Enforce disallowing empty structs

This patch enfoces an error when it encounters an empty struct,
effectively eliminating the deprecation warning.

Also adjust 419_interface_structs to explicitely test for (non-empty) structs,
as this behaviour "may" change in the future.

11 files changed, 26 insertions, 83 deletions

diff --git a/Changelog.md b/Changelog.md
index 61a6c693..c87a5380 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -6,6 +6,7 @@ Breaking Changes:
  * Commandline interface: Remove obsolete ``--formal`` option.
  * Commandline interface: Require ``-`` if standard input is used as source.
  * General: ``continue`` in a ``do...while`` loop jumps to the condition (it used to jump to the loop body). Warning: this may silently change the semantics of existing code.
+ * General: Disallow declaring empty structs.
  * General: Disallow ``sha3`` and ``suicide`` aliases.
  * General: Introduce ``emit`` as a keyword instead of parsing it as identifier.
  * General: New keywords: ``calldata``
diff --git a/libsolidity/analysis/SyntaxChecker.cpp b/libsolidity/analysis/SyntaxChecker.cpp
index 396058f4..f234dcaf 100644
--- a/libsolidity/analysis/SyntaxChecker.cpp
+++ b/libsolidity/analysis/SyntaxChecker.cpp
@@ -276,14 +276,8 @@ bool SyntaxChecker::visit(VariableDeclaration const& _declaration)
 
 bool SyntaxChecker::visit(StructDefinition const& _struct)
 {
-	bool const v050 = m_sourceUnit->annotation().experimentalFeatures.count(ExperimentalFeature::V050);
-
 	if (_struct.members().empty())
-	{
-		if (v050)
-			m_errorReporter.syntaxError(_struct.location(), "Defining empty structs is disallowed.");
-		else
-			m_errorReporter.warning(_struct.location(), "Defining empty structs is deprecated.");
-	}
+		m_errorReporter.syntaxError(_struct.location(), "Defining empty structs is disallowed.");
+
 	return true;
 }
diff --git a/test/libsolidity/ABIDecoderTests.cpp b/test/libsolidity/ABIDecoderTests.cpp
index b3ebb7a5..b588ca1b 100644
--- a/test/libsolidity/ABIDecoderTests.cpp
+++ b/test/libsolidity/ABIDecoderTests.cpp
@@ -659,26 +659,6 @@ BOOST_AUTO_TEST_CASE(struct_function)
 	)
 }
 
-BOOST_AUTO_TEST_CASE(empty_struct)
-{
-	string sourceCode = R"(
-		contract C {
-			struct S { }
-			function f(uint a, S s, uint b) public pure returns (uint x, uint y) {
-				assembly { x := a y := b }
-			}
-			function g() public returns (uint, uint) {
-				return this.f(7, S(), 8);
-			}
-		}
-	)";
-	NEW_ENCODER(
-		compileAndRun(sourceCode, 0, "C");
-		ABI_CHECK(callContractFunction("f(uint256,(),uint256)", 7, 8), encodeArgs(7, 8));
-		ABI_CHECK(callContractFunction("g()"), encodeArgs(7, 8));
-	)
-}
-
 BOOST_AUTO_TEST_CASE(mediocre_struct)
 {
 	string sourceCode = R"(
diff --git a/test/libsolidity/ABIEncoderTests.cpp b/test/libsolidity/ABIEncoderTests.cpp
index 5f15b28f..227eadb5 100644
--- a/test/libsolidity/ABIEncoderTests.cpp
+++ b/test/libsolidity/ABIEncoderTests.cpp
@@ -447,28 +447,6 @@ BOOST_AUTO_TEST_CASE(structs)
 	)
 }
 
