debugcommands: introduce new debugrequirements command

This for now just prints out the list of current requirements. In future this
will be helpful in reading requirements from couple of sources, and checking
which requirement comes from where.

Differential Revision: https://phab.mercurial-scm.org/D8632

mercurial/debugcommands.py

@@ -2651,6 +2651,13 b' def debugrename(ui, repo, *pats, **opts)'
             ui.write(_(b"%s not renamed\n") % rel)
 
 
+@command(b'debugrequires|debugrequirements', [], b'')
+def debugrequirements(ui, repo):
+    """ print the current repo requirements """
+    for r in sorted(repo.requirements):
+        ui.write(b"%s\n" % r)
+
+
 @command(
     b'debugrevlog',
     cmdutil.debugrevlogopts + [(b'd', b'dump', False, _(b'dump index data'))],

tests/test-completion.t

@@ -121,6 +121,7 b' Show debug commands if there are no othe'
   debugrebuilddirstate
   debugrebuildfncache
   debugrename
+  debugrequires
   debugrevlog
   debugrevlogindex
   debugrevspec
@@ -306,6 +307,7 b' Show all commands + options'
   debugrebuilddirstate: rev, minimal
   debugrebuildfncache: 
   debugrename: rev
+  debugrequires: 
   debugrevlog: changelog, manifest, dir, dump
   debugrevlogindex: changelog, manifest, dir, format
   debugrevspec: optimize, show-revs, show-set, show-stage, no-optimized, verify-optimized

tests/test-help.t

@@ -1051,6 +1051,8 b' Test list of internal help commands'
    debugrebuildfncache
                  rebuild the fncache file
    debugrename   dump rename information
+   debugrequires
+                 print the current repo requirements
    debugrevlog   show data and statistics about a revlog
    debugrevlogindex
                  dump the contents of a revlog index

tests/test-requires.t

@@ -48,6 +48,14 b' another repository of push/pull/clone on'
   > # enable extension locally
   > supportlocally = $TESTTMP/supported-locally/supportlocally.py
   > EOF
+  $ hg -R supported debugrequirements
+  dotencode
+  featuresetup-test
+  fncache
+  generaldelta
+  revlogv1
+  sparserevlog
+  store
   $ hg -R supported status
 
   $ hg init push-dst