Return RFC3339 UTC timestamps for machine-readable output (#470)

### ⚠️ breaking changes ⚠️

- unset timestamps will not be printed as `"0001-01-01 00:00"`, but as empty value `""`
- output formats `csv`, `tsv`, `yaml` output timestamps in UTC instead of local time, and adhere to [RFC3339](https://datatracker.ietf.org/doc/html/rfc3339)

Co-authored-by: Norwin <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/470
Reviewed-by: 6543 <6543@obermui.de>
Reviewed-by: John Olheiser <john.olheiser@gmail.com>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

modules/print/comment.go

@@ -38,12 +38,12 @@ func Comment(c *gitea.Comment) {
 func formatComment(c *gitea.Comment) string {
 	edited := ""
 	if c.Updated.After(c.Created) {
-		edited = fmt.Sprintf(" *(edited on %s)*", FormatTime(c.Updated))
+		edited = fmt.Sprintf(" *(edited on %s)*", FormatTime(c.Updated, false))
 	}
 	return fmt.Sprintf(
 		"---\n\n**@%s** wrote on %s%s:\n\n%s\n",
 		c.Poster.UserName,
-		FormatTime(c.Created),
+		FormatTime(c.Created, false),
 		edited,
 		c.Body,
 	)

modules/print/formatters.go

@@ -36,8 +36,18 @@ func formatSize(kb int64) string {
 	return fmt.Sprintf("%d Tb", gb/1024)
 }
 
-// FormatTime give a date-time in local timezone if available
+// FormatTime provides a string for the given time value.
-func FormatTime(t time.Time) string {
+// If machineReadable is set, a UTC RFC3339 string is returned,
+// otherwise a simplified string in local time is used.
+func FormatTime(t time.Time, machineReadable bool) string {
+	if t.IsZero() {
+		return ""
+	}
+
+	if machineReadable {
+		return t.UTC().Format(time.RFC3339)
+	}
+
 	location, err := time.LoadLocation("Local")
 	if err != nil {
 		return t.Format("2006-01-02 15:04 UTC")

modules/print/issue.go

@@ -20,7 +20,7 @@ func IssueDetails(issue *gitea.Issue, reactions []*gitea.Reaction) {
 		issue.Title,
 		issue.State,
 		issue.Poster.UserName,
-		FormatTime(issue.Created),
+		FormatTime(issue.Created, false),
 		issue.Body,
 	)
 
@@ -119,14 +119,14 @@ func (x printableIssue) FormatField(field string, machineReadable bool) string {
 	case "body":
 		return x.Body
 	case "created":
-		return FormatTime(x.Created)
+		return FormatTime(x.Created, machineReadable)
 	case "updated":
-		return FormatTime(x.Updated)
+		return FormatTime(x.Updated, machineReadable)
 	case "deadline":
 		if x.Deadline == nil {
 			return ""
 		}
-		return FormatTime(*x.Deadline)
+		return FormatTime(*x.Deadline, machineReadable)
 	case "milestone":
 		if x.Milestone != nil {
 			return x.Milestone.Title

modules/print/milestone.go

@@ -19,7 +19,7 @@ func MilestoneDetails(milestone *gitea.Milestone) {
 		fmt.Printf("\n%s\n", milestone.Description)
 	}
 	if milestone.Deadline != nil && !milestone.Deadline.IsZero() {
-		fmt.Printf("\nDeadline: %s\n", FormatTime(*milestone.Deadline))
+		fmt.Printf("\nDeadline: %s\n", FormatTime(*milestone.Deadline, false))
 	}
 }
 
@@ -42,7 +42,7 @@ func MilestonesList(miles []*gitea.Milestone, output string, state gitea.StateTy
 		var deadline = ""
 
 		if m.Deadline != nil && !m.Deadline.IsZero() {
-			deadline = FormatTime(*m.Deadline)
+			deadline = FormatTime(*m.Deadline, isMachineReadable(output))
 		}
 
 		item := []string{

modules/print/pull.go

@@ -31,7 +31,7 @@ func PullDetails(pr *gitea.PullRequest, reviews []*gitea.PullReview, ciStatus *g
 		pr.Title,
 		state,
 		pr.Poster.UserName,
-		FormatTime(*pr.Created),
+		FormatTime(*pr.Created, false),
 		base,
 		head,
 		pr.Body,
@@ -195,14 +195,14 @@ func (x printablePull) FormatField(field string, machineReadable bool) string {
 	case "body":
 		return x.Body
 	case "created":
-		return FormatTime(*x.Created)
+		return FormatTime(*x.Created, machineReadable)
 	case "updated":
-		return FormatTime(*x.Updated)
+		return FormatTime(*x.Updated, machineReadable)
 	case "deadline":
 		if x.Deadline == nil {
 			return ""
 		}
-		return FormatTime(*x.Deadline)
+		return FormatTime(*x.Deadline, machineReadable)
 	case "milestone":
 		if x.Milestone != nil {
 			return x.Milestone.Title

modules/print/release.go

@@ -28,7 +28,7 @@ func ReleasesList(releases []*gitea.Release, output string) {
 		t.addRow(
 			release.TagName,
 			release.Title,
-			FormatTime(release.PublishedAt),
+			FormatTime(release.PublishedAt, isMachineReadable(output)),
 			status,
 			release.TarURL,
 		)

modules/print/repo.go

@@ -124,7 +124,7 @@ func (x printableRepo) FormatField(field string, machineReadable bool) string {
 	case "ssh":
 		return x.SSHURL
 	case "updated":
-		return FormatTime(x.Updated)
+		return FormatTime(x.Updated, machineReadable)
 	case "url":
 		return x.HTMLURL
 	case "permission":

modules/print/times.go

@@ -50,7 +50,7 @@ func (t printableTrackedTime) FormatField(field string, machineReadable bool) st
 	case "id":
 		return fmt.Sprintf("%d", t.ID)
 	case "created":
-		return FormatTime(t.Created)
+		return FormatTime(t.Created, machineReadable)
 	case "repo":
 		return t.Issue.Repository.FullName
 	case "issue":