Add name-only flag to gh pr diff sub command

pkg/cmd/pr/diff/diff.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"regexp"
 	"strings"
 
 	"github.com/MakeNowJust/heredoc"
@@ -27,6 +28,7 @@ type DiffOptions struct {
 	SelectorArg string
 	UseColor    bool
 	Patch       bool
+	NameOnly    bool
 }
 
 func NewCmdDiff(f *cmdutil.Factory, runF func(*DiffOptions) error) *cobra.Command {
@@ -78,6 +80,7 @@ func NewCmdDiff(f *cmdutil.Factory, runF func(*DiffOptions) error) *cobra.Comman
 
 	cmdutil.StringEnumFlag(cmd, &colorFlag, "color", "", "auto", []string{"always", "never", "auto"}, "Use color in diff output")
 	cmd.Flags().BoolVar(&opts.Patch, "patch", false, "Display diff in patch format")
+	cmd.Flags().BoolVar(&opts.NameOnly, "name-only", false, "Display only names of changed files")
 
 	return cmd
 }
@@ -97,6 +100,10 @@ func diffRun(opts *DiffOptions) error {
 		return err
 	}
 
+	if opts.NameOnly {
+		opts.Patch = false
+	}
+
 	diff, err := fetchDiff(httpClient, baseRepo, pr.Number, opts.Patch)
 	if err != nil {
 		return fmt.Errorf("could not find pull request diff: %w", err)
@@ -109,6 +116,10 @@ func diffRun(opts *DiffOptions) error {
 		fmt.Fprintf(opts.IO.ErrOut, "failed to start pager: %v\n", err)
 	}
 
+	if opts.NameOnly {
+		return changedFilesNames(opts.IO.Out, diff)
+	}
+
 	if !opts.UseColor {
 		_, err = io.Copy(opts.IO.Out, diff)
 		return err
@@ -227,3 +238,22 @@ func isAdditionLine(l []byte) bool {
 func isRemovalLine(l []byte) bool {
 	return len(l) > 0 && l[0] == '-'
 }
+
+func changedFilesNames(w io.Writer, r io.Reader) error {
+	diff, err := io.ReadAll(r)
+	if err != nil {
+		return err
+	}
+
+	pattern := regexp.MustCompile(`(?:^|\n)diff\s--git.*\sb/(.*)`)
+	matches := pattern.FindAllStringSubmatch(string(diff), -1)
+
+	for _, val := range matches {
+		name := strings.TrimSpace(val[1])
+		if _, err := w.Write([]byte(name + "\n")); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}

pkg/cmd/pr/diff/diff_test.go

@@ -170,6 +170,18 @@ func Test_diffRun(t *testing.T) {
 			wantAccept: "application/vnd.github.v3.patch",
 			wantStdout: fmt.Sprintf(testDiff, "", "", "", ""),
 		},
+		{
+			name: "name only",
+			opts: DiffOptions{
+				SelectorArg: "123",
+				UseColor: false,
+				Patch: false,
+				NameOnly: true,
+			},
+			rawDiff: fmt.Sprintf(testDiff, "", "", "", ""),
+			wantAccept: "application/vnd.github.v3.diff",
+			wantStdout: fmt.Sprintf(".github/workflows/releases.yml\nMakefile\n"),
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -290,3 +302,43 @@ func Test_colorDiffLines(t *testing.T) {
 		}
 	}
 }
+
+func Test_changedFileNames(t *testing.T) {
+	inputs := []struct {
+		input, output string
+	}{
+		{
+			input:  "",
+			output: "",
+		},
+		{
+			input:  "\n",
+			output: "",
+		},
+		{
+			input:  "diff --git a/cmd.go b/cmd.go\n--- /dev/null\n+++ b/cmd.go\n@@ -0,0 +1,313 @@",
+			output: "cmd.go\n",
+		},
+		{
+			input:  "diff --git a/cmd.go b/cmd.go\n--- a/cmd.go\n+++ /dev/null\n@@ -0,0 +1,313 @@",
+			output: "cmd.go\n",
+		},
+		{
+			input: fmt.Sprintf("diff --git a/baz.go b/rename.go\n--- a/baz.go\n+++ b/rename.go\n+foo\n-b%sr", strings.Repeat("a", 2*lineBufferSize)),
+			output: "rename.go\n",
+		},
+		{
+			input: fmt.Sprintf("diff --git a/baz.go b/baz.go\n--- a/baz.go\n+++ b/baz.go\n+foo\n-b%sr", strings.Repeat("a", 2*lineBufferSize)),
+			output: "baz.go\n",
+		},
+	}
+	for _, tt := range inputs {
+		buf := bytes.Buffer{}
+		if err := changedFilesNames(&buf, strings.NewReader(tt.input)); err != nil {
+			t.Fatalf("unexpected error: %s", err)
+		}
+		if got := buf.String(); got != tt.output {
+			t.Errorf("expected: %q, got: %q", tt.output, got)
+		}
+	}
+}