[ParseableInterfaces] Re-escape multi-line strings in attribute messages

Previously, we would print multi-line string literals with single quotes, which were not re-parseable. Instead, re-escape their contents and print them out escaped.

Author: Harlan Haskins

include/swift/AST/ASTPrinter.h

@@ -207,6 +207,8 @@ class ASTPrinter {
     return *this;
   }
 
+  void printEscapedStringLiteral(StringRef str);
+
   void printName(Identifier Name,
                  PrintNameContext Context = PrintNameContext::Normal);
 

lib/AST/ASTPrinter.cpp

@@ -270,6 +270,22 @@ void ASTPrinter::printTextImpl(StringRef Text) {
   printText(Text);
 }
 
+void ASTPrinter::printEscapedStringLiteral(StringRef str) {
+  SmallString<128> encodeBuf;
+  StringRef escaped =
+    Lexer::getEncodedStringSegment(str, encodeBuf,
+                                   /*isFirstSegment*/true,
+                                   /*isLastSegment*/true,
+                                   /*indentToStrip*/~0U /* sentinel */);
+
+  // FIXME: This is wasteful, but ASTPrinter is an abstract class that doesn't
+  //        have a directly-accessible ostream.
+  SmallString<128> escapeBuf;
+  llvm::raw_svector_ostream os(escapeBuf);
+  os << QuotedString(escaped);
+  printTextImpl(escapeBuf.str());
+}
+
 void ASTPrinter::printTypeRef(Type T, const TypeDecl *RefTo, Identifier Name) {
   PrintNameContext Context = PrintNameContext::Normal;
   if (isa<GenericTypeParamDecl>(RefTo)) {

lib/AST/Attr.cpp

@@ -460,8 +460,10 @@ bool DeclAttribute::printImpl(ASTPrinter &Printer, const PrintOptions &Options,
     // If there's no message, but this is specifically an imported
     // "unavailable in Swift" attribute, synthesize a message to look good in
     // the generated interface.
-    if (!Attr->Message.empty())
-      Printer << ", message: \"" << Attr->Message << "\"";
+    if (!Attr->Message.empty()) {
+      Printer << ", message: ";
+      Printer.printEscapedStringLiteral(Attr->Message);
+    }
     else if (Attr->getPlatformAgnosticAvailability()
                == PlatformAgnosticAvailabilityKind::UnavailableInSwift)
       Printer << ", message: \"Not available in Swift\"";