Rollup merge of #105339 - BoxyUwU:wf_ct_kind_expr, r=TaKO8Ki

support `ConstKind::Expr` in `is_const_evaluatable` and `WfPredicates::compute`

Fixes #105205

Currently we haven't implemented a way to evaluate `ConstKind::Expr(Expr::Binop(Add, 1, 2))` so I just left that with a `FIXME` and a `delay_span_bug` since I have no idea how to do that and it would make this a much larger (and more complicated) PR :P

2 files changed, 42 insertions, 0 deletions

diff --git a/src/test/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.rs b/src/test/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.rs
new file mode 100644
index 00000000000..6093fc70b16
--- /dev/null
+++ b/src/test/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.rs
@@ -0,0 +1,22 @@
+#![feature(generic_const_exprs, generic_arg_infer)]
+#![allow(incomplete_features)]
+
+// minimized repro for #105205
+//
+// the `foo::<_, L>` call results in a `WellFormed(_)` obligation and a
+// `ConstEvaluatable(Unevaluated(_ + 1 + L))` obligation. Attempting to fulfill the latter
+// unifies the `_` with `Expr(L - 1)` from the paramenv which turns the `WellFormed`
+// obligation into `WellFormed(Expr(L - 1))`
+
+fn foo<const N: usize, const M: usize>(_: [(); N + 1 + M]) {}
+
+fn ice<const L: usize>()
+where
+    [(); (L - 1) + 1 + L]:,
+{
+    foo::<_, L>([(); L + 1 + L]);
+    //~^ ERROR: mismatched types
+    //~^^ ERROR: unconstrained generic constant
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.stderr b/src/test/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.stderr
new file mode 100644
index 00000000000..da5194696e6
--- /dev/null
+++ b/src/test/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.stderr
@@ -0,0 +1,20 @@
+error[E0308]: mismatched types
+  --> $DIR/wf_obligation.rs:17:17
+   |
+LL |     foo::<_, L>([(); L + 1 + L]);
+   |                 ^^^^^^^^^^^^^^^ expected `N + 1 + M`, found `L + 1 + L`
+   |
+   = note: expected constant `N + 1 + M`
+              found constant `L + 1 + L`
+
+error: unconstrained generic constant
+  --> $DIR/wf_obligation.rs:17:22
+   |
+LL |     foo::<_, L>([(); L + 1 + L]);
+   |                      ^^^^^^^^^
+   |
+   = help: try adding a `where` bound using this expression: `where [(); L + 1 + L]:`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.