Re-implement SourceFile::getIfConfigClauseRanges on top of SwiftIfConfig

The SwiftIfConfig library provides APIs for evaluating and extracting
the active #if regions in source code. Use its "configured regions" API
along with the ASTContext-backed build configuration to reimplement the
extraction of active/inactive regions from the source.

This approach has the benefit of being effectively stateless: where the
existing solution relies on the C++ parser recording all of the `#if`
clauses it sees as it is parsing (and then might have to sort them later),
this version does a scan of source to collect the list without requiring
any other state. The newer implementation is also conceptually cleaner,
and can be shared with other clients that have their own take on the
build configuration.

The primary client of this information is the SourceKit request that
identifies "inactive" regions within the source file, which IDEs can
use to grey out inactive code within the current build configuration.
There is also some profiling information that uses it. Those clients
should be unaffected by this under-the-hood change.

For the moment, I'm leaving the old code path in place for compiler
builds that don't have swift-syntax. This should be considered
temporary, and that code should be removed in favor of request'ifying
this function and removing the incrementally-built state entirely.

Author: DougGregor

include/swift/AST/ASTBridging.h

@@ -26,6 +26,7 @@
 #include "swift/AST/Attr.h"
 #include "swift/AST/DiagnosticConsumer.h"
 #include "swift/AST/DiagnosticEngine.h"
+#include "swift/AST/IfConfigClauseRangeInfo.h"
 #include "swift/AST/Stmt.h"
 #endif
 
@@ -1912,6 +1913,49 @@ BridgedParameterList BridgedParameterList_createParsed(
     BridgedASTContext cContext, BridgedSourceLoc cLeftParenLoc,
     BridgedArrayRef cParameters, BridgedSourceLoc cRightParenLoc);
 
+//===----------------------------------------------------------------------===//
+// MARK: #if handling
+//===----------------------------------------------------------------------===//
+
+/// Bridged version of IfConfigClauseRangeInfo::ClauseKind.
+enum ENUM_EXTENSIBILITY_ATTR(closed) BridgedIfConfigClauseKind : size_t {
+  IfConfigActive,
+  IfConfigInactive,
+  IfConfigEnd
+};
+
+/// Bridged version of IfConfigClauseRangeInfo.
+struct BridgedIfConfigClauseRangeInfo {
+  BridgedSourceLoc directiveLoc;
+  BridgedSourceLoc bodyLoc;
+  BridgedSourceLoc endLoc;
+  BridgedIfConfigClauseKind kind;
+
+#ifdef USED_IN_CPP_SOURCE
+  swift::IfConfigClauseRangeInfo unbridged() const {
+    swift::IfConfigClauseRangeInfo::ClauseKind clauseKind;
+    switch (kind) {
+    case IfConfigActive:
+      clauseKind = swift::IfConfigClauseRangeInfo::ActiveClause;
+      break;
+
+    case IfConfigInactive:
+      clauseKind = swift::IfConfigClauseRangeInfo::InactiveClause;
+      break;
+
+    case IfConfigEnd:
+      clauseKind = swift::IfConfigClauseRangeInfo::EndDirective;
+      break;
+    }
+
+    return swift::IfConfigClauseRangeInfo(directiveLoc.unbridged(),
+                                          bodyLoc.unbridged(),
+                                          endLoc.unbridged(),
+                                          clauseKind);
+  }
+#endif
+};
+
 //===----------------------------------------------------------------------===//
 // MARK: Plugins
 //===----------------------------------------------------------------------===//

