From 94d0d91c7bd5b65fef08fdb15c25f12b00159e65 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sat, 2 Jul 2022 22:20:22 +0000
Subject: [PATCH] Implement float literals in valtree

---
 compiler/rustc_mir_build/src/build/mod.rs        | 14 ++++++++++++--
 compiler/rustc_mir_build/src/thir/constant.rs    |  8 ++++++++
 src/test/ui/const-generics/issues/issue-98813.rs | 13 +++++++++++++
 3 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/const-generics/issues/issue-98813.rs

diff --git a/compiler/rustc_mir_build/src/build/mod.rs b/compiler/rustc_mir_build/src/build/mod.rs
index e27761381f633..6905642f5984a 100644
--- a/compiler/rustc_mir_build/src/build/mod.rs
+++ b/compiler/rustc_mir_build/src/build/mod.rs
@@ -1104,6 +1104,16 @@ pub(crate) fn parse_float_into_scalar(
     float_ty: ty::FloatTy,
     neg: bool,
 ) -> Option<Scalar> {
+    parse_float_into(num, float_ty, neg, |f| Scalar::from_f32(f), |f| Scalar::from_f64(f))
+}
+
+pub(crate) fn parse_float_into<T>(
+    num: Symbol,
+    float_ty: ty::FloatTy,
+    neg: bool,
+    on_f32: impl FnOnce(Single) -> T,
+    on_f64: impl FnOnce(Double) -> T,
+) -> Option<T> {
     let num = num.as_str();
     match float_ty {
         ty::FloatTy::F32 => {
@@ -1127,7 +1137,7 @@ pub(crate) fn parse_float_into_scalar(
                 f = -f;
             }
 
-            Some(Scalar::from_f32(f))
+            Some(on_f32(f))
         }
         ty::FloatTy::F64 => {
             let Ok(rust_f) = num.parse::<f64>() else { return None };
@@ -1150,7 +1160,7 @@ pub(crate) fn parse_float_into_scalar(
                 f = -f;
             }
 
-            Some(Scalar::from_f64(f))
+            Some(on_f64(f))
         }
     }
 }
diff --git a/compiler/rustc_mir_build/src/thir/constant.rs b/compiler/rustc_mir_build/src/thir/constant.rs
index a7e4403a242e1..1453159e54275 100644
--- a/compiler/rustc_mir_build/src/thir/constant.rs
+++ b/compiler/rustc_mir_build/src/thir/constant.rs
@@ -1,7 +1,10 @@
+use rustc_apfloat::Float;
 use rustc_ast as ast;
 use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
 use rustc_middle::ty::{self, ParamEnv, ScalarInt, TyCtxt};
 
+use crate::build::parse_float_into;
+
 pub(crate) fn lit_to_const<'tcx>(
     tcx: TyCtxt<'tcx>,
     lit_input: LitToConstInput<'tcx>,
@@ -42,6 +45,11 @@ pub(crate) fn lit_to_const<'tcx>(
                 trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?;
             ty::ValTree::from_scalar_int(scalar_int)
         }
+        (ast::LitKind::Float(n, _), ty::Float(fty)) => {
+            let bytes = parse_float_into(*n, *fty, neg, |f| f.to_bits(), |f| f.to_bits())
+                .ok_or_else(|| LitToConstError::Reported)?;
+            ty::ValTree::from_scalar_int(trunc(bytes)?)
+        }
         (ast::LitKind::Bool(b), ty::Bool) => ty::ValTree::from_scalar_int((*b).into()),
         (ast::LitKind::Char(c), ty::Char) => ty::ValTree::from_scalar_int((*c).into()),
         (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported),
diff --git a/src/test/ui/const-generics/issues/issue-98813.rs b/src/test/ui/const-generics/issues/issue-98813.rs
new file mode 100644
index 0000000000000..c7a457cd190f4
--- /dev/null
+++ b/src/test/ui/const-generics/issues/issue-98813.rs
@@ -0,0 +1,13 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(adt_const_params)]
+
+const F: f64 = 12.5;
+
+pub fn func<const F: f64>() {}
+
+fn main() {
+    let _ = func::<14.0>();
+    let _ = func::<F>();
+}