[Parser] Include all AST nodes from every #if regions in ParserUnit

'ParserUnit' is used for analyzing syntax structures _mainly_ in
SourceKit.

Since we removed IfConfigDecl from AST, ParserUnit didn't
inclue any AST in #if ... #endif regions even for active region because
it used to consider all inactive. Instead, consider every region
"active" and include all the AST nodes.

rdar://117387631

Author: rintaro

include/swift/AST/SourceFile.h

@@ -98,6 +98,9 @@ class SourceFile final : public FileUnit {
 
     /// Validate the new SwiftSyntax parser diagnostics.
     ValidateNewParserDiagnostics = 1 << 6,
+
+    /// Consider every #if ... #endif region active.
+    PoundIfAllActive = 1 << 7,
   };
   using ParsingOptions = OptionSet<ParsingFlags>;
 

lib/Parse/ParseIfConfig.cpp

@@ -834,6 +834,11 @@ Result Parser::parseIfConfigRaw(
       // determined solely by which block has the completion token.
       !ideInspectionClauseLoc.isValid();
 
+  // For constructing syntactic structures, we need AST nodes even for
+  // non-active regions.
+  bool allActive = SF.getParsingOptions().contains(
+      SourceFile::ParsingFlags::PoundIfAllActive);
+
   bool foundActive = false;
   bool isVersionCondition = false;
   CharSourceRange activeBodyRange;
@@ -893,6 +898,9 @@ Result Parser::parseIfConfigRaw(
     if (ideInspectionClauseLoc.isValid() && !foundActive)
       isActive = (ClauseLoc == ideInspectionClauseLoc);
 
+    if (allActive)
+      isActive = true;
+
     foundActive |= isActive;
 
     if (!Tok.isAtStartOfLine() && Tok.isNot(tok::eof)) {

lib/Parse/Parser.cpp

@@ -1145,6 +1145,7 @@ struct ParserUnit::Implementation {
     auto parsingOpts = SourceFile::getDefaultParsingOptions(LangOpts);
     parsingOpts |= ParsingFlags::DisableDelayedBodies;
     parsingOpts |= ParsingFlags::DisablePoundIfEvaluation;
+    parsingOpts |= ParsingFlags::PoundIfAllActive;
 
     auto *M = ModuleDecl::createEmpty(Ctx.getIdentifier(ModuleName), Ctx);
     SF = new (Ctx) SourceFile(*M, SFKind, BufferID, parsingOpts);