include/swift/AST/IfConfigClauseRangeInfo.h

@@ -0,0 +1,62 @@
+//===--- ASTBridging.h - header for the swift SILBridging module ----------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_AST_IFCONFIGCLAUSERANGEINFO_H
+#define SWIFT_AST_IFCONFIGCLAUSERANGEINFO_H
+
+#include "swift/Basic/SourceLoc.h"
+
+namespace swift {
+
+class SourceManager;
+
+/// Stores range information for a \c #if block in a SourceFile.
+class IfConfigClauseRangeInfo final {
+public:
+  enum ClauseKind {
+    // Active '#if', '#elseif', or '#else' clause.
+    ActiveClause,
+    // Inactive '#if', '#elseif', or '#else' clause.
+    InactiveClause,
+    // '#endif' directive.
+    EndDirective,
+  };
+
+private:
+  /// Source location of '#if', '#elseif', etc.
+  SourceLoc DirectiveLoc;
+  /// Character source location of body starts.
+  SourceLoc BodyLoc;
+  /// Location of the end of the body.
+  SourceLoc EndLoc;
+
+  ClauseKind Kind;
+
+public:
+  IfConfigClauseRangeInfo(SourceLoc DirectiveLoc, SourceLoc BodyLoc,
+                          SourceLoc EndLoc, ClauseKind Kind)
+      : DirectiveLoc(DirectiveLoc), BodyLoc(BodyLoc), EndLoc(EndLoc),
+        Kind(Kind) {
+    assert(DirectiveLoc.isValid() && BodyLoc.isValid() && EndLoc.isValid());
+  }
+
+  SourceLoc getStartLoc() const { return DirectiveLoc; }
+  CharSourceRange getDirectiveRange(const SourceManager &SM) const;
+  CharSourceRange getWholeRange(const SourceManager &SM) const;
+  CharSourceRange getBodyRange(const SourceManager &SM) const;
+
+  ClauseKind getKind() const { return Kind; }
+};
+
+}
+
+#endif /* SWIFT_AST_IFCONFIGCLAUSERANGEINFO_H */

include/swift/AST/SourceFile.h

@@ -15,6 +15,7 @@
 
 #include "swift/AST/ASTNode.h"
 #include "swift/AST/FileUnit.h"
+#include "swift/AST/IfConfigClauseRangeInfo.h"
 #include "swift/AST/Import.h"
 #include "swift/AST/SynthesizedFileUnit.h"
 #include "swift/Basic/Debug.h"
@@ -48,44 +49,6 @@ enum class RestrictedImportKind {
 /// Import that limits the access level of imported entities.
 using ImportAccessLevel = std::optional<AttributedImport<ImportedModule>>;
 
-/// Stores range information for a \c #if block in a SourceFile.
-class IfConfigClauseRangeInfo final {
-public:
-  enum ClauseKind {
-    // Active '#if', '#elseif', or '#else' clause.
-    ActiveClause,
-    // Inactive '#if', '#elseif', or '#else' clause.
-    InactiveClause,
-    // '#endif' directive.
-    EndDirective,
-  };
-
-private:
-  /// Source location of '#if', '#elseif', etc.
-  SourceLoc DirectiveLoc;
-  /// Character source location of body starts.
-  SourceLoc BodyLoc;
-  /// Location of the end of the body.
-  SourceLoc EndLoc;
-
-  ClauseKind Kind;
-
-public:
-  IfConfigClauseRangeInfo(SourceLoc DirectiveLoc, SourceLoc BodyLoc,
-                          SourceLoc EndLoc, ClauseKind Kind)
-      : DirectiveLoc(DirectiveLoc), BodyLoc(BodyLoc), EndLoc(EndLoc),
-        Kind(Kind) {
-    assert(DirectiveLoc.isValid() && BodyLoc.isValid() && EndLoc.isValid());
-  }
-
-  SourceLoc getStartLoc() const { return DirectiveLoc; }
-  CharSourceRange getDirectiveRange(const SourceManager &SM) const;
-  CharSourceRange getWholeRange(const SourceManager &SM) const;
-  CharSourceRange getBodyRange(const SourceManager &SM) const;
-
-  ClauseKind getKind() const { return Kind; }
-};
-
 /// A file containing Swift source code.
 ///
 /// This is a .swift or .sil file (or a virtual file, such as the contents of

include/swift/Bridging/ASTGen.h

@@ -151,6 +151,11 @@ bool swift_ASTGen_parseRegexLiteral(BridgedStringRef inputPtr,
                                     BridgedSourceLoc diagLoc,
                                     BridgedDiagnosticEngine diagEngine);
 
+intptr_t swift_ASTGen_configuredRegions(
+    BridgedASTContext astContext,
+    void *_Nonnull sourceFile,
+    BridgedIfConfigClauseRangeInfo *_Nullable *_Nonnull);
+
 #ifdef __cplusplus
 }
 #endif

lib/AST/Module.cpp

@@ -47,6 +47,7 @@
 #include "swift/Basic/SourceManager.h"
 #include "swift/Basic/Statistic.h"
 #include "swift/Basic/StringExtras.h"
+#include "swift/Bridging/ASTGen.h"
 #include "swift/Demangling/ManglingMacros.h"
 #include "swift/Parse/Token.h"
 #include "swift/Strings.h"
@@ -2964,6 +2965,21 @@ void SourceFile::recordIfConfigClauseRangeInfo(
 }
 
