Fix merge panic

[lunny]

To prevent potential bugs, the logic in #35543 makes gitcmd.Command panic when attempting to override stdout or stderr. Instead of using PrepareCmd, this PR now uses the WithXXX methods directly to avoid the panic.

Fix #35603

[badhezi]

we should probably also add a testcase that merges a pull request with the head_commit_id form value which is the default when merging from UI

[lunny]

we should probably also add a testcase that merges a pull request with the head_commit_id form value which is the default when merging from UI

The merge tests already exist, but they contained bugs that prevented the previous issue from being detected. I’ve submitted commit 50d3d94 to fix the test bug.

[badhezi]

@lunny
I meant that we need to modify this test case to include head_commit_id here

options := map[string]string{
  "_csrf": htmlDoc.GetCSRF(),
  "do":    string(mergeStyle),
}

Otherwise we will not reach the show-ref command and this is why this test did not catch this bug before

[lunny]

@lunny I meant that we need to modify this test case to include head_commit_id here

options := map[string]string{
  "_csrf": htmlDoc.GetCSRF(),
  "do":    string(mergeStyle),
}

Otherwise we will not reach the show-ref command and this is why this test did not catch this bug before

763d8c8 added a new merge test with head commit id.