From 7d675eda80c5f1eb4a9fe7d374023d71721bf2f1 Mon Sep 17 00:00:00 2001
From: Dawer <7803845+iDawer@users.noreply.github.com>
Date: Mon, 10 May 2021 22:40:35 +0500
Subject: Don't panic on a pattern of unresolved ADT variant.

---
 crates/hir_ty/src/diagnostics/match_check.rs |  1 +
 crates/hir_ty/src/diagnostics/pattern.rs     | 63 ++++++----------------------
 2 files changed, 14 insertions(+), 50 deletions(-)

diff --git a/crates/hir_ty/src/diagnostics/match_check.rs b/crates/hir_ty/src/diagnostics/match_check.rs
index e8dd669bf..52e9a5b1b 100644
--- a/crates/hir_ty/src/diagnostics/match_check.rs
+++ b/crates/hir_ty/src/diagnostics/match_check.rs
@@ -1357,6 +1357,7 @@ fn enum_(never: Never) {
 }
 fn enum_ref(never: &Never) {
     match never {}
+        //^^^^^ Missing match arm
 }
 fn bang(never: !) {
     match never {}
diff --git a/crates/hir_ty/src/diagnostics/pattern.rs b/crates/hir_ty/src/diagnostics/pattern.rs
index 85c01b178..4f88dfe60 100644
--- a/crates/hir_ty/src/diagnostics/pattern.rs
+++ b/crates/hir_ty/src/diagnostics/pattern.rs
@@ -21,6 +21,7 @@ pub(crate) type PatId = Idx<Pat>;
 #[derive(Clone, Debug)]
 pub(crate) enum PatternError {
     Unimplemented,
+    UnresolvedVariant,
 }
 
 #[derive(Clone, Debug, PartialEq)]
@@ -103,6 +104,7 @@ impl<'a> PatCtxt<'a> {
 
     fn lower_pattern_unadjusted(&mut self, pat: hir_def::expr::PatId) -> Pat {
         let ty = &self.infer[pat];
+        let variant = self.infer.variant_resolution_for_pat(pat);
 
         let kind = match self.body[pat] {
             hir_def::expr::Pat::Wild => PatKind::Wild,
@@ -126,21 +128,14 @@ impl<'a> PatCtxt<'a> {
                 PatKind::Binding { subpattern: self.lower_opt_pattern(subpat) }
             }
 
-            hir_def::expr::Pat::TupleStruct { ref args, ellipsis, .. } => {
-                let variant_data = match self.infer.variant_resolution_for_pat(pat) {
-                    Some(variant_id) => variant_id.variant_data(self.db.upcast()),
-                    None => panic!("tuple struct pattern not applied to an ADT {:?}", ty),
-                };
-                let subpatterns =
-                    self.lower_tuple_subpats(args, variant_data.fields().len(), ellipsis);
+            hir_def::expr::Pat::TupleStruct { ref args, ellipsis, .. } if variant.is_some() => {
+                let expected_len = variant.unwrap().variant_data(self.db.upcast()).fields().len();
+                let subpatterns = self.lower_tuple_subpats(args, expected_len, ellipsis);
                 self.lower_variant_or_leaf(pat, ty, subpatterns)
             }
 
-            hir_def::expr::Pat::Record { ref args, .. } => {
-                let variant_data = match self.infer.variant_resolution_for_pat(pat) {
-                    Some(variant_id) => variant_id.variant_data(self.db.upcast()),
-                    None => panic!("record pattern not applied to an ADT {:?}", ty),
-                };
+            hir_def::expr::Pat::Record { ref args, .. } if variant.is_some() => {
+                let variant_data = variant.unwrap().variant_data(self.db.upcast());
                 let subpatterns = args
                     .iter()
                     .map(|field| FieldPat {
@@ -151,6 +146,10 @@ impl<'a> PatCtxt<'a> {
                     .collect();
                 self.lower_variant_or_leaf(pat, ty, subpatterns)
             }
+            hir_def::expr::Pat::TupleStruct { .. } | hir_def::expr::Pat::Record { .. } => {
+                self.errors.push(PatternError::UnresolvedVariant);
+                PatKind::Wild
+            }
 
             hir_def::expr::Pat::Or(ref pats) => PatKind::Or { pats: self.lower_patterns(pats) },
 
@@ -208,7 +207,7 @@ impl<'a> PatCtxt<'a> {
                 }
             }
             None => {
-                self.errors.push(PatternError::Unimplemented);
+                self.errors.push(PatternError::UnresolvedVariant);
                 PatKind::Wild
             }
         };
@@ -223,7 +222,7 @@ impl<'a> PatCtxt<'a> {
         match self.infer.variant_resolution_for_pat(pat) {
             Some(_) => pat_from_kind(self.lower_variant_or_leaf(pat, ty, Vec::new())),
             None => {
-                self.errors.push(PatternError::Unimplemented);
+                self.errors.push(PatternError::UnresolvedVariant);
                 pat_from_kind(PatKind::Wild)
             }
         }
@@ -510,40 +509,4 @@ fn main() {
 "#,
         );
     }
-
-    /// These failing tests are narrowed down from "hir_ty::diagnostics::match_check::tests"
-    // TODO fix
-    mod failing {
-        use super::*;
-
-        #[test]
-        fn never() {
-            check_diagnostics(
-                r#"
-enum Never {}
-
-fn enum_ref(never: &Never) {
-    match never {}
-}
-"#,
-            );
-        }
-
-        #[test]
-        fn unknown_type() {
-            check_diagnostics(
-                r#"
-enum Option<T> { Some(T), None }
-
-fn main() {
-    // `Never` is deliberately not defined so that it's an uninferred type.
-    match Option::<Never>::None {
-        None => {}
-        Some(never) => {}
-    }
-}
-"#,
-            );
-        }
-    }
 }
-- 
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