Subject: [PATCH 0/3] Re: [PATCH] unpack-tree.c: remove dead code

From: Jonathan Nieder <[email-masked]>
Date: Tue, 12 Aug 2014 16:57:31 -0700

Stefan Beller wrote:

> In line 1763 of unpack-tree.c we have a condition on the current tree
[...]

The description is describing why the patch is *correct* (i.e., not
going to introduce a bug), while what the reader wants to know is why
the change is *desirable*.

Is this about making the code more readable, or robust, or suppressing
a static analysis error, or something else?  What did the user or
reader want to do that they couldn't do before and now can after this
patch?

[...]
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -1789,15 +1789,11 @@ int twoway_merge(const struct cache_entry * const *src,
>  			/* 20 or 21 */
>  			return merged_entry(newtree, current, o);
>  		}
> +		else if (o->gently) {
> +			return  -1 ;
> +		}

(not about this patch) Elsewhere git uses the 'cuddled else':

		if (foo) {
			...
		} else if (bar) {
			...
		} else {
			...
		}

That stylefix would be a topic for a different patch, though.

>  		else {
> -			/* all other failures */
> -			if (oldtree)
> -				return o->gently ? -1 : reject_merge(oldtree, o);
> -			if (current)
> -				return o->gently ? -1 : reject_merge(current, o);
> -			if (newtree)
> -				return o->gently ? -1 : reject_merge(newtree, o);
> -			return -1;

Does the static analysis tool support comments like

			if (oldtree)
				...
			if (current)
				...
			...

			/* not reached */
			return -1;

?  That might be the simplest minimally invasive fix for what coverity
pointed out.

Now that we're looking there, though, it's worth understanding why we
do the 'if oldtree exists, use it, else fall back to, etc' thing.  Was
this meant as futureproofing in case commands like 'git checkout' want
to do rename detection some day?

Everywhere else in the file that reject_merge is used, it is as

	return o->gently ? -1 : reject_merge(..., o);

The one exception is

	!current &&
	oldtree &&
	newtree &&
	oldtree != newtree &&
	!initial_checkout

(#17), which seems like a bug (it should have the same check).  Would
it make sense to inline the o->gently check into reject_merge so callers
don't have to care?

In that spirit, I suspect the simplest fix would be

		else
			return o->gently ? -1 : reject_merge(current, o);

and then all calls could be replaced in a followup patch.

Sensible?

Thanks,

Jonathan Nieder (2):
  unpack-trees: use 'cuddled' style for if-else cascade
  checkout -m: attempt merge when deletion of path was staged

Stefan Beller (1):
  unpack-trees: simplify 'all other failures' case

 unpack-trees.c | 31 ++++++++++---------------------
 1 file changed, 10 insertions(+), 21 deletions(-)