pr command scriptability improvements

This commit improves behavior and error handling for pr commands when
run unattached to a tty.

- error if pr create and no -t/-f
- error if pr create and -w
- machine readable pr list
- machine readable pr view
- various cleanup of informational messages

command/pr.go

@@ -293,8 +293,9 @@ func prList(cmd *cobra.Command, args []string) error {
 	})
 
 	title := listHeader(ghrepo.FullName(baseRepo), "pull request", len(listResult.PullRequests), listResult.TotalCount, hasFilters)
-	// TODO: avoid printing header if piped to a script
-	fmt.Fprintf(colorableErr(cmd), "\n%s\n\n", title)
+	if connectedToTerminal(cmd) {
+		fmt.Fprintf(colorableErr(cmd), "\n%s\n\n", title)
+	}
 
 	table := utils.NewTablePrinter(cmd.OutOrStdout())
 	for _, pr := range listResult.PullRequests {
@@ -303,6 +304,10 @@ func prList(cmd *cobra.Command, args []string) error {
 			prNum = "#" + prNum
 		}
 		table.AddField(prNum, nil, colorFuncForPR(pr))
+		if !table.IsTTY() {
+			table.AddField(pr.State, nil, nil)
+			table.AddField(prReadyState(&pr), nil, nil)
+		}
 		table.AddField(replaceExcessiveWhitespace(pr.Title), nil, nil)
 		table.AddField(pr.HeadLabel(), nil, utils.Cyan)
 		table.EndRow()
@@ -357,6 +362,10 @@ func prView(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
+	if web && !connectedToTerminal(cmd) {
+		return errors.New("--web unsupported when not attached to a tty")
+	}
+
 	pr, _, err := prFromArgs(ctx, apiClient, cmd, args)
 	if err != nil {
 		return err
@@ -367,8 +376,13 @@ func prView(cmd *cobra.Command, args []string) error {
 		fmt.Fprintf(cmd.ErrOrStderr(), "Opening %s in your browser.\n", openURL)
 		return utils.OpenInBrowser(openURL)
 	}
-	out := colorableOut(cmd)
-	return printPrPreview(out, pr)
+
+	if connectedToTerminal(cmd) {
+		out := colorableOut(cmd)
+		return printHumanPrPreview(out, pr)
+	}
+
+	return printRawPrPreview(cmd.OutOrStdout(), pr)
 }
 
 func prClose(cmd *cobra.Command, args []string) error {
@@ -482,6 +496,9 @@ func prMerge(cmd *cobra.Command, args []string) error {
 	}
 
 	if enabledFlagCount == 0 {
+		if !connectedToTerminal(cmd) {
+			return errors.New("--merge, --rebase, or --squash required when not attached to a tty")
+		}
 		isInteractive = true
 	} else if enabledFlagCount > 1 {
 		return errors.New("expected exactly one of --merge, --rebase, or --squash to be true")
@@ -513,7 +530,9 @@ func prMerge(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("API call failed: %w", err)
 	}
 
-	fmt.Fprintf(colorableOut(cmd), "%s %s pull request #%d (%s)\n", utils.Magenta("✔"), action, pr.Number, pr.Title)
+	if connectedToTerminal(cmd) {
+		fmt.Fprintf(colorableOut(cmd), "%s %s pull request #%d (%s)\n", utils.Magenta("✔"), action, pr.Number, pr.Title)
+	}
 
 	if deleteBranch {
 		branchSwitchString := ""
@@ -560,7 +579,9 @@ func prMerge(cmd *cobra.Command, args []string) error {
 			}
 		}
 
-		fmt.Fprintf(colorableOut(cmd), "%s Deleted branch %s%s\n", utils.Red("✔"), utils.Cyan(pr.HeadRefName), branchSwitchString)
+		if connectedToTerminal(cmd) {
+			fmt.Fprintf(colorableOut(cmd), "%s Deleted branch %s%s\n", utils.Red("✔"), utils.Cyan(pr.HeadRefName), branchSwitchString)
+		}
 	}
 
 	return nil
@@ -620,7 +641,46 @@ func prInteractiveMerge(deleteLocalBranch bool, crossRepoPR bool) (api.PullReque
 	return mergeMethod, deleteBranch, nil
 }
 
-func printPrPreview(out io.Writer, pr *api.PullRequest) error {
+func prReadyState(pr *api.PullRequest) string {
+	switch pr.State {
+	case "OPEN":
+		if pr.IsDraft {
+			return "draft"
+		} else {
+			return "ready"
+		}
+	case "CLOSED":
+		return "unreviewable"
+	case "MERGED":
+		return "unreviewable"
+	}
+
+	return "unknown"
+}
+
+func printRawPrPreview(out io.Writer, pr *api.PullRequest) error {
+	reviewers := prReviewerList(*pr)
+	assignees := prAssigneeList(*pr)
+	labels := prLabelList(*pr)
+	projects := prProjectList(*pr)
+
+	fmt.Fprintf(out, "title:\t%s\n", pr.Title)
+	fmt.Fprintf(out, "state:\t%s\n", pr.State)
+	fmt.Fprintf(out, "ready:\t%s\n", prReadyState(pr))
+	fmt.Fprintf(out, "author:\t%s\n", pr.Author.Login)
+	fmt.Fprintf(out, "labels:\t%s\n", labels)
+	fmt.Fprintf(out, "assignees:\t%s\n", assignees)
+	fmt.Fprintf(out, "reviewers:\t%s\n", reviewers)
+	fmt.Fprintf(out, "projects:\t%s\n", projects)
+	fmt.Fprintf(out, "milestone:\t%s\n", pr.Milestone.Title)
+
+	fmt.Fprintln(out, "--")
+	fmt.Fprintln(out, pr.Body)
+
+	return nil
+}
+
+func printHumanPrPreview(out io.Writer, pr *api.PullRequest) error {
 	// Header (Title and State)
 	fmt.Fprintln(out, utils.Bold(pr.Title))
 	fmt.Fprintf(out, "%s", prStateTitleWithColor(*pr))