simplemerge: make `localorother` a "mode" instead of a separate thing

simplemerge: make `localorother` a "mode" instead of a separate thing

`simplemerge()` takes a `mode` argument, which can be "union", "merge"
or "mergediff", and a `localorother` argument, which can be `None`,
"local", or "other". The two options are not at all orthogonal -- most
combinations don't make sense. Also, at least "union", "local", and
"other" are very closely related. Therefore, it makes sense to combine
them into one.

It probably makes sense to split the `mode` argument into `resolve`
and `marker_style`, where the former can be `None`, "union", "local",
or "other", and the latter can be "merge", "merge3", "mergediff", or
"minimize". This is a good step in that direction whether or not we
end up doing that.

Differential Revision: https://phab.mercurial-scm.org/D11887

--- a/mercurial/filemerge.py	Tue Dec 07 14:11:58 2021 -0800
+++ b/mercurial/filemerge.py	Tue Dec 07 17:48:50 2021 -0800
@@ -579,43 +579,24 @@
     )
 
 
-def _imergeauto(
-    repo,
-    mynode,
-    fcd,
-    fco,
-    fca,
-    toolconf,
-    backup,
-    labels=None,
-    localorother=None,
-):
-    """
-    Generic driver for _imergelocal and _imergeother
-    """
-    assert localorother is not None
-    r = simplemerge.simplemerge(
-        repo.ui, fcd, fca, fco, label=labels, localorother=localorother
-    )
-    return True, r
-
-
 @internaltool(b'merge-local', mergeonly, precheck=_mergecheck)
-def _imergelocal(*args, **kwargs):
+def _imergelocal(repo, mynode, fcd, fco, fca, toolconf, backup, labels=None):
     """
     Like :merge, but resolve all conflicts non-interactively in favor
     of the local `p1()` changes."""
-    success, status = _imergeauto(localorother=b'local', *args, **kwargs)
-    return success, status, False
+    return _merge(
+        repo, mynode, fcd, fco, fca, toolconf, backup, labels, b'local'
+    )
 
 
 @internaltool(b'merge-other', mergeonly, precheck=_mergecheck)
-def _imergeother(*args, **kwargs):
+def _imergeother(repo, mynode, fcd, fco, fca, toolconf, backup, labels=None):
     """
     Like :merge, but resolve all conflicts non-interactively in favor
     of the other `p2()` changes."""
-    success, status = _imergeauto(localorother=b'other', *args, **kwargs)
-    return success, status, False
+    return _merge(
+        repo, mynode, fcd, fco, fca, toolconf, backup, labels, b'other'
+    )
 
 
 @internaltool(

--- a/mercurial/simplemerge.py	Tue Dec 07 14:11:58 2021 -0800
+++ b/mercurial/simplemerge.py	Tue Dec 07 17:48:50 2021 -0800
@@ -516,13 +516,17 @@
 
     m3 = Merge3Text(basetext, localtext, othertext)
     extrakwargs = {
-        "localorother": opts.get("localorother", None),
+        "localorother": None,
         'minimize': True,
     }
     if mode == b'union':
         extrakwargs['start_marker'] = None
         extrakwargs['mid_marker'] = None
         extrakwargs['end_marker'] = None
+    elif mode == b'local':
+        extrakwargs['localorother'] = b'local'
+    elif mode == b'other':
+        extrakwargs['localorother'] = b'other'
     elif name_base is not None:
         extrakwargs['base_marker'] = b'|||||||'
         extrakwargs['name_base'] = name_base