Fix 500 error when comparing branches across fork repositories
## Problem
The compare API returns a 500 Internal Server Error when comparing
branches where the head commit exists only in the fork repository.
## Cause
The API was using the base repository's GitRepo and repository context
when converting commits. This fails when the commit does not exist in
the base repository, resulting in a "fatal: bad object" error.
## Solution
Use the head repository and HeadGitRepo when available to ensure commits
are resolved in the correct repository context.
## Result
* Fixes "fatal: bad object" error
* Enables proper comparison between base and fork repositories
* Prevents 500 Internal Server Error
Fixes#37168
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
- Add new `Compare` struct to represent comparison between two commits
- Introduce new API endpoint `/compare/*` to get commit comparison
information
- Create new file `repo_compare.go` with the `Compare` struct definition
- Add new file `compare.go` in `routers/api/v1/repo` to handle
comparison logic
- Add new file `compare.go` in `routers/common` to define `CompareInfo`
struct
- Refactor `ParseCompareInfo` function to use `common.CompareInfo`
struct
- Update Swagger documentation to include the new API endpoint for
commit comparison
- Remove duplicate `CompareInfo` struct from
`routers/web/repo/compare.go`
- Adjust base path in Swagger template to be relative (`/api/v1`)
GitHub API
https://docs.github.com/en/rest/commits/commits?apiVersion=2022-11-28#compare-two-commits
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Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
