Detect files with trailing space

On Windows, if you accidently add a space at the end of a file name, like
`files('myfile.txt ')`, the file is not reported as missing, because of
the normalization performed by the OS. However, ninja will reference it
with the trailing space, and will fail because the file does not exist.

See python/cpython#115104 for reference.

mesonbuild/interpreter/interpreter.py

@@ -3179,6 +3179,8 @@ def source_strings_to_files(self, sources: T.List['SourceInputs'], strict: bool
         results: T.List['SourceOutputs'] = []
         for s in sources:
             if isinstance(s, str):
+                if s.endswith(' '):
+                    raise MesonException(f'{s!r} ends with a space. This is probably an error.')
                 if not strict and s.startswith(self.environment.get_build_dir()):
                     results.append(s)
                     mlog.warning(f'Source item {s!r} cannot be converted to File object, because it is a generated file. '

mesonbuild/utils/universal.py

@@ -398,7 +398,7 @@ def __repr__(self) -> str:
 
     @staticmethod
     @lru_cache(maxsize=None)
-    def from_source_file(source_root: str, subdir: str, fname: str) -> 'File':
+    def from_source_file(source_root: str, subdir: str, fname: str) -> File:
         if not os.path.isfile(os.path.join(source_root, subdir, fname)):
             raise MesonException(f'File {fname} does not exist.')
         return File(False, subdir, fname)