Rollup merge of #126077 - oli-obk:revert_is_mir_available, r=BoxyUwU

Revert "Use the HIR instead of mir_keys for determining whether something will have a MIR body."

This reverts commit e5cba17.

turns out SMIR still needs it (model-checking/kani#3218). I'll create a full plan and MCP for what I intended this to be a part of. Maybe my plan is nonsense anyway.

compiler/rustc_mir_transform/src/lib.rs

@@ -211,7 +211,7 @@ fn remap_mir_for_const_eval_select<'tcx>(
 }
 
 fn is_mir_available(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
-    tcx.hir().maybe_body_owned_by(def_id).is_some()
+    tcx.mir_keys(()).contains(&def_id)
 }
 
 /// Finds the full set of `DefId`s within the current crate that have

tests/ui-fulldeps/stable-mir/check_instance.rs

@@ -33,7 +33,7 @@ fn test_stable_mir() -> ControlFlow<()> {
     // Get all items and split generic vs monomorphic items.
     let (generic, mono): (Vec<_>, Vec<_>) =
         items.into_iter().partition(|item| item.requires_monomorphization());
-    assert_eq!(mono.len(), 3, "Expected 2 mono functions and one constant");
+    assert_eq!(mono.len(), 4, "Expected 2 mono functions and one constant");
     assert_eq!(generic.len(), 2, "Expected 2 generic functions");
 
     // For all monomorphic items, get the correspondent instances.
@@ -57,8 +57,9 @@ fn test_body(body: mir::Body) {
     for term in body.blocks.iter().map(|bb| &bb.terminator) {
         match &term.kind {
             Call { func, .. } => {
-                let TyKind::RigidTy(ty) = func.ty(body.locals()).unwrap().kind() else { unreachable!
-                () };
+                let TyKind::RigidTy(ty) = func.ty(body.locals()).unwrap().kind() else {
+                    unreachable!()
+                };
                 let RigidTy::FnDef(def, args) = ty else { unreachable!() };
                 let instance = Instance::resolve(def, &args).unwrap();
                 let mangled_name = instance.mangled_name();
@@ -102,6 +103,9 @@ fn generate_input(path: &str) -> std::io::Result<()> {
     write!(
         file,
         r#"
+
+    struct Foo(());
+
     pub fn ty_param<T>(t: &T) -> T where T: Clone {{
         t.clone()
     }}
@@ -116,6 +120,7 @@ fn generate_input(path: &str) -> std::io::Result<()> {
     }}
 
     pub fn monomorphic() {{
+        Foo(());
         let v = vec![10];
         let dup = ty_param(&v);
         assert_eq!(v, dup);