Revert "Use SwiftIfConfig to determine where to emit new parser diagnostics

include/swift/Bridging/ASTGen.h

@@ -48,7 +48,6 @@ int swift_ASTGen_roundTripCheck(void *_Nonnull sourceFile);
 /// Emit parser diagnostics for given source file.. Returns non-zero if any
 /// diagnostics were emitted.
 int swift_ASTGen_emitParserDiagnostics(
-    BridgedASTContext astContext,
     void *_Nonnull diagEngine, void *_Nonnull sourceFile, int emitOnlyErrors,
     int downgradePlaceholderErrorsToWarnings);
 

lib/ASTGen/Sources/ASTGen/SourceFile.swift

@@ -12,7 +12,6 @@
 
 import ASTBridging
 import SwiftDiagnostics
-import SwiftIfConfig
 @_spi(ExperimentalLanguageFeatures) import SwiftParser
 import SwiftParserDiagnostics
 import SwiftSyntax
@@ -143,10 +142,20 @@ public func roundTripCheck(
   }
 }
 
+extension Syntax {
+  /// Whether this syntax node is or is enclosed within a #if.
+  fileprivate var isInIfConfig: Bool {
+    if self.is(IfConfigDeclSyntax.self) {
+      return true
+    }
+
+    return parent?.isInIfConfig ?? false
+  }
+}
+
 /// Emit diagnostics within the given source file.
 @_cdecl("swift_ASTGen_emitParserDiagnostics")
 public func emitParserDiagnostics(
-  ctx: BridgedASTContext,
   diagEnginePtr: UnsafeMutableRawPointer,
   sourceFilePtr: UnsafeMutablePointer<UInt8>,
   emitOnlyErrors: CInt,
@@ -163,18 +172,11 @@ public func emitParserDiagnostics(
     )
 
     let diagnosticEngine = BridgedDiagnosticEngine(raw: diagEnginePtr)
-    let buildConfiguration = CompilerBuildConfiguration(
-      ctx: ctx,
-      conditionLoc:
-        BridgedSourceLoc(
-        at: AbsolutePosition(utf8Offset: 0),
-        in: sourceFile.pointee.buffer
-      )
-    )
-
     for diag in diags {
-      // If the diagnostic is in an unparsed #if region, don't emit it.
-      if diag.node.isActive(in: buildConfiguration).state == .unparsed {
+      // Skip over diagnostics within #if, because we don't know whether
+      // we are in an active region or not.
+      // FIXME: This heuristic could be improved.
+      if diag.node.isInIfConfig {
         continue
       }
 

lib/Parse/ParseDecl.cpp

@@ -267,7 +267,7 @@ void Parser::parseTopLevelItems(SmallVectorImpl<ASTNode> &items) {
   if (parsingOpts.contains(ParsingFlags::ValidateNewParserDiagnostics) &&
       !Context.Diags.hadAnyError()) {
     auto hadSyntaxError = swift_ASTGen_emitParserDiagnostics(
-        Context, &Context.Diags, exportedSourceFile,
+        &Context.Diags, exportedSourceFile,
         /*emitOnlyErrors=*/true,
         /*downgradePlaceholderErrorsToWarnings=*/
         Context.LangOpts.Playground ||
@@ -346,7 +346,7 @@ void Parser::parseSourceFileViaASTGen(
   // If we're supposed to emit diagnostics from the parser, do so now.
   if (!suppressDiagnostics) {
     auto hadSyntaxError = swift_ASTGen_emitParserDiagnostics(
-        Context, &Context.Diags, exportedSourceFile, /*emitOnlyErrors=*/false,
+        &Context.Diags, exportedSourceFile, /*emitOnlyErrors=*/false,
         /*downgradePlaceholderErrorsToWarnings=*/langOpts.Playground ||
             langOpts.WarnOnEditorPlaceholder);
     if (hadSyntaxError && Context.Diags.hadAnyError() &&

test/ASTGen/if_config.swift

@@ -3,8 +3,8 @@
 // REQUIRES: asserts
 
 #if NOT_SET
-func f { } // expected-error{{expected parameter clause in function signature}}
-           // expected-note@-1{{insert parameter clause}}{{7-8=}}{{8-8=(}}{{8-8=) }}
+func f { } // FIXME: Error once the parser diagnostics generator knows to
+           // evaluate the active clause.
 #endif
 
 #if compiler(>=10.0)