MSVC Build: Support VS2017 command line compiler tools

Teach the top-level git Makefile to use whatever VS compiler
tool chain is installed on the system.

When building git from the command line in a git-sdk BASH
window with MAKE, the shell environment has environment
variables for GCC tools, but not MSVC tools.  MSVC bindings
are only avaliable from the various "VcVarsAll.bat" scripts
run by the "Developer Command Prompt" shortcuts.

Add compat/vcbuild/find_vs_env.bat to the Makefile.  It
uses the various "VcVarsAll.bat" scripts in a background
Developer Command Prompt process to compute the proper
environment variables and publish them for use by the Makefile.

[jes: fixed typos, replaced C:\WINDOWS by %SystemRoot%]

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

.gitignore

@@ -1,6 +1,7 @@
 /GIT-BUILD-OPTIONS
 /GIT-CFLAGS
 /GIT-LDFLAGS
+/GIT-MSVC-GEN
 /GIT-PREFIX
 /GIT-PERL-DEFINES
 /GIT-PYTHON-VARS

Makefile

@@ -2715,6 +2715,7 @@ ifdef MSVC
 	$(RM) $(patsubst %.exe,%.pdb,$(OTHER_PROGRAMS))
 	$(RM) $(patsubst %.exe,%.pdb,$(PROGRAMS))
 	$(RM) $(patsubst %.exe,%.pdb,$(TEST_PROGRAMS))
+	$(RM) GIT-MSVC-GEN
 endif
 
