commit 5bfd624afa79cf07e93d09306d8d97822fd62b8c
Author: Alex Janka <alex@alexjanka.com>
Date:   Fri Aug 2 12:11:20 2024 +1000

    repro

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..fac57f6
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+rustc-ice-*.txt
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..14a76d3
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,14 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "binary"
+version = "0.1.0"
+dependencies = [
+ "library",
+]
+
+[[package]]
+name = "library"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..1a1ffdc
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,3 @@
+[workspace]
+members = ["binary", "library"]
+resolver = "2"
diff --git a/binary/Cargo.toml b/binary/Cargo.toml
new file mode 100644
index 0000000..1920c4b
--- /dev/null
+++ b/binary/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "binary"
+version = "0.1.0"
+edition = "2021"
+
+[[bin]]
+name = "binary"
+path = "main.rs"
+
+
+[dependencies]
+library = { path = "../library" }
diff --git a/binary/main.rs b/binary/main.rs
new file mode 100644
index 0000000..ab26035
--- /dev/null
+++ b/binary/main.rs
@@ -0,0 +1,14 @@
+use library::*;
+
+fn main() {
+    // this doesn't compile
+    let mut inner = ImplementsTraitOverConstGeneric::<4>;
+
+    // but this would
+    // let mut inner = NonTraitWithConstGeneric::<4>;
+
+    // if we don't call this function then it'll compile fine
+    inner.configure(&Config {
+        config: [0, 0, 0, 0],
+    });
+}
diff --git a/library/Cargo.toml b/library/Cargo.toml
new file mode 100644
index 0000000..6a3c415
--- /dev/null
+++ b/library/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "library"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+path = "lib.rs"
diff --git a/library/lib.rs b/library/lib.rs
new file mode 100644
index 0000000..ca475dc
--- /dev/null
+++ b/library/lib.rs
@@ -0,0 +1,38 @@
+#![allow(incomplete_features)]
+#![feature(generic_const_exprs)]
+
+pub trait LibTrait {
+    const NUM: usize;
+
+    fn configure(&mut self, cfg: &Config<{ Self::NUM }>);
+}
+
+pub struct Config<const N: usize> {
+    pub config: [u8; N],
+}
+
+pub struct ImplementsTraitOverConstGeneric<const N: usize>;
+
+impl<const N: usize> LibTrait for ImplementsTraitOverConstGeneric<N> {
+    const NUM: usize = N;
+
+    fn configure(&mut self, _: &Config<{ Self::NUM }>) {}
+}
+
+// but this works:
+
+// impl LibTrait for ImplementsTraitOverConstGeneric<4> {
+//     const NUM: usize = 4;
+
+//     fn configure(&mut self, _: &Config<{ Self::NUM }>) {}
+// }
+
+// or this:
+
+pub struct NonTraitWithConstGeneric<const N: usize>;
+
+impl<const N: usize> NonTraitWithConstGeneric<N> {
+    pub const NUM: usize = N;
+
+    pub fn configure(&mut self, _: &Config<{ Self::NUM }>) {}
+}
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
new file mode 100644
index 0000000..5d56faf
--- /dev/null
+++ b/rust-toolchain.toml
@@ -0,0 +1,2 @@
+[toolchain]
+channel = "nightly"