Add watch button on issue

routers/repo/issue.go

@@ -465,6 +465,20 @@ func ViewIssue(ctx *context.Context) {
 	}
 	ctx.Data["Title"] = fmt.Sprintf("#%d - %s", issue.Index, issue.Title)
 
+	iw, exists, err := models.GetIssueWatch(ctx.User.ID, issue.ID)
+	if err != nil {
+		ctx.Handle(500, "GetIssueWatch", err)
+		return
+	}
+	if !exists {
+		iw = &models.IssueWatch{
+			UserID:     ctx.User.ID,
+			IssueID:    issue.ID,
+			IsWatching: models.IsWatching(ctx.User.ID, ctx.Repo.Repository.ID),
+		}
+	}
+	ctx.Data["IssueWatch"] = iw
+
 	// Make sure type and URL matches.
 	if ctx.Params(":type") == "issues" && issue.IsPull {
 		ctx.Redirect(ctx.Repo.RepoLink + "/pulls/" + com.ToStr(issue.Index))

routers/repo/issue_watch.go

@@ -0,0 +1,34 @@
+package repo
+
+import (
+	"fmt"
+	"net/http"
+	"strconv"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/context"
+)
+
+// IssueWatch sets issue watching
+func IssueWatch(c *context.Context) {
+	watch, err := strconv.ParseBool(c.Req.PostForm.Get("watch"))
+	if err != nil {
+		c.Handle(http.StatusInternalServerError, "watch is not bool", err)
+		return
+	}
+
+	issueIndex := c.ParamsInt64("index")
+	issue, err := models.GetIssueByIndex(c.Repo.Repository.ID, issueIndex)
+	if err != nil {
+		c.Handle(http.StatusInternalServerError, "GetIssueByIndex", err)
+		return
+	}
+
+	if err := models.CreateOrUpdateIssueWatch(c.User.ID, issue.ID, watch); err != nil {
+		c.Handle(http.StatusInternalServerError, "CreateOrUpdateIssueWatch", err)
+		return
+	}
+
+	url := fmt.Sprintf("%s/issues/%d", c.Repo.RepoLink, issueIndex)
+	c.Redirect(url, http.StatusSeeOther)
+}