Add SubListLength option

This allow you to set the indentation length for sublists. The default
is 1. Setting it to 2+ can be used when you want to be compatible with
non-CommonMark renderers that assume that a sub-list needs at minimum 4
spaces for indentation, like https://python-markdown.github.io/.

README.md

@@ -45,6 +45,7 @@ the renderer.
 | WithHeadingStyle | markdown.HeadingStyle | Render markdown headings as ATX (`#`-based), Setext (underlined with `===` or `---`), or variants thereof. |
 | WithThematicBreakStyle | markdown.ThematicBreakStyle | Render thematic breaks with `-`, `*`, or `_`. |
 | WithThematicBreakLength | markdown.ThematicBreakLength | Number of characters to use in a thematic break (minimum 3). |
+| WithSubListLength | markdown.SubListLength | Number of characters to use in a sub list indentation (minimum 1). |
 
 ## As a markdown transformer
 

options.go

@@ -6,10 +6,11 @@ import (
 
 // Config struct holds configurations for the markdown based renderer.
 type Config struct {
-	IndentStyle         IndentStyle
-	HeadingStyle        HeadingStyle
-	ThematicBreakStyle  ThematicBreakStyle
-	ThematicBreakLength ThematicBreakLength
+	IndentStyle
+	HeadingStyle
+	ThematicBreakStyle
+	ThematicBreakLength
+	SubListLength
 }
 
 // NewConfig returns a new Config with defaults and the given options.
@@ -19,6 +20,7 @@ func NewConfig(options ...Option) *Config {
 		HeadingStyle:        HeadingStyle(HeadingStyleATX),
 		ThematicBreakStyle:  ThematicBreakStyle(ThematicBreakStyleDashed),
 		ThematicBreakLength: ThematicBreakLength(ThematicBreakLengthMinimum),
+		SubListLength:       SubListLength(SubListLengthMinimum),
 	}
 	for _, opt := range options {
 		opt.SetMarkdownOption(c)
@@ -37,6 +39,8 @@ func (c *Config) SetOption(name renderer.OptionName, value interface{}) {
 		c.ThematicBreakStyle = value.(ThematicBreakStyle)
 	case optThematicBreakLength:
 		c.ThematicBreakLength = value.(ThematicBreakLength)
+	case optSubListLength:
+		c.SubListLength = value.(SubListLength)
 	}
 }
 
@@ -227,3 +231,41 @@ func WithThematicBreakLength(style ThematicBreakLength) interface {
 } {
 	return &withThematicBreakLength{style}
 }
+
+// ============================================================================
+// SubListLength Option
+// ============================================================================
+
+// optSubListLength is an option name used in WithSubListLength
+const optSubListLength renderer.OptionName = "SubListLength"
+
+// SubListLength configures the character length of sublist indentation
+type SubListLength int
+
+const (
+	// SubListLengthMinimum is the minimum length of a sublist length. This is the default.
+	// Any lengths less than this minimum are converted to the minimum.
+	// Ex: ---
+	SubListLengthMinimum = 1
+)
+
+type withSubListLength struct {
+	value SubListLength
+}
+
+func (o *withSubListLength) SetConfig(c *renderer.Config) {
+	c.Options[optSubListLength] = o.value
+}
+
+// SetMarkdownOption implements renderer.Option
+func (o *withSubListLength) SetMarkdownOption(c *Config) {
+	c.SubListLength = o.value
+}
+
+// WithSubListLength is a functional option that sets the length of sub lists indentation.
+func WithSubListLength(style SubListLength) interface {
+	renderer.Option
+	Option
+} {
+	return &withSubListLength{style}
+}

options_test.go

@@ -26,6 +26,7 @@ func TestRendererOptions(t *testing.T) {
 				WithHeadingStyle(HeadingStyleATX),
 				WithThematicBreakStyle(ThematicBreakStyleDashed),
 				WithThematicBreakLength(ThematicBreakLengthMinimum),
+				WithSubListLength(SubListLengthMinimum),
 			},
 			NewConfig(),
 		},

renderer.go

@@ -222,12 +222,7 @@ func (r *Renderer) renderThematicBreak(node ast.Node, entering bool) ast.WalkSta
 	if entering {
 		breakChars := []byte{'-', '*', '_'}
 		breakChar := breakChars[r.config.ThematicBreakStyle : r.config.ThematicBreakStyle+1]
-		var breakLen int
-		if r.config.ThematicBreakLength < ThematicBreakLengthMinimum {
-			breakLen = int(ThematicBreakLengthMinimum)
-		} else {
-			breakLen = int(r.config.ThematicBreakLength)
-		}
+		breakLen := int(max(r.config.ThematicBreakLength, ThematicBreakLengthMinimum))
 		r.rc.writer.WriteBytes(bytes.Repeat(breakChar, breakLen))
 	}
 	return ast.WalkContinue
@@ -294,7 +289,9 @@ func (r *Renderer) renderListItem(node ast.Node, entering bool) ast.WalkStatus {
 		// Prefix the current line with the item prefix
 		r.rc.writer.PushPrefix(itemPrefix, 0, 0)
 		// Prefix subsequent lines with padding the same length as the item prefix
-		r.rc.writer.PushPrefix(bytes.Repeat([]byte(" "), len(itemPrefix)), 1)
+		indentLen := int(max(r.config.SubListLength, SubListLengthMinimum))
+		indent := bytes.Repeat([]byte{' '}, indentLen)
+		r.rc.writer.PushPrefix(bytes.Repeat(indent, len(itemPrefix)), 1)
 	} else {
 		r.rc.writer.PopPrefix()
 		r.rc.writer.PopPrefix()

renderer_test.go

@@ -479,6 +479,12 @@ func TestRenderedOutput(t *testing.T) {
 			"1. A1\n2. B1\n   - C2\n     1. D3\n     2. E3\n   - F2\n   - G2\n3. H1\n",
 			"1. A1\n2. B1\n   - C2\n     1. D3\n     2. E3\n   - F2\n   - G2\n3. H1\n",
 		},
+		{
+			"Sub list length",
+			[]Option{WithSubListLength(2)},
+			"1. A1\n2. B1\n   - C2\n     1. D3\n     2. E3\n   - F2\n   - G2\n3. H1\n",
+			"1. A1\n2. B1\n      - C2\n          1. D3\n          2. E3\n      - F2\n      - G2\n3. H1\n",
+		},
 		// Block separators
 		{
 			"ATX heading block separator",