Allow constant integer variables as array lengths.

Changelog.md

@@ -1,6 +1,7 @@
 ### 0.4.19 (unreleased)
 
 Features:
+ * Allow constant variables to be used as array length
  * Syntax Checker: Turn the usage of ``callcode`` into an error as experimental 0.5.0 feature.
  * Type Checker: Improve address checksum warning.
  * Type Checker: More detailed errors for invalid array lengths (such as division by zero).

libsolidity/analysis/ConstantEvaluator.cpp

@@ -74,3 +74,21 @@ void ConstantEvaluator::endVisit(Literal const& _literal)
 	if (!_literal.annotation().type)
 		m_errorReporter.fatalTypeError(_literal.location(), "Invalid literal value.");
 }
+
+void ConstantEvaluator::endVisit(Identifier const& _identifier)
+{
+	VariableDeclaration const *variableDeclaration = dynamic_cast<VariableDeclaration const *>(_identifier.annotation().referencedDeclaration);
+	if (!variableDeclaration)
+		return;
+	if (!variableDeclaration->isConstant())
+		m_errorReporter.fatalTypeError(_identifier.location(), "Identifier must be declared constant.");
+
+	ASTPointer<Expression> value = variableDeclaration->value();
+	if (value)
+	{
+		if (!value->annotation().type)
+			ConstantEvaluator e(*value, m_errorReporter);
+
+		_identifier.annotation().type = value->annotation().type;
+	}
+}

libsolidity/analysis/ConstantEvaluator.h

@@ -48,6 +48,7 @@ private:
 	virtual void endVisit(BinaryOperation const& _operation);
 	virtual void endVisit(UnaryOperation const& _operation);
 	virtual void endVisit(Literal const& _literal);
+	virtual void endVisit(Identifier const& _identifier);
 
 	ErrorReporter& m_errorReporter;
 };

test/libsolidity/SolidityEndToEndTest.cpp

@@ -2345,6 +2345,24 @@ BOOST_AUTO_TEST_CASE(constructor_static_array_argument)
 	ABI_CHECK(callContractFunction("b(uint256)", u256(2)), encodeArgs(u256(4)));
 }
 
+BOOST_AUTO_TEST_CASE(constant_var_as_array_length)
+{
+	char const* sourceCode = R"(
+		contract C {
+			uint constant LEN = 3;
+			uint[LEN] public a;
+
+			function C(uint[LEN] _a) {
+				a = _a;
+			}
+		}
+	)";
+	compileAndRun(sourceCode, 0, "C", encodeArgs(u256(1), u256(2), u256(3)));
+	ABI_CHECK(callContractFunction("a(uint256)", u256(0)), encodeArgs(u256(1)));
+	ABI_CHECK(callContractFunction("a(uint256)", u256(1)), encodeArgs(u256(2)));
+	ABI_CHECK(callContractFunction("a(uint256)", u256(2)), encodeArgs(u256(3)));
+}
+
 BOOST_AUTO_TEST_CASE(functions_called_by_constructor)
 {
 	char const* sourceCode = R"(

test/libsolidity/SolidityNameAndTypeResolution.cpp

@@ -2107,7 +2107,7 @@ BOOST_AUTO_TEST_CASE(array_with_nonconstant_length)
 			function f(uint a) public { uint8[a] x; }
 		}
 	)";
-	CHECK_ERROR(text, TypeError, "Invalid array length, expected integer literal.");
+	CHECK_ERROR(text, TypeError, "Identifier must be declared constant");
 }
 
 BOOST_AUTO_TEST_CASE(array_with_negative_length)
@@ -7263,6 +7263,28 @@ BOOST_AUTO_TEST_CASE(array_length_not_convertible_to_integer)
 	CHECK_ERROR(text, TypeError, "Invalid array length, expected integer literal.");
 }
 
+BOOST_AUTO_TEST_CASE(array_length_constant_var)
+{
+	char const* text = R"(
+		contract C {
+			uint constant LEN = 10;
+			uint[LEN] ids;
+		}
+	)";
+	CHECK_SUCCESS(text);
+}
+
+BOOST_AUTO_TEST_CASE(array_length_non_integer_constant_var)
+{
+	char const* text = R"(
+		contract C {
+			bool constant LEN = true;
+			uint[LEN] ids;
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Invalid array length, expected integer literal.");
+}
+
 BOOST_AUTO_TEST_CASE(array_length_invalid_expression)
 {
 	char const* text = R"(