rust: dependencies need to cause a rebuild/relink not just reorder

Otherwise changes to a dependency don't propogate

mesonbuild/backend/ninjabackend.py

@@ -1651,7 +1651,10 @@ class NinjaBackend(backends.Backend):
         args += compilers.get_base_compile_args(base_proxy, rustc)
         self.generate_generator_list_rules(target)
 
-        orderdeps = [os.path.join(t.subdir, t.get_filename()) for t in target.link_targets]
+        # dependencies need to cause a relink, they're not just for odering
+        deps = [os.path.join(t.subdir, t.get_filename()) for t in target.link_targets]
+
+        orderdeps: T.List[str] = []
 
         main_rust_file = None
         for i in target.get_sources():
@@ -1772,6 +1775,8 @@ class NinjaBackend(backends.Backend):
         element = NinjaBuildElement(self.all_outputs, target_name, compiler_name, main_rust_file)
         if orderdeps:
             element.add_orderdep(orderdeps)
+        if deps:
+            element.add_dep(deps)
         element.add_item('ARGS', args)
         element.add_item('targetdep', depfile)
         element.add_item('cratetype', cratetype)

test cases/unit/100 rlib linkage/lib2.rs

@@ -0,0 +1,5 @@
+use lib;
+
+pub fn fun() {
+    lib::fun();
+}

test cases/unit/100 rlib linkage/main.rs

@@ -0,0 +1,5 @@
+use lib2::fun;
+
+fn main() {
+    fun();
+}

test cases/unit/100 rlib linkage/meson.build

@@ -0,0 +1,22 @@
+project('rlib linkage', 'rust', default_options : ['rust_std=2018'])
+
+lib = static_library(
+  'lib',
+  'lib.rs',
+  rust_crate_type : 'rlib',
+)
+
+lib2 = static_library(
+  'lib2',
+  'lib2.rs',
+  rust_crate_type : 'rlib',
+  link_with : lib,
+)
+
+exe = executable(
+  'exe',
+  'main.rs',
+  link_with : lib2,
+)
+
+test('main', exe)

unittests/allplatformstests.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from mesonbuild.mesonlib.universal import windows_proof_rm
 import subprocess
 import re
 import json
@@ -4062,6 +4063,37 @@ class AllPlatformTests(BasePlatformTests):
             self.build()
         self.assertIn('error: use of a blacklisted/placeholder name `foo`', cm.exception.stdout)
 
+    @skip_if_not_language('rust')
+    def test_rust_rlib_linkage(self) -> None:
+        if self.backend is not Backend.ninja:
+            raise unittest.SkipTest('Rust is only supported with ninja currently')
+        template = textwrap.dedent('''\
+                use std::process::exit;
+
+                pub fn fun() {{
+                    exit({});
+                }}
+            ''')
+
+        testdir = os.path.join(self.unit_test_dir, '100 rlib linkage')
+        gen_file = os.path.join(testdir, 'lib.rs')
+        with open(gen_file, 'w') as f:
+            f.write(template.format(0))
+        self.addCleanup(windows_proof_rm, gen_file)
+
+        self.init(testdir)
+        self.build()
+        self.run_tests()
+
+        with open(gen_file, 'w') as f:
+            f.write(template.format(39))
+
+        self.build()
+        with self.assertRaises(subprocess.CalledProcessError) as cm:
+            self.run_tests()
+        self.assertEqual(cm.exception.returncode, 1)
+        self.assertIn('exit status 39', cm.exception.stdout)
+
     def test_custom_target_name(self):
         testdir = os.path.join(self.unit_test_dir, '99 custom target name')
         self.init(testdir)