[interop][SwiftToCxx] allow emission of overloaded functions with the same name

Author: hyp

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -661,6 +661,9 @@ class ModuleWriter {
       int result = getSortName(*rhs).compare(getSortName(*lhs));
       if (result != 0)
         return result;
+      // Two overloaded functions can have the same name when emitting C++.
+      if (isa<AbstractFunctionDecl>(*rhs) && isa<AbstractFunctionDecl>(*lhs))
+        return result;
 
       // Prefer value decls to extensions.
       assert(!(isa<ValueDecl>(*lhs) && isa<ValueDecl>(*rhs)));

test/Interop/SwiftToCxx/functions/swift-function-overloads.swift

@@ -0,0 +1,18 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -typecheck -module-name Functions -clang-header-expose-decls=all-public -emit-clang-header-path %t/functions.h
+// RUN: %FileCheck %s < %t/functions.h
+
+// RUN: %check-interop-cxx-header-in-clang(%t/functions.h)
+
+
+
+public func overloadedFunc(_ x: Int) { }
+public func overloadedFunc(_ y: Float) { }
+
+public func overloadedFuncArgLabel(x _: Int) { }
+public func overloadedFuncArgLabel(y _: Float) { }
+
+// CHECK-DAG: void overloadedFunc(float y) noexcept
+// CHECK-DAG: void overloadedFunc(swift::Int x) noexcept
+// CHECK-DAG: void overloadedFuncArgLabel(float _1) noexcept
+// CHECK-DAG: void overloadedFuncArgLabel(swift::Int _1) noexcept