fix regression that broke type checking of CustomTarget outputs

We validate a few things here, such as the non-presence of '@INPUT' in
an output name. These got moved out of the CustomTarget constructor in
commit 11f9638035 and into KwargInfo, but
only for kwargs that took multiple values. This caused configure_file()
and unstable_rust.bindgen() to stop checking for this.

Add a shared single-output KW and use it in both places. This now
dispatches to _output_validator.

configure_file now validates subdirectories in output names the same way
we do elsewhere, directly in the typed_kwargs and by specifying the
erroring kwarg.

mesonbuild/interpreter/interpreter.py

@@ -58,6 +58,7 @@ from .type_checking import (
     CT_INPUT_KW,
     CT_INSTALL_DIR_KW,
     CT_OUTPUT_KW,
+    OUTPUT_KW,
     DEFAULT_OPTIONS,
     DEPENDS_KW,
     DEPEND_FILES_KW,
@@ -2392,7 +2393,7 @@ class Interpreter(InterpreterBase, HoldableObject):
         KwargInfo('install', (bool, NoneType), since='0.50.0'),
         KwargInfo('install_dir', (str, bool), default='',
                   validator=lambda x: 'must be `false` if boolean' if x is True else None),
-        KwargInfo('output', str, required=True),
+        OUTPUT_KW,
         KwargInfo('output_format', str, default='c', since='0.47.0',
                   validator=in_set_validator({'c', 'nasm'})),
     )
@@ -2448,8 +2449,6 @@ class Interpreter(InterpreterBase, HoldableObject):
             mlog.warning('Output file', mlog.bold(ofile_rpath, True), 'for configure_file() at', current_call, 'overwrites configure_file() output at', first_call)
         else:
             self.configure_file_outputs[ofile_rpath] = self.current_lineno
-        if os.path.dirname(output) != '':
-            raise InterpreterException('Output file name must not contain a subdirectory.')
         (ofile_path, ofile_fname) = os.path.split(os.path.join(self.subdir, output))
         ofile_abs = os.path.join(self.environment.build_dir, ofile_path, ofile_fname)
 

mesonbuild/interpreter/type_checking.py

@@ -277,6 +277,13 @@ CT_OUTPUT_KW: KwargInfo[T.List[str]] = KwargInfo(
     validator=_output_validator,
 )
 
+OUTPUT_KW: KwargInfo[str] = KwargInfo(
+    'output',
+    str,
+    required=True,
+    validator=lambda x: _output_validator([x])
+)
+
 CT_INPUT_KW: KwargInfo[T.List[T.Union[str, File, ExternalProgram, BuildTarget, CustomTarget, CustomTargetIndex, ExtractedObjects, GeneratedList]]] = KwargInfo(
     'input',
     ContainerTypeInfo(list, (str, File, ExternalProgram, BuildTarget, CustomTarget, CustomTargetIndex, ExtractedObjects, GeneratedList)),

mesonbuild/modules/unstable_rust.py

@@ -19,7 +19,7 @@ from . import ExtensionModule, ModuleReturnValue
 from .. import mlog
 from ..build import BothLibraries, BuildTarget, CustomTargetIndex, Executable, ExtractedObjects, GeneratedList, IncludeDirs, CustomTarget, StructuredSources
 from ..dependencies import Dependency, ExternalLibrary
-from ..interpreter.interpreter import TEST_KWARGS
+from ..interpreter.interpreter import TEST_KWARGS, OUTPUT_KW
 from ..interpreterbase import ContainerTypeInfo, InterpreterException, KwargInfo, FeatureNew, typed_kwargs, typed_pos_args, noPosargs
 from ..mesonlib import File
 
@@ -173,7 +173,7 @@ class RustModule(ExtensionModule):
             listify=True,
             required=True,
         ),
-        KwargInfo('output', str, required=True),
+        OUTPUT_KW,
     )
     def bindgen(self, state: 'ModuleState', args: T.List, kwargs: 'FuncBindgen') -> ModuleReturnValue:
         """Wrapper around bindgen to simplify it's use.

test cases/failing/26 output subdir/test.json

@@ -1,7 +1,7 @@
 {
   "stdout": [
     {
-      "line": "test cases/failing/26 output subdir/meson.build:3:0: ERROR: Output file name must not contain a subdirectory."
+      "line": "test cases/failing/26 output subdir/meson.build:3:0: ERROR: configure_file keyword argument \"output\" Output 'subdir/foo' must not contain a path segment."
     }
   ]
 }