Auto merge of #58098 - oli-obk:maybe_allow_internal_unstable, r=petrochenkov

Require a list of features in `#[allow_internal_unstable]`

The blanket-permission slip is not great and will likely give us trouble some point down the road.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/libsyntax_pos/lib.rs b/src/libsyntax_pos/lib.rs
index dbb4f8f8159..042005ea538 100644
--- a/src/libsyntax_pos/lib.rs
+++ b/src/libsyntax_pos/lib.rs
@@ -386,9 +386,13 @@ impl Span {
     /// Check if a span is "internal" to a macro in which `#[unstable]`
     /// items can be used (that is, a macro marked with
     /// `#[allow_internal_unstable]`).
-    pub fn allows_unstable(&self) -> bool {
+    pub fn allows_unstable(&self, feature: &str) -> bool {
         match self.ctxt().outer().expn_info() {
-            Some(info) => info.allow_internal_unstable,
+            Some(info) => info
+                .allow_internal_unstable
+                .map_or(false, |features| features.iter().any(|&f|
+                    f == feature || f == "allow_internal_unstable_backcompat_hack"
+                )),
             None => false,
         }
     }