meson(cargo): support Windows again

For over a year, Git has been moved to a more modern build system than
it had before (GNU make, or on Windows optionally CMake). Naturally,
this new system breaks Windows support left and right.

For example, c184795 (meson: add infrastructure to build internal
Rust library, 2025-10-02) added support for building a Rust library, and
it fails when Visual C is configured as compiler.

This is the reason that the `win+Meson` job of Git's `master` branch
fails for the past 16 days, i.e. the latest 9 pushes of the `master`
branch as of time of writing. The symptom is:

  [697/905] Generating src/git_rs with a custom command
  FAILED: [code=1] src/libgitcore.a "C:\Program Files\Git\bin\sh.exe" "D:/a/git/git/src/cargo-meson.sh" "D:/a/git/git" "D:/a/git/git/build/src" "--release"
  cp: cannot stat 'D:/a/git/git/build/src/release/libgitcore.a': No such file or directory

The reason is that Visual C's output is called `gitcore.lib`, not
`libgitcore.a`. Let's special-case Visual C and use the correct filename
in all cases.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

src/cargo-meson.sh

@@ -5,6 +5,9 @@ then
 	exit 1
 fi
 
+target="$1"
+shift
+
 SOURCE_DIR="$1"
 BUILD_DIR="$2"
 BUILD_TYPE=debug
@@ -26,7 +29,7 @@ then
 	exit $RET
 fi
 
-if ! cmp "$BUILD_DIR/$BUILD_TYPE/libgitcore.a" "$BUILD_DIR/libgitcore.a" >/dev/null 2>&1
+if ! cmp "$BUILD_DIR/$BUILD_TYPE/$target" "$BUILD_DIR/$target" >/dev/null 2>&1
 then
-	cp "$BUILD_DIR/$BUILD_TYPE/libgitcore.a" "$BUILD_DIR/libgitcore.a"
+	cp "$BUILD_DIR/$BUILD_TYPE/$target" "$BUILD_DIR/$target"
 fi

src/meson.build

@@ -3,13 +3,21 @@ libgit_rs_sources = [
   'varint.rs',
 ]
 
+# The exact file name depends on the compiler
+if meson.get_compiler('c').get_id() == 'msvc'
+  target = 'gitcore.lib'
+else
+  target = 'libgitcore.a'
+endif
+
 # Unfortunately we must use a wrapper command to move the output file into the
 # current build directory. This can fixed once `cargo build --artifact-dir`
 # stabilizes. See https://github.com/rust-lang/cargo/issues/6790 for that
 # effort.
 cargo_command = [
   shell,
   meson.current_source_dir() / 'cargo-meson.sh',
+  target,
   meson.project_source_root(),
   meson.current_build_dir(),
 ]
@@ -21,7 +29,7 @@ libgit_rs = custom_target('git_rs',
   input: libgit_rs_sources + [
     meson.project_source_root() / 'Cargo.toml',
   ],
-  output: 'libgitcore.a',
+  output: target,
   command: cargo_command,
 )
 libgit_dependencies += declare_dependency(link_with: libgit_rs)