION, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
 # ---------------------------------------------------------------------------
 # Run ACTION-IF-TRUE if the Python interpreter PROG has version >= VERSION