install_*: FileMode doesn't need to be None

There's no reason to allow None into the backend, it already has code to
check that all of the values of the FileMode object are None, so let's
use that, which is much simpler all the way down.

mesonbuild/backend/backends.py

@@ -42,9 +42,6 @@ if T.TYPE_CHECKING:
     from ..interpreter import Interpreter, Test
     from ..mesonlib import FileMode
 
-    InstallType = T.List[T.Tuple[str, str, T.Optional['FileMode']]]
-    InstallSubdirsType = T.List[T.Tuple[str, str, T.Optional['FileMode'], T.Tuple[T.Set[str], T.Set[str]]]]
-
 # Languages that can mix with C or C++ but don't support unity builds yet
 # because the syntax we use for unity builds is specific to C/++/ObjC/++.
 # Assembly files cannot be unitified and neither can LLVM IR files

mesonbuild/build.py

@@ -135,7 +135,7 @@ class DependencyOverride(HoldableObject):
 class Headers(HoldableObject):
 
     def __init__(self, sources: T.List[File], install_subdir: T.Optional[str],
-                 install_dir: T.Optional[str], install_mode: T.Optional['FileMode'],
+                 install_dir: T.Optional[str], install_mode: 'FileMode',
                  subproject: str):
         self.sources = sources
         self.install_subdir = install_subdir
@@ -158,14 +158,14 @@ class Headers(HoldableObject):
     def get_custom_install_dir(self) -> T.Optional[str]:
         return self.custom_install_dir
 
-    def get_custom_install_mode(self) -> T.Optional['FileMode']:
+    def get_custom_install_mode(self) -> 'FileMode':
         return self.custom_install_mode
 
 
 class Man(HoldableObject):
 
     def __init__(self, sources: T.List[File], install_dir: T.Optional[str],
-                 install_mode: T.Optional['FileMode'], subproject: str,
+                 install_mode: 'FileMode', subproject: str,
                  locale: T.Optional[str]):
         self.sources = sources
         self.custom_install_dir = install_dir
@@ -176,7 +176,7 @@ class Man(HoldableObject):
     def get_custom_install_dir(self) -> T.Optional[str]:
         return self.custom_install_dir
 
-    def get_custom_install_mode(self) -> T.Optional['FileMode']:
+    def get_custom_install_mode(self) -> 'FileMode':
         return self.custom_install_mode
 
     def get_sources(self) -> T.List['File']:
@@ -186,7 +186,7 @@ class Man(HoldableObject):
 class InstallDir(HoldableObject):
 
     def __init__(self, src_subdir: str, inst_subdir: str, install_dir: str,
-                 install_mode: T.Optional['FileMode'],
+                 install_mode: 'FileMode',
                  exclude: T.Tuple[T.Set[str], T.Set[str]],
                  strip_directory: bool, subproject: str,
                  from_source_dir: bool = True):
@@ -2611,7 +2611,7 @@ class ConfigurationData(HoldableObject):
 # during install.
 class Data(HoldableObject):
     def __init__(self, sources: T.List[File], install_dir: str,
-                 install_mode: T.Optional['FileMode'], subproject: str,
+                 install_mode: 'FileMode', subproject: str,
                  rename: T.List[str] = None):
         self.sources = sources
         self.install_dir = install_dir

mesonbuild/interpreter/interpreter.py

@@ -128,7 +128,7 @@ def _install_mode_validator(mode: T.List[T.Union[str, bool, int]]) -> T.Optional
     return None
 
 
-def _install_mode_convertor(mode: T.Optional[T.List[T.Union[str, bool, int]]]) -> T.Optional[FileMode]:
+def _install_mode_convertor(mode: T.Optional[T.List[T.Union[str, bool, int]]]) -> FileMode:
     """Convert the DSL form of the `install_mode` keyword arugment to `FileMode`
 
     This is not required, and if not required returns None
@@ -136,8 +136,6 @@ def _install_mode_convertor(mode: T.Optional[T.List[T.Union[str, bool, int]]]) -
     TODO: It's not clear to me why this needs to be None and not just return an
     emtpy FileMode.
     """
-    if mode is None:
-        return None
     # this has already been validated by the validator
     return FileMode(*[m if isinstance(m, str) else None for m in mode])