Add feature gates for f16 and f128

Includes related tests and documentation pages.

compiler/rustc_feature/src/unstable.rs

@@ -461,6 +461,10 @@ declare_features! (
     (unstable, extended_varargs_abi_support, "1.65.0", Some(100189)),
     /// Allows defining `extern type`s.
     (unstable, extern_types, "1.23.0", Some(43467)),
+    /// Allow using 128-bit (quad precision) floating point numbers.
+    (unstable, f128, "CURRENT_RUSTC_VERSION", Some(116909)),
+    /// Allow using 16-bit (half precision) floating point numbers.
+    (unstable, f16, "CURRENT_RUSTC_VERSION", Some(116909)),
     /// Allows the use of `#[ffi_const]` on foreign functions.
     (unstable, ffi_const, "1.45.0", Some(58328)),
     /// Allows the use of `#[ffi_pure]` on foreign functions.

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -15,7 +15,7 @@ use crate::collect::HirPlaceholderCollector;
 use crate::errors::AmbiguousLifetimeBound;
 use crate::middle::resolve_bound_vars as rbv;
 use crate::require_c_abi_if_c_variadic;
-use rustc_ast::TraitObjectSyntax;
+use rustc_ast::{FloatTy, TraitObjectSyntax};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_errors::{
     codes::*, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, FatalError, MultiSpan,
@@ -33,6 +33,7 @@ use rustc_middle::ty::{
     TypeVisitableExt,
 };
 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
+use rustc_session::parse::feature_err;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::{sym, BytePos, Span, DUMMY_SP};
@@ -2174,6 +2175,29 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         }
                     }
                 });
+
+                if let Some(e) = self.check_float_gate(
+                    prim_ty,
+                    FloatTy::F16,
+                    self.tcx().features().f16,
+                    sym::f16,
+                    path.span,
+                    "the feature `f16` is unstable",
+                ) {
+                    return e;
+                }
+
+                if let Some(e) = self.check_float_gate(
+                    prim_ty,
+                    FloatTy::F128,
+                    self.tcx().features().f128,
+                    sym::f128,
+                    path.span,
+                    "the feature `f128` is unstable",
+                ) {
+                    return e;
+                }
+
                 match prim_ty {
                     hir::PrimTy::Bool => tcx.types.bool,
                     hir::PrimTy::Char => tcx.types.char,
@@ -2803,6 +2827,31 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
         Some(r)
     }
+
+    /// If the float type is not enabled by the feature, return `Some(error)`. `None` if there are
+    /// no problems.
+    fn check_float_gate(
+        &self,
+        prim_ty: hir::PrimTy,
+        gated_ty: FloatTy,
+        feat_enabled: bool,
+        feat_sym: Symbol,
+        span: Span,
+        msg: &'static str,
+    ) -> Option<Ty<'tcx>> {
+        let hir::PrimTy::Float(float_ty) = prim_ty else {
+            return None;
+        };
+
+        if float_ty == gated_ty && !feat_enabled && !span.allows_unstable(feat_sym) {
+            let sess = self.tcx().sess;
+            let guar = feature_err(sess, sym::f16, span, msg).emit();
+            self.set_tainted_by_errors(guar);
+            Some(Ty::new_error(self.tcx(), guar))
+        } else {
+            None
+        }
+    }
 }
 
 fn assoc_kind_str(kind: ty::AssocKind) -> &'static str {

src/doc/unstable-book/src/language-features/f128.md

@@ -0,0 +1,9 @@
+# `f128`
+
+The tracking issue for this feature is: [#116909]
+
+[#116909]: https://github.com/rust-lang/rust/issues/116909
+
+---
+
+Enable the `f128` type for  IEEE 128-bit floating numbers (quad precision).

src/doc/unstable-book/src/language-features/f16.md

@@ -0,0 +1,9 @@
+# `f16`
+
+The tracking issue for this feature is: [#116909]
+
+[#116909]: https://github.com/rust-lang/rust/issues/116909
+
+---
+
+Enable the `f16` type for  IEEE 16-bit floating numbers (half precision).

