Parser: suppress diagnostics when parsing inside inactive code

Author: nkcsgexi

lib/Parse/ParseIfConfig.cpp

@@ -17,6 +17,7 @@
 #include "swift/Parse/Parser.h"
 
 #include "swift/AST/ASTVisitor.h"
+#include "swift/AST/DiagnosticSuppression.h"
 #include "swift/Basic/Defer.h"
 #include "swift/Basic/LangOptions.h"
 #include "swift/Basic/Version.h"
@@ -641,6 +642,7 @@ ParserResult<IfConfigDecl> Parser::parseIfConfig(
     } else if (SyntaxContext->isEnabled()) {
       // We shouldn't skip code if we are building syntax tree.
       // The parser will keep running and we just discard the AST part.
+      DiagnosticSuppression suppression(Context.Diags);
       SmallVector<ASTNode, 16> dropedElements;
       parseElements(dropedElements, false);
     } else {

test/Syntax/diagnostics_verify.swift

@@ -22,4 +22,7 @@ class { // expected-error {{unknown declaration syntax exists in the source}}
 
 #if swift(<1)
 print("Wat")
+class { // expected-error {{unknown declaration syntax exists in the source}}
+
+}
 #endif