Makefile: extract script to massage Python scripts

Extract a script that massages Python scripts. This provides a couple of
benefits:

  - The build logic is deduplicated across Make, CMake and Meson.

  - CMake learns to rewrite scripts as-needed at build time instead of
    only writing them at configure time.

Furthermore, we will use this script when introducing Meson to
deduplicate the logic across build systems.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

Makefile

@@ -2635,13 +2635,9 @@ endif # NO_PERL
 $(SCRIPT_PYTHON_GEN): GIT-BUILD-OPTIONS
 
 ifndef NO_PYTHON
-$(SCRIPT_PYTHON_GEN): GIT-CFLAGS GIT-PREFIX GIT-PYTHON-VARS
+$(SCRIPT_PYTHON_GEN): generate-python.sh
 $(SCRIPT_PYTHON_GEN): % : %.py
-	$(QUIET_GEN) \
-	sed -e '1s|#!.*python|#!$(PYTHON_PATH_SQ)|' \
-	    $< >$@+ && \
-	chmod +x $@+ && \
-	mv $@+ $@
+	$(QUIET_GEN)$(SHELL_PATH) generate-python.sh ./GIT-BUILD-OPTIONS "$<" "$@"
 else # NO_PYTHON
 $(SCRIPT_PYTHON_GEN): % : unimplemented.sh
 	$(QUIET_GEN) \

contrib/buildsystems/CMakeLists.txt

@@ -899,10 +899,17 @@ foreach(script ${git_perl_scripts} ${perl_modules})
 endforeach()
 add_custom_target(perl-gen ALL DEPENDS ${perl_gen})
 
-#python script
-file(STRINGS ${CMAKE_SOURCE_DIR}/git-p4.py content NEWLINE_CONSUME)
-string(REPLACE "#!/usr/bin/env python" "#!/usr/bin/python" content "${content}")
-file(WRITE ${CMAKE_BINARY_DIR}/git-p4 ${content})
+# Python script
+add_custom_command(OUTPUT "${CMAKE_BINARY_DIR}/git-p4"
+	COMMAND "${SH_EXE}" "${CMAKE_SOURCE_DIR}/generate-python.sh"
+		"${CMAKE_BINARY_DIR}/GIT-BUILD-OPTIONS"
+		"${CMAKE_SOURCE_DIR}/git-p4.py"
+		"${CMAKE_BINARY_DIR}/git-p4"
+	DEPENDS "${CMAKE_SOURCE_DIR}/generate-python.sh"
+		"${CMAKE_SOURCE_DIR}/git-p4.py"
+		"${CMAKE_BINARY_DIR}/GIT-BUILD-OPTIONS"
+	VERBATIM)
+add_custom_target(python-gen ALL DEPENDS "${CMAKE_BINARY_DIR}/git-p4")
 
 #templates
 file(GLOB templates "${CMAKE_SOURCE_DIR}/templates/*")

generate-python.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+set -e
+
+if test $# -ne 3
+then
+	echo >&2 "USAGE: $0 <GIT_BUILD_OPTIONS> <INPUT> <OUTPUT>"
+	exit 1
+fi
+
+GIT_BUILD_OPTIONS="$1"
+INPUT="$2"
+OUTPUT="$3"
+
+. "$GIT_BUILD_OPTIONS"
+
+sed -e "1s|#!.*python|#!$PYTHON_PATH|" \
+    "$INPUT" >"$OUTPUT+"
+chmod a+x "$OUTPUT+"
+mv "$OUTPUT+" "$OUTPUT"