Implement FromStr for f128.

[bjoernager]

Tracking issue: #116909.

This PR implements FromStr for f128. On the targets that natively support such numbers, this implementation will work as expected. On other targets, a run-time panic will encur for now (this is similarly done for f16 already).

Note that this PR is not currently in a mergeable state.

[rustbot]

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[bjoernager]

@rustbot label +F-f16_and_f128 +T-libs-api -T-libs

r? libs-api

[rust-log-analyzer]

The job aarch64-gnu-llvm-19-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RUSTC-TIMING] build_script_build test:false 0.115
[RUSTC-TIMING] cc test:false 0.674
   Compiling compiler_builtins v0.1.160 (/checkout/library/compiler-builtins/compiler-builtins)
[RUSTC-TIMING] build_script_build test:false 0.312
error[E0277]: the trait bound `f128: RawFloat` is not satisfied
   --> library/core/src/num/dec2flt/mod.rs:171:17
    |
110 | / macro_rules! from_str_float_impl {
111 | |     ($($ty:ty)*) => {
112 | |         $(#[stable(feature = "rust1", since = "1.0.0")]
113 | |         impl FromStr for $ty {
...   |
171 | |                 dec2flt(s)
    | |                 ^^^^^^^^^^ the trait `RawFloat` is not implemented for `f128`
...   |
174 | |     };
175 | | }
    | |_- in this expansion of `from_str_float_impl!`
...
182 |   from_str_float_impl!(f128);
    |   -------------------------- in this macro invocation
    |
    = help: the following other types implement trait `RawFloat`:
              f16
              f32
              f64
note: required by a bound in `dec2flt`
   --> library/core/src/num/dec2flt/mod.rs:268:19
    |
268 | pub fn dec2flt<F: RawFloat>(s: &str) -> Result<F, ParseFloatError> {
    |                   ^^^^^^^^ required by this bound in `dec2flt`

For more information about this error, try `rustc --explain E0277`.
[RUSTC-TIMING] core test:false 24.389
error: could not compile `core` (lib) due to 1 previous error
Bootstrap failed while executing `--stage 2 test --skip compiler --skip src`

[bjoernager]

Sorry, combining this with #146406 for the sake of maintainability.

[rust-log-analyzer]

The job aarch64-gnu-llvm-19-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RUSTC-TIMING] build_script_build test:false 0.128
[RUSTC-TIMING] cc test:false 0.679
   Compiling compiler_builtins v0.1.160 (/checkout/library/compiler-builtins/compiler-builtins)
[RUSTC-TIMING] build_script_build test:false 0.316
error[E0277]: the trait bound `f128: RawFloat` is not satisfied
   --> library/core/src/num/dec2flt/mod.rs:171:17
    |
110 | / macro_rules! from_str_float_impl {
111 | |     ($($ty:ty)*) => {
112 | |         $(#[stable(feature = "rust1", since = "1.0.0")]
113 | |         impl FromStr for $ty {
...   |
171 | |                 dec2flt(s)
    | |                 ^^^^^^^^^^ the trait `RawFloat` is not implemented for `f128`
...   |
174 | |     };
175 | | }
    | |_- in this expansion of `from_str_float_impl!`
...
182 |   from_str_float_impl!(f128);
    |   -------------------------- in this macro invocation
    |
    = help: the following other types implement trait `RawFloat`:
              f16
              f32
              f64
note: required by a bound in `dec2flt`
   --> library/core/src/num/dec2flt/mod.rs:268:19
    |
268 | pub fn dec2flt<F: RawFloat>(s: &str) -> Result<F, ParseFloatError> {
    |                   ^^^^^^^^ required by this bound in `dec2flt`

For more information about this error, try `rustc --explain E0277`.
[RUSTC-TIMING] core test:false 24.281
error: could not compile `core` (lib) due to 1 previous error
Bootstrap failed while executing `--stage 2 test --skip compiler --skip src`