Switch to GitHub REST API to load changed files (#5618)

Co-authored-by: 6543 <6543@obermui.de>

```
// GitHub has removed commit summaries from Events API payloads from 7th October 2025 onwards.
```

- switch to rest api to load changed files
- added some small wording/var name adjustment
- added test cases using GitHub mock client

server/forge/github/github.go

@@ -27,7 +27,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/google/go-github/v74/github"
+	"github.com/google/go-github/v75/github"
 	"github.com/rs/zerolog/log"
 	"golang.org/x/oauth2"
 
@@ -40,9 +40,12 @@ import (
 	"go.woodpecker-ci.org/woodpecker/v3/shared/utils"
 )
 
+type contextKey string
+
 const (
-	defaultURL = "https://github.com"      // Default GitHub URL
-	defaultAPI = "https://api.github.com/" // Default GitHub API URL
+	defaultURL                 = "https://github.com"      // Default GitHub URL
+	defaultAPI                 = "https://api.github.com/" // Default GitHub API URL
+	githubClientKey contextKey = "github_client"
 )
 
 // Opts defines configuration options.
@@ -459,7 +462,13 @@ func (c *client) newConfig() *oauth2.Config {
 }
 
 // newClientToken returns the GitHub oauth2 client.
+// It first checks if a client is available in the context, otherwise creates a new one.
 func (c *client) newClientToken(ctx context.Context, token string) *github.Client {
+	// Check if a client is already in the context
+	if ctxClient, ok := ctx.Value(githubClientKey).(*github.Client); ok {
+		return ctxClient
+	}
+
 	ts := oauth2.StaticTokenSource(
 		&oauth2.Token{AccessToken: token},
 	)
@@ -606,7 +615,7 @@ func (c *client) BranchHead(ctx context.Context, u *model.User, r *model.Repo, b
 // Hook parses the post-commit hook from the Request body
 // and returns the required data in a standard format.
 func (c *client) Hook(ctx context.Context, r *http.Request) (*model.Repo, *model.Pipeline, error) {
-	pull, repo, pipeline, err := parseHook(r, c.MergeRef)
+	pull, repo, pipeline, currCommit, prevCommit, err := parseHook(r, c.MergeRef)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -620,11 +629,17 @@ func (c *client) Hook(ctx context.Context, r *http.Request) (*model.Repo, *model
 		pipeline.Commit = sha
 	}
 
-	if pull != nil && len(pipeline.ChangedFiles) == 0 {
+	if pull != nil {
 		pipeline, err = c.loadChangedFilesFromPullRequest(ctx, pull, repo, pipeline)
 		if err != nil {
 			return nil, nil, err
 		}
+	} else if pipeline.Event == model.EventPush {
+		// GitHub has removed commit summaries from Events API payloads from 7th October 2025 onwards.
+		pipeline, err = c.loadChangedFilesFromCommits(ctx, repo, pipeline, prevCommit, currCommit)
+		if err != nil {
+			return nil, nil, err
+		}
 	}
 
 	return repo, pipeline, nil
@@ -647,24 +662,24 @@ func (c *client) loadChangedFilesFromPullRequest(ctx context.Context, pull *gith
 		return nil, err
 	}
 
-	pipeline.ChangedFiles, err = utils.Paginate(func(page int) ([]string, error) {
-		opts := &github.ListOptions{Page: page}
-		fileList := make([]string, 0, 16)
-		for opts.Page > 0 {
-			files, resp, err := c.newClientToken(ctx, user.AccessToken).PullRequests.ListFiles(ctx, repo.Owner, repo.Name, pull.GetNumber(), opts)
-			if err != nil {
-				return nil, err
-			}
+	gh := c.newClientToken(ctx, user.AccessToken)
+	fileList := make([]string, 0, 16)
 
-			for _, file := range files {
-				fileList = append(fileList, file.GetFilename(), file.GetPreviousFilename())
-			}
-
-			opts.Page = resp.NextPage
+	opts := &github.ListOptions{Page: 1}
+	for opts.Page > 0 {
+		files, resp, err := gh.PullRequests.ListFiles(ctx, repo.Owner, repo.Name, pull.GetNumber(), opts)
+		if err != nil {
+			return nil, err
 		}
-		return utils.DeduplicateStrings(fileList), nil
-	}, -1)
 
+		for _, file := range files {
+			fileList = append(fileList, file.GetFilename(), file.GetPreviousFilename())
+		}
+
+		opts.Page = resp.NextPage
+	}
+
+	pipeline.ChangedFiles = utils.DeduplicateStrings(fileList)
 	return pipeline, err
 }
 
@@ -710,3 +725,65 @@ func (c *client) getTagCommitSHA(ctx context.Context, repo *model.Repo, tagName
 	}
 	return tag.GetCommit().GetSHA(), nil
 }
+
+func (c *client) loadChangedFilesFromCommits(ctx context.Context, tmpRepo *model.Repo, pipeline *model.Pipeline, curr, prev string) (*model.Pipeline, error) {
+	_store, ok := store.TryFromContext(ctx)
+	if !ok {
+		log.Error().Msg("could not get store from context")
+		return pipeline, nil
+	}
+
+	switch prev {
+	case curr:
+		log.Error().Msg("GitHub push event contains the same commit before and after, no changes detected")
+		return pipeline, nil
+	case "0000000000000000000000000000000000000000":
+		prev = ""
+		fallthrough
+	case "":
+		// For tag events, prev is empty, but we can still fetch the changed files using the current commit
+		log.Trace().Msg("GitHub tag event, fetching changed files using current commit")
+	}
+
+	repo, err := _store.GetRepoNameFallback(tmpRepo.ForgeRemoteID, tmpRepo.FullName)
+	if err != nil {
+		return nil, err
+	}
+
+	user, err := _store.GetUser(repo.UserID)
+	if err != nil {
+		return nil, err
+	}
+
+	gh := c.newClientToken(ctx, user.AccessToken)
+	fileList := make([]string, 0, 16)
+
+	if prev == "" {
+		opts := &github.ListOptions{Page: 1}
+		for opts.Page > 0 {
+			commit, resp, err := gh.Repositories.GetCommit(ctx, repo.Owner, repo.Name, curr, &github.ListOptions{})
+			if err != nil {
+				return nil, err
+			}
+			for _, file := range commit.Files {
+				fileList = append(fileList, file.GetFilename(), file.GetPreviousFilename())
+			}
+			opts.Page = resp.NextPage
+		}
+	} else {
+		opts := &github.ListOptions{Page: 1}
+		for opts.Page > 0 {
+			comp, resp, err := gh.Repositories.CompareCommits(ctx, repo.Owner, repo.Name, prev, curr, opts)
+			if err != nil {
+				return nil, err
+			}
+			for _, file := range comp.Files {
+				fileList = append(fileList, file.GetFilename(), file.GetPreviousFilename())
+			}
+			opts.Page = resp.NextPage
+		}
+	}
+
+	pipeline.ChangedFiles = utils.DeduplicateStrings(fileList)
+	return pipeline, err
+}