histedit: add test for folding subtree commits

Summary:
Currently, histedit does not support merge and subtree metadata. This diff
adds a test to show that it will lose subtree metadata

Reviewed By: muirdm

Differential Revision: D75897811

fbshipit-source-id: 381208cd814e55d3c72dbf551602987c31e885bf

Author: zzl0

eden/scm/tests/test-subtree-histedit.t

@@ -0,0 +1,65 @@
+  $ setconfig diff.git=True
+  $ setconfig subtree.allow-any-source-commit=True
+  $ setconfig subtree.min-path-depth=1
+  $ enable histedit
+
+test histedit to fold subtree merge commits
+  $ newclientrepo
+  $ drawdag <<'EOS'
+  > D  # D/foo/x = 1a\n2a\n3a\n
+  > |
+  > C  # C/foo/x = 1a\n2a\n3\n
+  > |
+  > B  # B/foo/x = 1a\n2\n3\n
+  > |
+  > A  # A/foo/x = 1\n2\n3\n
+  > EOS
+  $ hg go -q $D
+  $ hg subtree copy -r $A --from-path foo --to-path foo2 -m "subtree copy foo to foo2"
+  copying foo to foo2
+  $ hg subtree copy -r $A --from-path foo --to-path foo3 -m "subtree copy foo to foo3"
+  copying foo to foo3
+  $ hg subtree merge -r $B --from-path foo --to-path foo2
+  computing merge base (timeout: 120 seconds)...
+  merge base: b4cb27eee4e2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (subtree merge, don't forget to commit)
+  $ hg ci -m "merge B from foo to foo2"
+  $ hg subtree merge -r $C --from-path foo --to-path foo3
+  computing merge base (timeout: 120 seconds)...
+  merge base: b4cb27eee4e2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (subtree merge, don't forget to commit)
+  $ hg ci -m "merge C from foo to foo3"
+  $ hg log -G -T '{node|short} {desc|firstline}\n'
+  @  c90acfc6d9e6 merge C from foo to foo3
+  │
+  o  23b8d4a76647 merge B from foo to foo2
+  │
+  o  f6ef74a89a69 subtree copy foo to foo3
+  │
+  o  44d9b171824f subtree copy foo to foo2
+  │
+  o  8451df1af03b D
+  │
+  o  4701d37a062f C
+  │
+  o  c4fbbcdf676b B
+  │
+  o  b4cb27eee4e2 A
+  $ hg histedit 23b8d4a76647 --commands - <<EOF
+  > pick 23b8d4a76647 merge B from foo to foo2
+  > f c90acfc6d9e6 merge C from foo to foo3
+  > EOF
+tofix: the combined commits should have two subtree merge metadata
+  $ hg subtree inspect -r .
+  {
+    "merges": [
+      {
+        "version": 1,
+        "from_commit": "c4fbbcdf676b67867d7a51393f12109974c5da59",
+        "from_path": "foo",
+        "to_path": "foo2"
+      }
+    ]
+  }