"`X...` range patterns are not supported" occurring in today's nightly

[wez]

The CI for libssh2-sys started to fail today with this error:

error: `X...` range patterns are not supported
   --> C:\Users\wez\.cargo\registry\src\github.com-1ecc6299db9ec823\extprim-1.7.0\src\traits.rs:94:21
    |
94  |                     1 ... $e => u128::new(mantissa) << exp,
    |                     ^^^^^ help: try using the maximum value for the type: `1...MAX`
...
117 | impl_to_extra_primitive_for_float!(f32, 23, 104, 103);
    | ------------------------------------------------------ in this macro invocation

It appears as though the compiler doesn't see 1 ... $e and only sees 1... as the range expression and then generates this error.

The expression is inside a macro_rules! expansion.

You can reproduce this by cloning the extprim repo and building it:

$ git clone git@github.com:kennytm/extprim.git
$ cd extprim
$ cargo +nightly build

The build succeeds on the stable channel and much older releases, so this appears to be a regression in the nightly.

Here's the version on my windows system, but note that this also fails on linux and macos too:

rustc 1.38.0-nightly (4560cb830 2019-07-28)
binary: rustc
commit-hash: 4560cb830fce63fcffdc4558f4281aaac6a3a1ba
commit-date: 2019-07-28
host: x86_64-pc-windows-msvc
release: 1.38.0-nightly
LLVM version: 9.0

[Centril]

Regression introduced in #62550.

[Centril]

More specifically the bug is in:

    fn is_pat_range_end_start(&self) -> bool {
        self.token.is_path_start() // e.g. `MY_CONST`;
            || self.token == token::Dot // e.g. `.5` for recovery;
            || self.token.can_begin_literal_or_bool() // e.g. `42`.
    }

which is called to see whether what follows ... is a valid start of a range pattern end expression.

This is strange tho... in the case of e.g.:

fn bar() {
    macro_rules! foo {
        ($e1:expr, $e2:expr) => {
            match 0 {
                $e1...A => {}
                _ => {}
            }
        }
    }

    foo!(0, 1);
}

the call to self.token.is_path_start() in https://github.com/rust-lang/rust/blob/master/src/libsyntax/parse/parser.rs#L3959 is used successfully to parse $e1 but somehow that doesn't work for $e1..$e2.

cc @petrochenkov

[Centril]

Similarly, with:

fn bar() {
    macro_rules! foo {
        ($e1:expr, $e2:expr) => {
            match 0 {
                ..$e2 => {}
                _ => {}
            }
        }
    }

    foo!(0, 1);
}

this does not trigger "error: ..X range patterns are not supported" but it should.