interpreter|build: Pass just the executable down to Generator

This requires that the interpreter has done the validation, which it now
does at all callsites. This simplifies the Generator initializer.

mesonbuild/build.py

@@ -1498,12 +1498,7 @@ You probably should put it in link_with instead.''')
                 return
 
 class Generator:
-    def __init__(self, args, kwargs):
-        if len(args) != 1:
-            raise InvalidArguments('Generator requires exactly one positional argument: the executable')
-        exe = unholder(args[0])
-        if not isinstance(exe, (Executable, programs.ExternalProgram)):
-            raise InvalidArguments('First generator argument must be an executable.')
+    def __init__(self, exe: T.Union['Executable', programs.ExternalProgram], kwargs):
         self.exe = exe
         self.depfile = None
         self.capture = False
@@ -1514,7 +1509,7 @@ class Generator:
         repr_str = "<{0}: {1}>"
         return repr_str.format(self.__class__.__name__, self.exe)
 
-    def get_exe(self):
+    def get_exe(self) -> T.Union['Executable', programs.ExternalProgram]:
         return self.exe
 
     def process_kwargs(self, kwargs):

mesonbuild/interpreter/interpreter.py

@@ -1954,8 +1954,10 @@ This will become a hard error in the future.''' % kwargs['input'], location=self
 
     @permittedKwargs({'arguments', 'output', 'depends', 'depfile', 'capture',
                       'preserve_path_from'})
-    def func_generator(self, node: mparser.FunctionNode, args, kwargs) -> GeneratorHolder:
-        gen = build.Generator(args, kwargs)
+    @typed_pos_args('generator', (ExecutableHolder, ExternalProgramHolder))
+    def func_generator(self, node: mparser.FunctionNode, args: T.Tuple[T.Union[ExecutableHolder, ExternalProgramHolder]],
+                       kwargs) -> GeneratorHolder:
+        gen = build.Generator(args[0].held_object, kwargs)
         holder = GeneratorHolder(self, gen, self)
         self.generators.append(holder)
         return holder

mesonbuild/modules/qt.py

@@ -348,7 +348,7 @@ class QtBaseModule(ExtensionModule):
             'output': 'ui_@BASENAME@.h',
             'arguments': kwargs['extra_args'] + ['-o', '@OUTPUT@', '@INPUT@']}
         # TODO: This generator isn't added to the generator list in the Interpreter
-        gen = build.Generator([self.uic], ui_kwargs)  # type: ignore
+        gen = build.Generator(self.uic, ui_kwargs)  # type: ignore
         out = gen.process_files(f'Qt{self.qt_version} ui', kwargs['sources'], state)
         return ModuleReturnValue(out, [out])
 
@@ -384,12 +384,12 @@ class QtBaseModule(ExtensionModule):
         if kwargs['headers']:
             moc_kwargs = {'output': 'moc_@BASENAME@.cpp',
                           'arguments': arguments}
-            moc_gen = build.Generator([self.moc], moc_kwargs)  # type: ignore
+            moc_gen = build.Generator(self.moc, moc_kwargs)  # type: ignore
             output.append(moc_gen.process_files(f'Qt{self.qt_version} moc header', kwargs['headers'], state))
         if kwargs['sources']:
             moc_kwargs = {'output': '@BASENAME@.moc',
                           'arguments': arguments}
-            moc_gen = build.Generator([self.moc], moc_kwargs)  # type: ignore
+            moc_gen = build.Generator(self.moc, moc_kwargs)  # type: ignore
             output.append(moc_gen.process_files(f'Qt{self.qt_version} moc source', kwargs['sources'], state))
 
         return ModuleReturnValue(output, [output])