enhancement of compare feature

[a1012112796]

splited from #25322

• split branch/tags dropdown as two parts: repository dropdown and branch/tags dropdown. that's same with github.

• user can search any repository in repository search box.

• show a single error log instead of a 404 page when the head repo or user, the head or base ref is not exist. then user still can choose other option easyly.

[silverwind]

I think it's supposed to render like this, at least does so for me on current main:

[a1012112796]

I think it's supposed to render like this, at least does so for me on current main:

fixed https://github.com/go-gitea/gitea/pull/29766/commits/94916dbfc057b345f82c3a66c6a4d35f5a3c3dff

[silverwind]

Test failures related.

[silverwind]

split branch/tags dropdown as two parts: repository dropdown and branch/tags dropdown. that's same with github.

Is there a condition when it shows 4 selection boxes or is it always?

Wondering because at least in some cases, github only shows 2 boxes, like here:

https://github.com/go-gitea/gitea/compare/release/v1.22

[a1012112796]

Is there a condition when it shows 4 selection boxes or is it always?

to chose other repository easily. then the server can save time loading branch information for the all associated repository it uses. at last user can chose all repos by ui now.

Wondering because at least in some cases, github only shows 2 boxes, like here:

yes, in fact github provide two optional views, one has repo chose options, the others don't have, and user can switch it by click the 'compare across forks' buttuon. I has try it in #25322 also. but as lunny says (https://github.com/go-gitea/gitea/pull/25322#issuecomment-1595791732), looks the second view is not so necessary.

[lunny]

Github has a link `compare across forks` to switch from 2 columns to 4 columns compare UI.