feat: format markdown in changelog entry

internal/markdown/goldmark.go

@@ -1,8 +1,12 @@
 package markdown
 
 import (
+	"bytes"
+
 	markdown "github.com/teekennedy/goldmark-markdown"
 	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/util"
 
 	"github.com/apricote/releaser-pleaser/internal/markdown/extensions"
 )
@@ -10,6 +14,23 @@ import (
 func New() goldmark.Markdown {
 	return goldmark.New(
 		goldmark.WithExtensions(extensions.Section),
+		goldmark.WithParserOptions(parser.WithASTTransformers(
+			util.Prioritized(&newLineTransformer{}, 1),
+		)),
 		goldmark.WithRenderer(markdown.NewRenderer()),
 	)
 }
+
+// Format the Markdown document in a style mimicking Prettier. This is done for compatibility with other tools
+// users might have installed in their IDE. This does not guarantee that the output matches Prettier exactly.
+func Format(input string) (string, error) {
+	var buf bytes.Buffer
+	buf.Grow(len(input))
+
+	err := New().Convert([]byte(input), &buf)
+	if err != nil {
+		return "", err
+	}
+
+	return buf.String(), nil
+}

internal/markdown/prettier.go

@@ -0,0 +1,31 @@
+package markdown
+
+import (
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+)
+
+type newLineTransformer struct{}
+
+var _ parser.ASTTransformer = (*newLineTransformer)(nil) // interface compliance
+
+func (t *newLineTransformer) Transform(doc *ast.Document, _ text.Reader, _ parser.Context) {
+	// No error can happen as they can only come from the walker function
+	_ = ast.Walk(doc, func(node ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering || node.Type() != ast.TypeBlock {
+			return ast.WalkContinue, nil
+		}
+
+		switch node.Kind() {
+		case ast.KindListItem:
+			// Do not add empty lines between every list item
+			break
+		default:
+			// Add empty lines between every other block
+			node.SetBlankPreviousLines(true)
+		}
+
+		return ast.WalkContinue, nil
+	})
+}