lint: Use rustc_apfloat for overflowing_literals, add f16 and f128

Switch to parsing float literals for overflow checks using
`rustc_apfloat` rather than host floats. This avoids small variations in
platform support and makes it possible to start checking `f16` and
`f128` as well.

Using APFloat matches what we try to do elsewhere to avoid platform
inconsistencies.

Author: tgross35

Cargo.lock

@@ -4170,6 +4170,7 @@ version = "0.0.0"
 dependencies = [
  "bitflags",
  "rustc_abi",
+ "rustc_apfloat",
  "rustc_ast",
  "rustc_ast_pretty",
  "rustc_attr_parsing",

compiler/rustc_lint/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2024"
 # tidy-alphabetical-start
 bitflags = "2.4.1"
 rustc_abi = { path = "../rustc_abi" }
+rustc_apfloat = "0.2.0"
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_attr_parsing = { path = "../rustc_attr_parsing" }

compiler/rustc_lint/src/types/literal.rs

@@ -1,10 +1,12 @@
 use hir::{ExprKind, Node};
 use rustc_abi::{Integer, Size};
+use rustc_apfloat::Float;
+use rustc_apfloat::ieee::{DoubleS, HalfS, IeeeFloat, QuadS, Semantics, SingleS};
 use rustc_hir::{HirId, attrs};
 use rustc_middle::ty::Ty;
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::{bug, ty};
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 use {rustc_ast as ast, rustc_hir as hir};
 
 use crate::LateContext;
@@ -383,6 +385,13 @@ fn lint_uint_literal<'tcx>(
     }
 }
 
+/// `None` if `v` does not parse as the float type, otherwise indicates whether a literal rounds
+/// to infinity.
+fn float_is_infinite<S: Semantics>(v: Symbol) -> Option<bool> {
+    let x: IeeeFloat<S> = v.as_str().parse().ok()?;
+    Some(x.is_infinite())
+}
+
 pub(crate) fn lint_literal<'tcx>(
     cx: &LateContext<'tcx>,
     type_limits: &TypeLimits,
@@ -405,18 +414,18 @@ pub(crate) fn lint_literal<'tcx>(
             lint_uint_literal(cx, hir_id, span, lit, t)
         }
         ty::Float(t) => {
-            let (is_infinite, sym) = match lit.node {
-                ast::LitKind::Float(v, _) => match t {
-                    // FIXME(f16_f128): add this check once `is_infinite` is reliable (ABI
-                    // issues resolved).
-                    ty::FloatTy::F16 => (Ok(false), v),
-                    ty::FloatTy::F32 => (v.as_str().parse().map(f32::is_infinite), v),
-                    ty::FloatTy::F64 => (v.as_str().parse().map(f64::is_infinite), v),
-                    ty::FloatTy::F128 => (Ok(false), v),
-                },
-                _ => bug!(),
+            let ast::LitKind::Float(v, _) = lit.node else {
+                bug!();
             };
-            if is_infinite == Ok(true) {
+
+            let is_infinite = match t {
+                ty::FloatTy::F16 => float_is_infinite::<HalfS>(v),
+                ty::FloatTy::F32 => float_is_infinite::<SingleS>(v),
+                ty::FloatTy::F64 => float_is_infinite::<DoubleS>(v),
+                ty::FloatTy::F128 => float_is_infinite::<QuadS>(v),
+            };
+
+            if is_infinite == Some(true) {
                 cx.emit_span_lint(
                     OVERFLOWING_LITERALS,
                     span,
@@ -426,7 +435,7 @@ pub(crate) fn lint_literal<'tcx>(
                             .sess()
                             .source_map()
                             .span_to_snippet(lit.span)
-                            .unwrap_or_else(|_| sym.to_string()),
+                            .unwrap_or_else(|_| v.to_string()),
                     },
                 );
             }

library/core/src/fmt/float.rs

@@ -13,8 +13,11 @@ macro_rules! impl_general_format {
     ($($t:ident)*) => {
         $(impl GeneralFormat for $t {
             fn already_rounded_value_should_use_exponential(&self) -> bool {
+                #[allow(overflowing_literals)] // f16 is always within this value
+                let max_abs = 1e+16;
+
                 let abs = $t::abs(*self);
-                (abs != 0.0 && abs < 1e-4) || abs >= 1e+16
+                (abs != 0.0 && abs < 1e-4) || abs >= max_abs
             }
         })*
     }

tests/ui/lint/lint-type-overflow2.rs

@@ -1,13 +1,19 @@
 //@ compile-flags: -O
 
+#![feature(f16)]
+#![feature(f128)]
 #![deny(overflowing_literals)]
 
 fn main() {
     let x2: i8 = --128; //~ ERROR literal out of range for `i8`
     //~| WARN use of a double negation
 
