From d66bbb0df825d2b77e5e589a03829e70de35fd88 Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Fri, 28 Dec 2018 01:31:24 +0000
Subject: [PATCH] tracer: factor out get_src_loc().

---
 nmigen/hdl/ast.py | 10 ++--------
 nmigen/hdl/mem.py |  8 ++------
 nmigen/tracer.py  | 13 ++++++++++++-
 3 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/nmigen/hdl/ast.py b/nmigen/hdl/ast.py
index 52e7dd3..462a422 100644
--- a/nmigen/hdl/ast.py
+++ b/nmigen/hdl/ast.py
@@ -39,12 +39,7 @@ class Value(metaclass=ABCMeta):
 
     def __init__(self, src_loc_at=0):
         super().__init__()
-
-        tb = traceback.extract_stack(limit=3 + src_loc_at)
-        if len(tb) < src_loc_at:
-            self.src_loc = None
-        else:
-            self.src_loc = (tb[0].filename, tb[0].lineno)
+        self.src_loc = tracer.get_src_loc(1 + src_loc_at)
 
     def __bool__(self):
         raise TypeError("Attempted to convert nMigen value to boolean")
@@ -721,8 +716,7 @@ class Array(MutableSequence):
     def __getitem__(self, index):
         if isinstance(index, Value):
             if self._mutable:
-                tb = traceback.extract_stack(limit=2)
-                self._proxy_at = (tb[0].filename, tb[0].lineno)
+                self._proxy_at = tracer.get_src_loc()
                 self._mutable  = False
             return ArrayProxy(self, index)
         else:
diff --git a/nmigen/hdl/mem.py b/nmigen/hdl/mem.py
index 7273118..4863fd8 100644
--- a/nmigen/hdl/mem.py
+++ b/nmigen/hdl/mem.py
@@ -1,5 +1,3 @@
-import traceback
-
 from .. import tracer
 from .ast import *
 from .ir import Instance
@@ -17,15 +15,13 @@ class Memory:
             raise TypeError("Memory depth must be a non-negative integer, not '{!r}'"
                             .format(depth))
 
-        tb = traceback.extract_stack(limit=2)
-        self.src_loc = (tb[0].filename, tb[0].lineno)
-
         if name is None:
             try:
                 name = tracer.get_var_name(depth=2)
             except tracer.NameNotFound:
                 name = "$memory"
-        self.name = name
+        self.name    = name
+        self.src_loc = tracer.get_src_loc()
 
         self.width = width
         self.depth = depth
diff --git a/nmigen/tracer.py b/nmigen/tracer.py
index e018c8f..225ee1a 100644
--- a/nmigen/tracer.py
+++ b/nmigen/tracer.py
@@ -1,8 +1,9 @@
+import traceback
 import inspect
 from opcode import opname
 
 
-__all__ = ["NameNotFound", "get_var_name"]
+__all__ = ["NameNotFound", "get_var_name", "get_src_loc"]
 
 
 class NameNotFound(Exception):
@@ -37,3 +38,13 @@ def get_var_name(depth=2):
             index += 2
         else:
             raise NameNotFound
+
+
+def get_src_loc(src_loc_at=0):
+    # n-th  frame: get_src_loc()
+    # n-1th frame: caller of get_src_loc() (usually constructor)
+    # n-2th frame: caller of caller (usually user code)
+    # Python returns the stack frames reversed, so it is enough to set limit and grab the very
+    # first one in the array.
+    tb = traceback.extract_stack(limit=3 + src_loc_at)
+    return (tb[0].filename, tb[0].lineno)
-- 
2.30.2