From 93b297cb2b87acc2793f3ff7fde9950d143c113a Mon Sep 17 00:00:00 2001
From: Alex Hoppen <ahoppen@apple.com>
Date: Tue, 10 Jun 2025 15:19:03 +0200
Subject: [PATCH] Relax precondition in `postProcessMultilineStringLiteral`
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The only place where we were dropping unexpected tokens or trivia around a string segment was when inferring the indentation of the closing quote. Instead of having a precondition, add the conditions that the last segment doesn’t have any of these here and fall back to the same logic that is used when the indentaiton could not be inferred.

Fixes #3097
---
 Sources/SwiftParser/StringLiterals.swift      | 31 ++++-------------
 .../translated/StringLiteralEofTests.swift    | 33 +++++++++++++++++++
 2 files changed, 40 insertions(+), 24 deletions(-)

diff --git a/Sources/SwiftParser/StringLiterals.swift b/Sources/SwiftParser/StringLiterals.swift
index b03c8877def..d3b9c8adc4d 100644
--- a/Sources/SwiftParser/StringLiterals.swift
+++ b/Sources/SwiftParser/StringLiterals.swift
@@ -340,22 +340,6 @@ extension Parser {
     unexpectedBeforeClosingQuote: [RawTokenSyntax],
     closingQuote: RawTokenSyntax
   ) {
-    // -------------------------------------------------------------------------
-    // Precondition
-
-    precondition(
-      allSegments.allSatisfy {
-        if case .stringSegment(let segment) = $0 {
-          return segment.unexpectedBeforeContent == nil
-            && segment.unexpectedAfterContent == nil
-            && segment.content.leadingTriviaByteLength == 0
-        } else {
-          return true
-        }
-      },
-      "String segment produced by the lexer should not have unexpected text or trivia because we would drop it during post-processing"
-    )
-
     // -------------------------------------------------------------------------
     // Variables
 
@@ -395,6 +379,9 @@ extension Parser {
     // Parse indentation of the closing quote
 
     if let lastSegment,
+      lastSegment.unexpectedBeforeContent == nil,
+      lastSegment.unexpectedAfterContent == nil,
+      lastSegment.content.leadingTriviaByteLength == 0,
       let parsedTrivia = parseIndentationTrivia(text: lastSegment.content.tokenText)
     {
       indentationTrivia = parsedTrivia
@@ -409,10 +396,9 @@ extension Parser {
         arena: self.arena
       )
     } else {
-      if let lastSegment = lastSegment {
-        indentationTrivia = TriviaParser.parseTrivia(lastSegment.content.tokenText, position: .leading).prefix(while: {
-          $0.isIndentationWhitespace
-        })
+      if let lastSegment {
+        indentationTrivia = TriviaParser.parseTrivia(lastSegment.content.tokenText, position: .leading)
+          .prefix(while: \.isIndentationWhitespace)
         let indentationByteLength = indentationTrivia.reduce(0, { $0 + $1.byteLength })
         indentation = SyntaxText(rebasing: lastSegment.content.tokenText[0..<indentationByteLength])
         middleSegments.append(.stringSegment(lastSegment))
@@ -703,10 +689,7 @@ extension Parser {
       }
     }
 
-    let (unexpectedBetweenSegmentAndCloseQuote, closeQuote) = self.expect(
-      anyIn: SimpleStringLiteralExprSyntax.ClosingQuoteOptions.self,
-      default: openQuote.closeTokenKind
-    )
+    let (unexpectedBetweenSegmentAndCloseQuote, closeQuote) = self.expect(openQuote.closeTokenKind.spec)
     let closeDelimiter = self.consume(if: .rawStringPoundDelimiter)
 
     if openQuote.tokenKind == .multilineStringQuote, !openQuote.isMissing, !closeQuote.isMissing {
diff --git a/Tests/SwiftParserTest/translated/StringLiteralEofTests.swift b/Tests/SwiftParserTest/translated/StringLiteralEofTests.swift
index 00dc1127bb8..ae17fe465fd 100644
--- a/Tests/SwiftParserTest/translated/StringLiteralEofTests.swift
+++ b/Tests/SwiftParserTest/translated/StringLiteralEofTests.swift
@@ -243,4 +243,37 @@ final class StringLiteralEofTests: ParserTestCase {
         """##
     )
   }
+
+  func testSimpleMultilineStringLiteralWith() {
+    assertParse(
+      #"""
+      #sourceLocation1️⃣(file: 2️⃣"""3️⃣\(4️⃣"5️⃣
+      """#,
+      diagnostics: [
+        DiagnosticSpec(locationMarker: "3️⃣", message: "argument cannot be an interpolated string literal"),
+        DiagnosticSpec(
+          locationMarker: "4️⃣",
+          message: #"expected '"""' to end simple string literal"#,
+          notes: [NoteSpec(locationMarker: "2️⃣", message: #"to match this opening '"""'"#)],
+          fixIts: [#"insert '"""'"#]
+        ),
+        DiagnosticSpec(
+          locationMarker: "4️⃣",
+          message: "expected ', line:' and line number in '#sourceLocation' arguments",
+          fixIts: ["insert ', line:' and line number"]
+        ),
+        DiagnosticSpec(
+          locationMarker: "4️⃣",
+          message: "expected ')' in '#sourceLocation' directive",
+          notes: [NoteSpec(locationMarker: "1️⃣", message: "to match this opening '('")],
+          fixIts: ["insert ')'"]
+        ),
+        DiagnosticSpec(locationMarker: "4️⃣", message: "extra tokens following the #sourceLocation directive"),
+      ],
+      fixedSource: #"""
+        #sourceLocation(file: """\(
+        """, line: <#integer literal#>)"
+        """#
+    )
+  }
 }