 ArrayRef<IfConfigClauseRangeInfo> SourceFile::getIfConfigClauseRanges() const {
+#if SWIFT_BUILD_SWIFT_SYNTAX
+  if (!IfConfigClauseRanges.IsSorted) {
+    IfConfigClauseRanges.Ranges.clear();
+
+    BridgedIfConfigClauseRangeInfo *regions;
+    intptr_t numRegions = swift_ASTGen_configuredRegions(
+        getASTContext(), getExportedSourceFile(), &regions);
+    IfConfigClauseRanges.Ranges.reserve(numRegions);
+    for (intptr_t i = 0; i != numRegions; ++i)
+      IfConfigClauseRanges.Ranges.push_back(regions[i].unbridged());
+    free(regions);
+
+    IfConfigClauseRanges.IsSorted = true;
+  }
+#else
   if (!IfConfigClauseRanges.IsSorted) {
     auto &SM = getASTContext().SourceMgr;
     // Sort the ranges if we need to.
@@ -2987,6 +3003,7 @@ ArrayRef<IfConfigClauseRangeInfo> SourceFile::getIfConfigClauseRanges() const {
                                       IfConfigClauseRanges.Ranges.end());
     IfConfigClauseRanges.IsSorted = true;
   }
+#endif
 
   return IfConfigClauseRanges.Ranges;
 }

lib/ASTGen/Sources/ASTGen/CompilerBuildConfiguration.swift

@@ -12,6 +12,7 @@
 
 import ASTBridging
 import SwiftIfConfig
+import SwiftSyntax
 
 /// A build configuration that uses the compiler's ASTContext to answer
 /// queries.
@@ -144,3 +145,52 @@ struct CompilerBuildConfiguration: BuildConfiguration {
     return version
   }
 }
+
+/// Extract the #if clause range information for the given source file.
+@_cdecl("swift_ASTGen_configuredRegions")
+public func configuredRegions(
+  astContext: BridgedASTContext,
+  sourceFilePtr: UnsafeRawPointer,
+  cRegionsOut: UnsafeMutablePointer<UnsafeMutablePointer<BridgedIfConfigClauseRangeInfo>?>
+) -> Int {
+  let sourceFilePtr = sourceFilePtr.bindMemory(to: ExportedSourceFile.self, capacity: 1)
+  let configuration = CompilerBuildConfiguration(ctx: astContext)
+  let regions = sourceFilePtr.pointee.syntax.configuredRegions(in: configuration)
+
+  var cRegions: [BridgedIfConfigClauseRangeInfo] = []
+  for (ifConfig, state) in regions {
+    let kind: BridgedIfConfigClauseKind
+    switch state {
+    case .active: kind = .IfConfigActive
+    case .inactive, .unparsed: kind = .IfConfigInactive
+    }
+
+    let bodyLoc: AbsolutePosition
+    if let elements = ifConfig.elements {
+      bodyLoc = elements.position
+    } else if let condition = ifConfig.condition {
+      bodyLoc = condition.endPosition
+    } else {
+      bodyLoc = ifConfig.endPosition
+    }
+
+    cRegions.append(
+      .init(
+        directiveLoc: sourceFilePtr.pointee.sourceLoc(
+          at: ifConfig.poundKeyword.positionAfterSkippingLeadingTrivia
+        ),
+        bodyLoc: sourceFilePtr.pointee.sourceLoc(at: bodyLoc),
+        endLoc: sourceFilePtr.pointee.sourceLoc(
+          at: ifConfig.endPosition
+        ),
+        kind: kind
+      )
+    )
+  }
+
+  let cRegionsBuf: UnsafeMutableBufferPointer<BridgedIfConfigClauseRangeInfo> =
+    .allocate(capacity: cRegions.count)
+  _ = cRegionsBuf.initialize(from: cRegions)
+  cRegionsOut.pointee = cRegionsBuf.baseAddress
+  return cRegionsBuf.count
+}

lib/ASTGen/Sources/ASTGen/SourceFile.swift

@@ -44,6 +44,12 @@ public struct ExportedSourceFile {
     }
     return AbsolutePosition(utf8Offset: opaqueValue - sourceFileBaseAddress)
   }
+
+  /// Retrieve a bridged source location for the given absolute position in
+  /// this source file.
+  public func sourceLoc(at position: AbsolutePosition) -> BridgedSourceLoc {
+    BridgedSourceLoc(at: position, in: buffer)
+  }
 }
 
 extension Parser.ExperimentalFeatures {