Type checking for pure expressions.

libsolidity/ast/ASTAnnotations.h

@@ -156,6 +156,8 @@ struct ExpressionAnnotation: ASTAnnotation
 	TypePointer type;
 	/// Whether the expression is a constant variable
 	bool isConstant = false;
+	/// Whether the expression is pure, i.e. compile-time constant.
+	bool isPure = false;
 	/// Whether it is an LValue (i.e. something that can be assigned to).
 	bool isLValue = false;
 	/// Whether the expression is used in a context where the LValue is actually required.

libsolidity/ast/Types.cpp

@@ -2456,6 +2456,18 @@ u256 FunctionType::externalIdentifier() const
 	return FixedHash<4>::Arith(FixedHash<4>(dev::keccak256(externalSignature())));
 }
 
+bool FunctionType::isPure() const
+{
+	return
+		m_location == Location::SHA3 ||
+		m_location == Location::ECRecover ||
+		m_location == Location::SHA256 ||
+		m_location == Location::RIPEMD160 ||
+		m_location == Location::AddMod ||
+		m_location == Location::MulMod ||
+		m_location == Location::ObjectCreation;
+}
+
 TypePointers FunctionType::parseElementaryTypeVector(strings const& _types)
 {
 	TypePointers pointers;

libsolidity/ast/Types.h

@@ -972,6 +972,10 @@ public:
 	}
 	bool hasDeclaration() const { return !!m_declaration; }
 	bool isConstant() const { return m_isConstant; }
+	/// @returns true if the the result of this function only depends on its arguments
+	/// and it does not modify the state.
+	/// Currently, this will only return true for internal functions like keccak and ecrecover.
+	bool isPure() const;
 	bool isPayable() const { return m_isPayable; }
 	/// @return A shared pointer of an ASTString.
 	/// Can contain a nullptr in which case indicates absence of documentation