Replace embedded cmark-gfm by swift-cmark (#348)

Package.resolved

@@ -9,6 +9,15 @@
         "version" : "6.0.0"
       }
     },
+    {
+      "identity" : "swift-cmark",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/swiftlang/swift-cmark",
+      "state" : {
+        "revision" : "3ccff77b2dc5b96b77db3da0d68d28068593fa53",
+        "version" : "0.5.0"
+      }
+    },
     {
       "identity" : "swift-snapshot-testing",
       "kind" : "remoteSourceControl",

Package.swift

@@ -20,13 +20,14 @@ let package = Package(
   dependencies: [
     .package(url: "https://github.com/gonzalezreal/NetworkImage", from: "6.0.0"),
     .package(url: "https://github.com/pointfreeco/swift-snapshot-testing", from: "1.10.0"),
+    .package(url: "https://github.com/swiftlang/swift-cmark", from: "0.4.0"),
   ],
   targets: [
-    .target(name: "cmark-gfm"),
     .target(
       name: "MarkdownUI",
       dependencies: [
-        "cmark-gfm",
+        .product(name: "cmark-gfm", package: "swift-cmark"),
+        .product(name: "cmark-gfm-extensions", package: "swift-cmark"),
         .product(name: "NetworkImage", package: "NetworkImage"),
       ]
     ),

Sources/MarkdownUI/Parser/MarkdownParser.swift

@@ -1,5 +1,6 @@
 import Foundation
 @_implementationOnly import cmark_gfm
+@_implementationOnly import cmark_gfm_extensions
 
 extension Array where Element == BlockNode {
   init(markdown: String) {
@@ -317,7 +318,7 @@ extension UnsafeNode {
       return node
     case .table(let columnAlignments, let rows):
       guard let table = cmark_find_syntax_extension("table"),
-        let node = cmark_node_new_with_ext(CMARK_NODE_TABLE, table)
+        let node = cmark_node_new_with_ext(ExtensionNodeTypes.shared.CMARK_NODE_TABLE, table)
       else {
         return nil
       }
@@ -354,7 +355,7 @@ extension UnsafeNode {
 
   fileprivate static func make(_ tableRow: RawTableRow) -> UnsafeNode? {
     guard let table = cmark_find_syntax_extension("table"),
-      let node = cmark_node_new_with_ext(CMARK_NODE_TABLE_ROW, table)
+      let node = cmark_node_new_with_ext(ExtensionNodeTypes.shared.CMARK_NODE_TABLE_ROW, table)
     else {
       return nil
     }
@@ -364,7 +365,7 @@ extension UnsafeNode {
 
   fileprivate static func make(_ tableCell: RawTableCell) -> UnsafeNode? {
     guard let table = cmark_find_syntax_extension("table"),
-      let node = cmark_node_new_with_ext(CMARK_NODE_TABLE_CELL, table)
+      let node = cmark_node_new_with_ext(ExtensionNodeTypes.shared.CMARK_NODE_TABLE_CELL, table)
     else {
       return nil
     }
@@ -400,7 +401,8 @@ extension UnsafeNode {
       return node
     case .strikethrough(let children):
       guard let strikethrough = cmark_find_syntax_extension("strikethrough"),
-        let node = cmark_node_new_with_ext(CMARK_NODE_STRIKETHROUGH, strikethrough)
+        let node = cmark_node_new_with_ext(
+          ExtensionNodeTypes.shared.CMARK_NODE_STRIKETHROUGH, strikethrough)
       else {
         return nil
       }
@@ -480,3 +482,34 @@ private struct UnsafeNodeSequence: Sequence {
     .init(self.node)
   }
 }
+
+// Extension node types are not exported in `cmark_gfm_extensions`,
+// so we need to look for them in the symbol table
+private struct ExtensionNodeTypes {
+  let CMARK_NODE_TABLE: cmark_node_type
+  let CMARK_NODE_TABLE_ROW: cmark_node_type
+  let CMARK_NODE_TABLE_CELL: cmark_node_type
+  let CMARK_NODE_STRIKETHROUGH: cmark_node_type
+
+  static let shared = ExtensionNodeTypes()
+
+  private init() {
+    func findNodeType(_ name: String, in handle: UnsafeMutableRawPointer!) -> cmark_node_type? {
+      guard let symbol = dlsym(handle, name) else {
+        return nil
+      }
+      return symbol.assumingMemoryBound(to: cmark_node_type.self).pointee
+    }
+
+    let handle = dlopen(nil, RTLD_LAZY)
+
+    self.CMARK_NODE_TABLE = findNodeType("CMARK_NODE_TABLE", in: handle) ?? CMARK_NODE_NONE
+    self.CMARK_NODE_TABLE_ROW = findNodeType("CMARK_NODE_TABLE_ROW", in: handle) ?? CMARK_NODE_NONE
+    self.CMARK_NODE_TABLE_CELL =
+      findNodeType("CMARK_NODE_TABLE_CELL", in: handle) ?? CMARK_NODE_NONE
+    self.CMARK_NODE_STRIKETHROUGH =
+      findNodeType("CMARK_NODE_STRIKETHROUGH", in: handle) ?? CMARK_NODE_NONE
+
+    dlclose(handle)
+  }
+}