# HG changeset patch
# User Martin von Zweigbergk <martinvonz@google.com>
# Date 1549526219 28800
# Node ID ec37db02fc728840fca4c9535ba4f4e96a104516
# Parent  d4c9eebdd72d1d97ae5071559c3e85f729152cc6
diff: make `hg diff --root=subrepo` work

The root prefix is currently stripped before adding the subrepo
prefix. It seems to me that if you run `hg diff --root=subrepo` and a
subrepo/ path is visited (say "subrepo/foo"), then the path generated
for the diff would initially be just "foo" and we then fail (if the
developer warning is active) to strip the "subrepo/" from the path. It
seems like we should first add the prefix in order to produce a path
that's relative to the top-level repo, and then we can remove the root
prefix from that. There are no tests for this, it seems, and I don't
care enough to add one.

Differential Revision: https://phab.mercurial-scm.org/D5895

diff -r d4c9eebdd72d -r ec37db02fc72 mercurial/logcmdutil.py
--- a/mercurial/logcmdutil.py	Wed Feb 06 23:12:56 2019 -0800
+++ b/mercurial/logcmdutil.py	Wed Feb 06 23:56:59 2019 -0800
@@ -66,6 +66,8 @@
     else:
         relroot = ''
     copysourcematch = None
+    def compose(f, g):
+        return lambda x: f(g(x))
     def pathfn(f):
         return posixpath.join(prefix, f)
     if relroot != '':
@@ -84,11 +86,12 @@
 
         checkroot = (repo.ui.configbool('devel', 'all-warnings') or
                      repo.ui.configbool('devel', 'check-relroot'))
-        def pathfn(f):
+        def relrootpathfn(f):
             if checkroot and not f.startswith(relroot):
                 raise AssertionError(
                     "file %s doesn't start with relroot %s" % (f, relroot))
-            return posixpath.join(prefix, f[len(relroot):])
+            return f[len(relroot):]
+        pathfn = compose(relrootpathfn, pathfn)
 
     if stat:
         diffopts = diffopts.copy(context=0, noprefix=False)