[PoCv2 05/15] qga/rust: build and link an empty static library

[marcandre . lureau]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

Meson doesn't integrate very smoothly with Cargo. Use the cargo-wrapper
script as a custom_target() always stale to build the Rust code. The
"build-lib" command will produce a static library in the meson expected
output directory, as well as link flags that must be employed to do the
final link.

Those link flags can't be queried during configure time (Cargo doesn't
have a user-queriable configure step), so we pass them to the linker
thanks to @file argument support at build time.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 Cargo.toml      |  2 +-
 qga/Cargo.toml  |  9 +++++++++
 qga/lib.rs      |  0
 qga/meson.build | 18 +++++++++++++++++-
 4 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 qga/Cargo.toml
 create mode 100644 qga/lib.rs

diff --git a/Cargo.toml b/Cargo.toml
index c4b464ff15..e69b04200f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,2 +1,2 @@
 [workspace]
-members = []
+members = ["qga"]
diff --git a/qga/Cargo.toml b/qga/Cargo.toml
new file mode 100644
index 0000000000..50c3415ab2
--- /dev/null
+++ b/qga/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "qga"
+version = "0.1.0"
+edition = "2018"
+license = "GPLv2"
+
+[lib]
+path = "lib.rs"
+crate-type = ["staticlib"]
diff --git a/qga/lib.rs b/qga/lib.rs
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/qga/meson.build b/qga/meson.build
index cd08bd953a..62e13a11b3 100644
--- a/qga/meson.build
+++ b/qga/meson.build
@@ -45,9 +45,25 @@ qga_ss.add(when: 'CONFIG_WIN32', if_true: files(
 
 qga_ss = qga_ss.apply(config_host, strict: false)
 
+qga_rs = declare_dependency()
+if with_rust
+  cargo_qga = custom_target('cargo-qga',
+                            build_by_default: true,
+                            output: ['libqga.args', 'libqga.a'],
+                            build_always_stale: true,
+                            command: [cargo_wrapper,
+                                      'build-lib',
+                                      meson.current_build_dir(),
+                                      meson.current_source_dir(),
+                                      meson.build_root(),
+                                      rs_build_type,
+                                      rs_target_triple])
+  qga_rs = declare_dependency(link_args: '@' + cargo_qga.full_path(), sources: 
cargo_qga)
+endif
+
 qga = executable('qemu-ga', qga_ss.sources(),
                  link_args: config_host['LIBS_QGA'].split(),
-                 dependencies: [qemuutil, libudev],
+                 dependencies: [qemuutil, libudev, qga_rs],
                  install: true)
 all_qga = [qga]
 
-- 
2.28.0