add rustfmt target

meson.build

@@ -5,9 +5,15 @@ project(
     default_options: {'rust_std': '2024', 'rust_nightly': 'enabled'},
 )
 
+rustfmt = find_program('rustfmt')
+
 rust = import('rust')
 fs = import('fs')
 
+sources = []
+
+subdir('src')
+
 mon = dependency('mon-0.1-rs')
 get = dependency('get-0.1-rs')
 itertools = dependency('itertools-0.14-rs')
@@ -20,6 +26,14 @@ gentoo_utils = static_library(
     link_with: [thiserror],
 )
 
+custom_target(
+    'rustfmt',
+    input: sources,
+    output: 'rustfmt',
+    command: [rustfmt, '--edition=2024', '--check', '@INPUT@'],
+    build_always_stale: true,
+)
+
 if get_option('tests').enabled()
     rust.test('unittests', gentoo_utils)
     subdir('tests')