Adding fixes for signedness warnings in libsolidity

Co-authored-by: Kamil Śliwak <kamil.sliwak@codepoets.it>

libsolidity/ast/AST.cpp

@@ -38,7 +38,7 @@ using namespace solidity;
 using namespace solidity::frontend;
 
 ASTNode::ASTNode(int64_t _id, SourceLocation _location):
-	m_id(_id),
+	m_id(static_cast<size_t>(_id)),
 	m_location(std::move(_location))
 {
 }

libsolidity/ast/AST.h

@@ -88,7 +88,7 @@ public:
 	virtual ~ASTNode() {}
 
 	/// @returns an identifier of this AST node that is unique for a single compilation run.
-	int64_t id() const { return m_id; }
+	int64_t id() const { return int64_t(m_id); }
 
 	virtual void accept(ASTVisitor& _visitor) = 0;
 	virtual void accept(ASTConstVisitor& _visitor) const = 0;

libsolidity/ast/ASTJsonConverter.cpp

@@ -37,6 +37,7 @@
 #include <utility>
 #include <vector>
 #include <algorithm>
+#include <limits>
 
 using namespace std;
 using namespace solidity::langutil;
@@ -134,7 +135,7 @@ size_t ASTJsonConverter::sourceIndexFromLocation(SourceLocation const& _location
 	if (_location.source && m_sourceIndices.count(_location.source->name()))
 		return m_sourceIndices.at(_location.source->name());
 	else
-		return size_t(-1);
+		return numeric_limits<size_t>::max();
 }
 
 string ASTJsonConverter::sourceLocationToString(SourceLocation const& _location) const

libsolidity/ast/ASTJsonImporter.cpp

@@ -92,7 +92,7 @@ SourceLocation const ASTJsonImporter::createSourceLocation(Json::Value const& _n
 {
 	astAssert(member(_node, "src").isString(), "'src' must be a string");
 
-	return solidity::langutil::parseSourceLocation(_node["src"].asString(), m_currentSourceName, int(m_sourceLocations.size()));
+	return solidity::langutil::parseSourceLocation(_node["src"].asString(), m_currentSourceName, m_sourceLocations.size());
 }
 
 template<class T>

libsolidity/ast/Types.cpp

@@ -773,7 +773,7 @@ tuple<bool, rational> RationalNumberType::parseRational(string const& _value)
 			denominator = bigint(string(fractionalBegin, _value.end()));
 			denominator /= boost::multiprecision::pow(
 				bigint(10),
-				distance(radixPoint + 1, _value.end())
+				static_cast<size_t>(distance(radixPoint + 1, _value.end()))
 			);
 			numerator = bigint(string(_value.begin(), radixPoint));
 			value = numerator + denominator;
@@ -1065,7 +1065,7 @@ TypeResult RationalNumberType::binaryOperatorResult(Token _operator, Type const*
 					if (_base == 1)
 						return 1;
 					else if (_base == -1)
-						return 1 - 2 * int(_exponent & 1);
+						return 1 - 2 * static_cast<int>(_exponent & 1);
 					else
 						return boost::multiprecision::pow(_base, _exponent);
 				};
@@ -1171,7 +1171,7 @@ string RationalNumberType::bigintToReadableString(bigint const& _num)
 	string str = _num.str();
 	if (str.size() > 32)
 	{
-		int omitted = str.size() - 8;
+		size_t omitted = str.size() - 8;
 		str = str.substr(0, 4) + "...(" + to_string(omitted) + " digits omitted)..." + str.substr(str.size() - 4, 4);
 	}
 	return str;
@@ -1201,7 +1201,7 @@ u256 RationalNumberType::literalValue(Literal const*) const
 	{
 		auto fixed = fixedPointType();
 		solAssert(fixed, "Rational number cannot be represented as fixed point type.");
-		int fractionalDigits = fixed->fractionalDigits();
+		unsigned fractionalDigits = fixed->fractionalDigits();
 		shiftedValue = m_value.numerator() * boost::multiprecision::pow(bigint(10), fractionalDigits) / m_value.denominator();
 	}
 
@@ -1291,7 +1291,7 @@ StringLiteralType::StringLiteralType(string _value):
 BoolResult StringLiteralType::isImplicitlyConvertibleTo(Type const& _convertTo) const
 {
 	if (auto fixedBytes = dynamic_cast<FixedBytesType const*>(&_convertTo))
-		return size_t(fixedBytes->numBytes()) >= m_value.size();
+		return static_cast<size_t>(fixedBytes->numBytes()) >= m_value.size();
 	else if (auto arrayType = dynamic_cast<ArrayType const*>(&_convertTo))
 		return
 			arrayType->isByteArray() &&