Include types in explicit conversion error message

Changelog.md

@@ -4,6 +4,7 @@ Features:
  * Inline Assembly: Show useful error message if trying to access calldata variables.
  * Inline Assembly: Support variable declaration without initial value (defaults to 0).
  * Type Checker: Disallow value transfers to contracts without a payable fallback function.
+ * Type Checker: Include types in explicit conversion error message.
  * Type Checker: Raise proper error for arrays too large for ABI encoding.
 
 Bugfixes:

libsolidity/analysis/TypeChecker.cpp

@@ -1364,7 +1364,14 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 				// (data location cannot yet be specified for type conversions)
 				resultType = ReferenceType::copyForLocationIfReference(argRefType->location(), resultType);
 			if (!argType->isExplicitlyConvertibleTo(*resultType))
-				m_errorReporter.typeError(_functionCall.location(), "Explicit type conversion not allowed.");
+				m_errorReporter.typeError(
+					_functionCall.location(),
+					"Explicit type conversion not allowed from \"" +
+					argType->toString() +
+					"\" to \"" +
+					resultType->toString() +
+					"\"."
+				);
 		}
 		_functionCall.annotation().type = resultType;
 		_functionCall.annotation().isPure = isPure;