[JExtract] Lazy Cdecl lowering and Java translation

Make `Swift2JavaTranslator.analyze()` analyze only Swift signatures.
Postpone Cdecl lowering and Java translation for cleaner separation of
responsibilities.

Author: rintaro

Sources/JExtractSwift/ImportedDecls.swift

@@ -52,30 +52,18 @@ public final class ImportedFunc: ImportedDecl, CustomStringConvertible {
 
   public var swiftDecl: any DeclSyntaxProtocol
 
-  var translatedSignature: TranslatedFunctionSignature
-
   package var apiKind: SwiftAPIKind
 
+  var functionSignature: SwiftFunctionSignature
+
   public var signatureString: String {
     // FIXME: Remove comments and normalize trivia.
     self.swiftDecl.signatureString
   }
 
-  var loweredSignature: LoweredFunctionSignature {
-    translatedSignature.loweredSignature
-  }
-
-  var swiftSignature: SwiftFunctionSignature {
-    loweredSignature.original
-  }
-
-  package func cFunctionDecl(cName: String) -> CFunction {
-    // 'try!' because we know 'loweredSignature' can be described with C.
-    try! loweredSignature.cFunctionDecl(cName: cName)
-  }
 
   var parentType: SwiftType? {
-    guard let selfParameter = swiftSignature.selfParameter else {
+    guard let selfParameter = functionSignature.selfParameter else {
       return nil
     }
     switch selfParameter {
@@ -92,7 +80,7 @@ public final class ImportedFunc: ImportedDecl, CustomStringConvertible {
   /// this will contain that declaration's imported name.
   ///
   /// This is necessary when rendering accessor Java code we need the type that "self" is expecting to have.
-  public var hasParent: Bool { translatedSignature.selfParameter != nil }
+  public var hasParent: Bool { functionSignature.selfParameter != nil }
 
   /// A display name to use to refer to the Swift declaration with its
   /// enclosing type, if there is one.
@@ -117,13 +105,13 @@ public final class ImportedFunc: ImportedDecl, CustomStringConvertible {
     swiftDecl: any DeclSyntaxProtocol,
     name: String,
     apiKind: SwiftAPIKind,
-    translatedSignature: TranslatedFunctionSignature
+    functionSignature: SwiftFunctionSignature
   ) {
     self.module = module
     self.name = name
     self.swiftDecl = swiftDecl
     self.apiKind = apiKind
-    self.translatedSignature = translatedSignature
+    self.functionSignature = functionSignature
   }
 
   public var description: String {

Sources/JExtractSwift/Swift2JavaTranslator+JavaBindingsPrinting.swift

@@ -19,6 +19,11 @@ extension Swift2JavaTranslator {
     _ printer: inout CodePrinter,
     _ decl: ImportedFunc
   ) {
+    guard let _ = translatedSignature(for: decl) else {
+      // Failed to translate. Skip.
+      return
+    }
+
     printer.printSeparator(decl.displayName)
 
     printJavaBindingDescriptorClass(&printer, decl)
@@ -33,7 +38,9 @@ extension Swift2JavaTranslator {
     _ decl: ImportedFunc
   ) {
     let thunkName = thunkNameRegistry.functionThunkName(decl: decl)
-    let cFunc = decl.cFunctionDecl(cName: thunkName)
+    let translatedSignature = self.translatedSignature(for: decl)!
+    // 'try!' because we know 'loweredSignature' can be described with C.
+    let cFunc = try! translatedSignature.loweredSignature.cFunctionDecl(cName: thunkName)
 
     printer.printBraceBlock(
       """
@@ -129,19 +136,20 @@ extension Swift2JavaTranslator {
     }
 
     var modifiers = "public"
-    switch decl.swiftSignature.selfParameter {
+    switch decl.functionSignature.selfParameter {
     case .staticMethod, .initializer, nil:
       modifiers.append(" static")
     default:
       break
     }
 
-    let returnTy = decl.translatedSignature.result.javaResultType
+    let translatedSignature = self.translatedSignature(for: decl)!
+    let returnTy = translatedSignature.result.javaResultType
 
-    var paramDecls = decl.translatedSignature.parameters
+    var paramDecls = translatedSignature.parameters
       .flatMap(\.javaParameters)
       .map { "\($0.type) \($0.name)" }
-    if decl.translatedSignature.requiresSwiftArena {
+    if translatedSignature.requiresSwiftArena {
       paramDecls.append("SwiftArena swiftArena$")
     }
 
