syntax errors for unsigned literals longer than 128 bits

[ScottPJones]

If you have hexadecimal literal, normally it produces an unsigned value, whose size is dependent on the length of the literal.
However, if you go past 128 bits (32 hex digits), then it will switch to a signed number, which could possibly lead to hard to find bugs.
For example:

julia> ~0x00000000000000000000000000000000
0xffffffffffffffffffffffffffffffff

julia> ~0x000000000000000000000000000000000
-1

I believe this at least deserves a warning from the compiler (a point I tried to raise in #11081, only to have the title of my issue changed out from under me and then have it closed)

[JeffBezanson]

I agree this should be a syntax error.

[ScottPJones]

@JeffBezanson Error, or warning (or do you not do warnings in Julia?)
There are definitely cases where it would be nice to define a BigInt literal as hex... but maybe there's some workaround?

[pao]

big"0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"should probably be made to work if it doesn't already.

[ihnorton]

warn("foo")

[ScottPJones]

@pao big"0xfffff....." works just fine, so people have an out if they really understand it will be signed... thx

[ScottPJones]

@ihnorton Thanks! Now I just need to figure out where to put the warn!
warn("Hexadecimal literal constant $(hex(value)) has overflowed a UInt128, and has been promoted to a signed BigInt. To avoid this warning, use big\"0x...\"")
Does that seem OK?

[JeffBezanson]

I try to avoid warnings. I think it's better to be decisive and make it an error, or allow it. Warnings just mean you later need to add -Werror, and then people need to write coding guidelines telling people to use it :)

[tkelman]

+1 for syntax error, bigints from literals make it harder to deploy a Julia runtime without needing gmp.

[ScottPJones]

@JeffBezanson Good point... can somebody please either tell me (at least in the general direction) where I'd fix this to give a syntax error, or else fix it themselves? (I'd rather just fix it myself, I'll learn more, and you can do more important stuff)