add default title setting based on h1

builder_suite_test.go

@@ -113,6 +113,27 @@ var _ = Describe("Builder", func() {
 		})
 	})
 
+	When("rendering documents without frontmatter", func() {
+		It("errors on no title", func() {
+			createLayout()
+			createFile("index.md", "some text")
+
+			err := cli.Run(logger)
+			Expect(err).To(HaveOccurred())
+		})
+
+		It("uses H1 for the title", func() {
+			createLayout()
+			createFile("index.md", "# some title")
+
+			err := cli.Run(logger)
+			Expect(err).NotTo(HaveOccurred())
+
+			contents := readFile("index.html")
+			Expect(contents).To(ContainSubstring("<title>some title</title>"))
+		})
+	})
+
 	When("rendering a file with template functions", func() {
 		BeforeEach(func() {
 			createLayout()

markdown_doc.go

@@ -6,6 +6,7 @@ import (
 	htmlTemplate "html/template"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 
 	"github.com/yuin/goldmark"
@@ -40,6 +41,8 @@ func NewMarkdownDoc(
 	}
 }
 
+var titleFromHeader = regexp.MustCompile(`(?m)^#\s+(.*)$`)
+
 func (m *markdownDoc) Write(
 	layout *htmlTemplate.Template,
 	converter goldmark.Markdown,
@@ -89,15 +92,21 @@ func (m *markdownDoc) Write(
 		return fmt.Errorf("could not create file (%s): %w", newPath, err)
 	}
 
-	d := frontmatter.Get(ctx)
-	if d == nil {
-		return fmt.Errorf("frontmatter required (%s)", m.filename)
-	}
-
 	meta := &metadataPayload{}
+	d := frontmatter.Get(ctx)
 
-	if err := d.Decode(meta); err != nil {
-		return fmt.Errorf("could not decode front matter (%s): %w", m.filename, err)
+	switch {
+	case d == nil:
+		matches := titleFromHeader.FindAllStringSubmatch(evaluated.String(), 1)
+		if len(matches) == 0 {
+			return fmt.Errorf("frontmatter required with (%s)", m.filename)
+		}
+
+		meta.Title = matches[0][1]
+	default:
+		if err := d.Decode(meta); err != nil {
+			return fmt.Errorf("could not decode front matter (%s): %w", m.filename, err)
+		}
 	}
 
 	err = layout.Execute(file, map[string]any{