git: fix a histedit edge case on git mode

Summary:
The signature of `gitcommittext` is a bit wrong, as the `date` parameter can actually receive a tuple of numbers, and not only a string. On top of that, `git_commit_fields_to_text` does not know how to process floats because the tuple gets serialized into an `HgTime` on the Rust side:

```
pub struct HgTime {
    pub unixtime: i64,
    pub offset: i32,
}
```

Reviewed By: muirdm

Differential Revision: D67353905

fbshipit-source-id: a563ccaea81cc6533a10b359a5bd067fe724887c

eden/scm/sapling/changelog.py

@@ -14,7 +14,7 @@
 
 import subprocess
 import textwrap
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Tuple, Union
 
 import bindings
 
@@ -312,7 +312,7 @@ def gitcommittext(
     parents: List[bytes],
     desc: str,
     user: str,
-    date: Optional[str],
+    date: Optional[Union[str, Tuple[Union[int, float], int]]],
     extra: Optional[Dict[str, str]],
     gpgkeyid: Optional[str] = None,
 ) -> bytes:
@@ -390,12 +390,14 @@ def gitcommittext(
     if date != authordate and date != committerdate:
         authordate = date
 
+    author_time, author_tz = util.parsedate(authordate)
+
     # see Rust format-util GitCommitFields for available fields
     fields = {
         "tree": tree,
         "parents": parents,
         "author": user,
-        "date": util.parsedate(authordate),
+        "date": (int(author_time), author_tz),
         "committer": committer,
         "committer_date": util.parsedate(committerdate),
         "message": desc,

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

@@ -15,25 +15,18 @@ setup repo
 
 folding should work
 
-FIXME: histedit should work
-  $ hg histedit -q --commands - 2>&1 << EOF | tail -n 5
+  $ hg histedit --commands - << EOF
   > pick fd2a67d81220 'A1'
   > pick bc8bd49c677f 'A2'
   > fold 081c9e396fa1 'A3'
   > pick 91ad706dafee 'A4'
   > EOF
-    File *, in add (glob)
-      text = gitcommittext(
-    File *, in gitcommittext (glob)
-      text = to_text(fields).encode()
-  TypeError: 'float' object cannot be interpreted as an integer
   $ hg st
-  A A3
   $ tglog
-  o  91ad706dafee 'A4'
+  @  17e3aa7dc15f 'A4'
   │
-  o  081c9e396fa1 'A3'
-  │
-  @  bc8bd49c677f 'A2'
+  o  594d4e89c0ff 'A2
   │
+  │  ***
+  │  A3'
   o  fd2a67d81220 'A1'