attempt to work around a bug in SwiftSyntax 510.0.2, and add a test

Author: tayloraswift

Sources/MarkdownPluginSwift/Signatures/Signature.Abridged (ext).swift

@@ -20,9 +20,22 @@ extension Signature.Abridged
         self.init(utf8: [UInt8].init(string.utf8))
     }
 
-    @usableFromInline internal
-    init(utf8:[UInt8])
+    @usableFromInline
+    init(utf8:consuming [UInt8])
     {
+        //  There seems to be a bug in SwiftSyntax that causes misalignment of source ranges
+        //  when trimming leading trivia from syntax nodes. As a temporary workaround, we
+        //  replace all newline characters with space characters before parsing the source.
+        for i:Int in utf8.indices
+        {
+            switch utf8[i]
+            {
+            case 0x0A:  utf8[i] = 0x20
+            case 0x0D:  utf8[i] = 0x20
+            default:    continue
+            }
+        }
+
         let signature:SignatureSyntax = utf8.withUnsafeBufferPointer { .abridged($0) }
         let bytecode:Markdown.Bytecode = .init
         {

Sources/MarkdownPluginSwiftTests/Main.Signatures.swift

@@ -450,5 +450,38 @@ extension Main.Signatures:TestBattery
             <wbr>) rethrows
             """)
         }
+        if  let tests:TestGroup = tests / "Abridged" / "BackDeployed"
+        {
+            let decl:String = """
+            @backDeployed(before: macOS 14.0, iOS 17.0, watchOS 10.0, tvOS 17.0)
+
+            nonisolated func assertIsolated(\
+            _ message: @autoclosure () -> String = String(), \
+            file: StaticString = #fileID, \
+            line: UInt = #line)
+            """
+
+            let abridged:Signature<Never>.Abridged = .init(decl)
+
+            let rendered:HTML = .init { $0 += abridged.bytecode.safe }
+            let expected:HTML = .init
+            {
+                $0 += "nonisolated func "
+                $0[.span] { $0.class = "xv" } = "assertIsolated"
+                $0 += "("
+                $0[.span] { $0.class = "xi" }
+                $0 += "@autoclosure () -> String, "
+                $0[.span] { $0.class = "xi" }
+                $0[.span] { $0.class = "xv" } = "file"
+                $0 += ": StaticString, "
+                $0[.span] { $0.class = "xi" }
+                $0[.span] { $0.class = "xv" } = "line"
+                $0 += ": UInt"
+                $0[.wbr]
+                $0 += ")"
+            }
+
+            tests.expect("\(rendered)" ==? "\(expected)")
+        }
     }
 }