Merge pull request swiftlang#24850 from nkcsgexi/syntax-tree-with-condition

Parser: avoid skipping inactive code if we are building syntax trees.

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"
@@ -638,6 +639,12 @@ ParserResult<IfConfigDecl> Parser::parseIfConfig(
     SmallVector<ASTNode, 16> Elements;
     if (isActive || !isVersionCondition) {
       parseElements(Elements, isActive);
+    } 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 {
       DiagnosticTransaction DT(Diags);
       skipUntilConditionalBlockClose();

test/Syntax/diagnostics_verify.swift

@@ -19,3 +19,10 @@ class { // expected-error {{unknown declaration syntax exists in the source}}
   // expected-error@-4 {{top-level statement cannot begin with a closure expression}}
 
 }
+
+#if swift(<1)
+print("Wat")
+class { // expected-error {{unknown declaration syntax exists in the source}}
+
+}
+#endif