Re: [PATCH 2/6] commit: add generation number to struct commmit

[Jonathan Tan <jonathantanmy@google.com>]

On Tue,  3 Apr 2018 12:51:39 -0400
Derrick Stolee <dstolee@microsoft.com> wrote:

> The generation number of a commit is defined recursively as follows:
> 
> * If a commit A has no parents, then the generation number of A is one.
> * If a commit A has parents, then the generation number of A is one
>   more than the maximum generation number among the parents of A.
> 
> Add a uint32_t generation field to struct commit so we can pass this
> information to revision walks. We use two special values to signal
> the generation number is invalid:
> 
> GENERATION_NUMBER_UNDEF 0xFFFFFFFF
> GENERATION_NUMBER_NONE 0
> 
> The first (_UNDEF) means the generation number has not been loaded or
> computed. The second (_NONE) means the generation number was loaded
> from a commit graph file that was stored before generation numbers
> were computed.
> 
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

This looks straightforward and correct, thanks. I think some of the
description above should appear as code comments.

> +#define GENERATION_NUMBER_UNDEF 0xFFFFFFFF
> +#define GENERATION_NUMBER_NONE 0

I would include the description above here as documentation, and would
replace "was stored before generation numbers were computed" by "was
written by a version of Git that did not support generation numbers".