From 08ee5f5e63afe3e6a3d852932484c506d0eaee87 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sat, 18 Jan 2025 23:40:27 +0000
Subject: [PATCH] Do not ICE on default_field_value const with lifetimes

Fix #135649.
---
 .../rustc_borrowck/src/universal_regions.rs   |  6 ++++-
 .../do-not-ice-on-invalid-lifetime.rs         |  6 +++++
 .../do-not-ice-on-invalid-lifetime.stderr     | 23 +++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.rs
 create mode 100644 tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.stderr

diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 26af86c0cdd49..b25f449079a76 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/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)
diff --git a/tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.rs b/tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.rs
new file mode 100644
index 0000000000000..71d90ddd935ff
--- /dev/null
+++ b/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() {}
diff --git a/tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.stderr b/tests/ui/structs/default-field-values/do-not-ice-on-invalid-lifetime.stderr
new file mode 100644
index 0000000000000..20b9afe80cdc8
--- /dev/null
+++ b/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`.