cargo: Fix crash when enabling feature on dev/build dependencies

mesonbuild/cargo/interpreter.py

@@ -543,18 +543,27 @@ def _load_manifest(self, subdir: str) -> Manifest:
                 raise MesonException(f'{subdir}/Cargo.toml does not have [package] section')
         return manifest_
 
-    def _add_dependency(self, pkg: PackageState, depname: str) -> None:
+    def _add_dependency(self, pkg: PackageState, depname: str) -> T.Optional[PackageState]:
         if depname in pkg.required_deps:
             return
+        dep = pkg.manifest.dependencies.get(depname)
+        if dep is None:
+            if depname in pkg.manifest.dev_dependencies:
+                # FIXME: Not supported yet
+                return None
+            if depname in pkg.manifest.build_dependencies:
+                # FIXME: Not supported yet
+                return None
+            raise MesonException(f'Dependency {depname} not defined in {pkg.manifest.package.name} manifest')
         pkg.required_deps.add(depname)
-        dep = pkg.manifest.dependencies[depname]
         dep_pkg, _ = self._fetch_package(dep.package, dep.api)
         if dep.default_features:
             self._enable_feature(dep_pkg, 'default')
         for f in dep.features:
             self._enable_feature(dep_pkg, f)
         for f in pkg.optional_deps_features[depname]:
             self._enable_feature(dep_pkg, f)
+        return dep_pkg
 
     def _enable_feature(self, pkg: PackageState, feature: str) -> None:
         if feature in pkg.features:
@@ -579,10 +588,9 @@ def _enable_feature(self, pkg: PackageState, feature: str) -> None:
                         # is later added.
                         pkg.optional_deps_features[depname].add(dep_f)
                 else:
-                    self._add_dependency(pkg, depname)
-                    dep = pkg.manifest.dependencies[depname]
-                    dep_pkg = self._dep_package(dep)
-                    self._enable_feature(dep_pkg, dep_f)
+                    dep_pkg = self._add_dependency(pkg, depname)
+                    if dep_pkg is not None:
+                        self._enable_feature(dep_pkg, dep_f)
             elif f.startswith('dep:'):
                 self._add_dependency(pkg, f[4:])
             else: