subprojects: add attrs crate

The attrs crate is a simple combinator-based for Rust attributes.  It
will be used instead of a handwritten parser.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

subprojects/.gitignore

@@ -8,6 +8,7 @@
 /slirp
 /anyhow-1.0.98
 /arbitrary-int-1.2.7
+/attrs-0.2.9
 /bilge-0.2.0
 /bilge-impl-0.2.0
 /either-1.12.0

subprojects/attrs-0.2-rs.wrap

@@ -0,0 +1,7 @@
+[wrap-file]
+directory = attrs-0.2.9
+source_url = https://crates.io/api/v1/crates/attrs/0.2.9/download
+source_filename = attrs-0.2.9.tar.gz
+source_hash = 2a207d40f43de65285f3de0509bb6cb16bc46098864fce957122bbacce327e5f
+#method = cargo
+patch_directory = attrs-0.2-rs

subprojects/packagefiles/attrs-0.2-rs/meson.build

@@ -0,0 +1,33 @@
+project('attrs-0.2-rs', 'rust',
+  meson_version: '>=1.5.0',
+  version: '0.2.9',
+  license: 'MIT OR Apache-2.0',
+  default_options: [])
+
+subproject('proc-macro2-1-rs', required: true)
+subproject('syn-2-rs', required: true)
+
+proc_macro2_dep = dependency('proc-macro2-1-rs', native: true)
+syn_dep = dependency('syn-2-rs', native: true)
+
+_attrs_rs = static_library(
+  'attrs',
+  files('src/lib.rs'),
+  gnu_symbol_visibility: 'hidden',
+  override_options: ['rust_std=2021', 'build.rust_std=2021'],
+  rust_abi: 'rust',
+  rust_args: [
+    '--cap-lints', 'allow',
+  ],
+  dependencies: [
+    proc_macro2_dep,
+    syn_dep,
+  ],
+  native: true,
+)
+
+attrs_dep = declare_dependency(
+  link_with: _attrs_rs,
+)
+
+meson.override_dependency('attrs-0.2-rs', attrs_dep, native: true)