Emit fatal on invalid const args with nested defs

compiler/rustc_ast_lowering/src/expr.rs

@@ -29,7 +29,7 @@ use super::{
 use crate::errors::{InvalidLegacyConstGenericArg, UseConstGenericArg, YieldInClosure};
 use crate::{AllowReturnTypeNotation, FnDeclKind, ImplTraitPosition, TryBlockScope};
 
-struct WillCreateDefIdsVisitor {}
+pub(super) struct WillCreateDefIdsVisitor;
 
 impl<'v> rustc_ast::visit::Visitor<'v> for WillCreateDefIdsVisitor {
     type Result = ControlFlow<Span>;
@@ -479,18 +479,18 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
                     DefPathData::LateAnonConst,
                     f.span,
                 );
-                let mut visitor = WillCreateDefIdsVisitor {};
-                let const_value = if let ControlFlow::Break(span) = visitor.visit_expr(&arg) {
-                    Box::new(Expr {
-                        id: self.next_node_id(),
-                        kind: ExprKind::Err(invalid_expr_error(self.tcx, span)),
-                        span: f.span,
-                        attrs: [].into(),
-                        tokens: None,
-                    })
-                } else {
-                    arg
-                };
+                let const_value =
+                    if let ControlFlow::Break(span) = WillCreateDefIdsVisitor.visit_expr(&arg) {
+                        Box::new(Expr {
+                            id: self.next_node_id(),
+                            kind: ExprKind::Err(invalid_expr_error(self.tcx, span)),
+                            span: f.span,
+                            attrs: [].into(),
+                            tokens: None,
+                        })
+                    } else {
+                        arg
+                    };
 
                 let anon_const = AnonConst {
                     id: node_id,

compiler/rustc_ast_lowering/src/lib.rs

@@ -39,6 +39,7 @@ use std::mem;
 use std::sync::Arc;
 
 use rustc_ast::node_id::NodeMap;
+use rustc_ast::visit::Visitor;
 use rustc_ast::{self as ast, *};
 use rustc_attr_parsing::{AttributeParser, Late, OmitDoc};
 use rustc_data_structures::fingerprint::Fingerprint;
@@ -2219,14 +2220,22 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
                 // since later compiler stages cannot handle them (and shouldn't need to be able to).
                 let default = default
                     .as_ref()
-                    .filter(|_| match source {
+                    .filter(|anon_const| match source {
                         hir::GenericParamSource::Generics => true,
                         hir::GenericParamSource::Binder => {
-                            self.dcx().emit_err(errors::GenericParamDefaultInBinder {
-                                span: param.span(),
-                            });
-
-                            false
+                            let err = errors::GenericParamDefaultInBinder { span: param.span() };
+                            if expr::WillCreateDefIdsVisitor
+                                .visit_expr(&anon_const.value)
+                                .is_break()
+                            {
+                                // FIXME(mgca): make this non-fatal once we have a better way
+                                // to handle nested items in anno const from binder
+                                // Issue: https://github.com/rust-lang/rust/issues/123629
+                                self.dcx().emit_fatal(err)
+                            } else {
+                                self.dcx().emit_err(err);
+                                false
+                            }
                         }
                     })
                     .map(|def| self.lower_anon_const_to_const_arg_and_alloc(def));
@@ -2563,12 +2572,17 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
         let span = self.lower_span(expr.span);
 
         let overly_complex_const = |this: &mut Self| {
-            let e = this.dcx().struct_span_err(
-                expr.span,
-                "complex const arguments must be placed inside of a `const` block",
-            );
+            let msg = "complex const arguments must be placed inside of a `const` block";
+            let e = if expr::WillCreateDefIdsVisitor.visit_expr(expr).is_break() {
+                // FIXME(mgca): make this non-fatal once we have a better way to handle
+                // nested items in const args
+                // Issue: https://github.com/rust-lang/rust/issues/154539
+                this.dcx().struct_span_fatal(expr.span, msg).emit()
+            } else {
+                this.dcx().struct_span_err(expr.span, msg).emit()
+            };
 
-            ConstArg { hir_id: this.next_id(), kind: hir::ConstArgKind::Error(e.emit()), span }
+            ConstArg { hir_id: this.next_id(), kind: hir::ConstArgKind::Error(e), span }
         };
 
         match &expr.kind {

tests/ui/const-generics/generic_const_exprs/bad-defaults-for-generic-param-in-binder-123629.rs

@@ -0,0 +1,12 @@
+#![feature(generic_assert)]
+
+fn foo()
+where
+    for<const N: usize = { assert!(u) }> ():,
+    //~^ ERROR cannot find value `u` in this scope
+    //~^^ ERROR only lifetime parameters can be used in this context
+    //~^^^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+{
+}
+
+fn main() {}

tests/ui/const-generics/generic_const_exprs/bad-defaults-for-generic-param-in-binder-123629.stderr

@@ -0,0 +1,26 @@
+error[E0425]: cannot find value `u` in this scope
+  --> $DIR/bad-defaults-for-generic-param-in-binder-123629.rs:5:36
+   |
+LL |     for<const N: usize = { assert!(u) }> ():,
+   |                                    ^ not found in this scope
+
+error[E0658]: only lifetime parameters can be used in this context
+  --> $DIR/bad-defaults-for-generic-param-in-binder-123629.rs:5:15
+   |
+LL |     for<const N: usize = { assert!(u) }> ():,
+   |               ^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = help: add `#![feature(non_lifetime_binders)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: defaults for generic parameters are not allowed in `for<...>` binders
+  --> $DIR/bad-defaults-for-generic-param-in-binder-123629.rs:5:9
+   |
+LL |     for<const N: usize = { assert!(u) }> ():,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0425, E0658.
+For more information about an error, try `rustc --explain E0425`.

