From ad6569e3e976cee0320939572d17eef228a6e7a0 Mon Sep 17 00:00:00 2001
From: Rob Taylor <rob.taylor@chipflow.io>
Date: Wed, 30 Jul 2025 18:52:20 +0100
Subject: [PATCH 1/2] Modify MustUse to iterate the stack frame and collate
 options from all frames.

Options in closer frames take precedence
---
 amaranth/_unused.py |  6 ++++--
 amaranth/_utils.py  | 27 +++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/amaranth/_unused.py b/amaranth/_unused.py
index 4f2507bc1..4d28bf8d3 100644
--- a/amaranth/_unused.py
+++ b/amaranth/_unused.py
@@ -18,7 +18,9 @@ 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 +33,7 @@ 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,
diff --git a/amaranth/_utils.py b/amaranth/_utils.py
index b6591fdbb..da90c9dcf 100644
--- a/amaranth/_utils.py
+++ b/amaranth/_utils.py
@@ -75,6 +75,7 @@ def decorator_like(*args, **kwargs):
         return decorator_like
 
 
+
 def get_linter_options(filename):
     first_line = linecache.getline(filename, 1)
     if first_line:
@@ -84,8 +85,30 @@ def get_linter_options(filename):
     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:
+
+    .. code::
+        # amaranth: {name}=value
+
+    The earliest option value in the stack takes precedence
+
+    Returns
+    -------
+    :class:`bool` or :class:`int`
+        Option value
+    """
+
+    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
 

From 5d8232351e01ab5bdab6a8542b62daf781a7d579 Mon Sep 17 00:00:00 2001
From: Rob Taylor <rob.taylor@chipflow.io>
Date: Tue, 5 Aug 2025 00:14:10 +0100
Subject: [PATCH 2/2] MustUse: Don't hold onto frame pointers

---
 amaranth/_unused.py | 6 +++---
 amaranth/_utils.py  | 7 +++++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/amaranth/_unused.py b/amaranth/_unused.py
index 4d28bf8d3..dbb9b0c33 100644
--- a/amaranth/_unused.py
+++ b/amaranth/_unused.py
@@ -1,7 +1,7 @@
 import sys
 import warnings
 
-from ._utils import get_linter_option
+from ._utils import get_linter_option, collate_linter_options
 
 
 __all__ = ["UnusedMustUse", "MustUse"]
@@ -20,7 +20,7 @@ def __new__(cls, *args, src_loc_at=0, **kwargs):
         self = super().__new__(cls)
 
         self._MustUse__used  = False
-        self._MustUse__frame = frame
+        self._MustUse__options = collate_linter_options(frame)
         self._MustUse__context = dict(
             filename=frame.f_code.co_filename,
             lineno=frame.f_lineno,
@@ -33,7 +33,7 @@ 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__frame,
+            if get_linter_option(self._MustUse__options,
                                  self._MustUse__warning.__qualname__, bool, True):
                 warnings.warn_explicit(
                     f"{self!r} created but never used", self._MustUse__warning,
diff --git a/amaranth/_utils.py b/amaranth/_utils.py
index da90c9dcf..f728e5153 100644
--- a/amaranth/_utils.py
+++ b/amaranth/_utils.py
@@ -85,9 +85,9 @@ def get_linter_options(filename):
     return dict()
 
 
-def get_linter_option(frame, name, type, default):
+def collate_linter_options(frame):
     """
-    Get given linter option for a given stack frame. This iterates down the frames, collating options of the form:
+    Get all linter options for a given stack frame. This iterates down the frames, collating options of the form:
 
     .. code::
         # amaranth: {name}=value
@@ -108,7 +108,10 @@ def get_linter_option(frame, name, type, default):
             break
         else:
             frame = frame.f_back
+    return options
 
+
+def get_linter_option(options, name, type, default):
     if name not in options:
         return default