Escape branch string before inserting it in URL

[k0ral]

When a branch name with special characters like % is passed to the RepositoryService.GetBranch() method as is, an error is currently returned:

invalid URL escape "%"

Passing an escaped branch name to RepositoriesService.GetBranch() works fine.

Here's a minimal reproducer

import (
	"context"
	"net/http"
	"testing"

	"github.com/google/go-github/v53/github"
	"github.com/stretchr/testify/require"
)

func TestGetBranch(t *testing.T) {
	t.Parallel()
	ctx := context.Background()

	githubClient := github.NewClient(&http.Client{
		Transport: http.DefaultTransport,
	})
	owner := "samstickkz"
	project := "curr"
	branchName := "Feature/authentication_90%"
	branch, response, err := githubClient.Repositories.GetBranch(ctx, owner, project, branchName, false)

	require.Nil(t, err)
	t.Logf("Response: %+v", response)
	t.Logf("Branch: %+v", branch)
}

This sounds like a bug to me, as I believe users of that method shouldn't be expected to escape the branch name before calling it, as this is a private implementation quirk that they shouldn't be aware of. This PR patches all branch-related methods to automatically escape the branch name in the endpoint URL.

There's actually a precedent for ref parameter, and I suspect that other variables are prone to the same issue. I am conservatively patching only the branch variable, as this is the only one I have tested thoroughly. Note that, contrary to ref use case, my tests suggest that it's okay to escape / characters for branch names.

⚠️ Breaking change: for users that currently bypass this issue by feeding escaped strings to RepositoryService.GetBranch() method (and other branch-related methods), this change will be breaking.

[codecov]

Codecov Report

Merging #2948 (f77ef83) into master (5224e34) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2948   +/-   ##
=======================================
  Coverage   98.17%   98.17%           
=======================================
  Files         145      145           
  Lines       12735    12735           
=======================================
  Hits        12502    12502           
  Misses        158      158           
  Partials       75       75           

Files	Coverage Δ
github/repos.go	98.89% <100.00%> (ø)

[gmlewis]

Honestly, I'm quite surprised that this issue has never come up before... as this repo is how many years old? 10?!?

However, I think you are right.

I'm wondering if each of the modified endpoints needs a comment in the documentation stating something like:

// Note that the branch name is URL path escaped for you. See: https://pkg.go.dev/net/url#PathEscape

[gmlewis]

Can you please add unit tests that demonstrate this new super power?

[k0ral]

@gmlewis PR updated with additional comments and unit tests.

[gmlewis]

Thank you, @k0ral !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[WillAbides]

I have a bit of concern about this being a subtle breaking change that could take a long time to discover after upgrading. I'm looking at ways to mitigate that. I'll be back to review later today.

[WillAbides]

I'm still a little hesitant about the breaking change, but after a some pondering I can't come up with anything better that doesn't add unnecessary complexity.

[gmlewis]

Thank you, @WillAbides !
Merging.