Integral literals larger than i64::MAX are not detected as overflow

[lilyball]

The type_overflow lint does not catch integral literals larger than i64::MAX. I have to assume the problem is the overflow happens when generating the AST, and the lint operates on the AST, so it can't tell that it overflowed.

Example:

println!("{}", 9223372036854775808i64);
// prints -9223372036854775808
println!("{}", 18446744073709551615i64);
// prints -1

It does manage to catch 18446744073709551616, which is a parse error ("int literal is too large"). This is u64::MAX + 1, so the parser can definitively tell it's too large even though it doesn't know which integral type is being used.

[hirschenberger]

Duplicate of #2252 ?

[lilyball]

@hirschenberger #2252 appears to be a specific issue about float literals.

[hirschenberger]

Right, but there #4220 was mentioned, which is closed but handeled a similar problem for ints.

[lilyball]

@hirschenberger Look closer. #4220 was fixed by the type_overflow lint. This issue here is describing an issue that the type_overflow lint doesn't catch.

[hirschenberger]

You're right, sorry.

[hirschenberger]

I have patch which solves this issue, but a runtime test is failing now which tests i64 overflowing.

https://github.com/rust-lang/rust/blob/master/src/test/run-pass/big-literals.rs#L18-L19

whereas the i32 type works, which is inconsistent. What's the required behaviour, shall we fail with a parse error on all overflowing literals?