Modify MustUse to iterate the stack frame and collate options from all frames.

Options in closer frames take precedence

Author: robtaylor

amaranth/_unused.py

@@ -1,5 +1,6 @@
 import sys
 import warnings
+import logging
 
 from ._utils import get_linter_option
 
@@ -18,7 +19,9 @@ class MustUse:
     def __new__(cls, *args, src_loc_at=0, **kwargs):
         frame = sys._getframe(1 + src_loc_at)
         self = super().__new__(cls)
-        self._MustUse__used    = False
+
+        self._MustUse__used  = False
+        self._MustUse__frame = frame
         self._MustUse__context = dict(
             filename=frame.f_code.co_filename,
             lineno=frame.f_lineno,
@@ -31,7 +34,7 @@ def __del__(self):
         if getattr(self._MustUse__warning, "_MustUse__silence", False):
             return
         if hasattr(self, "_MustUse__used") and not self._MustUse__used:
-            if get_linter_option(self._MustUse__context["filename"],
+            if get_linter_option(self._MustUse__frame,
                                  self._MustUse__warning.__qualname__, bool, True):
                 warnings.warn_explicit(
                     f"{self!r} created but never used", self._MustUse__warning,

amaranth/_utils.py

@@ -74,18 +74,39 @@ def decorator_like(*args, **kwargs):
                 return f(*args, **kwargs)
         return decorator_like
 
+_LINT_PATTERN = re.compile(r"^#\s*amaranth:\s*((?:\w+=\w+\s*)(?:,\s*\w+=\w+\s*)*)\n$")
+
 
 def get_linter_options(filename):
     first_line = linecache.getline(filename, 1)
     if first_line:
-        match = re.match(r"^#\s*amaranth:\s*((?:\w+=\w+\s*)(?:,\s*\w+=\w+\s*)*)\n$", first_line)
+        match = _LINT_PATTERN.match(first_line)
         if match:
             return dict(map(lambda s: s.strip().split("=", 2), match.group(1).split(",")))
     return dict()
 
 
-def get_linter_option(filename, name, type, default):
-    options = get_linter_options(filename)
+def get_linter_option(frame, name, type, default):
+    """
+    Get given linter option for a given stack frame. This iterates down the frames, collating options of the form:
+    ```
+    # amaranth: {name} = value
+    ```
+    The earliest option value in the stack takes precedence
+
+    Returns:
+        option value: bool | int
+    """
+
+    options = {}
+    while frame:
+        f_opts = get_linter_options(frame.f_code.co_filename)
+        options = f_opts | options
+        if frame.f_back is None:
+            break
+        else:
+            frame = frame.f_back
+
     if name not in options:
         return default