Remove assertion that the closing quote of a string literal must not have leading trivia

Author: ahoppen

Sources/SwiftParser/StringLiterals.swift

@@ -309,7 +309,6 @@ extension Parser {
     // -------------------------------------------------------------------------
     // Precondition
 
-    assert(closeQuote.leadingTriviaByteLength == 0, "Closing quote produced by the lexer should not have leading trivia because we would drop it during post-processing")
     assert(
       allSegments.allSatisfy {
         if case .stringSegment(let segment) = $0 {
@@ -349,7 +348,7 @@ extension Parser {
       middleSegments: &middleSegments
     )
 
-    if !closeDelimiterOnNewLine {
+    if !closeDelimiterOnNewLine || closeQuote.leadingTriviaByteLength != 0 {
       unexpectedBeforeCloseQuote = [closeQuote]
       closeQuote = RawTokenSyntax(missing: closeQuote.tokenKind, leadingTriviaPieces: [.newlines(1)], arena: self.arena)
 

Tests/SwiftParserTest/ExpressionTests.swift

@@ -1652,4 +1652,18 @@ final class StatementExpressionTests: XCTestCase {
       diagnostics: [DiagnosticSpec(message: "unexpected code '@case' in 'switch' statement")]
     )
   }
+
+  func testUnterminatedInterpolationAtEndOfMultilineStringLiteral() {
+    AssertParse(
+      #"""
+      """\({(1️⃣})
+      2️⃣"""3️⃣
+      """#,
+      diagnostics: [
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected value and ')' to end tuple"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: #"unexpected code '"""' in string literal"#),
+        DiagnosticSpec(locationMarker: "3️⃣", message: #"expected '"""' to end string literal"#),
+      ]
+    )
+  }
 }