-BOOST_AUTO_TEST_CASE(empty_struct)
-{
-	string sourceCode = R"(
-		contract C {
-			struct S { }
-			S s;
-			event e(uint16, S, uint16);
-			function f() returns (uint, S, uint) {
-				e(7, s, 8);
-				return (7, s, 8);
-			}
-		}
-	)";
-
-	NEW_ENCODER(
-		compileAndRun(sourceCode, 0, "C");
-		bytes encoded = encodeArgs(7, 8);
-		BOOST_CHECK(callContractFunction("f()") == encoded);
-		REQUIRE_LOG_DATA(encoded);
-	)
-}
-
 BOOST_AUTO_TEST_CASE(structs2)
 {
 	string sourceCode = R"(
diff --git a/test/libsolidity/SolidityEndToEndTest.cpp b/test/libsolidity/SolidityEndToEndTest.cpp
index 236d83ef..c80aa8ba 100644
--- a/test/libsolidity/SolidityEndToEndTest.cpp
+++ b/test/libsolidity/SolidityEndToEndTest.cpp
@@ -1271,7 +1271,6 @@ BOOST_AUTO_TEST_CASE(deleteStruct)
 		contract test {
 			struct topStruct {
 				nestedStruct nstr;
-				emptyStruct empty;
 				uint topValue;
 				mapping (uint => uint) topMapping;
 			}
@@ -1281,8 +1280,6 @@ BOOST_AUTO_TEST_CASE(deleteStruct)
 				uint nestedValue;
 				mapping (uint => bool) nestedMapping;
 			}
-			struct emptyStruct{
-			}
 			function test(){
 				toDelete = 5;
 				str.topValue = 1;
diff --git a/test/libsolidity/SolidityNameAndTypeResolution.cpp b/test/libsolidity/SolidityNameAndTypeResolution.cpp
index e1516f84..bca66d01 100644
--- a/test/libsolidity/SolidityNameAndTypeResolution.cpp
+++ b/test/libsolidity/SolidityNameAndTypeResolution.cpp
@@ -203,10 +203,10 @@ BOOST_AUTO_TEST_CASE(external_structs)
 		pragma experimental ABIEncoderV2;
 		contract Test {
 			enum ActionChoices { GoLeft, GoRight, GoStraight, Sit }
-			struct Empty {}
+			struct Simple { uint i; }
 			struct Nested { X[2][] a; uint y; }
-			struct X { bytes32 x; Test t; Empty[] e; }
-			function f(ActionChoices, uint, Empty) external {}
+			struct X { bytes32 x; Test t; Simple[] s; }
+			function f(ActionChoices, uint, Simple) external {}
 			function g(Test, Nested) external {}
 			function h(function(Nested) external returns (uint)[]) external {}
 			function i(Nested[]) external {}
@@ -218,10 +218,10 @@ BOOST_AUTO_TEST_CASE(external_structs)
 		{
 			auto functions = contract->definedFunctions();
 			BOOST_REQUIRE(!functions.empty());
-			BOOST_CHECK_EQUAL("f(uint8,uint256,())", functions[0]->externalSignature());
-			BOOST_CHECK_EQUAL("g(address,((bytes32,address,()[])[2][],uint256))", functions[1]->externalSignature());
+			BOOST_CHECK_EQUAL("f(uint8,uint256,(uint256))", functions[0]->externalSignature());
+			BOOST_CHECK_EQUAL("g(address,((bytes32,address,(uint256)[])[2][],uint256))", functions[1]->externalSignature());
 			BOOST_CHECK_EQUAL("h(function[])", functions[2]->externalSignature());
-			BOOST_CHECK_EQUAL("i(((bytes32,address,()[])[2][],uint256)[])", functions[3]->externalSignature());
+			BOOST_CHECK_EQUAL("i(((bytes32,address,(uint256)[])[2][],uint256)[])", functions[3]->externalSignature());
 		}
 }
 
