whereami: add extension

Summary:
This command will allow us to expose simple api to all automation checking
working copy parent.  It's meant to be overridden by our wrapper to read the
dirsate directly without shelling out to hg (see D4454504 )

Test Plan: see tests

Reviewers: #mercurial, durham, rmcelroy

Reviewed By: rmcelroy

Subscribers: mjpieters

Differential Revision: https://phabricator.intern.facebook.com/D4454502

Signature: t1:4454502:1485441135:09902c6437a7af55dfa5c97e3165681de687231f

hgext3rd/whereami.py

@@ -0,0 +1,18 @@
+from mercurial import cmdutil
+from mercurial.node import hex, nullid
+
+cmdtable = {}
+command = cmdutil.command(cmdtable)
+testedwith = 'ships-with-fb-hgext'
+
+@command('whereami')
+def whereami(ui, repo, *args, **opts):
+    """output the current working directory parents
+
+    Outputs the hashes of current working directory parents separated
+    by newline.
+    """
+    parents = repo.dirstate.parents()
+    ui.status('%s\n' % hex(parents[0]))
+    if parents[1] != nullid:
+        ui.status('%s\n' % hex(parents[1]))

tests/test-whereami.t

@@ -0,0 +1,38 @@
+Test whereami
+
+  $ hg init repo1
+  $ cd repo1
+  $ cat > .hg/hgrc <<EOF
+  > [extensions]
+  > whereami=$(dirname $TESTDIR)/hgext3rd/whereami.py
+  > EOF
+
+  $ hg whereami
+  0000000000000000000000000000000000000000
+
+  $ echo a > a
+  $ hg add a
+  $ hg commit -m a
+
+  $ hg whereami
+  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b
+
+  $ echo b > b
+  $ hg add  b
+  $ hg commit -m b
+
+  $ hg up ".^"
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+
+  $ echo c > c
+  $ hg add  c
+  $ hg commit -m c
+  created new head
+
+  $ hg merge 1
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+
+  $ hg whereami
+  d36c0562f908c692f5204d606d4ff3537d41f1bf
+  d2ae7f538514cd87c17547b0de4cea71fe1af9fb