debugcommands: add a debugpathcopies command

I've been working on storing copy metadata in the changelog instead of
the filelog and this has been useful for debugging.

Do we usually add tests for these?

Differential Revision: https://phab.mercurial-scm.org/D5791

mercurial/debugcommands.py

@@ -38,6 +38,7 b' from . import ('
     cmdutil,
     color,
     context,
+    copies,
     dagparser,
     encoding,
     error,
@@ -1804,6 +1805,18 b' def debugpathcomplete(ui, repo, *specs, '
     ui.write('\n'.join(repo.pathto(p, cwd) for p in sorted(files)))
     ui.write('\n')
 
+@command('debugpathcopies',
+         cmdutil.walkopts,
+         'hg debugcopies REV1 REV2 [FILE]',
+         inferrepo=True)
+def debugpathcopies(ui, repo, rev1, rev2, *pats, **opts):
+    """show copies between two revisions"""
+    ctx1 = scmutil.revsingle(repo, rev1)
+    ctx2 = scmutil.revsingle(repo, rev2)
+    m = scmutil.match(ctx1, pats, opts)
+    for dst, src in copies.pathcopies(ctx1, ctx2, m).items():
+        ui.write('%s -> %s\n' % (src, dst))
+
 @command('debugpeer', [], _('PATH'), norepo=True)
 def debugpeer(ui, path):
     """establish a connection to a peer repository"""

tests/test-completion.t

@@ -104,6 +104,7 b' Show debug commands if there are no othe'
   debugnamecomplete
   debugobsolete
   debugpathcomplete
+  debugpathcopies
   debugpeer
   debugpickmergetool
   debugpushkey
@@ -280,6 +281,7 b' Show all commands + options'
   debugnamecomplete: 
   debugobsolete: flags, record-parents, rev, exclusive, index, delete, date, user, template
   debugpathcomplete: full, normal, added, removed
+  debugpathcopies: include, exclude
   debugpeer: 
   debugpickmergetool: rev, changedelete, include, exclude, tool
   debugpushkey: 

tests/test-help.t

@@ -1014,6 +1014,8 b' Test list of internal help commands'
    debugoptEXP   (no help text available)
    debugpathcomplete
                  complete part or all of a tracked path
+   debugpathcopies
+                 show copies between two revisions
    debugpeer     establish a connection to a peer repository
    debugpickmergetool
                  examine which merge tool is chosen for specified file