Use :ident matcher instead of :ty matcher

[Aaron1011]

When a :ty matcher is used in a macro_rules! macro, the captured
argument can no longer be used to match a literal in a new
macro_rules! invocation. For example, the following code:

macro_rules! inner {
    (my_val) => {}
}

macro_rules! outer {
    ($val:ty) => {
        inner!($val);
    }
}

outer!(my_val);

produces the following error:

error: no rules expected the token `my_val`
  --> src/lib.rs:7:16
   |
1  | macro_rules! inner {
   | ------------------ when calling this macro
...
7  |         inner!($val);
   |                ^^^^ no rules expected this token in macro call
...
11 | outer!(my_val);
   | --------------- in this macro invocation
   |
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

That is, once my_val is captured as a :ty, it will not match a my_val literal
in the inner! invocation.

Due to a bug in rustc, code like this was accepted by the compiler
when a proc-macro attribute was applied to the macro invocation.
This affects fourier-algorithms due to the following code:

#[target_cfg(target = "[x86|x86_64]+avx")]
crate::avx_vector! { $type };

The avx_vector! macro is expecting either f32 or f64
as an ordinary token. However, the $type metavariable uses a
:ty matcher, which will prevent it from matching against f32
or f64 (even though the captured type is always f32 or f64).

Due to the target_cfg attribute proc-macro, this code was incorrectly
allowed to compile. When the underlying bug in rustc is fixed
in rust-lang/rust#73084, fourier-algorithms
will stop compiling.

This commit changes two :ty matchers to :ident matchers, which can
be used as arguments to a macro_rules! macro expecting a plain f32
or f64 token. This will still compile on existing compile versions,
and will allow fourier-algorithms to continue to compile once
rust-lang/rust#73084 is merged into rustc.

[calebzulawski]

Thanks! Looks good.

[Aaron1011]

@calebzulawski: Would you mind making a new point release? I'm planning to merge rust-lang/rust#73084 soon, and it would be nice for there to be an upgrade path for all downstream crates affected by it.

[calebzulawski]

Done!