rust: support for Windows

The initial patch series that introduced Rust into the core of Git only
cared about macOS and Linux. This specifically leaves out Windows, which
indeed fails to build right now due to two issues:

  - The Rust runtime requires `GetUserProfileDirectoryW()`, but we don't
    link against "userenv.dll".

  - The path of the Rust library built on Windows is different than on
    most other systems systems.

Fix both of these issues to support Windows.

Note that this commit fixes the Meson-based job in GitHub's CI. Meson
auto-detects the availability of Rust, and as the Windows runner has
Rust installed by default it already enabled Rust support there. But due
to the above issues that job fails consistently.

Install Rust on GitLab CI, as well, to improve test coverage there.

Based-on-patch-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Based-on-patch-by: Ezekiel Newren <ezekielnewren@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitlab-ci.yml

@@ -161,7 +161,7 @@ test:mingw64:
     - saas-windows-medium-amd64
   before_script:
     - *windows_before_script
-    - choco install -y git meson ninja
+    - choco install -y git meson ninja rust-ms
     - Import-Module $env:ChocolateyInstall\helpers\chocolateyProfile.psm1
     - refreshenv
 

Makefile

@@ -929,10 +929,17 @@ TEST_SHELL_PATH = $(SHELL_PATH)
 LIB_FILE = libgit.a
 XDIFF_LIB = xdiff/lib.a
 REFTABLE_LIB = reftable/libreftable.a
+
 ifdef DEBUG
-RUST_LIB = target/debug/libgitcore.a
+RUST_TARGET_DIR = target/debug
 else
-RUST_LIB = target/release/libgitcore.a
+RUST_TARGET_DIR = target/release
+endif
+
+ifeq ($(uname_S),Windows)
+RUST_LIB = $(RUST_TARGET_DIR)/gitcore.lib
+else
+RUST_LIB = $(RUST_TARGET_DIR)/libgitcore.a
 endif
 
 # xdiff and reftable libs may in turn depend on what is in libgit.a
@@ -1538,6 +1545,9 @@ ALL_LDFLAGS = $(LDFLAGS) $(LDFLAGS_APPEND)
 ifdef WITH_RUST
 BASIC_CFLAGS += -DWITH_RUST
 GITLIBS += $(RUST_LIB)
+ifeq ($(uname_S),Windows)
+EXTLIBS += -luserenv
+endif
 endif
 
 ifdef SANITIZE

meson.build

@@ -1707,6 +1707,10 @@ rust_option = get_option('rust').disable_auto_if(not cargo.found())
 if rust_option.allowed()
   subdir('src')
   libgit_c_args += '-DWITH_RUST'
+
+  if host_machine.system() == 'windows'
+    libgit_dependencies += compiler.find_library('userenv')
+  endif
 else
   libgit_sources += [
     'varint.c',

src/cargo-meson.sh

@@ -26,7 +26,14 @@ then
 	exit $RET
 fi
 
-if ! cmp "$BUILD_DIR/$BUILD_TYPE/libgitcore.a" "$BUILD_DIR/libgitcore.a" >/dev/null 2>&1
+case "$(cargo -vV | sed -s 's/^host: \(.*\)$/\1/')" in
+	*-windows-*)
+		LIBNAME=gitcore.lib;;
+	*)
+		LIBNAME=libgitcore.a;;
+esac
+
+if ! cmp "$BUILD_DIR/$BUILD_TYPE/$LIBNAME" "$BUILD_DIR/libgitcore.a" >/dev/null 2>&1
 then
-	cp "$BUILD_DIR/$BUILD_TYPE/libgitcore.a" "$BUILD_DIR/libgitcore.a"
+	cp "$BUILD_DIR/$BUILD_TYPE/$LIBNAME" "$BUILD_DIR/libgitcore.a"
 fi