@@ -157,7 +165,7 @@ extension Swift2JavaTranslator {
       \(modifiers) \(returnTy) \(methodName)(\(paramDecls.joined(separator: ", ")))
       """
     ) { printer in
-      if case .instance(_) =  decl.swiftSignature.selfParameter {
+      if case .instance(_) =  decl.functionSignature.selfParameter {
         // Make sure the object has not been destroyed.
         printer.print("$ensureAlive();")
       }
@@ -174,7 +182,9 @@ extension Swift2JavaTranslator {
     _ decl: ImportedFunc
   ) {
     //===  Part 1: prepare temporary arena if needed.
-    if decl.translatedSignature.requiresTemporaryArena {
+    let translatedSignature = self.translatedSignature(for: decl)!
+
+    if translatedSignature.requiresTemporaryArena {
       printer.print("try(var arena$ = Arena.ofConfined()) {")
       printer.indent();
     }
@@ -183,21 +193,21 @@ extension Swift2JavaTranslator {
     var downCallArguments: [String] = []
 
     // Regular parameters.
-    for (i, parameter) in decl.translatedSignature.parameters.enumerated() {
-      let original = decl.swiftSignature.parameters[i]
+    for (i, parameter) in translatedSignature.parameters.enumerated() {
+      let original = decl.functionSignature.parameters[i]
       let parameterName = original.parameterName ?? "_\(i)"
       let lowered = parameter.conversion.render(&printer, parameterName)
       downCallArguments.append(lowered)
     }
 
     // 'self' parameter.
-    if let selfParameter = decl.translatedSignature.selfParameter {
+    if let selfParameter = translatedSignature.selfParameter {
       let lowered = selfParameter.conversion.render(&printer, "this")
       downCallArguments.append(lowered)
     }
 
     // Indirect return receivers.
-    for outParameter in decl.translatedSignature.result.outParameters {
+    for outParameter in translatedSignature.result.outParameters {
       let memoryLayout = renderMemoryLayoutValue(for: outParameter.type)
 
       let arena = if let className = outParameter.type.className,
@@ -222,27 +232,27 @@ extension Swift2JavaTranslator {
     let downCall = "\(thunkName).call(\(downCallArguments.joined(separator: ", ")))"
 
     //=== Part 4: Convert the return value.
-    if decl.translatedSignature.result.javaResultType == .void {
+    if translatedSignature.result.javaResultType == .void {
       printer.print("\(downCall);")
     } else {
       let placeholder: String
-      if decl.translatedSignature.result.outParameters.isEmpty {
+      if translatedSignature.result.outParameters.isEmpty {
         placeholder = downCall
       } else {
         // FIXME: Support cdecl thunk returning a value while populating the out parameters.
         printer.print("\(downCall);")
         placeholder = "_result"
       }
-      let result = decl.translatedSignature.result.conversion.render(&printer, placeholder)
+      let result = translatedSignature.result.conversion.render(&printer, placeholder)
 
-      if decl.translatedSignature.result.javaResultType != .void {
+      if translatedSignature.result.javaResultType != .void {
         printer.print("return \(result);")
       } else {
         printer.print("\(result);")
       }
     }
 
-    if decl.translatedSignature.requiresTemporaryArena {
+    if translatedSignature.requiresTemporaryArena {
       printer.outdent()
       printer.print("}")
     }

Sources/JExtractSwift/Swift2JavaTranslator+JavaTranslation.swift

@@ -15,15 +15,26 @@
 import JavaTypes
 
 extension Swift2JavaTranslator {
-  func translate(
-    swiftSignature: SwiftFunctionSignature
-  ) throws -> TranslatedFunctionSignature {
-    let lowering = CdeclLowering(swiftStdlibTypes: self.swiftStdlibTypes)
-    let loweredSignature = try lowering.lowerFunctionSignature(swiftSignature)
+  func translatedSignature(
+    for decl: ImportedFunc
+  ) -> TranslatedFunctionSignature? {
+    if let cached = translatedSignatures[decl] {
+      return cached
+    }
 
-    let translation = JavaTranslation(swiftStdlibTypes: self.swiftStdlibTypes)
-    let translated = try translation.translate(loweredFunctionSignature: loweredSignature)
+    let translated: TranslatedFunctionSignature?
+    do {
+      let lowering = CdeclLowering(swiftStdlibTypes: self.swiftStdlibTypes)
+      let loweredSignature = try lowering.lowerFunctionSignature(decl.functionSignature)
+
+      let translation = JavaTranslation(swiftStdlibTypes: self.swiftStdlibTypes)
+      translated = try translation.translate(loweredFunctionSignature: loweredSignature)
+    } catch {
+      self.log.info("Failed to translate: '\(decl.swiftDecl.qualifiedNameForDebug)'; \(error)")
+      translated = nil
+    }
 
+    translatedSignatures[decl] = translated
     return translated
   }
 }

Sources/JExtractSwift/SwiftThunkTranslator.swift renamed to Sources/JExtractSwift/Swift2JavaTranslator+SwiftThunkPrinting.swift

