don't supply generics to AnonConsts in param lists

src/librustc_typeck/collect.rs

@@ -29,7 +29,7 @@ use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_hir::weak_lang_items;
-use rustc_hir::{GenericParamKind, Node};
+use rustc_hir::{GenericParamKind, HirId, Node};
 use rustc_middle::hir::map::blocks::FnLikeNode;
 use rustc_middle::hir::map::Map;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
@@ -1155,6 +1155,35 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
     }
 }
 
+struct AnonConstInParamListDetector {
+    in_param_list: bool,
+    found_anon_const_in_list: bool,
+    ct: HirId,
+}
+
+impl<'v> Visitor<'v> for AnonConstInParamListDetector {
+    type Map = intravisit::ErasedMap<'v>;
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+
+    fn visit_generic_param(&mut self, p: &'v hir::GenericParam<'v>) {
+        let prev = self.in_param_list;
+        self.in_param_list = true;
+        intravisit::walk_generic_param(self, p);
+        self.in_param_list = prev;
+    }
+
+    fn visit_anon_const(&mut self, c: &'v hir::AnonConst) {
+        if self.in_param_list && self.ct == c.hir_id {
+            self.found_anon_const_in_list = true;
+        } else {
+            intravisit::walk_anon_const(self, c)
+        }
+    }
+}
+
 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
     use rustc_hir::*;
 
@@ -1176,10 +1205,32 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
             let parent_id = tcx.hir().get_parent_item(hir_id);
             let parent_def_id = tcx.hir().local_def_id(parent_id);
 
-            // HACK(eddyb) this provides the correct generics when
+            let mut in_param_list = false;
-            // `feature(const_generics)` is enabled, so that const expressions
+            for (_parent, node) in tcx.hir().parent_iter(hir_id) {
-            // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
+                if let Some(generics) = node.generics() {
-            if tcx.lazy_normalization() {
+                    let mut visitor = AnonConstInParamListDetector {
+                        in_param_list: false,
+                        found_anon_const_in_list: false,
+                        ct: hir_id,
+                    };
+
+                    visitor.visit_generics(generics);
+                    in_param_list = visitor.found_anon_const_in_list;
+                    break;
+                }
+            }
+
+            if in_param_list {
+                // We do not allow generic parameters in anon consts if we are inside
+                // of a param list.
+                //
+                // This affects both default type bindings, e.g. `struct<T, U = [u8; std::mem::size_of::<T>()]>(T, U)`,
+                // and the types of const parameters, e.g. `struct V<const N: usize, const M: [u8; N]>();`.
+                None
+            } else if tcx.lazy_normalization() {
+                // HACK(eddyb) this provides the correct generics when
+                // `feature(const_generics)` is enabled, so that const expressions
+                // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
                 Some(parent_def_id.to_def_id())
             } else {
                 let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));

src/test/ui/const-generics/const-param-type-depends-on-const-param.rs

@@ -8,10 +8,8 @@
 
 pub struct Dependent<const N: usize, const X: [u8; N]>([(); N]);
 //~^ ERROR: the type of const parameters must not depend on other generic parameters
-//~| ERROR: cycle detected when computing type of `Dependent::X`
 
 pub struct SelfDependent<const N: [u8; N]>;
 //~^ ERROR: the type of const parameters must not depend on other generic parameters
-//~| ERROR: cycle detected when computing type of `SelfDependent::N`
 
 fn main() {}

src/test/ui/const-generics/const-param-type-depends-on-const-param.stderr

@@ -4,8 +4,8 @@ error[E0770]: the type of const parameters must not depend on other generic para
 LL | pub struct Dependent<const N: usize, const X: [u8; N]>([(); N]);
    |                                                    ^ const parameters must have a concrete type
 
-error[E0769]: the type of const parameters must not depend on other generic parameters
+error[E0770]: the type of const parameters must not depend on other generic parameters
-  --> $DIR/const-param-type-depends-on-const-param.rs:13:40
+  --> $DIR/const-param-type-depends-on-const-param.rs:12:40
    |
 LL | pub struct SelfDependent<const N: [u8; N]>;
    |                                        ^ const parameters must have a concrete type
@@ -19,32 +19,5 @@ LL | #![feature(const_generics)]
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
 
-error[E0391]: cycle detected when computing type of `Dependent::X`
+error: aborting due to 2 previous errors; 1 warning emitted
-  --> $DIR/const-param-type-depends-on-const-param.rs:9:44
-   |
-LL | pub struct Dependent<const N: usize, const X: [u8; N]>([(); N]);
-   |                                            ^
-   |
-   = note: ...which again requires computing type of `Dependent::X`, completing the cycle
-note: cycle used when computing type of `Dependent`
-  --> $DIR/const-param-type-depends-on-const-param.rs:9:1
-   |
-LL | pub struct Dependent<const N: usize, const X: [u8; N]>([(); N]);
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0391]: cycle detected when computing type of `SelfDependent::N`
-  --> $DIR/const-param-type-depends-on-const-param.rs:13:32
-   |
-LL | pub struct SelfDependent<const N: [u8; N]>;
-   |                                ^
-   |
-   = note: ...which again requires computing type of `SelfDependent::N`, completing the cycle
-note: cycle used when computing type of `SelfDependent`
-  --> $DIR/const-param-type-depends-on-const-param.rs:13:1
-   |
-LL | pub struct SelfDependent<const N: [u8; N]>;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 4 previous errors; 1 warning emitted
-
-For more information about this error, try `rustc --explain E0391`.

src/test/ui/const-generics/issues/issue-74101.rs

@@ -0,0 +1,9 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+fn test<const N: [u8; 1 + 2]>() {}
+
+struct Foo<const N: [u8; 1 + 2]>;
+
+fn main() {}