rust: fix linking with external dependencies

Rust can link with any dependency that uses c linkage, which is pretty
much what we assume across the board anyway.

mesonbuild/backend/ninjabackend.py

@@ -1598,6 +1598,7 @@ int dummy;
         args += rustc.get_output_args(os.path.join(target.subdir, target.get_filename()))
         args += self.environment.coredata.get_external_args(target.for_machine, rustc.language)
         linkdirs = mesonlib.OrderedSet()
+        external_deps = target.external_deps.copy()
         for d in target.link_targets:
             linkdirs.add(d.subdir)
             if d.uses_rust():
@@ -1609,6 +1610,22 @@ int dummy;
                 # Rust uses -l for non rust dependencies, but we still need to add (shared|static)=foo
                 _type = 'static' if d.typename == 'static library' else 'shared'
                 args += ['-l', f'{_type}={d.name}']
+                if d.typename == 'static library':
+                    external_deps.extend(d.external_deps)
+        for e in external_deps:
+            for a in e.get_link_args():
+                if a.endswith(('.dll', '.so', '.dylib')):
+                    dir_, lib = os.path.split(a)
+                    linkdirs.add(dir_)
+                    lib, ext = os.path.splitext(lib)
+                    if lib.startswith('lib'):
+                        lib = lib[3:]
+                    args.extend(['-l', f'dylib={lib}'])
+                elif a.startswith('-L'):
+                    args.append(a)
+                elif a.startswith('-l'):
+                    # This should always be a static lib, I think
+                    args.extend(['-l', f'static={a[2:]}'])
         for d in linkdirs:
             if d == '':
                 d = '.'

test cases/rust/13 external c dependencies/test.json

@@ -10,6 +10,9 @@
         { "val": "cmake" },
         { "val": "system" }
       ]
-    }
+    },
+    "exclude": [
+      { "static": true, "method": "pkg-config" }
+    ]
   }
 }