extdiff: refactor logic which does diff of patches

The current extdiff code is hard to understand on first look. Took me few hours
to grasp the code. Before adding more things, decided to do some refactoring.

Differential Revision: https://phab.mercurial-scm.org/D8686

hgext/extdiff.py

@@ -350,6 +350,38 b' def _runperfilediff('
                 proc.wait()
 
 
+def diffpatch(ui, repo, node1a, node2, tmproot, matcher, cmdline, do3way):
+    template = b'hg-%h.patch'
+    with formatter.nullformatter(ui, b'extdiff', {}) as fm:
+        cmdutil.export(
+            repo,
+            [repo[node1a].rev(), repo[node2].rev()],
+            fm,
+            fntemplate=repo.vfs.reljoin(tmproot, template),
+            match=matcher,
+        )
+    label1a = cmdutil.makefilename(repo[node1a], template)
+    label2 = cmdutil.makefilename(repo[node2], template)
+    dir1a = repo.vfs.reljoin(tmproot, label1a)
+    dir2 = repo.vfs.reljoin(tmproot, label2)
+    dir1b = None
+    label1b = None
+    cmdline = formatcmdline(
+        cmdline,
+        repo.root,
+        do3way=do3way,
+        parent1=dir1a,
+        plabel1=label1a,
+        parent2=dir1b,
+        plabel2=label1b,
+        child=dir2,
+        clabel=label2,
+    )
+    ui.debug(b'running %r in %s\n' % (pycompat.bytestr(cmdline), tmproot))
+    ui.system(cmdline, cwd=tmproot, blockedtag=b'extdiff')
+    return 1
+
+
 def dodiff(ui, repo, cmdline, pats, opts, guitool=False):
     '''Do the actual diff:
 
@@ -416,18 +448,20 b' def dodiff(ui, repo, cmdline, pats, opts'
 
     tmproot = pycompat.mkdtemp(prefix=b'extdiff.')
     try:
-        if not opts.get(b'patch'):
+        if opts.get(b'patch'):
+            return diffpatch(
+                ui, repo, node1a, node2, tmproot, matcher, cmdline, do3way
+            )
+
             # Always make a copy of node1a (and node1b, if applicable)
             dir1a_files = mod_a | rem_a | ((mod_b | add_b) - add_a)
-            dir1a = snapshot(ui, repo, dir1a_files, node1a, tmproot, subrepos)[
-                0
-            ]
+        dir1a = snapshot(ui, repo, dir1a_files, node1a, tmproot, subrepos)[0]
             rev1a = b'@%d' % repo[node1a].rev()
             if do3way:
                 dir1b_files = mod_b | rem_b | ((mod_a | add_a) - add_b)
-                dir1b = snapshot(
-                    ui, repo, dir1b_files, node1b, tmproot, subrepos
-                )[0]
+            dir1b = snapshot(ui, repo, dir1b_files, node1b, tmproot, subrepos)[
+                0
+            ]
                 rev1b = b'@%d' % repo[node1b].rev()
             else:
                 dir1b = None
@@ -473,23 +507,6 b' def dodiff(ui, repo, cmdline, pats, opts'
                         dir1b = pycompat.osdevnull
                 dir2 = os.path.join(dir2root, dir2, common_file)
                 label2 = common_file + rev2
-        else:
-            template = b'hg-%h.patch'
-            with formatter.nullformatter(ui, b'extdiff', {}) as fm:
-                cmdutil.export(
-                    repo,
-                    [repo[node1a].rev(), repo[node2].rev()],
-                    fm,
-                    fntemplate=repo.vfs.reljoin(tmproot, template),
-                    match=matcher,
-                )
-            label1a = cmdutil.makefilename(repo[node1a], template)
-            label2 = cmdutil.makefilename(repo[node2], template)
-            dir1a = repo.vfs.reljoin(tmproot, label1a)
-            dir2 = repo.vfs.reljoin(tmproot, label2)
-            dir1b = None
-            label1b = None
-            fnsandstat = []
 
         if not perfile:
             # Run the external tool on the 2 temp directories or the patches