Rollup merge of rust-lang#147642 - camelid:misc-const-fixes, r=BoxyUwU

Miscellaneous const-generics-related fixes

Fixes rust-lang#129209.
Fixes rust-lang#131295.
Fixes rust-lang#139738.

Author: Zalathar

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -77,20 +77,6 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
         // stable enough and does not need a feature gate anymore.
         Node::AnonConst(_) => {
             let parent_did = tcx.parent(def_id.to_def_id());
-
-            // We don't do this unconditionally because the `DefId` parent of an anon const
-            // might be an implicitly created closure during `async fn` desugaring. This would
-            // have the wrong generics.
-            //
-            // i.e. `async fn foo<'a>() { let a = [(); { 1 + 2 }]; bar().await() }`
-            // would implicitly have a closure in its body that would be the parent of
-            // the `{ 1 + 2 }` anon const. This closure's generics is simply a witness
-            // instead of `['a]`.
-            let parent_did = if let DefKind::AnonConst = tcx.def_kind(parent_did) {
-                parent_did
-            } else {
-                tcx.hir_get_parent_item(hir_id).to_def_id()
-            };
             debug!(?parent_did);
 
             let mut in_param_ty = false;

compiler/rustc_mir_build/src/thir/constant.rs

@@ -58,8 +58,12 @@ pub(crate) fn lit_to_const<'tcx>(
         (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
             ty::ValTree::from_scalar_int(tcx, n.into())
         }
-        (ast::LitKind::CStr(byte_sym, _), ty::Ref(_, inner_ty, _)) if matches!(inner_ty.kind(), ty::Adt(def, _) if tcx.is_lang_item(def.did(), LangItem::CStr)) => {
-            ty::ValTree::from_raw_bytes(tcx, byte_sym.as_byte_str())
+        (ast::LitKind::CStr(byte_sym, _), ty::Ref(_, inner_ty, _)) if matches!(inner_ty.kind(), ty::Adt(def, _) if tcx.is_lang_item(def.did(), LangItem::CStr)) =>
+        {
+            // A CStr is a newtype around a byte slice, so we create the inner slice here.
+            // We need a branch for each "level" of the data structure.
+            let bytes = ty::ValTree::from_raw_bytes(tcx, byte_sym.as_byte_str());
+            ty::ValTree::from_branches(tcx, [bytes])
         }
         (ast::LitKind::Int(n, _), ty::Uint(ui)) if !neg => {
             let scalar_int = trunc(n.get(), *ui);

tests/crashes/129209.rs

@@ -0,0 +1,6 @@
+impl<const A: i32 = { || [0; B] }> Tr {}
+//~^ ERROR cannot find type `Tr`
+//~| ERROR cannot find value `B`
+//~| ERROR defaults for generic parameters are not allowed here
+
+fn main() {}

tests/crashes/131295.rs

@@ -0,0 +1,24 @@
+error[E0412]: cannot find type `Tr` in this scope
+  --> $DIR/parent_generics_of_nested_in_default.rs:1:36
+   |
+LL | impl<const A: i32 = { || [0; B] }> Tr {}
+   |                                    ^^ not found in this scope
+
+error[E0425]: cannot find value `B` in this scope
+  --> $DIR/parent_generics_of_nested_in_default.rs:1:30
+   |
+LL | impl<const A: i32 = { || [0; B] }> Tr {}
+   |            -                 ^ help: a const parameter with a similar name exists: `A`
+   |            |
+   |            similarly named const parameter `A` defined here
+
+error: defaults for generic parameters are not allowed here
+  --> $DIR/parent_generics_of_nested_in_default.rs:1:6
+   |
+LL | impl<const A: i32 = { || [0; B] }> Tr {}
+   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0412, E0425.
+For more information about an error, try `rustc --explain E0412`.