Subject: Re: [PATCH 7/8] combine-diff: Fast changed-to-all-parents paths scanning

From: Junio C Hamano <[email-masked]>
Date: Wed, 05 Feb 2014 09:36:55 -0800

Kirill Smelkov <[email-masked]> writes:

> Only, before I clean things up, I'd like to ask - would the following
> patch be accepted
>
> ---- 8< ---
> diff --git a/tree-walk.c b/tree-walk.c
> index 79dba1d..4dc86c7 100644
> --- a/tree-walk.c
> +++ b/tree-walk.c
> @@ -37,7 +37,7 @@ static void decode_tree_entry(struct tree_desc *desc, const char *buf, unsigned
>  
>  	/* Initialize the descriptor entry */
>  	desc->entry.path = path;
> -	desc->entry.mode = mode;
> +	desc->entry.mode = canon_mode(mode);
>  	desc->entry.sha1 = (const unsigned char *)(path + len);
>  }
>  
> diff --git a/tree-walk.h b/tree-walk.h
> index ae04b64..ae7fb3a 100644
> --- a/tree-walk.h
> +++ b/tree-walk.h
> @@ -16,7 +16,7 @@ struct tree_desc {
>  static inline const unsigned char *tree_entry_extract(struct tree_desc *desc, const char **pathp, unsigned int *modep)
>  {
>  	*pathp = desc->entry.path;
> -	*modep = canon_mode(desc->entry.mode);
> +	*modep = desc->entry.mode;
>  	return desc->entry.sha1;
>  }
> ---- 8< ---
>  
> ?

Doesn't desc point into and walks over the data we read from the
tree object directly?

We try to keep (tree|commit)->buffer intact and that is done pretty
deliberately.  While you are walking a tree or parsing a commit,
somebody else, perhaps called indirectly by a helper function you
call, may call lookup_object() for the same object, get the copy
that has already been read and start using it.  This kind of change
will introduce bugs that are hard to debug unless it is done very
carefully (e.g. starting from making tree.buffer into a const pointer
and propagating constness throughout the system), which might not be
worth the pain.