Could Postgres warn about incorrect volatility class?

Hi all,
I recently discovered that a custom function that I thought was being inlined was not being inlined because I had
declaredit IMMUTABLE, but the function body cast an enum value to text which is a STABLE operator. Once I corrected my
function'sdefinition to declare it STABLE, Postgres inlined it.  

Since Postgres can apparently determine during query parsing that my function has a volatility class mismatch, is there
areason that Postgres can't make the same determination and inform me about it when I define the function? In this case
ahelpful message would have been "I sure hope you know what you're doing..." :-) 

Thanks
Philip