Redirect issue if repo has configured external tracker.

Author: davidsvantesson

docs/content/doc/usage/linked-references.en-us.md

@@ -156,7 +156,7 @@ In the examples, `User1/Repo1` refers to the repository where the reference is u
 | `User1/Repo1!1234`        |    yes                    |    N/A                    | A link to _PR_ 1234 for `User1/Repo1` |
 | `UserZ/RepoZ#1234`        |    N/A                    |     no                    | A link to issue/pull 1234 in `UserZ/RepoZ` |
 | `UserZ/RepoZ!1234`        |    N/A                    |     no                    | A link to issue/pull 1234 in `UserZ/RepoZ` |
-| _Not supported_           |    N/A                    |    yes                    | A link to _external issue_ 1234 for `UserZ/RepoZ` |
+| `UserZ/RepoZ#1234`        |    N/A                    |    yes                    | A link to _external issue_ 1234 for `UserZ/RepoZ` |
 | `UserZ/RepoZ!1234`        |    N/A                    |    yes                    | A link to _PR_ 1234 for `UserZ/RepoZ` |
 | **Alphanumeric issue IDs:** | -                       | -                         | - |
 | `AAA-1234`                |    yes                    |    N/A                    | A link to _external issue_ `AAA-1234` for `User1/Repo1` |

routers/repo/issue.go

@@ -21,6 +21,7 @@ import (
 	"code.gitea.io/gitea/modules/git"
 	issue_indexer "code.gitea.io/gitea/modules/indexer/issues"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/markup/markdown"
 	"code.gitea.io/gitea/modules/notification"
 	"code.gitea.io/gitea/modules/setting"
@@ -605,6 +606,15 @@ func commentTag(repo *models.Repository, poster *models.User, issue *models.Issu
 
 // ViewIssue render issue view page
 func ViewIssue(ctx *context.Context) {
+	if extIssueUnit, _ := ctx.Repo.Repository.GetUnit(models.UnitTypeExternalTracker); extIssueUnit != nil {
+		if extIssueUnit.ExternalTrackerConfig().ExternalTrackerStyle == markup.IssueNameStyleNumeric {
+			metas := ctx.Repo.Repository.ComposeMetas()
+			metas["index"] = ctx.Params(":index")
+			ctx.Redirect(com.Expand(extIssueUnit.ExternalTrackerConfig().ExternalTrackerFormat, metas))
+			return
+		}
+	}
+
 	issue, err := models.GetIssueByIndex(ctx.Repo.Repository.ID, ctx.ParamsInt64(":index"))
 	if err != nil {
 		if models.IsErrIssueNotExist(err) {