From cc6314cd019be80a9212f6bd5b0c86206be16c88 Mon Sep 17 00:00:00 2001
From: chriseth <c@ethdev.com>
Date: Tue, 21 Jun 2016 14:36:23 +0200
Subject: Warn about unused return values.

---
 libsolidity/analysis/TypeChecker.cpp               | 17 +++++++++++++++
 libsolidity/analysis/TypeChecker.h                 |  3 +++
 test/libsolidity/SolidityNameAndTypeResolution.cpp | 25 ++++++++++++++++++++++
 3 files changed, 45 insertions(+)

diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index ce55de00..c2fd3e7e 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -830,6 +830,13 @@ void TypeChecker::endVisit(ExpressionStatement const& _statement)
 	if (type(_statement.expression())->category() == Type::Category::RationalNumber)
 		if (!dynamic_cast<RationalNumberType const&>(*type(_statement.expression())).mobileType())
 			typeError(_statement.expression().location(), "Invalid rational number.");
+
+	bool unusedReturnValue = true;
+	if (auto t = dynamic_cast<TupleType const*>(type(_statement.expression()).get()))
+		if (t->components().empty())
+			unusedReturnValue = false;
+	if (unusedReturnValue)
+		warning(_statement.location(), "Unused return value.");
 }
 
 bool TypeChecker::visit(Conditional const& _conditional)
@@ -1570,6 +1577,16 @@ void TypeChecker::typeError(SourceLocation const& _location, string const& _desc
 	m_errors.push_back(err);
 }
 
+void TypeChecker::warning(SourceLocation const& _location, string const& _description)
+{
+	auto err = make_shared<Error>(Error::Type::Warning);
+	*err <<
+		errinfo_sourceLocation(_location) <<
+		errinfo_comment(_description);
+
+	m_errors.push_back(err);
+}
+
 void TypeChecker::fatalTypeError(SourceLocation const& _location, string const& _description)
 {
 	typeError(_location, _description);
diff --git a/libsolidity/analysis/TypeChecker.h b/libsolidity/analysis/TypeChecker.h
index 48f8285a..be1e02be 100644
--- a/libsolidity/analysis/TypeChecker.h
+++ b/libsolidity/analysis/TypeChecker.h
@@ -59,6 +59,9 @@ private:
 	/// Adds a new error to the list of errors.
 	void typeError(SourceLocation const& _location, std::string const& _description);
 
+	/// Adds a new warning to the list of errors.
+	void warning(SourceLocation const& _location, std::string const& _description);
+
 	/// Adds a new error to the list of errors and throws to abort type checking.
 	void fatalTypeError(SourceLocation const& _location, std::string const& _description);
 
diff --git a/test/libsolidity/SolidityNameAndTypeResolution.cpp b/test/libsolidity/SolidityNameAndTypeResolution.cpp
index 697b3fa9..1f42c23e 100644
--- a/test/libsolidity/SolidityNameAndTypeResolution.cpp
+++ b/test/libsolidity/SolidityNameAndTypeResolution.cpp
@@ -3750,6 +3750,31 @@ BOOST_AUTO_TEST_CASE(one_divided_by_three_integer_conversion)
 	BOOST_CHECK(!success(text));
 }
 
+BOOST_AUTO_TEST_CASE(unused_return_value)
+{
+	char const* text = R"(
+		contract test {
+			function g() returns (uint) {}
+			function f() {
+				g();
+			}
+		}
+	)";
+	BOOST_CHECK(expectError(text, true) == Error::Type::Warning);
+}
+
+BOOST_AUTO_TEST_CASE(unused_return_value_send)
+{
+	char const* text = R"(
+		contract test {
+			function f() {
+				address(0x12).send(1);
+			}
+		}
+	)";
+	BOOST_CHECK(expectError(text, true) == Error::Type::Warning);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }
-- 
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