From 7a3ea61ffd226cc09ef419c47c0506699aa69b50 Mon Sep 17 00:00:00 2001
From: Federico Bond <federicobond@gmail.com>
Date: Thu, 22 Jun 2017 11:14:14 -0300
Subject: [PATCH] Warn if decimal literals are used in a bytesXX context

Fixes #2349
---
 libsolidity/analysis/TypeChecker.cpp          | 19 ++++++++++-
 .../SolidityNameAndTypeResolution.cpp         | 34 +++++++++++++++++--
 2 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index 2a8d1ff6a..cb9435e8d 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -22,6 +22,7 @@
 
 #include <libsolidity/analysis/TypeChecker.h>
 #include <memory>
+#include <boost/algorithm/string/predicate.hpp>
 #include <boost/range/adaptor/reversed.hpp>
 #include <libsolidity/ast/AST.h>
 #include <libsolidity/inlineasm/AsmAnalysis.h>
@@ -1793,7 +1794,23 @@ void TypeChecker::expectType(Expression const& _expression, Type const& _expecte
 				_expectedType.toString() +
 				"."
 			);
-	}		
+	}
+
+	if (
+		type(_expression)->category() == Type::Category::RationalNumber &&
+		_expectedType.category() == Type::Category::FixedBytes
+	)
+	{
+		auto literal = dynamic_cast<Literal const*>(&_expression);
+
+		if (literal && !boost::starts_with(literal->value(), "0x"))
+			m_errorReporter.warning(
+				_expression.location(),
+				"Decimal literal assigned to bytesXX variable will be left-aligned. "
+				"Use an explicit conversion to silence this warning."
+			);
+	}
+
 }
 
 void TypeChecker::requireLValue(Expression const& _expression)
diff --git a/test/libsolidity/SolidityNameAndTypeResolution.cpp b/test/libsolidity/SolidityNameAndTypeResolution.cpp
index 0b3cb481b..fc8cdc35a 100644
--- a/test/libsolidity/SolidityNameAndTypeResolution.cpp
+++ b/test/libsolidity/SolidityNameAndTypeResolution.cpp
@@ -2173,6 +2173,36 @@ BOOST_AUTO_TEST_CASE(test_byte_is_alias_of_byte1)
 	ETH_TEST_REQUIRE_NO_THROW(parseAndAnalyse(text), "Type resolving failed");
 }
 
+BOOST_AUTO_TEST_CASE(warns_assigning_decimal_to_bytesxx)
+{
+	char const* text = R"(
+		contract Foo {
+			bytes32 a = 7;
+		}
+	)";
+	CHECK_WARNING(text, "Decimal literal assigned to bytesXX variable will be left-aligned.");
+}
+
+BOOST_AUTO_TEST_CASE(does_not_warn_assigning_hex_number_to_bytesxx)
+{
+	char const* text = R"(
+		contract Foo {
+			bytes32 a = 0x1234;
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+}
+
+BOOST_AUTO_TEST_CASE(explicit_conversion_from_decimal_to_bytesxx)
+{
+	char const* text = R"(
+		contract Foo {
+			bytes32 a = bytes32(7);
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+}
+
 BOOST_AUTO_TEST_CASE(assigning_value_to_const_variable)
 {
 	char const* text = R"(
@@ -3698,12 +3728,12 @@ BOOST_AUTO_TEST_CASE(conditional_with_all_types)
 				byte[2] memory a;
 				byte[2] memory b;
 				var k = true ? a : b;
-				k[0] = 0; //Avoid unused var warning
+				k[0] = byte(0); //Avoid unused var warning
 
 				bytes memory e;
 				bytes memory f;
 				var l = true ? e : f;
-				l[0] = 0; // Avoid unused var warning
+				l[0] = byte(0); // Avoid unused var warning
 
 				// fixed bytes
 				bytes2 c;