Support cross-compiling and testing in WSL

CONTRIBUTING.md

@@ -85,6 +85,65 @@ CMake, either by letting Visual Studio configure it automatically (simply open G
 top-level directory via `File>Open>Folder...`) or by (downloading and) running
 [CMake](https://cmake.org) manually.
 
+## Building and testing in Windows Subsystem for Linux ("WSL")
+
+Install the Linux packages `gcc-mingw-w64-x86-64` and
+`libz-mingw-w64-dev`. From the source directory in Linux Bash:
+
+```bash
+cross=x86_64-w64-mingw32
+MSYSTEM=MINGW64 make -j"$(nproc)" uname_S=MINGW \
+	CC="$cross-gcc" AR="$cross-ar" RC="$cross-windres -O coff" \
+	MINGW_CHOST="$cross" NO_CURL=1 NO_GETTEXT=1 \
+	NO_ICONV=1 NO_OPENSSL=1 NO_PERL=1 NO_PYTHON=1 \
+	NO_RUST=1 NO_TCLTK=1 USE_LIBPCRE=
+```
+
+Prefer WSL Bash for speed. Use SDK Bash for Windows-specific prerequisites,
+MSYS path handling or integrations such as `git svn` with Perl/SVN enabled.
+
+### Run tests with WSL Bash
+
+Install the Git for Windows SDK before testing.
+
+```bash
+sdk=/mnt/d/git-sdk-64
+script=t0014-alias.sh
+zlib=/usr/$cross/lib
+ssp=$(dirname "$("$cross-gcc" -print-file-name=libssp-0.dll)")
+output=$(mktemp -d)
+(
+	export MSYSTEM=MINGW64 GIT_TEST_WSL=1
+	export TEST_OUTPUT_DIRECTORY="$output"
+	export PATH="$ssp:$zlib:$sdk/mingw64/bin:$sdk/usr/bin:$PATH"
+	export Path="$PATH"
+	export WSLENV=MSYSTEM:Path/pl
+	# -V will write the detailed output to t/test-results/<test>.out
+	cd t && time bash "$script" -iVx
+)
+```
+
+Use `Path/pl`, not `PATH/pl`, to avoid duplicate Windows path entries.
+
+### Run tests with Git SDK Bash
+
+```bash
+# MSYS2 `mkdir` cannot create directories in UNC paths; use $env:Temp
+scratch=$(wslpath -u "$("$sdk/usr/bin/cygpath.exe" -m /tmp)")
+output=$(mktemp -d -p "$scratch")
+runtime="$(wslpath -m "$ssp"):$(wslpath -m "$zlib")"
+
+(
+	cd t &&
+	time "$sdk/usr/bin/env.exe" MSYSTEM=MINGW64 \
+		"PATH=$runtime:/mingw64/bin:/usr/bin" \
+		"TEST_OUTPUT_DIRECTORY=$(wslpath -m "$output")" \
+		"GIT_TEST_TEMPLATE_DIR=$(wslpath -m "$PWD/../templates/blt")" \
+		"$(wslpath -m "$sdk")/usr/bin/bash.exe" \
+		"$script" -iVx --no-bin-wrappers
+)
+```
+
 What to Change?
 ---------------
 

GIT-BUILD-OPTIONS.in

@@ -16,7 +16,7 @@ GIT_TEST_GITPERLLIB=@GIT_TEST_GITPERLLIB@
 GIT_TEST_INDEX_VERSION=@GIT_TEST_INDEX_VERSION@
 GIT_TEST_OPTS=@GIT_TEST_OPTS@
 GIT_TEST_PERL_FATAL_WARNINGS=@GIT_TEST_PERL_FATAL_WARNINGS@
-GIT_TEST_TEMPLATE_DIR=@GIT_TEST_TEMPLATE_DIR@
+GIT_TEST_TEMPLATE_DIR=${GIT_TEST_TEMPLATE_DIR:-@GIT_TEST_TEMPLATE_DIR@}
 GIT_TEST_TEXTDOMAINDIR=@GIT_TEST_TEXTDOMAINDIR@
 GIT_TEST_UTF8_LOCALE=@GIT_TEST_UTF8_LOCALE@
 LOCALEDIR=@LOCALEDIR@

bin-wrappers/wrap-for-bin.sh

@@ -21,6 +21,26 @@ PATH='@BUILD_DIR@/bin-wrappers:'"$PATH"
 
 export MERGE_TOOLS_DIR GIT_EXEC_PATH GITPERLLIB PATH GIT_TEXTDOMAINDIR
 
+if test "$GIT_TEST_WSL" = 1
+then
+	export Path="$PATH"
+	if test -n "$TEST_OUTPUT_DIRECTORY"
+	then
+		safe=$(wslpath -m "$TEST_OUTPUT_DIRECTORY") || exit
+		safe=$(printf '%s' "$safe" | sed "s/'/'\\\\''/g") || exit
+		params="${GIT_CONFIG_PARAMETERS:+$GIT_CONFIG_PARAMETERS }"
+		export GIT_CONFIG_PARAMETERS="$params'safe.directory'='$safe/*'"
+	fi
+	WSLENV="$WSLENV:HOME/p:GITPERLLIB/pl:LANG:LC_ALL:TZ:TERM"
+	WSLENV="$WSLENV:EDITOR:PAGER:COLUMNS:$(env -0 | sed -zE '
+		/^(TEST|GIT)_/!d
+		s/=.*//
+		s/^GIT_(EXEC_PATH|TEMPLATE_DIR|TEXTDOMAINDIR)$/&\/p/
+		s/^GIT_CEILING_DIRECTORIES$/&\/pl/
+	' | tr '\0' :)"
+	export WSLENV
+fi
+
 case "$GIT_DEBUGGER" in
 '')
 	exec "@PROG@" "$@"

t/README

@@ -356,6 +356,14 @@ that cannot be easily covered by a few specific test cases. These
 could be enabled by running the test suite with correct GIT_TEST_
 environment set.
 
+GIT_TEST_TEMPLATE_DIR=<path> overrides the generated location of the
+templates used by the tests.
+
+GIT_TEST_WSL=1 forwards the test environment when the generated wrappers
+run Windows executables from WSL. It also grants a command-scope
+safe.directory exception for repositories under TEST_OUTPUT_DIRECTORY.
+See CONTRIBUTING.md for the cross-build and runner setup.
+
 GIT_TEST_FAIL_PREREQS=<boolean> fails all prerequisites. This is
 useful for discovering issues with the tests where say a later test
 implicitly depends on an optional earlier test.