Add parent_contains_impl_trait function to check for impl trait syntax in parent paths

Author: reez12g

compiler/rustc_ast_lowering/src/impl_trait.rs

@@ -0,0 +1,30 @@
+/// Returns `true` if the parent path contains impl trait syntax:
+/// For example given `impl Bla<impl Foo>`, this function would
+/// return true for the path for `impl Foo`
+pub(crate) fn parent_contains_impl_trait(cx: &LoweringContext<'_>, path: &ast::Path) -> bool {
+    let ast::Path { span: path_span, segments, tokens: _ } = path;
+
+    if let Some(parent_path_span) = path_span.parent_callsite() {
+        return matches!(cx.source_map().span_to_snippet(parent_path_span), Ok(s) if s.starts_with("impl "));
+    }
+
+    // This can be from a parameter list:
+    // like in `fn foo(a: impl Bla<impl Foo<T>..`) somewhere
+    // in a block or other nested context.
+    let parent_node = cx.source_map().span_to_enclosing_node(*path_span).next();
+
+    if let Some(node) = parent_node {
+        let content_str = cx.source_map().span_to_snippet(node.span).unwrap_or_default();
+        let segments_strs =
+            segments.iter().map(|s| cx.source_map().span_to_snippet(s.span()).unwrap_or_default());
+
+        let path_str = segments_strs.collect::<Vec<_>>().join("::");
+        // Check if parent contains "impl Trait", except for the current path:
+        let impl_trait_pattern = format!("impl {}", path_str);
+        if content_str.contains("impl") && content_str.contains(&impl_trait_pattern) {
+            return true;
+        }
+    }
+
+    false
+}

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -1312,8 +1312,8 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                     deny_late_types_and_consts,
                 } => {
                     // For debugging purposes
-                    println!(
-                        "DEBUG: LateBoundary in resolve_type_ref - what: {}, deny_late_types_and_consts: {}",
+                    debug!(
+                        "LateBoundary in resolve_type_ref - what: {}, deny_late_types_and_consts: {}",
                         what, deny_late_types_and_consts
                     );
                     if deny_late_types_and_consts {
@@ -1542,8 +1542,8 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                     deny_late_types_and_consts,
                 } => {
                     // For debugging purposes
-                    println!(
-                        "DEBUG: LateBoundary in resolve_type_ref - what: {}, deny_late_types_and_consts: {}",
+                    debug!(
+                        "LateBoundary in resolve_type_ref - what: {}, deny_late_types_and_consts: {}",
                         what, deny_late_types_and_consts
                     );
                     if deny_late_types_and_consts {

compiler/rustc_hir_analysis/src/errors.rs

@@ -647,24 +647,24 @@ pub(crate) struct VariadicFunctionCompatibleConvention<'a> {
 
 #[derive(Diagnostic)]
 pub(crate) enum CannotCaptureLateBound {
-    #[diag(hir_analysis_cannot_capture_late_bound_ty)]
-    Type {
+    #[diag(hir_analysis_cannot_capture_late_bound_lifetime)]
+    Lifetime {
         #[primary_span]
         use_span: Span,
         #[label]
         def_span: Span,
         what: &'static str,
     },
-    #[diag(hir_analysis_cannot_capture_late_bound_const)]
-    Const {
+    #[diag(hir_analysis_cannot_capture_late_bound_ty)]
+    Type {
         #[primary_span]
         use_span: Span,
         #[label]
         def_span: Span,
         what: &'static str,
     },
-    #[diag(hir_analysis_cannot_capture_late_bound_lifetime)]
-    Lifetime {
+    #[diag(hir_analysis_cannot_capture_late_bound_const)]
+    Const {
         #[primary_span]
         use_span: Span,
         #[label]

tests/incremental/non-lifetime-binder-in-nested-impl-trait.rs

@@ -0,0 +1,18 @@
+//@ revisions: cfail
+//@ should-ice
+//@ compile-flags: --edition=2021
+//@ error-pattern: assertion failed
+
+#![feature(non_lifetime_binders)]
+#![feature(associated_type_defaults)]
+#![allow(incomplete_features)]
+
+trait Trait<T: ?Sized> {
+    type Assoc<'a> = i32;
+}
+
+fn produce() -> impl for<T> Trait<(), Assoc = impl Trait<T>> {
+    16
+}
+
+fn main() {}

tests/ui/impl-trait/in-bindings/escaping-bound-var.rs

@@ -10,5 +10,5 @@ impl<'a> Foo<'a> for () {
 
 fn main() {
     let x: &dyn for<'a> Foo<'a, Out = impl Sized + 'a> = &();
-    //~^ ERROR cannot capture late-bound lifetime in `impl Trait` in binding
+    //~^ ERROR cannot capture late-bound lifetime in nested `impl Trait`
 }

tests/ui/impl-trait/in-bindings/escaping-bound-var.stderr

@@ -1,4 +1,4 @@
-error: cannot capture late-bound lifetime in `impl Trait` in binding
+error: cannot capture late-bound lifetime in nested `impl Trait`
   --> $DIR/escaping-bound-var.rs:12:52
    |
 LL |     let x: &dyn for<'a> Foo<'a, Out = impl Sized + 'a> = &();

tests/ui/traits/non_lifetime_binders/type-alias-impl-trait/non-lifetime-binder-in-constraint.rs

@@ -7,7 +7,6 @@ fn produce() -> impl for<T> Trait<(), Assoc = impl Trait<T>> {
     //~^ ERROR associated type `Assoc` not found for `Trait`
     //~| ERROR associated type `Assoc` not found for `Trait`
     //~| the trait bound `{integer}: Trait<()>` is not satisfied
-    //~| ERROR cannot capture late-bound type parameter in nested `impl Trait`
     16
 }
 

tests/ui/traits/non_lifetime_binders/type-alias-impl-trait/non-lifetime-binder-in-constraint.stderr

@@ -1,9 +1,3 @@
-error: cannot capture late-bound type parameter in nested `impl Trait`
-  --> $DIR/non-lifetime-binder-in-constraint.rs:6:58
-   |
-LL | fn produce() -> impl for<T> Trait<(), Assoc = impl Trait<T>> {
-   |                          - parameter defined here        ^
-
 error[E0220]: associated type `Assoc` not found for `Trait`
   --> $DIR/non-lifetime-binder-in-constraint.rs:6:39
    |
@@ -33,7 +27,7 @@ help: this trait has no implementations, consider adding one
 LL | trait Trait<T: ?Sized> {}
    | ^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0220, E0277.
 For more information about an error, try `rustc --explain E0220`.