Re: [RFC PATCH v3 1/5] build-sys: Add rust feature option

[Paolo Bonzini <pbonzini@redhat.com>]

On 6/19/24 22:13, Manos Pitsidianakis wrote:
> Add options for Rust in meson_options.txt, meson.build, configure to
> prepare for adding Rust code in the followup commits.
> 
> `rust` is a reserved meson name, so we have to use an alternative.
> `with_rust` was chosen.
> 
> A cargo_wrapper.py script is added that is heavily based on the work of
> Marc-André Lureau from 2021.
> 
> https://patchew.org/QEMU/20210907121943.3498701-1-marcandre.lureau@redhat.com/
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>

The cargo_wrapper.py script is not used yet, so it should be
delayed until it's used.

For the detection of the toolchain, I'd rather do everything in
configure since that's where the cross file is built.  Something like:

diff --git a/configure b/configure
index 8b6a2f16ceb..6412a1021c3 100755
--- a/configure
+++ b/configure
@@ -173,6 +173,8 @@ fi
  
  # default parameters
  container_engine="auto"
+rust_target_triple=""
+with_rust="no"
  cpu=""
  cross_compile="no"
  cross_prefix=""
@@ -201,6 +202,8 @@ for opt do
    --cross-prefix=*) cross_prefix="$optarg"
                      cross_compile="yes"
    ;;
+  --cargo=*) CARGO="$optarg"
+  ;;
    --cc=*) CC="$optarg"
    ;;
    --cxx=*) CXX="$optarg"
@@ -317,6 +322,8 @@ windmc="${WINDMC-${cross_prefix}windmc}"
  pkg_config="${PKG_CONFIG-${cross_prefix}pkg-config}"
  sdl2_config="${SDL2_CONFIG-${cross_prefix}sdl2-config}"
  
+cargo="${CARGO-cargo}"
+
  check_define() {
  cat > $TMPC <<EOF
  #if !defined($1)
@@ -628,6 +635,8 @@ for opt do
    ;;
    --cross-prefix=*)
    ;;
+  --cargo=*)
+  ;;
    --cc=*)
    ;;
    --host-cc=*) host_cc="$optarg"
@@ -755,8 +764,14 @@ for opt do
    ;;
    --container-engine=*) container_engine="$optarg"
    ;;
+  --rust-target-triple=*) rust_target_triple="$optarg"
+  ;;
    --gdb=*) gdb_bin="$optarg"
    ;;
+  --with-rust) with_rust=yes
+  ;;
+  --without-rust) with_rust=no
+  ;;
    # everything else has the same name in configure and meson
    --*) meson_option_parse "$opt" "$optarg"
    ;;
@@ -854,6 +869,7 @@ $(echo Available targets: $default_target_list | \
  Advanced options (experts only):
    -Dmesonoptname=val       passthrough option to meson unmodified
    --cross-prefix=PREFIX    use PREFIX for compile tools, PREFIX can be blank [$cross_prefix]
+  --cargo=CARGO            use Cargo binary CARGO [$cargo]
    --cc=CC                  use C compiler CC [$cc]
    --host-cc=CC             when cross compiling, use C compiler CC for code run
                             at build time [$host_cc]
@@ -869,11 +885,13 @@ Advanced options (experts only):
    --python=PYTHON          use specified python [$python]
    --ninja=NINJA            use specified ninja [$ninja]
    --static                 enable static build [$static]
-  --without-default-features default all --enable-* options to "disabled"
-  --without-default-devices  do not include any device that is not needed to
+  --rust-target-triple=TRIPLE  target for Rust cross compilation
+  --without-default-features   default all --enable-* options to "disabled"
+  --without-default-devices    do not include any device that is not needed to
                             start the emulator (only use if you are including
                             desired devices in configs/devices/)
    --with-devices-ARCH=NAME override default configs/devices
+  --with-rust              enable experimental Rust code
    --enable-debug           enable common debug build options
    --cpu=CPU                Build for host CPU [$cpu]
    --disable-containers     don't use containers for cross-building
@@ -1138,6 +1159,20 @@ EOF
    fi
  fi
  
+##########################################
+# detect rust triples
+
+if test "$with_rust" = yes; then
+  $CARGO -vV > "${TMPDIR1}/${TMPB}.out"
+  if test $? != 0; then
+    error_exit "could not execute cargo binary \"$CARGO\""
+  fi
+  rust_host_triple=$(sed -n 's/^host: //p' "${TMPDIR1}/${TMPB}.out")
+  if test "$rust_target_triple" = ""; then
+    rust_target_triple=$rust_host_triple
+  fi
+fi
+
  ##########################################
  # functions to probe cross compilers
  
@@ -1604,6 +1639,10 @@ if test "$container" != no; then
      echo "RUNC=$runc" >> $config_host_mak
  fi
  echo "SUBDIRS=$subdirs" >> $config_host_mak
+if test "$with_rust" = yes; then
+  echo "RUST_HOST_TRIPLE=$rust_host_triple" >> $config_host_mak
+  echo "RUST_TARGET_TRIPLE=$rust_target_triple" >> $config_host_mak
+fi
  echo "PYTHON=$python" >> $config_host_mak
  echo "MKVENV_ENSUREGROUP=$mkvenv ensuregroup $mkvenv_online_flag" >> $config_host_mak
  echo "GENISOIMAGE=$genisoimage" >> $config_host_mak
@@ -1731,6 +1770,13 @@ if test "$skip_meson" = no; then
    echo "c = [$(meson_quote $cc $CPU_CFLAGS)]" >> $cross
    test -n "$cxx" && echo "cpp = [$(meson_quote $cxx $CPU_CFLAGS)]" >> $cross
    test -n "$objcc" && echo "objc = [$(meson_quote $objcc $CPU_CFLAGS)]" >> $cross
+  if test "$with_rust" = yes; then
+    if test "$rust_host_triple" != "$rust_target_triple"; then
+      echo "cargo = [$(meson_quote $cargo --target "$rust_target_triple")]" >> $cross
+    else
+      echo "cargo = [$(meson_quote $cargo)]" >> $cross
+    fi
+  fi
    echo "ar = [$(meson_quote $ar)]" >> $cross
    echo "dlltool = [$(meson_quote $dlltool)]" >> $cross
    echo "nm = [$(meson_quote $nm)]" >> $cross
diff --git a/meson.build b/meson.build
index c5360fbd299..ad7dbc0d641 100644
--- a/meson.build
+++ b/meson.build
@@ -290,6 +290,11 @@ foreach lang : all_languages
    endif
  endforeach
  
+cargo = not_found
+if 'RUST_TARGET_TRIPLE' in config_host
+  cargo = find_program('cargo', required: true)
+endif
+
  # default flags for all hosts
  # We use -fwrapv to tell the compiler that we require a C dialect where
  # left shift of signed integers is well defined and has the expected
@@ -4239,6 +4244,10 @@ if 'objc' in all_languages
  else
    summary_info += {'Objective-C compiler': false}
  endif
+summary_info += {'Rust support':      cargo.found()}
+if cargo.found() and config_host['RUST_TARGET_TRIPLE']) != config_host['RUST_HOST_TRIPLE']
+  summary_info += {'Rust target':     config_host['RUST_TARGET_TRIPLE']}
+endif
  option_cflags = (get_option('debug') ? ['-g'] : [])
  if get_option('optimization') != 'plain'
    option_cflags += ['-O' + get_option('optimization')]