tests: test more cases where a file got replaced by a copy

This adds a test where a file is modified on one branch and is renamed
onto another file in another branch. That should ideally be
automatically resolved (by propagating the modification to the rename
destination). Alternatively, it could be considered a modify/delete
conflict. It should at least not be automatically resolved by ignoring
the modification. However, that is what actually happens with the
changeset-centric algorithm since I broke it in b4057d001760 (merge:
when rename was made on both sides, use ancestor as merge base,
2020-01-22). Before that commit, it resulted in a modify/delete
conflict. The filelog-centric algorithm was broken already before that
commit.

Differential Revision: https://phab.mercurial-scm.org/D8652

tests/test-copies.t

@@ -462,6 +462,73 b' Try merging the other direction too'
   $ hg debugpathcopies 0 5
   x -> z
 
+Create x and y, then remove y and rename x to y on one side of merge, and
+modify x on the other side. The modification to x from the second side
+should be propagated to y.
+  $ newrepo
+  $ echo original > x
+  $ hg add x
+  $ echo unrelated > y
+  $ hg add y
+  $ hg commit -m 'add x and y'
+  $ hg remove y
+  $ hg commit -m 'remove y'
+  $ hg rename x y
+  $ hg commit -m 'rename x to y'
+  $ hg checkout -q 0
+  $ echo modified > x
+  $ hg commit -m 'modify x'
+  created new head
+  $ hg l
+  @  3 modify x
+  |  x
+  | o  2 rename x to y
+  | |  x y
+  | o  1 remove y
+  |/   y
+  o  0 add x and y
+     x y
+#if filelog
+  $ hg merge 2
+  file 'x' was deleted in other [merge rev] but was modified in local [working copy].
+  You can use (c)hanged version, (d)elete, or leave (u)nresolved.
+  What do you want to do? u
+  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
+  [1]
+BROKEN: should be "modified"
+  $ cat y
+  original
+#else
+  $ hg merge 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+BROKEN: should be "modified"
+  $ cat y
+  original
+#endif
+Same as above, but in the opposite direction
+#if filelog
+  $ hg co -qC 2
+  $ hg merge 3
+  file 'x' was deleted in local [working copy] but was modified in other [merge rev].
+  You can use (c)hanged version, leave (d)eleted, or leave (u)nresolved.
+  What do you want to do? u
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
+  [1]
+BROKEN: should be "modified"
+  $ cat y
+  original
+#else
+  $ hg co -qC 2
+  $ hg merge 3
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+BROKEN: should be "modified"
+  $ cat y
+  original
+#endif
 
 Create x and y, then rename x to z on one side of merge, and rename y to z and
 then delete z on the other side.