@@ -231,10 +231,10 @@ BOOST_AUTO_TEST_CASE(external_structs_in_libraries)
 		pragma experimental ABIEncoderV2;
 		library Test {
 			enum ActionChoices { GoLeft, GoRight, GoStraight, Sit }
-			struct Empty {}
+			struct Simple { uint i; }
 			struct Nested { X[2][] a; uint y; }
-			struct X { bytes32 x; Test t; Empty[] e; }
-			function f(ActionChoices, uint, Empty) external {}
+			struct X { bytes32 x; Test t; Simple[] s; }
+			function f(ActionChoices, uint, Simple) external {}
 			function g(Test, Nested) external {}
 			function h(function(Nested) external returns (uint)[]) external {}
 			function i(Nested[]) external {}
@@ -246,7 +246,7 @@ BOOST_AUTO_TEST_CASE(external_structs_in_libraries)
 		{
 			auto functions = contract->definedFunctions();
 			BOOST_REQUIRE(!functions.empty());
-			BOOST_CHECK_EQUAL("f(Test.ActionChoices,uint256,Test.Empty)", functions[0]->externalSignature());
+			BOOST_CHECK_EQUAL("f(Test.ActionChoices,uint256,Test.Simple)", functions[0]->externalSignature());
 			BOOST_CHECK_EQUAL("g(Test,Test.Nested)", functions[1]->externalSignature());
 			BOOST_CHECK_EQUAL("h(function[])", functions[2]->externalSignature());
 			BOOST_CHECK_EQUAL("i(Test.Nested[])", functions[3]->externalSignature());
diff --git a/test/libsolidity/syntaxTests/empty_struct.sol b/test/libsolidity/syntaxTests/empty_struct.sol
index 12655309..0a52fb72 100644
--- a/test/libsolidity/syntaxTests/empty_struct.sol
+++ b/test/libsolidity/syntaxTests/empty_struct.sol
@@ -2,4 +2,4 @@ contract test {
 	struct A {}
 }
 // ----
-// Warning: (17-28): Defining empty structs is deprecated.
+// SyntaxError: (17-28): Defining empty structs is disallowed.
diff --git a/test/libsolidity/syntaxTests/empty_struct_050.sol b/test/libsolidity/syntaxTests/empty_struct_050.sol
deleted file mode 100644
index 886f1f83..00000000
--- a/test/libsolidity/syntaxTests/empty_struct_050.sol
+++ /dev/null
@@ -1,6 +0,0 @@
-pragma experimental "v0.5.0";
-contract test {
-	struct A {}
-}
-// ----
-// SyntaxError: (47-58): Defining empty structs is disallowed.
diff --git a/test/libsolidity/syntaxTests/nameAndTypeResolution/039_functions_with_identical_structs_in_interface.sol b/test/libsolidity/syntaxTests/nameAndTypeResolution/039_functions_with_identical_structs_in_interface.sol
index df4f5879..0be0bb2b 100644
--- a/test/libsolidity/syntaxTests/nameAndTypeResolution/039_functions_with_identical_structs_in_interface.sol
+++ b/test/libsolidity/syntaxTests/nameAndTypeResolution/039_functions_with_identical_structs_in_interface.sol
@@ -1,13 +1,11 @@
 pragma experimental ABIEncoderV2;
 
 contract C {
-    struct S1 { }
-    struct S2 { }
+    struct S1 { int i; }
+    struct S2 { int i; }
     function f(S1) pure {}
     function f(S2) pure {}
 }
 // ----
 // Warning: (0-33): Experimental features are turned on. Do not use experimental features on live deployments.
-// Warning: (52-65): Defining empty structs is deprecated.
-// Warning: (70-83): Defining empty structs is deprecated.
-// TypeError: (115-137): Function overload clash during conversion to external types for arguments.
+// TypeError: (129-151): Function overload clash during conversion to external types for arguments.
diff --git a/test/libsolidity/syntaxTests/nameAndTypeResolution/419_interface_structs.sol b/test/libsolidity/syntaxTests/nameAndTypeResolution/419_interface_structs.sol
index 2afef06c..c74d52d3 100644
--- a/test/libsolidity/syntaxTests/nameAndTypeResolution/419_interface_structs.sol
+++ b/test/libsolidity/syntaxTests/nameAndTypeResolution/419_interface_structs.sol
@@ -1,7 +1,9 @@
 interface I {
     struct A {
+        // This is currently expected to break, but it *may* change in the future.
+        int dummy;
     }
 }
 // ----
-// Warning: (18-34): Defining empty structs is deprecated.
-// TypeError: (18-34): Structs cannot be defined in interfaces.
+// TypeError: (18-136): Structs cannot be defined in interfaces.
+// TypeError: (120-129): Variables cannot be declared in interfaces.
diff --git a/test/libsolidity/syntaxTests/specialFunctions/types_with_unspecified_encoding_types.sol b/test/libsolidity/syntaxTests/specialFunctions/types_with_unspecified_encoding_types.sol
index d10c1718..e46a9050 100644
--- a/test/libsolidity/syntaxTests/specialFunctions/types_with_unspecified_encoding_types.sol
+++ b/test/libsolidity/syntaxTests/specialFunctions/types_with_unspecified_encoding_types.sol
@@ -1,7 +1,7 @@
 contract C {
     struct S { uint x; }
     S s;
-    struct T { }
+    struct T { uint y; }
     T t;
     enum A { X, Y }
     function f() public pure {
@@ -9,9 +9,8 @@ contract C {
     }
 }
 // ----
-// Warning: (51-63): Defining empty structs is deprecated.
-// TypeError: (168-169): This type cannot be encoded.
-// TypeError: (171-172): This type cannot be encoded.
+// TypeError: (176-177): This type cannot be encoded.
 // TypeError: (179-180): This type cannot be encoded.
-// TypeError: (182-186): This type cannot be encoded.
-// TypeError: (188-194): This type cannot be encoded.
+// TypeError: (187-188): This type cannot be encoded.
+// TypeError: (190-194): This type cannot be encoded.
+// TypeError: (196-202): This type cannot be encoded.