Add support for rust proc-macro crates

docs/markdown/snippets/rust_proc_macro_crates.md

@@ -0,0 +1,16 @@
+## Rust proc-macro crates
+
+Rust has these handy things called proc-macro crates, which are a bit like a
+compiler plugin. We can now support them, simply build a [[shared_library]] with
+the `rust_crate_type` set to `proc-macro`.
+
+```meson
+proc = shared_library(
+  'proc',
+  'proc.rs',
+  rust_crate_type : 'proc-macro',
+  install : false,
+)
+
+user = executable('user, 'user.rs', link_with : proc)
+```

mesonbuild/build.py

@@ -1982,8 +1982,8 @@ class SharedLibrary(BuildTarget):
                 mlog.debug('Defaulting Rust dynamic library target crate type to "dylib"')
                 self.rust_crate_type = 'dylib'
             # Don't let configuration proceed with a non-dynamic crate type
-            elif self.rust_crate_type not in ['dylib', 'cdylib']:
+            elif self.rust_crate_type not in ['dylib', 'cdylib', 'proc-macro']:
-                raise InvalidArguments(f'Crate type "{self.rust_crate_type}" invalid for dynamic libraries; must be "dylib" or "cdylib"')
+                raise InvalidArguments(f'Crate type "{self.rust_crate_type}" invalid for dynamic libraries; must be "dylib", "cdylib", or "proc-macro"')
         if not hasattr(self, 'prefix'):
             self.prefix = None
         if not hasattr(self, 'suffix'):
@@ -2215,6 +2215,8 @@ class SharedLibrary(BuildTarget):
                 self.rust_crate_type = rust_crate_type
             else:
                 raise InvalidArguments(f'Invalid rust_crate_type "{rust_crate_type}": must be a string.')
+            if rust_crate_type == 'proc-macro':
+                FeatureNew.single_use('Rust crate type "proc-macro"', '0.62.0', self.subproject)
 
     def get_import_filename(self) -> T.Optional[str]:
         """

test cases/failing/54 wrong shared crate type/test.json

@@ -1,7 +1,7 @@
 {
   "stdout": [
     {
-      "line": "test cases/failing/54 wrong shared crate type/meson.build:7:0: ERROR: Crate type \"staticlib\" invalid for dynamic libraries; must be \"dylib\" or \"cdylib\""
+      "line": "test cases/failing/54 wrong shared crate type/meson.build:7:0: ERROR: Crate type \"staticlib\" invalid for dynamic libraries; must be \"dylib\", \"cdylib\", or \"proc-macro\""
     }
   ]
 }

test cases/rust/18 proc-macro/meson.build

@@ -0,0 +1,19 @@
+project('rust proc-macro', 'rust')
+
+if build_machine.system() != 'linux'
+    error('MESON_SKIP_TEST, this test only works on Linux. Patches welcome.')
+endif
+
+pm = shared_library(
+  'proc_macro_examples',
+  'proc.rs',
+  rust_crate_type : 'proc-macro',
+)
+
+main = executable(
+  'main',
+  'use.rs',
+  link_with : pm
+)
+
+test('main_test', main)

test cases/rust/18 proc-macro/proc.rs

@@ -0,0 +1,7 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn make_answer(_item: TokenStream) -> TokenStream {
+    "fn answer() -> u32 { 42 }".parse().unwrap()
+}

test cases/rust/18 proc-macro/use.rs

@@ -0,0 +1,8 @@
+extern crate proc_macro_examples;
+use proc_macro_examples::make_answer;
+
+make_answer!();
+
+fn main() {
+    assert_eq!(42, answer());
+}