1 files changed, 21 insertions, 8 deletions
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/usefulness.rs b/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/usefulness.rs
index 1221327b9..c4d709a97 100644
--- a/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/usefulness.rs
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/usefulness.rs
@@ -277,7 +277,7 @@ use hir_def::{AdtId, DefWithBodyId, HasModule, ModuleId};
 use smallvec::{smallvec, SmallVec};
 use typed_arena::Arena;
 
-use crate::{db::HirDatabase, Ty, TyExt};
+use crate::{db::HirDatabase, inhabitedness::is_ty_uninhabited_from, Ty, TyExt};
 
 use super::deconstruct_pat::{Constructor, DeconstructedPat, Fields, SplitWildcard};
 
@@ -289,13 +289,27 @@ pub(crate) struct MatchCheckCtx<'a, 'p> {
     pub(crate) db: &'a dyn HirDatabase,
     /// Lowered patterns from arms plus generated by the check.
     pub(crate) pattern_arena: &'p Arena<DeconstructedPat<'p>>,
+    exhaustive_patterns: bool,
 }
 
 impl<'a, 'p> MatchCheckCtx<'a, 'p> {
-    pub(super) fn is_uninhabited(&self, _ty: &Ty) -> bool {
-        // FIXME(iDawer) implement exhaustive_patterns feature. More info in:
-        // Tracking issue for RFC 1872: exhaustive_patterns feature https://github.com/rust-lang/rust/issues/51085
-        false
+    pub(crate) fn new(
+        module: ModuleId,
+        body: DefWithBodyId,
+        db: &'a dyn HirDatabase,
+        pattern_arena: &'p Arena<DeconstructedPat<'p>>,
+    ) -> Self {
+        let def_map = db.crate_def_map(module.krate());
+        let exhaustive_patterns = def_map.is_unstable_feature_enabled("exhaustive_patterns");
+        Self { module, body, db, pattern_arena, exhaustive_patterns }
+    }
+
+    pub(super) fn is_uninhabited(&self, ty: &Ty) -> bool {
+        if self.feature_exhaustive_patterns() {
+            is_ty_uninhabited_from(ty, self.module, self.db)
+        } else {
+            false
+        }
     }
 
     /// Returns whether the given type is an enum from another crate declared `#[non_exhaustive]`.
@@ -311,10 +325,9 @@ impl<'a, 'p> MatchCheckCtx<'a, 'p> {
         }
     }
 
-    // Rust feature described as "Allows exhaustive pattern matching on types that contain uninhabited types."
+    // Rust's unstable feature described as "Allows exhaustive pattern matching on types that contain uninhabited types."
     pub(super) fn feature_exhaustive_patterns(&self) -> bool {
-        // FIXME see MatchCheckCtx::is_uninhabited
-        false
+        self.exhaustive_patterns
     }
 }