[cxx-interop] Estend _SwiftifyImport with basic std::span support

This is a preliminary PR to transform nonescaping std::span parameters
to Swift's Span type in safe wrappers. To hook this up with
ClangImporter, we will need generalize the noescape attribute to
non-pointer types (PR is already in review). To transform potentially
escaping spans and spans in the return position, a follow-up PR will
add lifetime annotation support. This is a building block towards
rdar://139074571.

Author: Gabor Horvath

lib/Macros/Sources/SwiftMacros/SwiftifyImportMacro.swift

@@ -6,7 +6,7 @@ import SwiftSyntaxMacros
 
 protocol ParamInfo: CustomStringConvertible {
   var description: String { get }
-  var original: ExprSyntax { get }
+  var original: SyntaxProtocol { get }
   var pointerIndex: Int { get }
   var nonescaping: Bool { get set }
 
@@ -16,12 +16,31 @@ protocol ParamInfo: CustomStringConvertible {
   ) -> BoundsCheckedThunkBuilder
 }
 
+struct CxxSpan: ParamInfo {
+  var pointerIndex: Int
+  var nonescaping: Bool
+  var original: SyntaxProtocol
+  var typeMappings: [String: String]
+
+  var description: String {
+    return "std::span(pointer: \(pointerIndex), nonescaping: \(nonescaping))"
+  }
+
+  func getBoundsCheckedThunkBuilder(
+    _ base: BoundsCheckedThunkBuilder, _ funcDecl: FunctionDeclSyntax,
+    _ variant: Variant
+  ) -> BoundsCheckedThunkBuilder {
+    CxxSpanThunkBuilder(base: base, index: pointerIndex - 1, signature: funcDecl.signature, 
+      typeMappings: typeMappings, node: original)
+  }
+}
+
 struct CountedBy: ParamInfo {
   var pointerIndex: Int
   var count: ExprSyntax
   var sizedBy: Bool
   var nonescaping: Bool
-  var original: ExprSyntax
+  var original: SyntaxProtocol
 
   var description: String {
     if sizedBy {
@@ -43,11 +62,12 @@ struct CountedBy: ParamInfo {
       nonescaping: nonescaping, isSizedBy: sizedBy)
   }
 }
+
 struct EndedBy: ParamInfo {
   var pointerIndex: Int
   var endIndex: Int
   var nonescaping: Bool
-  var original: ExprSyntax
+  var original: SyntaxProtocol
 
   var description: String {
     return ".endedBy(start: \(pointerIndex), end: \(endIndex), nonescaping: \(nonescaping))"
@@ -196,6 +216,7 @@ func getParam(_ signature: FunctionSignatureSyntax, _ paramIndex: Int) -> Functi
     return params[params.startIndex]
   }
 }
+
 func getParam(_ funcDecl: FunctionDeclSyntax, _ paramIndex: Int) -> FunctionParameterSyntax {
   return getParam(funcDecl.signature, paramIndex)
 }
@@ -257,6 +278,43 @@ struct FunctionCallBuilder: BoundsCheckedThunkBuilder {
   }
 }
 
