bug#38044: 27.0.50; There should be an easier way to look at a specific vc commit

[Dmitry Gutov]

On 24.11.2019 0:43, Juri Linkov wrote:
> I rewrote the patch to make it more flexible, so now the function
> can check 'vc-log-view-type' for the value 'with-diff'.

Generally, an explicit argument is better than an implicit one.

So what's the idea here? Gracefully degrading to just showing a log 
entry when the backend doesn't support the WITH-DIFF feature? (BTW, the 
print-revision approach seems better for graceful degradation, but I'm 
tired of arguing for that).

I think it would work, but for that all backends need support for 
region-history-mode anyway. The caller function doesn't have a way to 
check the lack of support.

So I guess the "proper" choice here is to extract region-history-mode is 
a way that doesn't need redefinition by all backends.

Or a shortcut: catch the vc-not-supported error and call backend's 
log-view-mode instead.