install: call git cmds in Makefile only if needed

Update Makefile to call git command only if the version.inc file needs
to get rebuilt (if it does not exist or if the git repository has been
updated after version.inc built).

Include version.inc file in main Makefile only if its variables have not
been just generated within Makefile flow.

Author: xdelaruelle

Makefile

@@ -78,10 +78,21 @@ endif
 
 # define rule prereq when target need to be rebuilt when git repository change
 ifeq ($(wildcard .git),.git)
-GIT_DIR := $(shell git rev-parse --git-dir)
-GIT_REFRESH_PREREQ := $(GIT_DIR)/index
+GIT_REFRESH_PREREQ := .git/objects
+
+# determine if version.inc needs to get updated as git repository has changed
+ifeq ($(wildcard version.inc), version.inc)
+MTIME_VERSION := $(shell date +%s -r version.inc)
+MTIME_GIT_REPO := $(shell date +%s -r $(GIT_REFRESH_PREREQ))
+REFRESH_VERSION_INC := $(shell if [ $(MTIME_GIT_REPO) -gt $(MTIME_VERSION) ]; \
+	then echo y; else echo n; fi)
 else
-GIT_REFRESH_PREREQ := 
+REFRESH_VERSION_INC := y
+endif
+
+else
+GIT_REFRESH_PREREQ :=
+REFRESH_VERSION_INC := n
 endif
 
 # setup summary echo rules unless silent mode set
@@ -109,6 +120,11 @@ pkgdoc: version.inc
 doc: version.inc
 	$(MAKE) --no-print-directory -C doc all
 
+# source version definitions if built and no need to get refreshed
+# skip calls to git command if this file is available
+ifeq ($(wildcard version.inc) $(REFRESH_VERSION_INC), version.inc n)
+-include version.inc
+else
 # build version.inc shared definitions from git repository info
 ifeq ($(wildcard .git) $(wildcard version.inc.in),.git version.inc.in)
 GIT_CURRENT_TAG := $(shell git describe --tags --abbrev=0)
@@ -155,6 +171,9 @@ MODULES_BUILD := +$(notdir $(lastword $(MODULES_BUILD_REFS)))-XX-g$(MODULES_BUIL
 endif
 endif
 endif
+# no need to include generated version.inc file as the MODULES_* variables
+# have just been computed
+endif
 
 # determine RPM release
 # use last release if we currently sat on tag, append build number to it elsewhere
@@ -349,11 +368,6 @@ Makefile.inc: ;
 version.inc: version.inc.in $(GIT_REFRESH_PREREQ)
 	$(translate-in-script)
 
-# source version definitions shared across the Makefiles of this project
-ifeq ($(findstring clean,$(MAKECMDGOALS)),)
--include version.inc
-endif
-
 contrib/rpm/environment-modules.spec: contrib/rpm/environment-modules.spec.in $(GIT_REFRESH_PREREQ)
 	$(translate-in-script)
 

NEWS.rst

@@ -30,6 +30,8 @@ Modules 5.1.1 (not yet released)
   (fix issue #460)
 * Install: include the ``lib/config.guess`` and ``lib/config.sub`` scripts in
   distribution tarball if generated by :command:`autoreconf`.
+* Install: call ``git`` command in ``Makefile`` only if the definitions of
+  ``version.inc`` need to get built or refreshed.
 
 
 Modules 5.1.0 (2022-04-30)