[PATCH v2 10/19] rust: zerocopy: remove float `Display` support

[Miguel Ojeda <ojeda@kernel.org>]

The kernel builds `core` with the `no_fp_fmt_parse` `--cfg`, which means
we do not have support for formatting floating point primitives. However,
`zerocopy` expects those implementations to exist:

    error[E0277]: `f32` doesn't implement `core::fmt::Display`
       --> rust/zerocopy/src/byteorder.rs:172:29
        |
    172 |                   $trait::fmt(&self.get(), f)
        |                   ----------- ^^^^^^^^^^^ the trait `core::fmt::Display` is not implemented for `f32`
        |                   |
        |                   required by a bound introduced by this call
    ...
    907 | / define_type!(
    908 | |     An,
    909 | |     "A 32-bit floating point number",
    910 | |     F32,
    ...   |
    922 | |     []
    923 | | );
        | |_- in this macro invocation
        |
        = help: the following other types implement trait `core::fmt::Display`:
                  i128
                  i16
                  i32
                  i64
                  i8
                  isize
                  u128
                  u16
                and 4 others
        = note: this error originates in the macro `impl_fmt_trait` which comes from the expansion of the macro `define_type` (in Nightly builds, run with -Z macro-backtrace for more info)

Thus work around it by skipping those implementations in `zerocopy`.

Ideally, `zerocopy` would have the equivalent of `no_fp_fmt_parse`;
and, indeed, upstream just added it [1] after I filed an issue [2]
about it as requested. We can try it in a future update of our
vendored copy.

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://github.com/google/zerocopy/pull/3429 [1]
Link: https://github.com/google/zerocopy/issues/3426 [2]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/zerocopy/src/byteorder.rs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/rust/zerocopy/src/byteorder.rs b/rust/zerocopy/src/byteorder.rs
index 36ca4c0c88b0..8f70048f1eb0 100644
--- a/rust/zerocopy/src/byteorder.rs
+++ b/rust/zerocopy/src/byteorder.rs
@@ -177,7 +177,6 @@ fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
 
 macro_rules! impl_fmt_traits {
     ($name:ident, $native:ident, "floating point number") => {
-        impl_fmt_trait!($name, $native, Display);
     };
     ($name:ident, $native:ident, "unsigned integer") => {
         impl_fmt_traits!($name, $native, @all_types);
-- 
2.54.0