Warn when `generic_associated_types` feature gate is enabled

1 files changed, 15 insertions, 0 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 56e69b9df9e..98fbbe4bdef 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -1920,6 +1920,11 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
         err.emit();
     }
 
+    // Some features are known to be incomplete and using them is likely to have
+    // unanticipated results, such as compiler crashes. We warn the user about these
+    // to alert them.
+    let incomplete_features = ["generic_associated_types"];
+
     let mut features = Features::new();
     let mut edition_enabled_features = FxHashMap();
 
@@ -1955,6 +1960,16 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
                 continue
             };
 
+            if incomplete_features.iter().any(|f| *f == name.as_str()) {
+                span_handler.struct_span_warn(
+                    mi.span,
+                    &format!(
+                        "the feature `{}` is incomplete and may cause the compiler to crash",
+                        name
+                    )
+                ).emit();
+            }
+
             if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
                 if *edition <= crate_edition {
                     continue