tests/ui/const-generics/mgca/array-expr-complex.r1.stderr

@@ -0,0 +1,8 @@
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr-complex.rs:11:28
+   |
+LL |     takes_array::<{ [1, 2, 1 + 2] }>();
+   |                            ^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/mgca/array-expr-complex.r2.stderr

@@ -0,0 +1,8 @@
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr-complex.rs:14:21
+   |
+LL |     takes_array::<{ [X; 3] }>();
+   |                     ^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/mgca/array-expr-complex.r3.stderr

@@ -0,0 +1,8 @@
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr-complex.rs:17:21
+   |
+LL |     takes_array::<{ [0; Y] }>();
+   |                     ^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/mgca/array-expr-complex.rs

@@ -1,16 +1,21 @@
+//@ revisions: r1 r2 r3
+
 #![expect(incomplete_features)]
 #![feature(min_generic_const_args, adt_const_params)]
 
 fn takes_array<const A: [u32; 3]>() {}
 
 fn generic_caller<const X: u32, const Y: usize>() {
     // not supported yet
+    #[cfg(r1)]
     takes_array::<{ [1, 2, 1 + 2] }>();
-    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    //[r1]~^ ERROR: complex const arguments must be placed inside of a `const` block
+    #[cfg(r2)]
     takes_array::<{ [X; 3] }>();
-    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    //[r2]~^ ERROR: complex const arguments must be placed inside of a `const` block
+    #[cfg(r3)]
     takes_array::<{ [0; Y] }>();
-    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    //[r3]~^ ERROR: complex const arguments must be placed inside of a `const` block
 }
 
 fn main() {}

tests/ui/const-generics/mgca/bad-const-arg-fn-154539.rs

@@ -0,0 +1,12 @@
+#![feature(min_generic_const_args)]
+
+trait Iter<
+    const FN: fn() = {
+        || { //~ ERROR complex const arguments must be placed inside of a `const` block
+            use std::io::*;
+            write!(_, "")
+        }
+    },
+>
+{
+}

tests/ui/const-generics/mgca/bad-const-arg-fn-154539.stderr

@@ -0,0 +1,11 @@
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/bad-const-arg-fn-154539.rs:5:9
+   |
+LL | /         || {
+LL | |             use std::io::*;
+LL | |             write!(_, "")
+LL | |         }
+   | |_________^
+
+error: aborting due to 1 previous error
+

tests/ui/delegation/hir-crate-items-before-lowering-ices.ice_155125.stderr

@@ -0,0 +1,23 @@
+error[E0428]: the name `foo` is defined multiple times
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:13:17
+   |
+LL |                 fn foo() {}
+   |                 -------- previous definition of the value `foo` here
+LL |                 reuse foo;
+   |                 ^^^^^^^^^^ `foo` redefined here
+   |
+   = note: `foo` must be defined only once in the value namespace of this block
+
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:11:13
+   |
+LL | /             {
+LL | |                 fn foo() {}
+LL | |                 reuse foo;
+LL | |                 2
+LL | |             },
+   | |_____________^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0428`.

tests/ui/delegation/hir-crate-items-before-lowering-ices.ice_155127.stderr

@@ -0,0 +1,12 @@
+error: `#[deprecated]` attribute cannot be used on delegations
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:27:9
+   |
+LL |         #[deprecated]
+   |         ^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = help: `#[deprecated]` can be applied to associated consts, associated types, constants, crates, data types, enum variants, foreign statics, functions, inherent impl blocks, macro defs, modules, statics, struct fields, traits, type aliases, and use statements
+   = note: `#[deny(useless_deprecated)]` on by default
+
+error: aborting due to 1 previous error
+

tests/ui/delegation/hir-crate-items-before-lowering-ices.ice_155128.stderr

@@ -0,0 +1,24 @@
+error[E0061]: this function takes 0 arguments but 1 argument was supplied
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:37:11
+   |
+LL |       reuse a as b {
+   |  ___________^______-
+LL | |         fn foo<T>() {};
+LL | |         foo
+LL | |     }
+   | |_____- unexpected argument of type `fn() {foo::<_>}`
+   |
+note: function defined here
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:35:8
+   |
+LL |     fn a() {}
+   |        ^
+help: remove the extra argument
+   |
+LL -     reuse a as b {
+LL +     reuse {
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0061`.

tests/ui/delegation/hir-crate-items-before-lowering-ices.ice_155164.stderr

@@ -0,0 +1,13 @@
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:47:13
+   |
+LL | /             {
+LL | |
+LL | |                 struct W<I>;
+LL | |                 impl<I> W<I> {
+...  |
+LL | |             },
+   | |_____________^
+
+error: aborting due to 1 previous error
+

tests/ui/delegation/hir-crate-items-before-lowering-ices.ice_155202.stderr

@@ -0,0 +1,16 @@
+error[E0425]: cannot find value `async` in this scope
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:66:13
+   |
+LL |             async || {};
+   |             ^^^^^ not found in this scope
+
+error[E0308]: mismatched types
+  --> $DIR/hir-crate-items-before-lowering-ices.rs:66:22
+   |
+LL |             async || {};
+   |                      ^^ expected `bool`, found `()`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0308, E0425.
+For more information about an error, try `rustc --explain E0308`.