Simplify module API

- ModuleState is now a real class that will have methods in the future
  for actions modules needs, instead of using interpreter internal API.
- New ModuleObject base class, similar to InterpreterObject, that should
  be used by all objects returned by modules. Its methods gets the
  ModuleState passed as first argument. It has a `methods` dictionary to
  define what is public API that can be called from build definition.
- Method return value is not required to be a ModuleReturnValue any
  more, it can be any type that interpreter can holderify, including
  ModuleObject.
- Legacy module API is maintained until we port all modules.

In the future modules should be updated:
- Use methods dict.
- Remove snippets.
- Custom objects returned by modules should all be subclass of
  ModuleObject to get the state iface in their methods.
- Modules should never call into interpreter directly and instead state
  object should have wrapper API.
- Stop using ModuleReturnValue in methods that just return simple
  objects like strings. Possibly remove ModuleReturnValue completely
  since all objects that needs to be processed by interpreter (e.g.
  CustomTarget) should be created through ModuleState API.

1 files changed, 44 insertions, 7 deletions

diff --git a/mesonbuild/modules/__init__.py b/mesonbuild/modules/__init__.py
index ff27a112b..1cf7c1cf5 100644
--- a/mesonbuild/modules/__init__.py
+++ b/mesonbuild/modules/__init__.py
@@ -18,21 +18,58 @@
 import os
 
 from .. import build
-from ..mesonlib import unholder
+from ..mesonlib import unholder, relpath
 import typing as T
 
 if T.TYPE_CHECKING:
     from ..interpreter import Interpreter
-    from ..interpreterbase import TYPE_var
+    from ..interpreterbase import TYPE_var, TYPE_nvar, TYPE_nkwargs
+
+class ModuleState:
+    """Object passed to all module methods.
+
+    This is a WIP API provided to modules, it should be extended to have everything
+    needed so modules does not touch any other part of Meson internal APIs.
+    """
 
-class ExtensionModule:
     def __init__(self, interpreter: 'Interpreter') -> None:
+        self.source_root = interpreter.environment.get_source_dir()
+        self.build_to_src = relpath(interpreter.environment.get_source_dir(),
+                                    interpreter.environment.get_build_dir())
+        self.subproject = interpreter.subproject
+        self.subdir = interpreter.subdir
+        self.current_lineno = interpreter.current_lineno
+        self.environment = interpreter.environment
+        self.project_name = interpreter.build.project_name
+        self.project_version = interpreter.build.dep_manifest[interpreter.active_projectname]
+        # The backend object is under-used right now, but we will need it:
+        # https://github.com/mesonbuild/meson/issues/1419
+        self.backend = interpreter.backend
+        self.targets = interpreter.build.targets
+        self.data = interpreter.build.data
+        self.headers = interpreter.build.get_headers()
+        self.man = interpreter.build.get_man()
+        self.global_args = interpreter.build.global_args.host
+        self.project_args = interpreter.build.projects_args.host.get(interpreter.subproject, {})
+        self.build_machine = interpreter.builtin['build_machine'].held_object
+        self.host_machine = interpreter.builtin['host_machine'].held_object
+        self.target_machine = interpreter.builtin['target_machine'].held_object
+        self.current_node = interpreter.current_node
+
+class ModuleObject:
+    """Base class for all objects returned by modules
+    """
+    def __init__(self, interpreter: T.Optional['Interpreter'] = None) -> None:
+        self.methods = {}  # type: T.Dict[str, T.Callable[[T.List[TYPE_nvar], TYPE_nkwargs], TYPE_var]]
+        # FIXME: Port all modules to stop using self.interpreter and use API on
+        # ModuleState instead.
         self.interpreter = interpreter
-        self.snippets = set()  # type: T.Set[str] # List of methods that operate only on the interpreter.
-
-    def is_snippet(self, funcname: str) -> bool:
-        return funcname in self.snippets
+        # FIXME: Port all modules to remove snippets methods.
+        self.snippets: T.Set[str] = set()
 
+# FIXME: Port all modules to use ModuleObject directly.
+class ExtensionModule(ModuleObject):
+    pass
 
 def get_include_args(include_dirs, prefix='-I'):
     '''