Re: [PATCH 03/30] merge-recursive: Add explanation for src_entry and dst_entry

[Junio C Hamano <gitster@pobox.com>]

Elijah Newren <newren@gmail.com> writes:

> If I have to walk through the debugger and inspect the values found in
> here in order to figure out their meaning, despite having known these
> things inside and out some years back, then they probably need a comment
> for the casual reader to explain their purpose.
>
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  merge-recursive.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/merge-recursive.c b/merge-recursive.c
> index 52521faf09..3526c8d0b8 100644
> --- a/merge-recursive.c
> +++ b/merge-recursive.c
> @@ -513,6 +513,28 @@ static void record_df_conflict_files(struct merge_options *o,
>  
>  struct rename {
>  	struct diff_filepair *pair;
> +	/*
> +	 * Because I keep forgetting every few years what src_entry and
> +	 * dst_entry are and have to walk through a debugger and puzzle
> +	 * through it to remind myself...

Very much appreciated.  I recall having trouble reasoning about
them myself, too (even though I admit I wasn't involved in the
implementation of this part very much and know this code a lot less
intimately than you do in the first place).

> +	 *
> +	 * If 'before' is renamed to 'after' then src_entry will contain
> +	 * the versions of 'before' from the merge_base, HEAD, and MERGE in
> +	 * stages 1, 2, and 3; dst_entry will contain the versions of
> +	 * 'after' from the merge_base, HEAD, and MERGE in stages 1, 2, and
> +	 * 3.  Thus, we have a total of six modes and oids, though some
> +	 * will be null.  (Stage 0 is ignored; we're interested in handling
> +	 * conflicts.)
> +	 *
> +	 * Since we don't turn on break-rewrites by default, neither
> +	 * src_entry nor dst_entry can have all three of their stages have
> +	 * non-null oids, meaning at most four of the six will be non-null.
> +	 * Also, since this is a rename, both src_entry and dst_entry will
> +	 * have at least one non-null oid, meaning at least two will be
> +	 * non-null.  Of the six oids, a typical rename will have three be
> +	 * non-null.  Only two implies a rename/delete, and four implies a
> +	 * rename/add.
> +	 */
>  	struct stage_data *src_entry;
>  	struct stage_data *dst_entry;
>  	unsigned processed:1;