commitctx: extract all the manual logic to process the files

commitctx: extract all the manual logic to process the files

That branch of the if is significantly more complicated than the other two.
Moving it to its own function make it simple to keep the scope limited and to
read to the higher level function.

--- a/mercurial/commit.py	Thu Jul 23 23:08:00 2020 +0200
+++ b/mercurial/commit.py	Thu Jul 23 18:25:45 2020 +0200
@@ -84,66 +84,10 @@
             mn = p1.manifestnode()
             files = []
         else:
-            m1ctx = p1.manifestctx()
-            m2ctx = p2.manifestctx()
-            mctx = m1ctx.copy()
-
-            m = mctx.read()
-            m1 = m1ctx.read()
-            m2 = m2ctx.read()
-
-            # check in files
-            added = []
-            files_added = []
-            removed = list(ctx.removed())
-            touched = []
-            linkrev = len(repo)
-            repo.ui.note(_(b"committing files:\n"))
-            uipathfn = scmutil.getuipathfn(repo)
-            for f in sorted(ctx.modified() + ctx.added()):
-                repo.ui.note(uipathfn(f) + b"\n")
-                try:
-                    fctx = ctx[f]
-                    if fctx is None:
-                        removed.append(f)
-                    else:
-                        added.append(f)
-                        m[f], is_touched = _filecommit(
-                            repo, fctx, m1, m2, linkrev, tr, writefilecopymeta,
-                        )
-                        if is_touched:
-                            touched.append(f)
-                            if is_touched == 'added':
-                                files_added.append(f)
-                        m.setflag(f, fctx.flags())
-                except OSError:
-                    repo.ui.warn(_(b"trouble committing %s!\n") % uipathfn(f))
-                    raise
-                except IOError as inst:
-                    errcode = getattr(inst, 'errno', errno.ENOENT)
-                    if error or errcode and errcode != errno.ENOENT:
-                        repo.ui.warn(
-                            _(b"trouble committing %s!\n") % uipathfn(f)
-                        )
-                    raise
-
-            # update manifest
-            removed = [f for f in removed if f in m1 or f in m2]
-            drop = sorted([f for f in removed if f in m])
-            for f in drop:
-                del m[f]
-            if p2.rev() != nullrev:
-                rf = metadata.get_removal_filter(ctx, (p1, p2, m1, m2))
-                removed = [f for f in removed if not rf(f)]
-
-            touched.extend(removed)
-
-            files = touched
-            mn = _commit_manifest(tr, linkrev, ctx, mctx, files, added, drop)
-
+            mn, files, added, removed = _process_files(tr, ctx, error=error)
             if writechangesetcopy:
                 filesremoved = removed
-                filesadded = files_added
+                filesadded = added
 
         if not writefilecopymeta:
             # If writing only to changeset extras, use None to indicate that
@@ -192,6 +136,71 @@
         return n
 
 
+def _process_files(tr, ctx, error=False):
+    repo = ctx.repo()
+    p1 = ctx.p1()
+    p2 = ctx.p2()
+
+    writechangesetcopy, writefilecopymeta = _write_copy_meta(repo)
+
+    m1ctx = p1.manifestctx()
+    m2ctx = p2.manifestctx()
+    mctx = m1ctx.copy()
+
+    m = mctx.read()
+    m1 = m1ctx.read()
+    m2 = m2ctx.read()
+
+    # check in files
+    added = []
+    filesadded = []
+    removed = list(ctx.removed())
+    touched = []
+    linkrev = len(repo)
+    repo.ui.note(_(b"committing files:\n"))
+    uipathfn = scmutil.getuipathfn(repo)
+    for f in sorted(ctx.modified() + ctx.added()):
+        repo.ui.note(uipathfn(f) + b"\n")
+        try:
+            fctx = ctx[f]
+            if fctx is None:
+                removed.append(f)
+            else:
+                added.append(f)
+                m[f], is_touched = _filecommit(
+                    repo, fctx, m1, m2, linkrev, tr, writefilecopymeta,
+                )
+                if is_touched:
+                    touched.append(f)
+                    if is_touched == 'added':
+                        filesadded.append(f)
+                m.setflag(f, fctx.flags())
+        except OSError:
+            repo.ui.warn(_(b"trouble committing %s!\n") % uipathfn(f))
+            raise
+        except IOError as inst:
+            errcode = getattr(inst, 'errno', errno.ENOENT)
+            if error or errcode and errcode != errno.ENOENT:
+                repo.ui.warn(_(b"trouble committing %s!\n") % uipathfn(f))
+            raise
+
+    # update manifest
+    removed = [f for f in removed if f in m1 or f in m2]
+    drop = sorted([f for f in removed if f in m])
+    for f in drop:
+        del m[f]
+    if p2.rev() != nullrev:
+        rf = metadata.get_removal_filter(ctx, (p1, p2, m1, m2))
+        removed = [f for f in removed if not rf(f)]
+
+    touched.extend(removed)
+
+    files = touched
+    mn = _commit_manifest(tr, linkrev, ctx, mctx, files, added, drop)
+
+    return mn, files, filesadded, removed
+
+
 def _filecommit(
     repo, fctx, manifest1, manifest2, linkrev, tr, includecopymeta,
 ):