 .PHONY: all install profile-clean clean strip

compat/vcbuild/find_vs_env.bat

@@ -0,0 +1,167 @@
+@ECHO OFF
+REM ================================================================
+REM You can use either GCC (the default) or MSVC to build git
+REM using the GIT-SDK command line tools.
+REM        $ make
+REM        $ make MSVC=1
+REM
+REM GIT-SDK BASH windows inherit environment variables with all of
+REM the bin/lib/include paths for GCC.  It DOES NOT inherit values
+REM for the corresponding MSVC tools.
+REM
+REM During normal (non-git) Windows development, you launch one
+REM of the provided "developer command prompts" to set environment
+REM variables for the MSVC tools.
+REM
+REM Therefore, to allow MSVC command line builds of git from BASH
+REM and MAKE, we must blend these two different worlds.  This script
+REM attempts to do that.
+REM ================================================================
+REM This BAT file starts in a plain (non-developer) command prompt,
+REM searches for the "best" commmand prompt setup script, installs
+REM it into the current CMD process, and exports the various MSVC
+REM environment variables for use by MAKE.
+REM
+REM The output of this script should be written to a make "include
+REM file" and referenced by the top-level Makefile.
+REM
+REM See "config.mak.uname" (look for GIT-MSVC-GEN).
+REM ================================================================
+REM The provided command prompts are custom to each VS release and
+REM filled with lots of internal knowledge (such as Registry settings);
+REM even their names vary by release, so it is not appropriate for us
+REM to look inside them.  Rather, just run them in a subordinate
+REM process and extract the settings we need.
+REM ================================================================
+REM
+REM Current (VS2017 and beyond)
+REM -------------------
+REM Visual Studio 2017 introduced a new installation layout and
+REM support for side-by-side installation of multiple versions of
+REM VS2017.  Furthermore, these can all coexist with installations
+REM of previous versions of VS (which have a completely different
+REM layout on disk).
+REM
+REM VS2017 Update 2 introduced a "vswhere.exe" command:
+REM https://github.com/Microsoft/vswhere
+REM https://blogs.msdn.microsoft.com/heaths/2017/02/25/vswhere-available/
+REM https://blogs.msdn.microsoft.com/vcblog/2017/03/06/finding-the-visual-c-compiler-tools-in-visual-studio-2017/
+REM
+REM VS2015
+REM ------
+REM Visual Studio 2015 uses the traditional VcVarsAll.
+REM
+REM Earlier Versions
+REM ----------------
+REM TODO
+REM
+REM ================================================================
+REM Note: Throughout this script we use "dir <path> && <cmd>" rather
+REM than "if exist <path>" because of script problems with pathnames
+REM containing spaces.
+REM ================================================================
+
+REM Sanitize PATH to prevent git-sdk paths from confusing "wmic.exe"
+REM (called internally in some of the system BAT files).
+SET PATH=%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;
+
+REM ================================================================
+
+:current
+   SET vs_where=C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe
+   dir "%vs_where%" >nul 2>nul && GOTO have_vs_where
+   GOTO not_2017
+
+:have_vs_where
+   REM Try to use VsWhere to get the location of VsDevCmd.
+
+   REM Keep VsDevCmd from cd'ing away.
+   SET VSCMD_START_DIR=.
+
+   REM Get the root of the VS product installation.
+   FOR /F "usebackq tokens=*" %%i IN (`"%vs_where%" -latest -requires Microsoft.VisualStudio.Workload.NativeDesktop -property installationPath`) DO @SET vs_ip=%%i
+
+   SET vs_devcmd=%vs_ip%\Common7\Tools\VsDevCmd.bat
+   dir "%vs_devcmd%" >nul 2>nul && GOTO have_vs_devcmd
+   GOTO not_2017
+
+:have_vs_devcmd
+   REM Use VsDevCmd to setup the environment of this process.
+   REM Setup CL for building 64-bit apps using 64-bit tools.
+   @call "%vs_devcmd%" -no_logo -arch=x64 -host_arch=x64
+
+   SET tgt=%VSCMD_ARG_TGT_ARCH%
+
+   SET mn=%VCToolsInstallDir%
+   SET msvc_includes=-I"%mn%INCLUDE"
+   SET msvc_libs=-L"%mn%lib\%tgt%"
+   SET msvc_bin_dir=%mn%bin\Host%VSCMD_ARG_HOST_ARCH%\%tgt%
+
+   SET sdk_dir=%WindowsSdkDir%
+   SET sdk_ver=%WindowsSDKVersion%
+   SET si=%sdk_dir%Include\%sdk_ver%
+   SET sdk_includes=-I"%si%ucrt" -I"%si%um" -I"%si%shared"
+   SET sl=%sdk_dir%lib\%sdk_ver%
+   SET sdk_libs=-L"%sl%ucrt\%tgt%" -L"%sl%um\%tgt%"
+
+   SET vs_ver=%VisualStudioVersion%
+
+   GOTO print_vars
+
+REM ================================================================
+
+:not_2017
+   REM See if VS2015 is installed.
+
+   SET vs_2015_bat=C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat
+   dir "%vs_2015_bat%" >nul 2>nul && GOTO have_vs_2015
+   GOTO not_2015
+
+:have_vs_2015
+   REM Use VcVarsAll like the "x64 Native" command prompt.
+   REM Setup CL for building 64-bit apps using 64-bit tools.
+   @call "%vs_2015_bat%" amd64
+
+   REM Note that in VS2015 they use "x64" in some contexts and "amd64" in others.
+   SET mn=C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\
+   SET msvc_includes=-I"%mn%INCLUDE"
+   SET msvc_libs=-L"%mn%lib\amd64"
+   SET msvc_bin_dir=%mn%bin\amd64
+
+   SET sdk_dir=%WindowsSdkDir%
+   SET sdk_ver=%WindowsSDKVersion%
+   SET si=%sdk_dir%Include\%sdk_ver%
+   SET sdk_includes=-I"%si%ucrt" -I"%si%um" -I"%si%shared" -I"%si%winrt"
+   SET sl=%sdk_dir%lib\%sdk_ver%
+   SET sdk_libs=-L"%sl%ucrt\x64" -L"%sl%um\x64"
+
+   SET vs_ver=%VisualStudioVersion%
+
+   GOTO print_vars
+
+REM ================================================================
+
+:not_2015
+   REM TODO....
+   echo TODO support older versions of VS.
+   EXIT /B 1
+
+REM ================================================================
+
+:print_vars
+   REM Dump the essential vars to stdout to allow the main
+   REM Makefile to include it.  See config.mak.uname.
+   REM Include DOS-style and BASH-style path for bin dir.
+
+   echo msvc_bin_dir=%msvc_bin_dir%
+   echo msvc_bin_dir_msys=%msvc_bin_dir:C:=/C%
+
+   echo msvc_includes=%msvc_includes%
+   echo msvc_libs=%msvc_libs%
+
+   echo sdk_includes=%sdk_includes%
+   echo sdk_libs=%sdk_libs%
+
+   echo vs_ver=%vs_ver%
+
+   EXIT /B 0