@@ -174,8 +174,13 @@ struct SwiftThunkTranslator {
 
   func render(forFunc decl: ImportedFunc) -> [DeclSyntax] {
     st.log.trace("Rendering thunks for: \(decl.displayName)")
+
     let thunkName = st.thunkNameRegistry.functionThunkName(decl: decl)
-    let thunkFunc = decl.loweredSignature.cdeclThunk(
+    guard let translatedSignatures = st.translatedSignature(for: decl) else {
+      return []
+    }
+
+    let thunkFunc = translatedSignatures.loweredSignature.cdeclThunk(
       cName: thunkName,
       swiftAPIName: decl.name,
       as: decl.apiKind,

Sources/JExtractSwift/Swift2JavaTranslator.swift

@@ -56,6 +56,9 @@ public final class Swift2JavaTranslator {
 
   package var thunkNameRegistry: ThunkNameRegistry = ThunkNameRegistry()
 
+  /// Cached Java translation result. 'nil' indicates failed translation.
+  var translatedSignatures: [ImportedFunc: TranslatedFunctionSignature?] = [:]
+
   /// The name of the Swift module being translated.
   var swiftModuleName: String {
     symbolTable.moduleName

Sources/JExtractSwift/Swift2JavaVisitor.swift

@@ -121,16 +121,15 @@ final class Swift2JavaVisitor: SyntaxVisitor {
 
     self.log.debug("Import function: '\(node.qualifiedNameForDebug)'")
 
-    let translatedSignature: TranslatedFunctionSignature
+    let signature: SwiftFunctionSignature
     do {
-      let swiftSignature = try SwiftFunctionSignature(
+      signature = try SwiftFunctionSignature(
         node,
         enclosingType: self.currentSwiftType,
         symbolTable: self.translator.symbolTable
       )
-      translatedSignature = try translator.translate(swiftSignature: swiftSignature)
     } catch {
-      self.log.debug("Failed to translate: '\(node.qualifiedNameForDebug)'; \(error)")
+      self.log.debug("Failed to import: '\(node.qualifiedNameForDebug)'; \(error)")
       return .skipChildren
     }
 
@@ -139,7 +138,7 @@ final class Swift2JavaVisitor: SyntaxVisitor {
       swiftDecl: node,
       name: node.name.text,
       apiKind: .function,
-      translatedSignature: translatedSignature
+      functionSignature: signature
     )
 
     log.debug("Record imported method \(node.qualifiedNameForDebug)")
@@ -166,26 +165,19 @@ final class Swift2JavaVisitor: SyntaxVisitor {
     self.log.debug("Import variable: \(node.kind) '\(node.qualifiedNameForDebug)'")
 
     func importAccessor(kind: SwiftAPIKind) throws {
-      let translatedSignature: TranslatedFunctionSignature
-      do {
-        let swiftSignature = try SwiftFunctionSignature(
-          node,
-          isSet: kind == .setter,
-          enclosingType: self.currentSwiftType,
-          symbolTable: self.translator.symbolTable
-        )
-        translatedSignature = try translator.translate(swiftSignature: swiftSignature)
-      } catch {
-        self.log.debug("Failed to translate: \(node.qualifiedNameForDebug); \(error)")
-        throw error
-      }
+      let signature = try SwiftFunctionSignature(
+        node,
+        isSet: kind == .setter,
+        enclosingType: self.currentSwiftType,
+        symbolTable: self.translator.symbolTable
+      )
 
       let imported = ImportedFunc(
         module: translator.swiftModuleName,
         swiftDecl: node,
         name: varName,
         apiKind: kind,
-        translatedSignature: translatedSignature
+        functionSignature: signature
       )
 
       log.debug("Record imported variable accessor \(kind == .getter ? "getter" : "setter"):\(node.qualifiedNameForDebug)")
@@ -222,14 +214,13 @@ final class Swift2JavaVisitor: SyntaxVisitor {
 
     self.log.debug("Import initializer: \(node.kind) '\(node.qualifiedNameForDebug)'")
 
-    let translatedSignature: TranslatedFunctionSignature
+    let signature: SwiftFunctionSignature
     do {
-      let swiftSignature = try SwiftFunctionSignature(
+      signature = try SwiftFunctionSignature(
         node,
         enclosingType: self.currentSwiftType,
         symbolTable: self.translator.symbolTable
       )
-      translatedSignature = try translator.translate(swiftSignature: swiftSignature)
     } catch {
       self.log.debug("Failed to translate: \(node.qualifiedNameForDebug); \(error)")
       return .skipChildren
@@ -239,7 +230,7 @@ final class Swift2JavaVisitor: SyntaxVisitor {
       swiftDecl: node,
       name: "init",
       apiKind: .initializer,
-      translatedSignature: translatedSignature
+      functionSignature: signature
     )
 
     currentType.initializers.append(imported)

Sources/JExtractSwift/ThunkNameRegistry.swift

@@ -37,7 +37,7 @@ package struct ThunkNameRegistry {
     case .setter:
       suffix = "$set"
     default:
-      suffix = decl.swiftSignature.parameters
+      suffix = decl.functionSignature.parameters
         .map { "_" + ($0.argumentLabel ?? "_") }
         .joined()
     }