[PoCv2 03/15] build-sys: add --with-rust{-target} & basic build infrastructure

[marcandre . lureau]

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

Add the build-sys infrastructure to build Rust code. Introduce a
top-level workspace, so various sub-projects (libraries, executables
etc) can be developed together, sharing the dependencies and output
directory.

If not Tier 1, many of the platforms QEMU supports are considered Tier
2: https://doc.rust-lang.org/nightly/rustc/platform-support.html

Rust is generally available on various distributions (thanks to Firefox,
I suppose). If not, it can usually be installed with rustup by
developpers.

configure will enable Rust support automatically if cargo is present.
Rust support can be disabled --without-rust. When detecting windows
cross building, it will use the $cpu-pc-windows-gnu target by
default (more default mappings could be added over time). This can be
changed with --with-rust-target=RTT.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 Cargo.toml  |  2 ++
 configure   | 18 ++++++++++++++++++
 meson.build | 23 +++++++++++++++++++++++
 3 files changed, 43 insertions(+)
 create mode 100644 Cargo.toml

diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000000..c4b464ff15
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,2 @@
+[workspace]
+members = []
diff --git a/configure b/configure
index b553288c5e..7945ceac63 100755
--- a/configure
+++ b/configure
@@ -446,6 +446,8 @@ meson=""
 ninja=""
 skip_meson=no
 gettext=""
+with_rust="auto"
+with_rust_target=""
 
 bogus_os="no"
 malloc_trim="auto"
@@ -1519,6 +1521,12 @@ for opt do
   ;;
   --disable-libdaxctl) libdaxctl=no
   ;;
+  --with-rust) with_rust=yes
+  ;;
+  --without-rust) with_rust=no
+  ;;
+  --with-rust-target=*) with_rust_target="$optarg"
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1666,6 +1674,8 @@ Advanced options (experts only):
   --extra-ldflags=LDFLAGS  append extra linker flags LDFLAGS
   --cross-cc-ARCH=CC       use compiler when building ARCH guest test cases
   --cross-cc-flags-ARCH=   use compiler flags when building ARCH guest tests
+  --with-rust              enable Rust compilation
+  --with-rust-target=RTT   use the given Rust target triple
   --make=MAKE              use specified make [$make]
   --python=PYTHON          use specified python [$python]
   --sphinx-build=SPHINX    use specified sphinx-build [$sphinx_build]
@@ -1918,6 +1928,10 @@ if test -z "$ninja"; then
     done
 fi
 
+if test "$with_rust" = auto && has cargo; then
+    with_rust=yes
+fi
+
 # Check that the C compiler works. Doing this here before testing
 # the host CPU ensures that we had a valid CC to autodetect the
 # $cpu var (and we should bail right here if that's not the case).
@@ -7046,6 +7060,10 @@ fi
 if test "$safe_stack" = "yes"; then
   echo "CONFIG_SAFESTACK=y" >> $config_host_mak
 fi
+if test "$with_rust" = "yes" ; then
+  echo "CONFIG_WITH_RUST=y" >> $config_host_mak
+  echo "CONFIG_WITH_RUST_TARGET=$with_rust_target" >> $config_host_mak
+fi
 
 # If we're using a separate build tree, set it up now.
 # DIRS are directories which we simply mkdir in the build tree;
diff --git a/meson.build b/meson.build
index 17c89c87c6..d8526dc999 100644
--- a/meson.build
+++ b/meson.build
@@ -73,6 +73,28 @@ if cpu in ['x86', 'x86_64']
   }
 endif
 
+with_rust = 'CONFIG_WITH_RUST' in config_host
+cargo = find_program('cargo', required: with_rust)
+
+if with_rust
+  rs_target_triple = config_host['CONFIG_WITH_RUST_TARGET']
+  if meson.is_cross_build()
+    # more default target mappings may be added over time
+    if rs_target_triple == '' and targetos == 'windows'
+      rs_target_triple = host_machine.cpu() + '-pc-windows-gnu'
+    endif
+    if rs_target_triple == ''
+      error('cross-compiling, but no Rust target-triple defined.')
+    endif
+  endif
+endif
+
+if get_option('optimization') in ['0', '1', 'g']
+  rs_build_type = 'debug'
+else
+  rs_build_type = 'release'
+endif
+
 ##################
 # Compiler flags #
 ##################
@@ -1770,6 +1792,7 @@ endif
 if targetos == 'darwin'
   summary_info += {'Objective-C compiler': 
meson.get_compiler('objc').cmd_array()[0]}
 endif
+summary_info += {'Rust support':      with_rust}
 summary_info += {'ARFLAGS':           config_host['ARFLAGS']}
 summary_info += {'CFLAGS':            ' '.join(get_option('c_args')
                                                + ['-O' + 
get_option('optimization')]
-- 
2.28.0