config.mak.uname

@@ -15,6 +15,12 @@ ifdef MSVC
 	# avoid the MingW and Cygwin configuration sections
 	uname_S := Windows
 	uname_O := Windows
+
+	# Generate and include makefile variables that point to the
+	# currently installed set of MSVC command line tools.
+GIT-MSVC-GEN: ./compat/vcbuild/find_vs_env.bat
+	@./compat/vcbuild/find_vs_env.bat | sed 's|\\|/|g' >GIT-MSVC-GEN
+-include GIT-MSVC-GEN
 endif
 
 # We choose to avoid "if .. else if .. else .. endif endif"
@@ -341,7 +347,7 @@ ifeq ($(uname_S),Windows)
 	# link.exe next to, and required by, cl.exe, we have to prepend this
 	# onto the existing $PATH.
 	#
-	SANE_TOOL_PATH ?= /c/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/amd64
+	SANE_TOOL_PATH ?= $(msvc_bin_dir_msys)
 	HAVE_ALLOCA_H = YesPlease
 	NO_PREAD = YesPlease
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
@@ -399,26 +405,12 @@ ifeq ($(uname_S),Windows)
 	lib =
 	# Path to the unpacked third-party libraries
 	MSVC_DEPS = compat/vcbuild/GEN.DEPS
-	# Compensate for lack of %VCINSTALLDIR%, %LIB%, %LIBPATH%, and etc.
-	# since vcvars*.bat did not get a chance to setup the environment of
-	# the user's shell window.
-	#
-	# TODO If we ask the user to launch a "x64 Native" command prompt
-	# TODO and then have it start a git-bash window, these could be
-	# TODO inherited.  So we wouldn't need to add these lines here.
-	#
-	MSVC_SDK81 = "c:/Program Files (x86)/Windows Kits/8.1"
-	MSVC_SDK10 = "c:/Program Files (x86)/Windows Kits/10"
-	MSVC_VCDIR = "c:/Program Files (x86)/Microsoft Visual Studio 14.0/VC"
 	BASIC_CFLAGS += \
 		     -I$(MSVC_DEPS)/include -I$(MSVC_DEPS)/include/expat -I$(MSVC_DEPS)/include/zlib \
 		     -L$(MSVC_DEPS)/lib \
-		     -I$(MSVC_SDK81)/Include/um -I$(MSVC_SDK81)/Include/shared \
-		     -L$(MSVC_SDK81)/lib/winv6.3/um/x64 \
-		     -I$(MSVC_SDK10)/Include/10.0.10240.0/ucrt \
-		     -L$(MSVC_SDK10)/lib/10.0.10240.0/ucrt/x64 \
-		     -I$(MSVC_VCDIR)/INCLUDE \
-		     -L$(MSVC_VCDIR)/lib/amd64
+		     $(sdk_includes) $(sdk_libs) \
+		     $(msvc_includes) $(msvc_libs)
+
 	# Optionally enable memory leak reporting.
 	# BASIC_CLFAGS += -DUSE_MSVC_CRTDBG
 	BASIC_CFLAGS += -DPROTECT_NTFS_DEFAULT=1