Re: [RFC PATCH 1/2] add-patch: compare object id instead of literal string

> Add a new function reveq(), which takes repository struct and two revision
> strings as arguments and returns 0 if the revisions point to the same
> object. Passing a rev which does not point to an object is considered
> undefined behavior as the underlying function memcmp() will be called
> with NULL hash strings.
> 
> Subsequently, replace literal string comparison to HEAD in run_add_p()
> with reveq() to handle more ways of saying HEAD (such as '@' or '$branch'
> where $branch points to same commit as HEAD). This addresses the
> NEEDSWORK comment in run_add_p().
> 
> However, in ADD_P_RESET mode keep string comparison in logical OR with
> reveq() to handle unborn HEAD.
> 
> As for the behavior change, with this patch applied if the given
> revision points to the same object as HEAD, the patch mode will be set to
> patch_mode_(reset,checkout,worktree)_head instead of
> patch_mode_(...)_nothead. That is equivalent of not setting -R flag in
> diff-index, which would have been otherwise set before this patch.
> However, when given same set of inputs, the actual outcome is same as
> before this patch. Therefore, this does not affect any automated scripts.

> Also, add testcases to check the similarity of result between different
> ways of saying HEAD.
> 
> Signed-off-by: Ghanshyam Thakkar <shyamthakkar001@gmail.com>
> ---
> Should the return values of repo_get_oid() be checked in reveq()? As
> reveq() is not a global function and is only used in run_add_p(), the
> validity of revisions is already checked beforehand by builtin/checkout.c
> and builtin/reset.c before the call to run_add_p().
> 
>  add-patch.c               | 28 +++++++++++++++-------
>  t/t2016-checkout-patch.sh | 50 +++++++++++++++++++++++----------------
>  t/t2071-restore-patch.sh  | 21 ++++++++++------
>  t/t7105-reset-patch.sh    | 14 +++++++++++
>  4 files changed, 77 insertions(+), 36 deletions(-)
> 
> diff --git a/add-patch.c b/add-patch.c
> index 79eda168eb..01eb71d90e 100644
> --- a/add-patch.c
> +++ b/add-patch.c
> @@ -14,6 +14,7 @@
>  #include "color.h"
>  #include "compat/terminal.h"
>  #include "prompt.h"
> +#include "hash.h"
>  
>  enum prompt_mode_type {
>  	PROMPT_MODE_CHANGE = 0, PROMPT_DELETION, PROMPT_ADDITION, PROMPT_HUNK,
> @@ -316,6 +317,18 @@ static void setup_child_process(struct add_p_state *s,
>  		     INDEX_ENVIRONMENT "=%s", s->s.r->index_file);
>  }
>  
> +// Check if two revisions point to the same object. Passing a rev which does not
> +// point to an object is undefined behavior.

> +static inline int reveq(struct repository *r, const char *rev1,
> +			const char *rev2)
> +{
> +	struct object_id oid_rev1, oid_rev2;
> +	repo_get_oid(r, rev1, &oid_rev1);
> +	repo_get_oid(r, rev2, &oid_rev2);
> +
> +	return !oideq(&oid_rev1, &oid_rev2);
> +}