Delay is_intrinsic query until after we've determined the callee is a function

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -909,8 +909,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     return;
                 }
 
-                let is_intrinsic = tcx.is_intrinsic(callee);
-
                 if !tcx.is_const_fn_raw(callee) {
                     if !tcx.is_const_default_method(callee) {
                         // To get to here we must have already found a const impl for the
@@ -970,7 +968,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     // We do not use `const` modifiers for intrinsic "functions", as intrinsics are
                     // `extern` functions, and these have no way to get marked `const`. So instead we
                     // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const`
-                    if self.ccx.is_const_stable_const_fn() || is_intrinsic {
+                    if self.ccx.is_const_stable_const_fn() || tcx.is_intrinsic(callee) {
                         self.check_op(ops::FnCallUnstable(callee, None));
                         return;
                     }

src/test/ui/rfc-2632-const-trait-impl/issue-102985.rs

@@ -0,0 +1,11 @@
+#![feature(const_trait_impl)]
+
+struct Bug {
+    inner: [(); match || 1 {
+        n => n(),
+        //~^ ERROR the trait bound
+        //~| ERROR cannot call non-const fn `Bug::inner::{constant#0}::{closure#0}` in constants
+    }],
+}
+
+fn main() {}

src/test/ui/rfc-2632-const-trait-impl/issue-102985.stderr

@@ -0,0 +1,26 @@
+error[E0277]: the trait bound `[closure@$DIR/issue-102985.rs:4:23: 4:25]: ~const Fn<()>` is not satisfied
+  --> $DIR/issue-102985.rs:5:14
+   |
+LL |         n => n(),
+   |              ^^^ expected an `Fn<()>` closure, found `[closure@$DIR/issue-102985.rs:4:23: 4:25]`
+   |
+   = help: the trait `~const Fn<()>` is not implemented for closure `[closure@$DIR/issue-102985.rs:4:23: 4:25]`
+note: the trait `Fn<()>` is implemented for `[closure@$DIR/issue-102985.rs:4:23: 4:25]`, but that implementation is not `const`
+  --> $DIR/issue-102985.rs:5:14
+   |
+LL |         n => n(),
+   |              ^^^
+   = note: wrap the `[closure@$DIR/issue-102985.rs:4:23: 4:25]` in a closure with no arguments: `|| { /* code */ }`
+
+error[E0015]: cannot call non-const fn `Bug::inner::{constant#0}::{closure#0}` in constants
+  --> $DIR/issue-102985.rs:5:14
+   |
+LL |         n => n(),
+   |              ^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0015, E0277.
+For more information about an error, try `rustc --explain E0015`.