Move "self" parameter to the end of the @_cdecl thunk

This matches what we're doing elsewhere, and also the way that the Swift
calling convention is lowered to LLVM IR by the compiler.

Author: DougGregor

Sources/JExtractSwift/Swift2JavaTranslator+FunctionLowering.swift

@@ -41,14 +41,6 @@ extension Swift2JavaTranslator {
     _ signature: SwiftFunctionSignature
   ) throws -> LoweredFunctionSignature {
     // Lower all of the parameters.
-    let loweredSelf = try signature.selfParameter.map { selfParameter in
-      try lowerParameter(
-        selfParameter.type,
-        convention: selfParameter.convention, 
-        parameterName: selfParameter.parameterName ?? "self"
-      )
-    }
-
     let loweredParameters = try signature.parameters.enumerated().map { (index, param) in
       try lowerParameter(
         param.type,
@@ -83,13 +75,17 @@ extension Swift2JavaTranslator {
       indirectResult = true
     }
 
+    let loweredSelf = try signature.selfParameter.map { selfParameter in
+      try lowerParameter(
+        selfParameter.type,
+        convention: selfParameter.convention,
+        parameterName: selfParameter.parameterName ?? "self"
+      )
+    }
+
     // Collect all of the lowered parameters for the @_cdecl function.
     var allLoweredParameters: [LoweredParameters] = []
     var cdeclLoweredParameters: [SwiftParameter] = []
-    if let loweredSelf {
-      allLoweredParameters.append(loweredSelf)
-      cdeclLoweredParameters.append(contentsOf: loweredSelf.cdeclParameters)
-    }
     allLoweredParameters.append(contentsOf: loweredParameters)
     cdeclLoweredParameters.append(
       contentsOf: loweredParameters.flatMap { $0.cdeclParameters }
@@ -110,6 +106,11 @@ extension Swift2JavaTranslator {
       fatalError("Improper lowering of result for \(signature)")
     }
 
+    if let loweredSelf {
+      allLoweredParameters.append(loweredSelf)
+      cdeclLoweredParameters.append(contentsOf: loweredSelf.cdeclParameters)
+    }
+
     let cdeclSignature = SwiftFunctionSignature(
       isStaticOrClass: false,
       selfParameter: nil,
@@ -532,9 +533,10 @@ extension LoweredFunctionSignature {
     // Lower "self", if there is one.
     let parametersToLower: ArraySlice<LoweredParameters>
     let cdeclToOriginalSelf: ExprSyntax?
-    if let originalSelfParam = original.selfParameter {
-      cdeclToOriginalSelf = parameters[0].cdeclToOriginalArgumentExpr(isSelf: true, value: originalSelfParam.parameterName ?? "self")
-      parametersToLower = parameters[1...]
+    if let originalSelfParam = original.selfParameter,
+       let selfParameter = parameters.last {
+      cdeclToOriginalSelf = selfParameter.cdeclToOriginalArgumentExpr(isSelf: true, value: originalSelfParam.parameterName ?? "self")
+      parametersToLower = parameters.dropLast()
     } else {
       cdeclToOriginalSelf = nil
       parametersToLower = parameters[...]

Tests/JExtractSwiftTests/FunctionLoweringTests.swift

@@ -78,11 +78,11 @@ final class FunctionLoweringTests {
       enclosingType: "Point",
       expectedCDecl: """
       @_cdecl("c_shifted")
-      func c_shifted(_ self: UnsafeRawPointer, _ delta_0: Double, _ delta_1: Double, _ _result: UnsafeMutableRawPointer) {
+      func c_shifted(_ delta_0: Double, _ delta_1: Double, _ _result: UnsafeMutableRawPointer, _ self: UnsafeRawPointer) {
         _result.assumingMemoryBound(to: Point.self).pointee = self.assumingMemoryBound(to: Point.self).pointee.shifted(by: (delta_0, delta_1))
       }
       """,
-      expectedCFunction: "void c_shifted(void const* self, double delta_0, double delta_1, void* _result)"
+      expectedCFunction: "void c_shifted(double delta_0, double delta_1, void* _result, void const* self)"
     )
   }
 
@@ -97,11 +97,11 @@ final class FunctionLoweringTests {
       enclosingType: "Point",
       expectedCDecl: """
       @_cdecl("c_shift")
-      func c_shift(_ self: UnsafeMutableRawPointer, _ delta_0: Double, _ delta_1: Double) {
+      func c_shift(_ delta_0: Double, _ delta_1: Double, _ self: UnsafeMutableRawPointer) {
         self.assumingMemoryBound(to: Point.self).pointee.shift(by: (delta_0, delta_1))
       }
       """,
-      expectedCFunction: "void c_shift(void* self, double delta_0, double delta_1)"
+      expectedCFunction: "void c_shift(double delta_0, double delta_1, void* self)"
     )
   }
 
@@ -116,11 +116,11 @@ final class FunctionLoweringTests {
       enclosingType: "Point",
       expectedCDecl: """
       @_cdecl("c_shift")
-      func c_shift(_ self: UnsafeRawPointer, _ delta_0: Double, _ delta_1: Double) {
+      func c_shift(_ delta_0: Double, _ delta_1: Double, _ self: UnsafeRawPointer) {
         unsafeBitCast(self, to: Point.self).shift(by: (delta_0, delta_1))
       }
       """,
-      expectedCFunction: "void c_shift(void const* self, double delta_0, double delta_1)"
+      expectedCFunction: "void c_shift(double delta_0, double delta_1, void const* self)"
     )
   }