[PATCH 08/10] Makefile: skip git-gui if dir is missing

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

As an effort to promote "dogfooding" the sparse-checkout feature within
the Git codebase, it is helpful to explore which portions of the
codebase are optional.

The NO_TCLTK variable in the Makefile allows ignoring the git-gui
application at build time. If the local sparse-checkout removes that
directory, then the build will fail without manually defining that
variable. Instead, check to see if the directory exists at build time to
see if we can automatically ignore this directory.

With this change, the following list of directories can be supplied to
"git sparse-checkout set" and Git will build and test on Linux:

	Documentation
	builtin
	compat/.depend
	contrib
	ewah
	mergetools
	negotiator
	perl
	refs
	sha1dc
	sha256
	t
	templates
	trace2
	vcs-svn
	xdiff

The "make install" command requires the "gitweb" and "po" directories.
The "po" directory will become optional in the next change.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Makefile | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 2e8029b8026..70760d315cb 100644
--- a/Makefile
+++ b/Makefile
@@ -313,7 +313,8 @@ all::
 #
 # Define NO_PYTHON if you do not want Python scripts or libraries at all.
 #
-# Define NO_TCLTK if you do not want Tcl/Tk GUI.
+# Define NO_TCLTK if you do not want Tcl/Tk GUI. This will also be defined
+# if the git-gui directory is missing.
 #
 # Define SANE_TEXT_GREP to "-a" if you use recent versions of GNU grep
 # and egrep that are pickier when their input contains non-ASCII data.
@@ -1860,6 +1861,12 @@ ifeq ($(TCLTK_PATH),)
 NO_TCLTK = NoThanks
 endif
 
+ifndef NO_TCLTK
+	ifeq ($(ls git-gui),)
+		NO_TCLTK = NoThanks
+	endif
+endif
+
 ifeq ($(PERL_PATH),)
 NO_PERL = NoThanks
 endif
-- 
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