From e210026e7455f61a93a2b89bdc50f4d2f5c2097a Mon Sep 17 00:00:00 2001
From: Christian Parpart <christian@parpart.family>
Date: Tue, 3 Mar 2020 12:20:04 +0100
Subject: [PATCH] [Sol2Yul] Implements function-to-function cast.

---
 libsolidity/codegen/YulUtilFunctions.cpp      | 29 +++++++++++++++++++
 .../viaYul/conversion/function_cast.sol       | 23 +++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 test/libsolidity/semanticTests/viaYul/conversion/function_cast.sol

diff --git a/libsolidity/codegen/YulUtilFunctions.cpp b/libsolidity/codegen/YulUtilFunctions.cpp
index 0472dd588..a2af5f777 100644
--- a/libsolidity/codegen/YulUtilFunctions.cpp
+++ b/libsolidity/codegen/YulUtilFunctions.cpp
@@ -1333,6 +1333,35 @@ string YulUtilFunctions::allocateMemoryArrayFunction(ArrayType const& _type)
 
 string YulUtilFunctions::conversionFunction(Type const& _from, Type const& _to)
 {
+	if (_from.category() == Type::Category::Function)
+	{
+		solAssert(_to.category() == Type::Category::Function, "");
+		FunctionType const& fromType = dynamic_cast<FunctionType const&>(_from);
+		FunctionType const& targetType = dynamic_cast<FunctionType const&>(_to);
+		solAssert(
+			fromType.isImplicitlyConvertibleTo(targetType) &&
+			fromType.sizeOnStack() == targetType.sizeOnStack() &&
+			(fromType.kind() == FunctionType::Kind::Internal || fromType.kind() == FunctionType::Kind::External) &&
+			fromType.kind() == targetType.kind(),
+			"Invalid function type conversion requested."
+		);
+		string const functionName =
+			"convert_" +
+			_from.identifier() +
+			"_to_" +
+			_to.identifier();
+		return m_functionCollector->createFunction(functionName, [&]() {
+			return Whiskers(R"(
+				function <functionName>(addr, functionId) -> outAddr, outFunctionId {
+					outAddr := addr
+					outFunctionId := functionId
+				}
+			)")
+			("functionName", functionName)
+			.render();
+		});
+	}
+
 	if (_from.sizeOnStack() != 1 || _to.sizeOnStack() != 1)
 		return conversionFunctionSpecial(_from, _to);
 
diff --git a/test/libsolidity/semanticTests/viaYul/conversion/function_cast.sol b/test/libsolidity/semanticTests/viaYul/conversion/function_cast.sol
new file mode 100644
index 000000000..08462c5f8
--- /dev/null
+++ b/test/libsolidity/semanticTests/viaYul/conversion/function_cast.sol
@@ -0,0 +1,23 @@
+contract C {
+	function f(uint x) public pure returns (uint) {
+		return 2 * x;
+	}
+	function g() public view returns (function (uint) external returns (uint)) {
+		return this.f;
+	}
+	function h(uint x) public returns (uint) {
+		return this.g()(x) + 1;
+	}
+	function t() external view returns (
+			function(uint) external returns (uint) a,
+			function(uint) external view returns (uint) b) {
+		a = this.f;
+		b = this.f;
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// f(uint256): 2 -> 4
+// h(uint256): 2 -> 5
+// t() -> 0xFDD67305928FCAC8D213D1E47BFA6165CD0B87BB3DE648B0000000000000000, 0xFDD67305928FCAC8D213D1E47BFA6165CD0B87BB3DE648B0000000000000000