Ensure FormatRawStringLiteral produces valid swift syntax for special characters

[itsdevandy]

Summary

Currently, the FormatRawStringLiteral refactoring can produce invalid Swift code when moving from extended delimiters to a regular string literal. For example:

• #"""# becomes """ (Unmatched multi-line literal)
• #"He says "Hi""# becomes "He says "Hi"" (Syntax error)
• #"C:\Users"# becomes "C:\Users" (Invalid escape sequence)

This PR adjusts the logic to ensure that the minimum number of # symbols is is always sufficient to represent the content safely. The minimum safe number of # delimiters is now 1.

Alternative: Auto-escaping on hitting string literal

I have also explored an implementation where it can convert these to string literals while injecting the escape characters ( eg: #"He says "Hi""# -> "He says \"Hi\"" ).

I can use this alternative, or a different approach if the preference is to favor standard literals over delimited ones. Open to suggestions!

---

Test Plan:

• Modified unit tests for new cases
• Remaining existing tests pass
• Files formatted using swift format -ipr

Linked Issue

Closes swiftlang/sourcekit-lsp#2465

[rickhohler]

Hey @itsdevandy! 👋

I'm just a guest here looking to contribute, and I actually started working on this same issue today before realizing you had already been working it! I've closed my PR to defer to yours.

While I was exploring the issue, I did notice one small edge case: checking max(1, ...) might accidentally prevent standard strings like #"hello"# from being simplified down to "hello", which I think is the goal of the "minimal" refactoring.

I wrote a little snippet to handle the tricky #""" case while keeping that minimization behavior. Just thought I'd share it here in case it saves you any time!

    // Logic to safely check implementation
    var shouldRemoveHashes = maximumHashes == 0
    let quote = lit.openingQuote.text 

    if shouldRemoveHashes {
      if quote == "\"" {
         // Check for the #"""..."""# case which parses as quote=""" and content wrapped in quotes.
         for segment in lit.segments {
            if case .stringSegment(let s) = segment {
               if s.content.text.hasPrefix("\"") && s.content.text.hasSuffix("\"") {
                  shouldRemoveHashes = false
                  break
               }
            }
         }
      } else if quote == "\"\"\"" {
         // Check for single-line multiline strings
         let containsNewline =
          lit.openingQuote.trailingTrivia.description.contains("\n")
          || lit.segments.contains(where: { $0.description.contains("\n") })
          || lit.closingQuote.leadingTrivia.description.contains("\n")

        if !containsNewline {
          shouldRemoveHashes = false
        }
      }
    }

Thanks. Rick.