[PATCH RESEND] merge: clarify error message when merging a branch with one head

[Matt Mackall]

On Tue, 2011-05-31 at 15:04 -0400, Michael Tharp wrote:
> # HG changeset patch
> # User Michael Tharp <gxti at partiallystapled.com>
> # Date 1306509586 14400
> # Node ID 93df25a7776ceccc58a6925b4a042e9ad7c10fb8
> # Parent  d1a1578c5f7860b17f2f238b2c1e6adb555ffa4f
> merge: clarify error message when merging a branch with one head
> 
> Previously the error said only that there was one head, which is not
> consistent with the error displayed on on a repository with no branches.
> Now the key phrase "nothing to merge" appears in both cases.
> 
> diff --git a/mercurial/commands.py b/mercurial/commands.py
> --- a/mercurial/commands.py
> +++ b/mercurial/commands.py
> @@ -3498,8 +3498,8 @@
>          parent = repo.dirstate.p1()
>          if len(bheads) == 1:
>              if len(repo.heads()) > 1:
> -                raise util.Abort(_("branch '%s' has one head - "
> -                                   "please merge with an explicit rev")
> +                raise util.Abort(_("there is nothing to merge on branch '%s' - "
> +                                 "please specify a branch or revision to merge")

Was waiting for other folks to bikeshed this, but here are my thoughts:

Looks like this fails to actually achieve stylistic consistency with the
message in merge.py: 

                    raise util.Abort(_("nothing to merge (use 'hg update'"
                                       " or check 'hg heads')"))

The preferred style is in fact:

abort: brief message (brief hint)

So I think we should aim for something like:

raise util.Abort(_("nothing to merge on branch '%s'" % branch),
	hint=_("specify a branch or revision to merge"))

Note the use of hint and the additional brevity.

>                                   % branch,
>                                   hint=_("run 'hg heads' to see all heads"))
>              msg = _('there is nothing to merge')
> diff --git a/tests/test-merge-default.t b/tests/test-merge-default.t
> --- a/tests/test-merge-default.t
> +++ b/tests/test-merge-default.t
> @@ -89,7 +89,7 @@
>  Should fail because merge with other branch:
>  
>    $ hg merge
> -  abort: branch 'foobranch' has one head - please merge with an explicit rev
> +  abort: there is nothing to merge on branch 'foobranch' - please specify a branch or revision to merge
>    (run 'hg heads' to see all heads)
>    [255]
>  
> diff --git a/tests/test-newbranch.t b/tests/test-newbranch.t
> --- a/tests/test-newbranch.t
> +++ b/tests/test-newbranch.t
> @@ -294,7 +294,7 @@
>  Implicit merge with test branch as parent:
>  
>    $ hg merge
> -  abort: branch 'test' has one head - please merge with an explicit rev
> +  abort: there is nothing to merge on branch 'test' - please specify a branch or revision to merge
>    (run 'hg heads' to see all heads)
>    [255]
>    $ hg up -C default
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