util: add debugstacktrace depth limit

util: add debugstacktrace depth limit

Useful when you don't care about the start of the stack, but only want to see
the last entries.

--- a/mercurial/util.py	Fri Jan 16 04:26:40 2015 +0100
+++ b/mercurial/util.py	Wed Jan 14 01:15:26 2015 +0100
@@ -2841,9 +2841,9 @@
             results.append(hook(*args))
         return results
 
-def getstackframes(skip=0, line=' %-*s in %s\n', fileline='%s:%s'):
+def getstackframes(skip=0, line=' %-*s in %s\n', fileline='%s:%s', depth=0):
     '''Yields lines for a nicely formatted stacktrace.
-    Skips the 'skip' last entries.
+    Skips the 'skip' last entries, then return the last 'depth' entries.
     Each file+linenumber is formatted according to fileline.
     Each line is formatted according to line.
     If line is None, it yields:
@@ -2854,7 +2854,8 @@
     Not be used in production code but very convenient while developing.
     '''
     entries = [(fileline % (fn, ln), func)
-        for fn, ln, func, _text in traceback.extract_stack()[:-skip - 1]]
+        for fn, ln, func, _text in traceback.extract_stack()[:-skip - 1]
+        ][-depth:]
     if entries:
         fnmax = max(len(entry[0]) for entry in entries)
         for fnln, func in entries:
@@ -2863,16 +2864,18 @@
             else:
                 yield line % (fnmax, fnln, func)
 
-def debugstacktrace(msg='stacktrace', skip=0, f=stderr, otherf=stdout):
+def debugstacktrace(msg='stacktrace', skip=0,
+                    f=stderr, otherf=stdout, depth=0):
     '''Writes a message to f (stderr) with a nicely formatted stacktrace.
-    Skips the 'skip' last entries. By default it will flush stdout first.
+    Skips the 'skip' entries closest to the call, then show 'depth' entries.
+    By default it will flush stdout first.
     It can be used everywhere and intentionally does not require an ui object.
     Not be used in production code but very convenient while developing.
     '''
     if otherf:
         otherf.flush()
     f.write('%s at:\n' % msg.rstrip())
-    for line in getstackframes(skip + 1):
+    for line in getstackframes(skip + 1, depth=depth):
         f.write(line)
     f.flush()
 

--- a/tests/test-debugcommands.t	Fri Jan 16 04:26:40 2015 +0100
+++ b/tests/test-debugcommands.t	Wed Jan 14 01:15:26 2015 +0100
@@ -122,7 +122,7 @@
   >     dst('hello from g\\n', skip=1)
   >     h()
   > def h():
-  >     dst('hi ...\\nfrom h hidden in g', 1)
+  >     dst('hi ...\\nfrom h hidden in g', 1, depth=2)
   > f()
   > EOF
   $ python debugstacktrace.py
@@ -134,6 +134,5 @@
    debugstacktrace.py:4  in f
   hi ...
   from h hidden in g at:
-   debugstacktrace.py:10 in * (glob)
-   debugstacktrace.py:4  in f
-   debugstacktrace.py:7  in g
+   debugstacktrace.py:4 in f
+   debugstacktrace.py:7 in g