Method validateExpression

Engine/Knob.cpp:2572–2729

} // KnobHelperPrivate::parseListenersFromExpression

std::string
KnobHelper::validateExpression(const std::string& expression,
                               int dimension,
                               bool hasRetVariable,
                               std::string* resultAsString)
{

#ifdef NATRON_RUN_WITHOUT_PYTHON
    throw std::invalid_argument("NATRON_RUN_WITHOUT_PYTHON is defined");
#endif
    PythonGILLocker pgl;

    if ( expression.empty() ) {
        throw std::invalid_argument("empty expression");;
    }

    std::string error;
#if 0
    // the following is OK to detect that there's no "return" in the expression,
    // but fails if the expression contains e.g. "thisGroup"
    // see https://github.com/NatronGitHub/Natron/issues/294

    ///Try to compile the expression and evaluate it, if it doesn't have a good syntax, throw an exception
    ///with the error.
    {
        // first check that the expression does not contain return
        EXPR_RECURSION_LEVEL();

        if ( !NATRON_PYTHON_NAMESPACE::interpretPythonScript(expression, &error, 0) ) {
            throw std::runtime_error(error);
        }
    }
#endif

    std::string exprCpy = expression;

    //if !hasRetVariable the expression is expected to be single-line
    if (!hasRetVariable) {
        std::size_t foundNewLine = expression.find("\n");
        if (foundNewLine != std::string::npos) {
            throw std::invalid_argument("unexpected new line character \'\\n\'");
        }
        //preprend the line with "ret = ..."
        std::string toInsert("    ret = ");
        exprCpy.insert(0, toInsert);
    } else {
        exprCpy.insert(0, "    ");
        std::size_t foundNewLine = exprCpy.find("\n");
        while (foundNewLine != std::string::npos) {
            exprCpy.insert(foundNewLine + 1, "    ");
            foundNewLine = exprCpy.find("\n", foundNewLine + 1);
        }
    }

    KnobHolder* holder = getHolder();
    if (!holder) {
        throw std::runtime_error("This parameter cannot have an expression");
    }