From 540d5f41f155bee7e8712e3abe8e88d896d86b41 Mon Sep 17 00:00:00 2001
From: mejrs <59372212+mejrs@users.noreply.github.com>
Date: Mon, 2 Nov 2026 21:39:32 +0100
Subject: [PATCH] declare_tool_lint: allow use without `default_field_values`
 feature

---
 compiler/rustc_hir_typeck/src/expr.rs                     | 4 +++-
 compiler/rustc_lint_defs/src/lib.rs                       | 3 +++
 .../default-field-values/allow_internal_unstable_user.rs  | 8 ++++++++
 .../auxiliary/allow_internal_unstable.rs                  | 8 ++++++++
 4 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/structs/default-field-values/allow_internal_unstable_user.rs
 create mode 100644 tests/ui/structs/default-field-values/auxiliary/allow_internal_unstable.rs

diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 39b4b8c1417d7..fe36aa95479f4 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -2055,7 +2055,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         }
                     }
                 }
-                if !self.tcx.features().default_field_values() {
+                if !(self.tcx.features().default_field_values()
+                    || span.allows_unstable(sym::default_field_values))
+                {
                     let sugg = self.tcx.crate_level_attribute_injection_span();
                     self.dcx().emit_err(BaseExpressionDoubleDot {
                         span: span.shrink_to_hi(),
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index 5e7b417ef68a4..956975536c424 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -1,4 +1,6 @@
 // tidy-alphabetical-start
+#![allow(internal_features)]
+#![feature(allow_internal_unstable)]
 #![feature(default_field_values)]
 // tidy-alphabetical-end
 
@@ -698,6 +700,7 @@ macro_rules! declare_lint {
 }
 
 #[macro_export]
+#[allow_internal_unstable(default_field_values)]
 macro_rules! declare_tool_lint {
     (
         $(#[$attr:meta])* $vis:vis $tool:ident ::$NAME:ident, $Level: ident, $desc: expr
diff --git a/tests/ui/structs/default-field-values/allow_internal_unstable_user.rs b/tests/ui/structs/default-field-values/allow_internal_unstable_user.rs
new file mode 100644
index 0000000000000..b9445c2491f72
--- /dev/null
+++ b/tests/ui/structs/default-field-values/allow_internal_unstable_user.rs
@@ -0,0 +1,8 @@
+//@check-pass
+//@aux-build:allow_internal_unstable.rs
+
+extern crate allow_internal_unstable;
+
+allow_internal_unstable::foo!();
+
+fn main(){}
diff --git a/tests/ui/structs/default-field-values/auxiliary/allow_internal_unstable.rs b/tests/ui/structs/default-field-values/auxiliary/allow_internal_unstable.rs
new file mode 100644
index 0000000000000..3fae6565fad05
--- /dev/null
+++ b/tests/ui/structs/default-field-values/auxiliary/allow_internal_unstable.rs
@@ -0,0 +1,8 @@
+#![allow(internal_features)]
+#![feature(allow_internal_unstable)]
+
+#[macro_export]
+#[allow_internal_unstable(default_field_values)]
+macro_rules! foo {
+    () => { fn foo() { struct Foo {x: usize = 0, } Foo {..}; } };
+}