Render HTML line breaks (#221)

Sources/MarkdownUI/Parser/HTMLTag.swift

@@ -0,0 +1,25 @@
+import Foundation
+
+struct HTMLTag {
+  let name: String
+}
+
+extension HTMLTag {
+  private enum Constants {
+    static let tagExpression = try! NSRegularExpression(pattern: "<\\/?([a-zA-Z0-9]+)[^>]*>")
+  }
+
+  init?(_ description: String) {
+    guard
+      let match = Constants.tagExpression.firstMatch(
+        in: description,
+        range: NSRange(description.startIndex..., in: description)
+      ),
+      let nameRange = Range(match.range(at: 1), in: description)
+    else {
+      return nil
+    }
+
+    self.name = String(description[nameRange])
+  }
+}

Sources/MarkdownUI/Renderer/AttributedStringInlineRenderer.swift

@@ -22,6 +22,7 @@ private struct AttributedStringInlineRenderer {
   private let baseURL: URL?
   private let textStyles: InlineTextStyles
   private var attributes: AttributeContainer
+  private var shouldSkipNextWhitespace = false
 
   init(baseURL: URL?, textStyles: InlineTextStyles, attributes: AttributeContainer) {
     self.baseURL = baseURL
@@ -55,26 +56,45 @@ private struct AttributedStringInlineRenderer {
   }
 
   private mutating func renderText(_ text: String) {
+    var text = text
+
+    if self.shouldSkipNextWhitespace {
+      self.shouldSkipNextWhitespace = false
+      text = text.replacingOccurrences(of: "^\\s+", with: "", options: .regularExpression)
+    }
+
     self.result += .init(text, attributes: self.attributes)
   }
 
   private mutating func renderSoftBreak() {
-    self.result += .init(" ", attributes: self.attributes)
+    if self.shouldSkipNextWhitespace {
+      self.shouldSkipNextWhitespace = false
+    } else {
+      self.result += .init(" ", attributes: self.attributes)
+    }
   }
 
   private mutating func renderLineBreak() {
     self.result += .init("\n", attributes: self.attributes)
   }
 
-  mutating func renderCode(_ code: String) {
+  private mutating func renderCode(_ code: String) {
     self.result += .init(code, attributes: self.textStyles.code.mergingAttributes(self.attributes))
   }
 
-  mutating func renderHTML(_ html: String) {
-    self.result += .init(html, attributes: self.attributes)
+  private mutating func renderHTML(_ html: String) {
+    let tag = HTMLTag(html)
+
+    switch tag?.name.lowercased() {
+    case "br":
+      self.renderLineBreak()
+      self.shouldSkipNextWhitespace = true
+    default:
+      self.renderText(html)
+    }
   }
 
-  mutating func renderEmphasis(children: [InlineNode]) {
+  private mutating func renderEmphasis(children: [InlineNode]) {
     let savedAttributes = self.attributes
     self.attributes = self.textStyles.emphasis.mergingAttributes(self.attributes)
 
@@ -85,7 +105,7 @@ private struct AttributedStringInlineRenderer {
     self.attributes = savedAttributes
   }
 
-  mutating func renderStrong(children: [InlineNode]) {
+  private mutating func renderStrong(children: [InlineNode]) {
     let savedAttributes = self.attributes
     self.attributes = self.textStyles.strong.mergingAttributes(self.attributes)
 
@@ -96,7 +116,7 @@ private struct AttributedStringInlineRenderer {
     self.attributes = savedAttributes
   }
 
-  mutating func renderStrikethrough(children: [InlineNode]) {
+  private mutating func renderStrikethrough(children: [InlineNode]) {
     let savedAttributes = self.attributes
     self.attributes = self.textStyles.strikethrough.mergingAttributes(self.attributes)
 
@@ -107,7 +127,7 @@ private struct AttributedStringInlineRenderer {
     self.attributes = savedAttributes
   }
 
-  mutating func renderLink(destination: String, children: [InlineNode]) {
+  private mutating func renderLink(destination: String, children: [InlineNode]) {
     let savedAttributes = self.attributes
     self.attributes = self.textStyles.link.mergingAttributes(self.attributes)
     self.attributes.link = URL(string: destination, relativeTo: self.baseURL)
@@ -119,7 +139,7 @@ private struct AttributedStringInlineRenderer {
     self.attributes = savedAttributes
   }
 
