Create and register SourceFiles for pretty-printed buffers

This will allow the macro system to find them.

Author: DougGregor

lib/Sema/TypeCheckDecl.cpp

@@ -3350,6 +3350,7 @@ SourceLoc PrettyPrintDeclRequest::evaluate(Evaluator &eval, const Decl *decl) co
         getBufferAccessLevel(decl),
         ctx.TypeCheckerOpts.PrintFullConvention);
     decl->print(printer, options);
+
     // Close all of the enclosing types.
     for (const auto & enclosingType: enclosingTypes) {
       (void)enclosingType;
@@ -3381,5 +3382,11 @@ SourceLoc PrettyPrintDeclRequest::evaluate(Evaluator &eval, const Decl *decl) co
       }
   );
 
+  // Add a source file for the buffer.
+  auto moduleDecl = decl->getDeclContext()->getParentModule();
+  auto sourceFile = new (ctx) SourceFile(
+      *moduleDecl, SourceFileKind::Library, bufferID);
+  sourceFile->setImports({ });
+
   return memBufferStartLoc.getAdvancedLoc(targetDeclOffsetInBuffer);
 }