[llvm-rc] Add support for multiplication and division in expressions

[mstorsjo]

This is supported by GNU windres. MS rc.exe does accept these expressions, but doesn't evalulate them correctly, it only returns the left hand side.

This fixes one aspect of #143157.

[cjacek]

I was wondering if we should handle operator precedence correctly, like in 1 + 2 * 3. With this PR, we currently evaluate addition first, resulting in 9. GNU windres seems to handle precedence properly and gives 7. MSVC rc.exe is odd, it appears to ignore multiplication and division entirely, just outputting 3.

I'm not sure what the best approach is here, what do you think?

[mstorsjo]

I was wondering if we should handle operator precedence correctly, like in 1 + 2 * 3. With this PR, we currently evaluate addition first, resulting in 9. GNU windres seems to handle precedence properly and gives 7. MSVC rc.exe is odd, it appears to ignore multiplication and division entirely, just outputting 3.

I'm not sure what the best approach is here, what do you think?

Oh, that's indeed a good point, thanks for catching it!

That's weird if rc.exe does accept them but actually doesn't act on them. So perhaps they're not really a thing in canonical MS rc files - I guess that's why they're not implemented so far.

The case where I ran into this, https://github.com/DerellLicht/winwiz/blob/ed4134c44c22acc3746228eec34538d1e857dd6c/winwiz.rc#L250-L253, has parentheses so it should be unambiguous anyway (I think, or does it not honor them correctly either?), but if we do implement them I do think we should get the precedence right as well.

[mstorsjo]

Thanks, now it should handle operator precedence correctly.

(It may have been possible to handle this by sticking to two levels of expression evaluation, but for clarity, I made a second level inbetween the preexisting low precendence binary operators, and the existing unary operators.)

[cjacek]

The code looks good to me, but please update the parser summary comment above RCParser::readInt.

[mstorsjo]

The code looks good to me, but please update the parser summary comment above RCParser::readInt.

Thanks for catching this detail as well! Updated now, will push later today.