-  mutating func renderImage(source: String, children: [InlineNode]) {
+  private mutating func renderImage(source: String, children: [InlineNode]) {
     // AttributedString does not support images
   }
 }

Sources/MarkdownUI/Renderer/TextInlineRenderer.swift

@@ -25,6 +25,7 @@ private struct TextInlineRenderer {
   private let textStyles: InlineTextStyles
   private let images: [String: Image]
   private let attributes: AttributeContainer
+  private var shouldSkipNextWhitespace = false
 
   init(
     baseURL: URL?,
@@ -46,20 +47,65 @@ private struct TextInlineRenderer {
 
   private mutating func render(_ inline: InlineNode) {
     switch inline {
+    case .text(let content):
+      self.renderText(content)
+    case .softBreak:
+      self.renderSoftBreak()
+    case .html(let content):
+      self.renderHTML(content)
     case .image(let source, _):
-      if let image = self.images[source] {
-        self.result = self.result + Text(image)
-      }
+      self.renderImage(source)
     default:
-      self.result =
-        self.result
-        + Text(
-          inline.renderAttributedString(
-            baseURL: self.baseURL,
-            textStyles: self.textStyles,
-            attributes: self.attributes
-          )
-        )
+      self.defaultRender(inline)
+    }
+  }
+
+  private mutating func renderText(_ text: String) {
+    var text = text
+
+    if self.shouldSkipNextWhitespace {
+      self.shouldSkipNextWhitespace = false
+      text = text.replacingOccurrences(of: "^\\s+", with: "", options: .regularExpression)
+    }
+
+    self.defaultRender(.text(text))
+  }
+
+  private mutating func renderSoftBreak() {
+    if self.shouldSkipNextWhitespace {
+      self.shouldSkipNextWhitespace = false
+    } else {
+      self.defaultRender(.softBreak)
+    }
+  }
+
+  private mutating func renderHTML(_ html: String) {
+    let tag = HTMLTag(html)
+
+    switch tag?.name.lowercased() {
+    case "br":
+      self.defaultRender(.lineBreak)
+      self.shouldSkipNextWhitespace = true
+    default:
+      self.defaultRender(.html(html))
+    }
+  }
+
+  private mutating func renderImage(_ source: String) {
+    if let image = self.images[source] {
+      self.result = self.result + Text(image)
     }
   }
+
+  private mutating func defaultRender(_ inline: InlineNode) {
+    self.result =
+      self.result
+      + Text(
+        inline.renderAttributedString(
+          baseURL: self.baseURL,
+          textStyles: self.textStyles,
+          attributes: self.attributes
+        )
+      )
+  }
 }

Tests/MarkdownUITests/HTMLTagTests.swift

@@ -0,0 +1,40 @@
+import Foundation
+import XCTest
+
+@testable import MarkdownUI
+
+final class HTMLTagTests: XCTestCase {
+  func testInvalidTag() {
+    XCTAssertNil(HTMLTag(""))
+    XCTAssertNil(HTMLTag("foo"))
+    XCTAssertNil(HTMLTag("<"))
+    XCTAssertNil(HTMLTag("<>"))
+  }
+
+  func testOpeningTag() {
+    // given
+    let tag = HTMLTag("<sub>")
+
+    // then
+    XCTAssertEqual("sub", tag?.name)
+  }
+
+  func testOpeningTagWithAttributes() {
+    // given
+    let tag = HTMLTag(
+      "<img src=\"img_girl.jpg\" alt=\"Girl in a jacket\" width=\"500\" height=\"600\">"
+    )
+
+    // then
+    XCTAssertEqual("img", tag?.name)
+  }
+
+  func testClosingTag() {
+    let tag = HTMLTag("</sub>")
+    XCTAssertEqual(tag?.name, "sub")
+  }
+
+  func testSelfClosingTag() {
+    XCTAssertEqual("br", HTMLTag("<br />")?.name)
+  }
+}

Tests/MarkdownUITests/MarkdownTests.swift

@@ -241,6 +241,10 @@
         Visit https://github.com.
 
         Use `git status` to list all new or modified files that haven't yet been committed.
+
+        You can insert a line break<br>
+        using the HTML `<br>`
+        <br>      tag.
         """#
       }
       .border(Color.accentColor)