interpreter: Add docstring and fix types of source_strings_to_files

2 files changed, 24 insertions, 11 deletions

diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index c67e840..891f67e 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -64,6 +64,13 @@ if T.TYPE_CHECKING:
     from ..envconfig import MachineInfo
     from ..environment import Environment
 
+    # Input source types passed to Targets
+    SourceInputs = T.Union[mesonlib.File, GeneratedListHolder, TargetHolder,
+                           CustomTargetIndexHolder, GeneratedObjectsHolder, str]
+    # Input source types passed to the build.Target5 classes
+    SourceOutputs = T.Union[mesonlib.File, GeneratedListHolder, TargetHolder,
+                            CustomTargetIndexHolder, GeneratedObjectsHolder]
+
 def stringifyUserArguments(args, quote=False):
     if isinstance(args, list):
         return '[%s]' % ', '.join([stringifyUserArguments(x, True) for x in args])
@@ -2683,20 +2690,25 @@ Try setting b_lundef to false instead.'''.format(self.coredata.options[OptionKey
         if project_root / self.subproject_dir in norm.parents:
             raise InterpreterException(f'Sandbox violation: Tried to grab {inputtype} {norm.name} from a nested subproject.')
 
-    def source_strings_to_files(self, sources: T.List[str]) -> T.List[mesonlib.File]:
+    def source_strings_to_files(self, sources: T.List['SourceInputs']) -> T.List['SourceOutputs']:
+        """Lower inputs to a list of Targets and Files, replacing any strings.
+
+        :param sources: A raw (Meson DSL) list of inputs (targets, files, and
+            strings)
+        :raises InterpreterException: if any of the inputs are of an invalid type
+        :return: A list of Targets and Files
+        """
         mesonlib.check_direntry_issues(sources)
         if not isinstance(sources, list):
             sources = [sources]
-        results: T.List[mesonlib.File] = []
+        results: T.List['SourceOutputs'] = []
         for s in sources:
-            if isinstance(s, (mesonlib.File, GeneratedListHolder,
-                              TargetHolder, CustomTargetIndexHolder,
-                              GeneratedObjectsHolder)):
-                pass
-            elif isinstance(s, str):
+            if isinstance(s, str):
                 self.validate_within_subproject(self.subdir, s)
                 s = mesonlib.File.from_source_file(self.environment.source_dir, self.subdir, s)
-            else:
+            elif not isinstance(s, (mesonlib.File, GeneratedListHolder,
+                                    TargetHolder, CustomTargetIndexHolder,
+                                    GeneratedObjectsHolder)):
                 raise InterpreterException('Source item is {!r} instead of '
                                            'string or File-type object'.format(s))
             results.append(s)
diff --git a/mesonbuild/modules/unstable_rust.py b/mesonbuild/modules/unstable_rust.py
index 7ae12c4..1db6722 100644
--- a/mesonbuild/modules/unstable_rust.py
+++ b/mesonbuild/modules/unstable_rust.py
@@ -27,6 +27,7 @@ if T.TYPE_CHECKING:
     from . import ModuleState
     from ..interpreter import Interpreter
     from ..programs import ExternalProgram
+    from ..interpreter.interpreter import SourceOutputs
 
 
 class RustModule(ExtensionModule):
@@ -139,8 +140,8 @@ class RustModule(ExtensionModule):
         The main thing this simplifies is the use of `include_directory`
         objects, instead of having to pass a plethora of `-I` arguments.
         """
-        header: T.Union[File, CustomTarget, GeneratedList, CustomTargetIndex]
-        _deps: T.Sequence[T.Union[File, CustomTarget, GeneratedList, CustomTargetIndex]]
+        header: 'SourceOutputs'
+        _deps: T.Sequence['SourceOutputs']
         try:
             header, *_deps = unholder(self.interpreter.source_strings_to_files(listify(kwargs['input'])))
         except KeyError:
@@ -158,7 +159,7 @@ class RustModule(ExtensionModule):
         bind_args: T.List[str] = stringlistify(listify(kwargs.get('args', [])))
 
         # Split File and Target dependencies to add pass to CustomTarget
-        depends: T.List[BuildTarget] = []
+        depends: T.List[T.Union[GeneratedList, BuildTarget, CustomTargetIndex]] = []
         depend_files: T.List[File] = []
         for d in _deps:
             if isinstance(d, File):