+struct CxxSpanThunkBuilder: BoundsCheckedThunkBuilder {
+  public let base: BoundsCheckedThunkBuilder
+  public let index: Int
+  public let signature: FunctionSignatureSyntax
+  public let typeMappings: [String: String] 
+  public let node: SyntaxProtocol
+
+  func buildBoundsChecks(_ variant: Variant) throws -> [CodeBlockItemSyntax.Item] {
+    return []
+  }
+
+  func buildFunctionSignature(_ argTypes: [Int: TypeSyntax?], _ variant: Variant) throws
+    -> FunctionSignatureSyntax {
+    var types = argTypes
+    let param = getParam(signature, index)
+    let typeName = try getTypeName(param.type).text;
+    guard let desugaredType = typeMappings[typeName] else {
+      throw DiagnosticError(
+        "unable to desugar type with name '\(typeName)'", node: node)
+    }
+
+    let parsedDesugaredType = try TypeSyntax("\(raw: desugaredType)")
+    types[index] = TypeSyntax(IdentifierTypeSyntax(name: "Span",
+      genericArgumentClause: parsedDesugaredType.as(IdentifierTypeSyntax.self)!.genericArgumentClause))
+    return try base.buildFunctionSignature(types, variant)
+  }
+
+  func buildFunctionCall(_ pointerArgs: [Int: ExprSyntax], _ variant: Variant) throws -> ExprSyntax {
+    var args = pointerArgs
+    let param = getParam(signature, index)
+    let typeName = try getTypeName(param.type).text;
+    assert(args[index] == nil)
+    args[index] = ExprSyntax("\(raw: typeName)(\(raw: param.secondName ?? param.firstName))")
+    return try base.buildFunctionCall(args, variant)
+  }
+}
+
 protocol PointerBoundsThunkBuilder: BoundsCheckedThunkBuilder {
   var name: TokenSyntax { get }
   var nullable: Bool { get }
@@ -461,7 +519,8 @@ func getParameterIndexForDeclRef(
 /// Depends on bounds, escapability and lifetime information for each pointer.
 /// Intended to map to C attributes like __counted_by, __ended_by and __no_escape,
 /// for automatic application by ClangImporter when the C declaration is annotated
-/// appropriately.
+/// appropriately. Moreover, it can wrap C++ APIs using unsafe C++ types like
+/// std::span with APIs that use their safer Swift equivalents.
 public struct SwiftifyImportMacro: PeerMacro {
   static func parseEnumName(_ enumConstructorExpr: FunctionCallExprSyntax) throws -> String {
     guard let calledExpr = enumConstructorExpr.calledExpression.as(MemberAccessExprSyntax.self)
@@ -558,6 +617,54 @@ public struct SwiftifyImportMacro: PeerMacro {
     return pointerParamIndex
   }
 
+  static func parseTypeMappingParam(_ paramAST: LabeledExprSyntax?) throws -> [String: String]? {
+    guard let unwrappedParamAST = paramAST else {
+      return nil
+    }
+    let paramExpr = unwrappedParamAST.expression
+    guard let dictExpr = paramExpr.as(DictionaryExprSyntax.self) else {
+      return nil
+    }
+    var dict : [String: String] = [:]
+    switch dictExpr.content {
+      case .colon(_):
+        return dict
+      case .elements(let types):
+        for element in types {
+          guard let key = element.key.as(StringLiteralExprSyntax.self) else {
+            throw DiagnosticError("expected a string literal, got '\(element.key)'", node: element.key)
+          }
+          guard let value = element.value.as(StringLiteralExprSyntax.self) else {
+            throw DiagnosticError("expected a string literal, got '\(element.value)'", node: element.value)
+          }
+          dict[key.representedLiteralValue!] = value.representedLiteralValue!
+        }
+      default:
+        throw DiagnosticError("unknown dictionary literal", node: dictExpr)
+    }
+    return dict
+  }
+
+  static func parseCxxSpanParams(
+    _ signature: FunctionSignatureSyntax,
+    _ typeMappings: [String: String]?
+  ) throws -> [ParamInfo] {
+    guard let typeMappings else {
+      return []
+    }
+    var result : [ParamInfo] = []
+    for (idx, param) in signature.parameterClause.parameters.enumerated() {
+      let typeName = try getTypeName(param.type).text;
+      if let desugaredType = typeMappings[typeName] {
+        if desugaredType.starts(with: "span") {
+          result.append(CxxSpan(pointerIndex: idx + 1, nonescaping: false,
+            original: param, typeMappings: typeMappings))
+        }
+      }
+    }
+    return result
+  }
+
   static func parseMacroParam(
     _ paramAST: LabeledExprSyntax, _ signature: FunctionSignatureSyntax,
     nonescapingPointers: inout Set<Int>
@@ -652,11 +759,20 @@ public struct SwiftifyImportMacro: PeerMacro {
       }
 
