--- a/hgext/uncommit.py	Mon Mar 25 12:33:41 2019 +0530
+++ b/hgext/uncommit.py	Fri Mar 29 21:53:15 2019 -0400
@@ -33,6 +33,7 @@
     registrar,
     rewriteutil,
     scmutil,
+    util,
 )
 
 cmdtable = {}
@@ -133,8 +134,34 @@
         if len(old.parents()) > 1:
             raise error.Abort(_("cannot uncommit merge changeset"))
 
+        match = scmutil.match(old, pats, opts)
+
+        # Check all explicitly given files; abort if there's a problem.
+        if match.files():
+            s = old.status(old.p1(), match, listclean=True)
+            eligible = set(s.added) | set(s.modified) | set(s.removed)
+
+            badfiles = set(match.files()) - eligible
+
+            # Naming a parent directory of an eligible file is OK, even
+            # if not everything tracked in that directory can be
+            # uncommitted.
+            if badfiles:
+                badfiles -= set([f for f in util.dirs(eligible)])
+
+            for f in sorted(badfiles):
+                if f in s.clean:
+                    hint = _(b"file was not changed in working directory "
+                             b"parent")
+                elif repo.wvfs.exists(f):
+                    hint = _(b"file was untracked in working directory parent")
+                else:
+                    hint = _(b"file does not exist")
+
+                raise error.Abort(_(b'cannot uncommit "%s"')
+                                  % scmutil.getuipathfn(repo)(f), hint=hint)
+
         with repo.transaction('uncommit'):
-            match = scmutil.match(old, pats, opts)
             keepcommit = pats
             if not keepcommit:
                 if opts.get('keep') is not None:

--- a/tests/test-uncommit.t	Mon Mar 25 12:33:41 2019 +0530
+++ b/tests/test-uncommit.t	Fri Mar 29 21:53:15 2019 -0400
@@ -102,14 +102,16 @@
   $ hg heads -T '{rev}:{node} {desc}'
   5:0c07a3ccda771b25f1cb1edbd02e683723344ef1 new change abcde (no-eol)
 
-Uncommit of non-existent and unchanged files has no effect
+Uncommit of non-existent and unchanged files aborts
   $ hg uncommit nothinghere
-  nothing to uncommit
-  [1]
+  abort: cannot uncommit "nothinghere"
+  (file does not exist)
+  [255]
   $ hg status
   $ hg uncommit file-abc
-  nothing to uncommit
-  [1]
+  abort: cannot uncommit "file-abc"
+  (file was not changed in working directory parent)
+  [255]
   $ hg status
 
 Try partial uncommit, also moves bookmark
@@ -513,3 +515,57 @@
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     add a
   
+Removes can be uncommitted
+
+  $ hg ci -m 'modified b'
+  $ hg rm b
+  $ hg ci -m 'remove b'
+  $ hg uncommit b
+  note: keeping empty commit
+  $ hg status
+  R b
+
+Uncommitting a directory won't run afoul of the checks that an explicit file
+can be uncommitted.
+
+  $ mkdir dir
+  $ echo 1 > dir/file.txt
+  $ hg ci -Aqm 'add file in directory'
+  $ hg uncommit dir
+  $ hg status
+  A dir/file.txt
+
+`uncommit <dir>` and `cd <dir> && uncommit .` behave the same...
+
+  $ hg rollback -q --config ui.rollback=True
+  $ echo 2 > dir/file2.txt
+  $ hg ci -Aqm 'add file2 in directory'
+  $ hg uncommit dir
+  note: keeping empty commit
+  $ hg status
+  A dir/file2.txt
+
+  $ hg rollback -q --config ui.rollback=True
+  $ cd dir
+  $ hg uncommit .
+  note: keeping empty commit
+  $ hg status
+  A dir/file2.txt
+  $ cd ..
+
+... and errors out the same way when nothing can be uncommitted
+
+  $ hg rollback -q --config ui.rollback=True
+  $ mkdir emptydir
+  $ hg uncommit emptydir
+  abort: cannot uncommit "emptydir"
+  (file was untracked in working directory parent)
+  [255]
+
+  $ cd emptydir
+  $ hg uncommit .
+  abort: cannot uncommit "emptydir"
+  (file was untracked in working directory parent)
+  [255]
+  $ hg status
+  $ cd ..