trim trailing whitespace when parsing single-line directives (#114)

rdar://106458003

Author: QuietMisdreavus

Sources/Markdown/Parser/BlockDirectiveParser.swift

@@ -182,6 +182,7 @@ struct PendingBlockDirective {
             // "@xx { yy } zz }" "yy } zz" will be parsed
 
             var reversedRemainingContent = TrimmedLine(Substring(line.text.reversed()), source: line.source, lineNumber: line.lineNumber)
+            reversedRemainingContent.lexWhitespace()
             if !line.text.isEmpty,
                reversedRemainingContent.lex("}") != nil {
                 let trailingWhiteSpaceCount = reversedRemainingContent.lexWhitespace()?.text.count ?? 0

Tests/MarkdownTests/Parsing/BlockDirectiveParserTests.swift

@@ -982,4 +982,25 @@ class BlockDirectiveArgumentParserTests: XCTestCase {
         """#
         XCTAssertEqual(document.debugDescription(options: .printSourceLocations), expectedDump)
     }
+
+    func testSingleLineDirectiveWithTrailingWhitespace() {
+        let source = """
+        @blah { content }\(" ")
+        @blah {
+            content
+        }
+        """
+        let document = Document(parsing: source, options: [.parseBlockDirectives])
+
+        let expectedDump = #"""
+        Document @1:1-4:2
+        ├─ BlockDirective @1:1-1:19 name: "blah"
+        │  └─ Paragraph @1:9-1:17
+        │     └─ Text @1:9-1:16 "content"
+        └─ BlockDirective @2:1-4:2 name: "blah"
+           └─ Paragraph @3:5-3:12
+              └─ Text @3:5-3:12 "content"
+        """#
+        XCTAssertEqual(document.debugDescription(options: .printSourceLocations), expectedDump)
+    }
 }