How to extend cast-expression pre-checking
In `cif2plc` the "nop" cast and the "int to real" cast must be allowed by the pre-checker, implemented as
``` java
@Override
protected void preprocessCastExpression(CastExpression expr) {
// Check supported.
CifType ctype = normalizeType(expr.getChild().getType());
CifType rtype = normalizeType(expr.getType());
if (ctype instanceof IntType && rtype instanceof RealType) {
// Integer to real conversion supported by PLC code.
return;
}
if (CifTypeUtils.checkTypeCompat(ctype, rtype, RangeCompat.EQUAL)) {
// Keeping the type the same is supported by removing the cast.
return;
}
// Unsupported.
String msg = fmt(
"Unsupported expression \"%s\": casts from type \"%s\" to type \"%s\" are currently not supported.",
exprToStr(expr), typeToStr(ctype), typeToStr(rtype));
problems.add(msg);
}
```
In `ExprNoSpecificExprsCheck` (`oee.cif.common.checkers.checks`) a cast expression can be limited to types, which current lists values
``` java
/** Disallow all cast expressions. */
CAST_EXPRS,
/** Disallow cast expressions that cast to a different type. */
CAST_EXPRS_NON_EQUAL_TYPE,
```
As far as I can see there is no extension path in the above checks. You can set `CAST_EXPRS_NON_EQUAL_TYPE`, but then the int-to-real conversion get flagged as violation.
Theoretically you could make "override" constants, but that doesn't seem like a good solution.
You can make a `CAST_EXPRS_INT_TO_REAL` values that behaves like `CAST_EXPRS_NON_EQUAL_TYPE` except for the int-to-real conversion, but that breaks again as soon as you need a second exception.
Addresses #424
issue