Not all compilers support depfile

mesonbuild/backend/ninjabackend.py

@@ -2824,7 +2824,8 @@ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47485'''))
         element.add_dep(pch_dep)
         for i in self.get_fortran_orderdeps(target, compiler):
             element.add_orderdep(i)
-        element.add_item('DEPFILE', dep_file)
+        if dep_file:
+            element.add_item('DEPFILE', dep_file)
         element.add_item('ARGS', commands)
 
         self.add_dependency_scanner_entries_to_element(target, compiler, element, src)

mesonbuild/compilers/compilers.py

@@ -1147,7 +1147,7 @@ class Compiler(HoldableObject, metaclass=abc.ABCMeta):
     def get_include_args(self, path: str, is_system: bool) -> T.List[str]:
         return []
 
-    def depfile_for_object(self, objfile: str) -> str:
+    def depfile_for_object(self, objfile: str) -> T.Optional[str]:
         return objfile + '.' + self.get_depfile_suffix()
 
     def get_depfile_suffix(self) -> str:

mesonbuild/compilers/swift.py

@@ -59,7 +59,7 @@ class SwiftCompiler(Compiler):
     def get_dependency_gen_args(self, outtarget: str, outfile: str) -> T.List[str]:
         return ['-emit-dependencies']
 
-    def depfile_for_object(self, objfile: str) -> str:
+    def depfile_for_object(self, objfile: str) -> T.Optional[str]:
         return os.path.splitext(objfile)[0] + '.' + self.get_depfile_suffix()
 
     def get_depfile_suffix(self) -> str: