Rollup merge of rust-lang#135711 - estebank:issue-135649, r=davidtwco

Do not ICE on default_field_value const with lifetimes

`#![feature(default_field_values)]` uses a `const` body that should be treated as inline `const`s, but is actually being detected otherwise. This is similar to the situation in rust-lang#78174, so we take the same solution: we check if the const actually comes from a field, and if it does, we use that logic to get the appropriate lifetimes and not ICE during borrowck.

Fix rust-lang#135649.

Author: matthiaskrgr

compiler/rustc_borrowck/src/universal_regions.rs

@@ -21,6 +21,7 @@ use std::iter;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::Diag;
 use rustc_hir::BodyOwnerKind;
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_index::IndexVec;
@@ -603,7 +604,10 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
 
             BodyOwnerKind::Const { .. } | BodyOwnerKind::Static(..) => {
                 let identity_args = GenericArgs::identity_for_item(tcx, typeck_root_def_id);
-                if self.mir_def.to_def_id() == typeck_root_def_id {
+                if self.mir_def.to_def_id() == typeck_root_def_id
+                    // Do not ICE when checking default_field_values consts with lifetimes (#135649)
+                    && DefKind::Field != tcx.def_kind(tcx.parent(typeck_root_def_id))
+                {
                     let args =
                         self.infcx.replace_free_regions_with_nll_infer_vars(FR, identity_args);
                     DefiningTy::Const(self.mir_def.to_def_id(), args)

tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.rs

@@ -0,0 +1,6 @@
+#![feature(default_field_values)]
+struct A<'a> { //~ ERROR lifetime parameter `'a` is never used
+    x: Vec<A> = Vec::new(), //~ ERROR missing lifetime specifier
+}
+
+fn main() {}

tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.stderr

@@ -0,0 +1,23 @@
+error[E0106]: missing lifetime specifier
+  --> $DIR/do-not-ice-on-invalid-lifetime.rs:3:12
+   |
+LL |     x: Vec<A> = Vec::new(),
+   |            ^ expected named lifetime parameter
+   |
+help: consider using the `'a` lifetime
+   |
+LL |     x: Vec<A<'a>> = Vec::new(),
+   |             ++++
+
+error[E0392]: lifetime parameter `'a` is never used
+  --> $DIR/do-not-ice-on-invalid-lifetime.rs:2:10
+   |
+LL | struct A<'a> {
+   |          ^^ unused lifetime parameter
+   |
+   = help: consider removing `'a`, referring to it in a field, or using a marker such as `PhantomData`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0106, E0392.
+For more information about an error, try `rustc --explain E0106`.