From a3380ea8d0e02da1eb68eb15906015faf4e8bc3c Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Sat, 16 Sep 2017 16:10:23 +0100
Subject: [PATCH] Force fallback to be external (experimental 0.5.0 change)

---
 Changelog.md                                  |  3 +-
 libsolidity/analysis/TypeChecker.cpp          |  5 +++
 .../SolidityNameAndTypeResolution.cpp         | 32 +++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/Changelog.md b/Changelog.md
index 0b9295d06..26a4862ac 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,7 +1,7 @@
 ### 0.4.17 (unreleased)
 
 Features:
- * Support ``pragma experimental v0.5.0;`` to turn on upcoming breaking changes.
+ * Support ``pragma experimental "v0.5.0";`` to turn on upcoming breaking changes.
  * Code Generator: Added ``.selector`` member on external function types to retrieve their signature.
  * Code Generator: Keep a single copy of encoding functions when using the experimental "ABIEncoderV2".
  * Optimizer: Add new optimization step to remove unused ``JUMPDEST``s.
@@ -12,6 +12,7 @@ Features:
  * Type Checker: Warn on using literals as tight packing parameters in ``keccak256``, ``sha3``, ``sha256`` and ``ripemd160``.
  * Type Checker: Enforce ``view`` and ``pure``.
  * Type Checker: Enforce ``view`` / ``constant`` with error as experimental 0.5.0 feature.
+ * Type Checker: Enforce fallback functions to be ``external`` as experimental 0.5.0 feature.
 
 Bugfixes:
  * ABI JSON: Include all overloaded events.
diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index 26529c229..529a4f8d7 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -120,6 +120,11 @@ bool TypeChecker::visit(ContractDefinition const& _contract)
 					m_errorReporter.typeError(fallbackFunction->parameterList().location(), "Fallback function cannot take parameters.");
 				if (!fallbackFunction->returnParameters().empty())
 					m_errorReporter.typeError(fallbackFunction->returnParameterList()->location(), "Fallback function cannot return values.");
+				if (
+					_contract.sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::V050) &&
+					fallbackFunction->visibility() != FunctionDefinition::Visibility::External
+				)
+					m_errorReporter.typeError(fallbackFunction->location(), "Fallback function must be defined as \"external\".");
 			}
 		}
 	}
diff --git a/test/libsolidity/SolidityNameAndTypeResolution.cpp b/test/libsolidity/SolidityNameAndTypeResolution.cpp
index 8c271fe10..be3b56f3f 100644
--- a/test/libsolidity/SolidityNameAndTypeResolution.cpp
+++ b/test/libsolidity/SolidityNameAndTypeResolution.cpp
@@ -6691,6 +6691,38 @@ BOOST_AUTO_TEST_CASE(tight_packing_literals)
 	CHECK_WARNING(text, "The type of \"int_const 1\" was inferred as uint8.");
 }
 
+BOOST_AUTO_TEST_CASE(non_external_fallback)
+{
+	char const* text = R"(
+		pragma experimental "v0.5.0";
+		contract C {
+			function () external { }
+		}
+	)";
+	CHECK_WARNING(text, "Experimental features are turned on.");
+	text = R"(
+		pragma experimental "v0.5.0";
+		contract C {
+			function () internal { }
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Fallback function must be defined as \"external\".");
+	text = R"(
+		pragma experimental "v0.5.0";
+		contract C {
+			function () private { }
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Fallback function must be defined as \"external\".");
+	text = R"(
+		pragma experimental "v0.5.0";
+		contract C {
+			function () public { }
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Fallback function must be defined as \"external\".");
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }