[PATCH 1 of 2] templatekw: add utility function numrevs

[Jordi Gutiérrez Hermoso]

On Thu, 2018-01-18 at 21:03 +0900, Yuya Nishihara wrote:
> On Wed, 17 Jan 2018 22:14:29 -0500, Jordi Gutiérrez Hermoso wrote:
> > # HG changeset patch
> > # User Jordi Gutiérrez Hermoso <jordigh at octave.org>
> > # Date 1516242948 18000
> > #      Wed Jan 17 21:35:48 2018 -0500
> > # Node ID 701f8a9defdc09bb63f2596e2fc426f2e78da313
> > # Parent  0e369eca888fc80ee980fe8200c59dc7b0024dae
> > templatekw: add utility function numrevs
> > 
> > len(repo) calls incur noticeable overhead if called for each
> > revision
> > a template keyword is evaluated.
> 
> Do you have some number? It's just a proxy to revlog.__len__(), so I
> think it
> is super fast.

The Python function calls leading up to it are not that fast. Without
this caching, it takes 7.2 seconds on average on my machine to to do
`hg log -T '{negrev}\n' > /dev/null`. With the caching, it takes 6.4
seconds on average.

Not a huge difference, but a difference. I wanted to match the speed
of `hg log -T '{rev}\n' > /dev/null`, and this caching helped me match
it.