cmdutil: add special string that ignores rest of text

Similar to git, we add a special string:

  HG: ------------------------ >8 ------------------------

that means anything below it is ignored in a commit message.

This is helpful for integrating with third-party tools that display the

mercurial/cmdutil.py

@@ -49,6 +49,10 b' from . import ('
 )
 stringio = util.stringio
 
+# special string such that everything below this line will be ingored in the
+# editor text
+_linebelow = "^HG: ------------------------ >8 ------------------------$"
+
 def ishunk(x):
     hunkclasses = (crecordmod.uihunk, patch.recordhunk)
     return isinstance(x, hunkclasses)
@@ -2767,6 +2771,13 b' def commitforceeditor(repo, ctx, subs, f'
 
     editortext = repo.ui.edit(committext, ctx.user(), ctx.extra(),
                         editform=editform, pending=pending)
+
+    # strip away anything below this special string (used for editors that want
+    # to display the diff)
+    stripbelow = re.search(_linebelow, editortext, flags=re.MULTILINE)
+    if stripbelow:
+        editortext = editortext[:stripbelow.start()]
+
     text = re.sub("(?m)^HG:.*(\n|$)", "", editortext)
     os.chdir(olddir)
 

tests/test-commit.t

@@ -689,4 +689,97 b' verify pathauditor blocks evil filepaths'
   $ HGEDITOR="sh $TESTTMP/notouching.sh" hg commit
   abort: commit message unchanged
   [255]
+
+test that text below the --- >8 --- special string is ignored
+
+  $ hg init ignore_below_special_string
+  $ cd ignore_below_special_string
+  $ echo foo > foo
+  $ hg add foo
+  $ hg commit -m "foo"
+  $ cat >> .hg/hgrc <<EOF
+  > [committemplate]
+  > changeset.commit = first line
+  >     HG: this is customized commit template
+  >     HG: {extramsg}
+  >     HG: ------------------------ >8 ------------------------
+  >     {diff()}
+  > EOF
+  $ echo foo2 > foo2
+  $ hg add foo2
+  $ HGEDITOR=cat hg ci
+  first line
+  HG: this is customized commit template
+  HG: Leave message empty to abort commit.
+  HG: ------------------------ >8 ------------------------
+  diff -r e63c23eaa88a foo2
+  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/foo2	Thu Jan 01 00:00:00 1970 +0000
+  @@ -0,0 +1,1 @@
+  +foo2
+  $ hg log -T '{desc}\n' -r .
+  first line
+
+test that the special string --- >8 --- isn't used when not at the beginning of
+a line
+
+  $ cat >> .hg/hgrc <<EOF
+  > [committemplate]
+  > changeset.commit = first line2
+  >     another line HG: ------------------------ >8 ------------------------
+  >     HG: this is customized commit template
+  >     HG: {extramsg}
+  >     HG: ------------------------ >8 ------------------------
+  >     {diff()}
+  > EOF
+  $ echo foo >> foo
+  $ HGEDITOR=cat hg ci
+  first line2
+  another line HG: ------------------------ >8 ------------------------
+  HG: this is customized commit template
+  HG: Leave message empty to abort commit.
+  HG: ------------------------ >8 ------------------------
+  diff -r 3661b22b0702 foo
+  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
+  @@ -1,1 +1,2 @@
+   foo
+  +foo
+  $ hg log -T '{desc}\n' -r .
+  first line2
+  another line HG: ------------------------ >8 ------------------------
+
+also test that this special string isn't accepted when there is some extra text
+at the end
+
+  $ cat >> .hg/hgrc <<EOF
+  > [committemplate]
+  > changeset.commit = first line3
+  >     HG: ------------------------ >8 ------------------------foobar
+  >     second line
+  >     HG: this is customized commit template
+  >     HG: {extramsg}
+  >     HG: ------------------------ >8 ------------------------
+  >     {diff()}
+  > EOF
+  $ echo foo >> foo
+  $ HGEDITOR=cat hg ci
+  first line3
+  HG: ------------------------ >8 ------------------------foobar
+  second line
+  HG: this is customized commit template
+  HG: Leave message empty to abort commit.
+  HG: ------------------------ >8 ------------------------
+  diff -r ce648f5f066f foo
+  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
+  @@ -1,2 +1,3 @@
+   foo
+   foo
+  +foo
+  $ hg log -T '{desc}\n' -r .
+  first line3
+  second line
+
   $ cd ..
+