Number of commits ahead/behind in branch overview (#6695)

* Call Git API to determine divergence of a branch and its base branch

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Show commit divergance in branch list

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Adds missing comment

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Adds test for diverging commits

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Try comparing commits instead of branches

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Removes test as CI can't run it

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Adjusts signature of percentage function to allow providing multiple integers as numerator

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Moves CountDivergingCommits function into repofiles module

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

routers/repo/branch.go

@@ -14,6 +14,7 @@ import (
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/repofiles"
 	"code.gitea.io/gitea/modules/util"
 )
 
@@ -28,6 +29,8 @@ type Branch struct {
 	IsProtected   bool
 	IsDeleted     bool
 	DeletedBranch *models.DeletedBranch
+	CommitsAhead  int
+	CommitsBehind int
 }
 
 // Branches render repository branch page
@@ -168,16 +171,25 @@ func loadBranches(ctx *context.Context) []*Branch {
 			return nil
 		}
 
-		isProtected, err := ctx.Repo.Repository.IsProtectedBranch(rawBranches[i].Name, ctx.User)
+		branchName := rawBranches[i].Name
+		isProtected, err := ctx.Repo.Repository.IsProtectedBranch(branchName, ctx.User)
 		if err != nil {
 			ctx.ServerError("IsProtectedBranch", err)
 			return nil
 		}
 
+		divergence, divergenceError := repofiles.CountDivergingCommits(ctx.Repo.Repository, branchName)
+		if divergenceError != nil {
+			ctx.ServerError("CountDivergingCommits", divergenceError)
+			return nil
+		}
+
 		branches[i] = &Branch{
-			Name:        rawBranches[i].Name,
-			Commit:      commit,
-			IsProtected: isProtected,
+			Name:          branchName,
+			Commit:        commit,
+			IsProtected:   isProtected,
+			CommitsAhead:  divergence.Ahead,
+			CommitsBehind: divergence.Behind,
 		}
 	}