Re: [PATCH] branch: allow "-" as a short-hand for "previous branch"

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Rubén,

On Sun, 7 Aug 2022, Rubén Justo via GitGitGadget wrote:

> From: rjusto <rjusto@gmail.com>
>
> Align "branch" with the intuitive use of "-" as a short-hand
> for "@{-1}", like in "checkout" and "merge" commands.
>
> $ git branch -d -      # short-hand for: "git branch -d @{-1}"
> $ git branch -D -      # short-hand for: "git branch -D @{-1}"

A valuable goal!

> diff --git a/builtin/branch.c b/builtin/branch.c
> index 55cd9a6e998..59c19f38d2e 100644
> --- a/builtin/branch.c
> +++ b/builtin/branch.c
> @@ -241,6 +241,10 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,

Touching only the `delete_branches()` function suggests that other
commands are left as before, e.g. `git branch --unset-upstream -` would
probably fail.

That's fine, but the commit message claims that the `"-"` special-casing
is introduced for the `git branch` command, not just for `git branch -d`.

>  			die(_("Couldn't look up commit object for HEAD"));
>  	}

At this stage, we already handled the `--remotes` flag, therefore I think
that this patch does not do the intended thing for this command-line:

	git branch -d --remotes -

>
> +	if ((argc == 1) && !strcmp(argv[0], "-")) {
> +		argv[0] = "@{-1}";
> +	}

This means that we only handle `git branch -d -`, but not `git branch -d
some-branch - some-other-branch`.

Could you fix that?

My thinking is that this probably should be a sibling of the `@{-1}`
handling, most likely somewhat like this (I only compile-tested this
patch, please take it from here):

-- snip --
diff --git a/object-name.c b/object-name.c
index 4d2746574cd..ae6c2ed7b83 100644
--- a/object-name.c
+++ b/object-name.c
@@ -1420,6 +1420,12 @@ static int interpret_nth_prior_checkout(struct repository *r,
 	const char *brace;
 	char *num_end;

+	if (namelen == 1 && *name == '-') {
+		brace = name;
+		nth = 1;
+		goto find_nth_checkout;
+	}
+
 	if (namelen < 4)
 		return -1;
 	if (name[0] != '@' || name[1] != '{' || name[2] != '-')
@@ -1432,6 +1438,8 @@ static int interpret_nth_prior_checkout(struct repository *r,
 		return -1;
 	if (nth <= 0)
 		return -1;
+
+find_nth_checkout:
 	cb.remaining = nth;
 	cb.sb = buf;

-- snap --

Naturally, this has much bigger ramifications than just `git branch -d -`,
and might even obsolete some `-` special-casing elsewhere; I have not
looked to see if there is any such special-casing, and would like to ask
you to see whether you can find those and remove them in separate commits
after implementing (and testing) the above
`interpret_nth_prior_checkout()` approach.

Thanks,
Johannes

> +
>  	for (i = 0; i < argc; i++, strbuf_reset(&bname)) {
>  		char *target = NULL;
>  		int flags = 0;
>
> base-commit: 679aad9e82d0dfd8ef3d1f98fa4629665496cec9
> --
> gitgitgadget
>