tests/ui/feature-gates/feature-gate-f128.rs

@@ -0,0 +1,36 @@
+#![allow(unused)]
+
+// ensure gating for primitive use
+mod m1 {
+    const A: f128 = 10.0; //~ ERROR the feature `f128` is unstable
+
+    pub fn main() {
+        let a: f128 = 100.0; //~ ERROR the feature `f128` is unstable
+        let b = 0.0f128; //~ ERROR the feature `f128` is unstable
+        foo(1.23);
+    }
+
+    fn foo(a: f128) {} //~ ERROR the feature `f128` is unstable
+
+    struct Bar {
+        a: f128, //~ ERROR the feature `f128` is unstable
+    }
+}
+
+// ensure we don't restrict name as an identifier or custom types
+mod mod1 {
+    #[allow(non_camel_case_types)]
+    struct f128 {
+        a: i32,
+    }
+
+    fn foo() {
+        let f128 = ();
+    }
+
+    fn bar(a: f128) -> i32 {
+        a.a
+    }
+}
+
+fn main() {}

tests/ui/feature-gates/feature-gate-f128.stderr

@@ -0,0 +1,43 @@
+error[E0658]: the feature `f128` is unstable
+  --> $DIR/feature-gate-f128.rs:5:14
+   |
+LL |     const A: f128 = 10.0;
+   |              ^^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: the feature `f128` is unstable
+  --> $DIR/feature-gate-f128.rs:13:15
+   |
+LL |     fn foo(a: f128) {}
+   |               ^^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: the feature `f128` is unstable
+  --> $DIR/feature-gate-f128.rs:16:12
+   |
+LL |         a: f128,
+   |            ^^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: the feature `f128` is unstable
+  --> $DIR/feature-gate-f128.rs:8:16
+   |
+LL |         let a: f128 = 100.0;
+   |                ^^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/feature-gates/feature-gate-f16.rs

@@ -0,0 +1,36 @@
+#![allow(unused)]
+
+// ensure gating for primitive use
+mod m1 {
+    const A: f16 = 10.0; //~ ERROR the feature `f16` is unstable
+
+    pub fn main() {
+        let a: f16 = 100.0; //~ ERROR the feature `f16` is unstable
+        let b = 0.0f16; //~ ERROR the feature `f16` is unstable
+        foo(1.23);
+    }
+
+    fn foo(a: f16) {} //~ ERROR the feature `f16` is unstable
+
+    struct Bar {
+        a: f16, //~ ERROR the feature `f16` is unstable
+    }
+}
+
+// ensure we don't restrict name as an identifier or custom types
+mod m2 {
+    #[allow(non_camel_case_types)]
+    struct f16 {
+        a: i32,
+    }
+
+    fn foo() {
+        let f16 = ();
+    }
+
+    fn bar(a: f16) -> i32 {
+        a.a
+    }
+}
+
+fn main() {}

tests/ui/feature-gates/feature-gate-f16.stderr

@@ -0,0 +1,43 @@
+error[E0658]: the feature `f16` is unstable
+  --> $DIR/feature-gate-f16.rs:5:14
+   |
+LL |     const A: f16 = 10.0;
+   |              ^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: the feature `f16` is unstable
+  --> $DIR/feature-gate-f16.rs:13:15
+   |
+LL |     fn foo(a: f16) {}
+   |               ^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: the feature `f16` is unstable
+  --> $DIR/feature-gate-f16.rs:16:12
+   |
+LL |         a: f16,
+   |            ^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: the feature `f16` is unstable
+  --> $DIR/feature-gate-f16.rs:8:16
+   |
+LL |         let a: f16 = 100.0;
+   |                ^^^
+   |
+   = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information
+   = help: add `#![feature(f16)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.