From 0ab0842c2944680c3f92119ee4185822b9a63350 Mon Sep 17 00:00:00 2001
From: Daniel Kirchner <daniel@ekpyron.org>
Date: Mon, 26 Jun 2023 17:00:52 +0200
Subject: [PATCH] Disallow conversions between declaration function types.

---
 Changelog.md                                          |  1 +
 libsolidity/ast/Types.cpp                             |  6 ++++++
 .../functionTypes/declaration_type_conversion.sol     | 11 +++++++++++
 .../declaration_type_conversion_internal_base.sol     | 11 +++++++++++
 4 files changed, 29 insertions(+)
 create mode 100644 test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion.sol
 create mode 100644 test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion_internal_base.sol

diff --git a/Changelog.md b/Changelog.md
index fa2ea9666..723df4583 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -29,6 +29,7 @@ Bugfixes:
  * SMTChecker: Fix false negative when a verification target can be violated only by trusted external call from another public function.
  * SMTChecker: Fix internal error caused by using external identifier to encode member access to functions that take an internal function as a parameter.
  * Standard JSON Interface: Fix an incomplete AST being returned when analysis is interrupted by certain kinds of fatal errors.
+ * Type Checker: Function declaration types referring to different declarations are no longer convertible to each other.
  * Yul Optimizer: Ensure that the assignment of memory slots for variables moved to memory does not depend on AST IDs that may depend on whether additional files are included during compilation.
  * Yul Optimizer: Fix ``FullInliner`` step not ignoring code that is not in expression-split form.
  * Yul Optimizer: Fix optimized IR being unnecessarily passed through the Yul optimizer again before bytecode generation.
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index 6308dbe3d..915440caa 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -3127,6 +3127,12 @@ BoolResult FunctionType::isImplicitlyConvertibleTo(Type const& _convertTo) const
 	if (convertTo.kind() != kind())
 		return BoolResult::err("Special functions cannot be converted to function types.");
 
+	if (
+		kind() == FunctionType::Kind::Declaration &&
+		m_declaration != convertTo.m_declaration
+	)
+		return BoolResult::err("Function declaration types referring to different functions cannot be converted to each other.");
+
 	if (!equalExcludingStateMutability(convertTo))
 		return false;
 
diff --git a/test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion.sol b/test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion.sol
new file mode 100644
index 000000000..a26460dc1
--- /dev/null
+++ b/test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion.sol
@@ -0,0 +1,11 @@
+contract D {
+	function f() external {}
+	function g() external {}
+}
+contract C {
+	function f(bool c) public pure {
+		(c ? D.f : D.g);
+	}
+}
+// ----
+// TypeError 1080: (117-130): True expression's type function D.f() does not match false expression's type function D.g().
diff --git a/test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion_internal_base.sol b/test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion_internal_base.sol
new file mode 100644
index 000000000..210211b28
--- /dev/null
+++ b/test/libsolidity/syntaxTests/functionTypes/declaration_type_conversion_internal_base.sol
@@ -0,0 +1,11 @@
+contract C {
+    function f() internal {}
+    function g() internal {}
+}
+
+contract D is C {
+    function h(bool b) public pure {
+        (b ? C.f : C.g);
+    }
+}
+// ----