       let argumentList = node.arguments!.as(LabeledExprListSyntax.self)!
+      var arguments = Array<LabeledExprSyntax>(argumentList)
+      let typeMappings = try parseTypeMappingParam(arguments.last)
+      if typeMappings != nil {
+        arguments = arguments.dropLast()
+      }
       var nonescapingPointers = Set<Int>()
-      var parsedArgs = try argumentList.compactMap {
+      var parsedArgs = try arguments.compactMap {
         try parseMacroParam($0, funcDecl.signature, nonescapingPointers: &nonescapingPointers)
       }
+      parsedArgs.append(contentsOf: try parseCxxSpanParams(funcDecl.signature, typeMappings))
       setNonescapingPointers(&parsedArgs, nonescapingPointers)
+      parsedArgs = parsedArgs.filter {
+        !($0 is CxxSpan) || ($0 as! CxxSpan).nonescaping
+      }
       try checkArgs(parsedArgs, funcDecl)
       let baseBuilder = FunctionCallBuilder(funcDecl)
 

stdlib/public/core/SwiftifyImport.swift

@@ -32,17 +32,19 @@ public enum _SwiftifyInfo {
     case nonescaping(pointer: Int)
 }
 
-/// Generates a bounds safe wrapper for function with Unsafe[Mutable][Raw]Pointer[?] arguments.
+/// Generates a safe wrapper for function with Unsafe[Mutable][Raw]Pointer[?] or std::span arguments.
 /// Intended to be automatically attached to function declarations imported by ClangImporter.
 /// The wrapper function will replace Unsafe[Mutable][Raw]Pointer[?] parameters with
 /// [Mutable][Raw]Span[?] or Unsafe[Mutable][Raw]BufferPointer[?] if they have bounds information
 /// attached. Where possible "count" parameters will be elided from the wrapper signature, instead
 /// fetching the count from the buffer pointer. In these cases the bounds check is also skipped.
+/// It will replace some std::span arguments with Swift's Span type when sufficient information is
+/// available.
 ///
 /// Currently not supported: return pointers, nested pointers, pointee "count" parameters, endedBy.
 ///
 /// Parameter paramInfo: information about how the function uses the pointer passed to it. The
 /// safety of the generated wrapper function depends on this info being extensive and accurate.
 @attached(peer, names: overloaded)
-public macro _SwiftifyImport(_ paramInfo: _SwiftifyInfo...) =
+public macro _SwiftifyImport(_ paramInfo: _SwiftifyInfo..., typeMappings: [String: String] = [:]) =
     #externalMacro(module: "SwiftMacros", type: "SwiftifyImportMacro")

test/Macros/SwiftifyImport/CxxSpan/NoEscapeSpan.swift

@@ -0,0 +1,17 @@
+// REQUIRES: swift_swift_parser
+// REQUIRES: swift_feature_Span
+
+// RUN: %target-swift-frontend %s -swift-version 5 -module-name main -disable-availability-checking -typecheck -enable-experimental-feature Span  -plugin-path %swift-plugin-dir -dump-macro-expansions 2>&1 | %FileCheck --match-full-lines %s
+
+public struct SpanOfInt {
+    init(_ x: Span<CInt>) {}
+}
+
+@_SwiftifyImport(.nonescaping(pointer: 1), typeMappings: ["SpanOfInt" : "span<CInt>"])
+func myFunc(_ span: SpanOfInt, _ secondSpan: SpanOfInt) {
+}
+
+// CHECK:      @_alwaysEmitIntoClient
+// CHECK-NEXT: func myFunc(_ span: Span<CInt>, _ secondSpan: SpanOfInt) {
+// CHECK-NEXT:     return myFunc(SpanOfInt(span), secondSpan)
+// CHECK-NEXT: }