Mercurial has a bunch of features for debugging problems that are useful for developers to know about.

global options

-v, --verbose
  • show more verbose output
--debug
  • show extended debugging output
--traceback
  • show Python tracebacks that are otherwise hidden
--profile
  • generate performance profiling information
--debugger
  • drop into the built-in source-level debugger (more below)

debug commands

debugcheckstate
  • validate the correctness of the current dirstate
debugconfig
  • show combined config settings from all hgrc files
debugdata
  • dump the contents of an data file revision
debugindex
  • dump the contents of an index file
debugindexdot
  • dump an index DAG as a .dot file
debugrename
  • dump rename information
debugstate
  • show the contents of the current dirstate
debugwalk
  • show how files match on given patterns

using the debugger

hg --debugger <command> will drop you at the debug prompt shortly before command execution. This will allow you to set breakpoints, singlestep code, inspect data structures, and run arbitrary bits of Python code. Help is available with '?'.

If you let Mercurial run (with 'cont'), the debugger will be reinvoked if an exception occurs. This is useful for diagnosing tracebacks in situ.