Skip match diagnostics for partially unknown types

Author: lnicola

crates/hir-ty/src/diagnostics/expr.rs

@@ -182,7 +182,7 @@ impl ExprValidator {
         db: &dyn HirDatabase,
     ) {
         let scrut_ty = &self.infer[scrutinee_expr];
-        if scrut_ty.is_unknown() {
+        if scrut_ty.contains_unknown() {
             return;
         }
 
@@ -267,6 +267,9 @@ impl ExprValidator {
             };
             let Some(initializer) = initializer else { continue };
             let ty = &self.infer[initializer];
+            if ty.contains_unknown() {
+                continue;
+            }
 
             let mut have_errors = false;
             let deconstructed_pat = self.lower_pattern(&cx, pat, db, &mut have_errors);

crates/ide-diagnostics/src/handlers/missing_match_arms.rs

@@ -597,28 +597,38 @@ fn bang(never: !) {
 
     #[test]
     fn unknown_type() {
-        cov_mark::check_count!(validate_match_bailed_out, 1);
-
-        check_diagnostics(
+        check_diagnostics_no_bails(
             r#"
 enum Option<T> { Some(T), None }
 
 #[allow(unused)]
 fn main() {
     // `Never` is deliberately not defined so that it's an uninferred type.
+    // We ignore these to avoid triggering bugs in the analysis.
     match Option::<Never>::None {
         None => (),
         Some(never) => match never {},
     }
     match Option::<Never>::None {
-        //^^^^^^^^^^^^^^^^^^^^^ error: missing match arm: `None` not covered
         Option::Some(_never) => {},
     }
 }
 "#,
         );
     }
 
+    #[test]
+    fn arity_mismatch_issue_16746() {
+        check_diagnostics_with_disabled(
+            r#"
+fn main() {
+    let (a, ) = (0, 0);
+}
+"#,
+            &["E0308"],
+        );
+    }
+
     #[test]
     fn tuple_of_bools_with_ellipsis_at_end_missing_arm() {
         check_diagnostics_no_bails(