Move repository sub menu data loading to the shared file and only display license on repository home page

[lunny]

#24872 introduce display license in code, branch, commits and tags page. But it's unnecessary to load licenses data for branches or commit list pages.

This PR will keep license display only for repository home page. It also extracts licenses loading from RepoAssignment middleware to a shared/license.go file.

This will avoid loading commits/branches/tags/license number or information in issues/pulls/releases and other unrelated pages. It at least reduced 3 database queries for every page of these features.

[wxiaoguang]

Think about another case: "main" branch's license is MIT and "feature/other" branch/tag's license is Apache2, then the license stored in database is always MIT, if you show the license on "feature/other" branch/tag/release page, then it confuses users.

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Overall the optimization should be like this: only show License on the repo's home page. Then the code could also be simplified, no need to introduce any more tricks.

[lunny]

Think about another case: "main" branch's license is MIT and "feature/other" branch/tag's license is Apache2, then the license stored in database is always MIT, if you show the license on "feature/other" branch/tag/release page, then it confuses users.

Overall the optimization should be like this: only show License on the repo's home page. Then the code could also be simplified, no need to introduce any more tricks.

I also find the LICENSE may be different between different branches. I will not change the previous design in this PR. 9ec4bdd Please review again, removed the permission check.

[wxiaoguang]

I also find the LICENSE may be different between different branches. I will not change the previous design in this PR. 9ec4bdd Please review again, removed the permission check.

I do not understand why "you will not change the previous License design in this PR" but you changed the template and might break the design of "Add tags list for repos whose release setting is disabled (#23465)"

There are indeed simple approaches, why make it so complex?

[delvh]

I know, this code was simply moved.
But… why are we storing request-specific data inside a global variable?

[lunny]

I cannot answer the question. I guess it may allow a different license file name in the future. Maybe @yp05327 can answer.

[yp05327]

LicenseFileName in context data is used for the link.

At first, I reused the code of detecting README file, so the license file name is not a specific value, but according to the review of #24872 (comment) and #24872 (comment), I changed it into a specific value.
But I think is not enough, e.g. LICENSES or license is not supported, and if it is necessary, we can improve it in the future.

[yp05327]

only show License on the repo's home page

This is the second step in my plan, it will be/maybe done in #32213

[yp05327]

Can this PR fix 500 error in https://gitea.com/gitea/docs/tags?

I can not access the logs, but it looks like it is caused by license. (sorry, my bad)

I got the error in my dev environment.

[yp05327]

It is safe to do some changes of preparing license related data, as it is newly added, no other places start using them, but why you touch others like branch/tag/commit?
I can image your reason, but is it really safe? I don't think so.
By my experience, the global variables of branch/tag/commit are deeply used in many places, simply remove them will cause bugs.
So I tried to find an example, then I got this:

How to reproduce? See:

Advice:
Only do some changes for license data (only preparing data in home page instead of in repoAssignment), it is a good change, and will fix the bug mentioned above.
You can finish it in this PR or do it directly in #32213.

[yp05327]

Most necessary changes have been implemented in #32213