+    let x = -65520.0_f16; //~ ERROR literal out of range for `f16`
+    let x =  65520.0_f16; //~ ERROR literal out of range for `f16`
     let x = -3.40282357e+38_f32; //~ ERROR literal out of range for `f32`
     let x =  3.40282357e+38_f32; //~ ERROR literal out of range for `f32`
     let x = -1.7976931348623159e+308_f64; //~ ERROR literal out of range for `f64`
     let x =  1.7976931348623159e+308_f64; //~ ERROR literal out of range for `f64`
+    let x = -1.1897314953572317650857593266280075e+4932_f128; //~ ERROR literal out of range for `f128`
+    let x =  1.1897314953572317650857593266280075e+4932_f128; //~ ERROR literal out of range for `f128`
 }

tests/ui/lint/lint-type-overflow2.stderr

@@ -1,5 +1,5 @@
 warning: use of a double negation
-  --> $DIR/lint-type-overflow2.rs:6:18
+  --> $DIR/lint-type-overflow2.rs:8:18
    |
 LL |     let x2: i8 = --128;
    |                  ^^^^^
@@ -13,50 +13,82 @@ LL |     let x2: i8 = -(-128);
    |                   +    +
 
 error: literal out of range for `i8`
-  --> $DIR/lint-type-overflow2.rs:6:20
+  --> $DIR/lint-type-overflow2.rs:8:20
    |
 LL |     let x2: i8 = --128;
    |                    ^^^
    |
    = note: the literal `128` does not fit into the type `i8` whose range is `-128..=127`
    = help: consider using the type `u8` instead
 note: the lint level is defined here
-  --> $DIR/lint-type-overflow2.rs:3:9
+  --> $DIR/lint-type-overflow2.rs:5:9
    |
 LL | #![deny(overflowing_literals)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
+error: literal out of range for `f16`
+  --> $DIR/lint-type-overflow2.rs:11:14
+   |
+LL |     let x = -65520.0_f16;
+   |              ^^^^^^^^^^^
+   |
+   = note: the literal `65520.0_f16` does not fit into the type `f16` and will be converted to `f16::INFINITY`
+
+error: literal out of range for `f16`
+  --> $DIR/lint-type-overflow2.rs:12:14
+   |
+LL |     let x =  65520.0_f16;
+   |              ^^^^^^^^^^^
+   |
+   = note: the literal `65520.0_f16` does not fit into the type `f16` and will be converted to `f16::INFINITY`
+
 error: literal out of range for `f32`
-  --> $DIR/lint-type-overflow2.rs:9:14
+  --> $DIR/lint-type-overflow2.rs:13:14
    |
 LL |     let x = -3.40282357e+38_f32;
    |              ^^^^^^^^^^^^^^^^^^
    |
    = note: the literal `3.40282357e+38_f32` does not fit into the type `f32` and will be converted to `f32::INFINITY`
 
 error: literal out of range for `f32`
-  --> $DIR/lint-type-overflow2.rs:10:14
+  --> $DIR/lint-type-overflow2.rs:14:14
    |
 LL |     let x =  3.40282357e+38_f32;
    |              ^^^^^^^^^^^^^^^^^^
    |
    = note: the literal `3.40282357e+38_f32` does not fit into the type `f32` and will be converted to `f32::INFINITY`
 
 error: literal out of range for `f64`
-  --> $DIR/lint-type-overflow2.rs:11:14
+  --> $DIR/lint-type-overflow2.rs:15:14
    |
 LL |     let x = -1.7976931348623159e+308_f64;
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: the literal `1.7976931348623159e+308_f64` does not fit into the type `f64` and will be converted to `f64::INFINITY`
 
 error: literal out of range for `f64`
-  --> $DIR/lint-type-overflow2.rs:12:14
+  --> $DIR/lint-type-overflow2.rs:16:14
    |
 LL |     let x =  1.7976931348623159e+308_f64;
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: the literal `1.7976931348623159e+308_f64` does not fit into the type `f64` and will be converted to `f64::INFINITY`
 
-error: aborting due to 5 previous errors; 1 warning emitted
+error: literal out of range for `f128`
+  --> $DIR/lint-type-overflow2.rs:17:14
+   |
+LL |     let x = -1.1897314953572317650857593266280075e+4932_f128;
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: the literal `1.1897314953572317650857593266280075e+4932_f128` does not fit into the type `f128` and will be converted to `f128::INFINITY`
+
+error: literal out of range for `f128`
+  --> $DIR/lint-type-overflow2.rs:18:14
+   |
+LL |     let x =  1.1897314953572317650857593266280075e+4932_f128;
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: the literal `1.1897314953572317650857593266280075e+4932_f128` does not fit into the type `f128` and will be converted to `f128::INFINITY`
+
+error: aborting due to 9 previous errors; 1 warning emitted