Add script to install files in the dist tarball.

Add a check inside Meson to detect if we're building from a git clone
or a dist tarball.
(in thie later, don't generated INSTALL.in and git-version.h)

meson.build

@@ -15,6 +15,11 @@ conf = configuration_data()
 
 warnings = []
 
+# git-version.h is already present and not generated if dist tarball
+is_dist_tarball = run_command('python', '-c',
+  'import sys,os; sys.exit(0 if os.path.exists("git-version.h") else 1)'
+).returncode() == 0
+
 ################################################################################
 # Project info
 
@@ -919,20 +924,20 @@ else
 
   if (not python_found) and (not always_install)
     error('''
-    Python @0@ or PyGObject was not found.
+    Python >=@0@ or PyGObject was not found.
     Note that you may install the Python plug-ins even if you have no Python
     interpreter at build-time by passing the configure option -Dpython=always.
-    Just make sure that a Python @0@ interpreter is available at run-time.
-    '''.format(python3_required_version))
+    Just make sure that a Python >=@0@ interpreter is available at run-time.
+    '''.format(python3_minver))
   endif
 
   if (not python_found) and (always_install)
     python_warning = '''
-    Python @0@ or PyGObject was not found.
+    Python >=@0@ or PyGObject was not found.
     Python plug-ins will be installed anyway but you should make sure that
     a compatible Python interpreter is available at installation, otherwise
     installed plug-ins won't be usable.
-    '''.format(python3_required_version)
+    '''.format(python3_minver)
     warning(python_warning)
     warnings += python_warning
   endif
@@ -1401,7 +1406,9 @@ endif
   #####   ####  #    # #      #  ####     #       # ###### ######  ####
 
 
-
+if is_dist_tarball
+  gitversion_h = files('git-version.h')
+else
   gitversion_h1 = vcs_tag(
     input : 'app/git-version.h.in',
     output: 'git-version.h.in.1',
@@ -1423,7 +1430,7 @@ gitversion_h = vcs_tag(
     replace_string: '@GIMP_GIT_LAST_COMMIT_YEAR@',
     fallback: '',
   )
-
+endif
 
 install_conf = configuration_data()
 install_conf.set('GIMP_APP_VERSION', gimp_app_version)
@@ -1460,11 +1467,13 @@ install_conf.set('WEBP_REQUIRED_VERSION',         webp_minver)
 install_conf.set('WMF_REQUIRED_VERSION',          wmf_minver)
 install_conf.set('XGETTEXT_REQUIRED_VERSION',     '0.19')
 
-configure_file(
+if not is_dist_tarball
+  INSTALL = configure_file(
     input : 'INSTALL.in',
     output: 'INSTALL',
     configuration: install_conf
   )
+endif
 
 
 configure_file(
@@ -1547,6 +1556,8 @@ custom_target('Changelog',
   build_by_default: false,
 )
 
+meson.add_dist_script('meson_dist_script.sh')
+
 
 ################################################################################
 # Subdirs

meson_dist_script.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+cp -f 'INSTALL' "${MESON_DIST_ROOT}"
+# rm -f "${MESON_DIST_ROOT}/INSTALL.in"
+
+cp 'git-version.h' "${MESON_DIST_ROOT}"