handle array pattern matching type inference

Author: JoshMcguigan

crates/ra_hir_ty/src/infer/pat.rs

@@ -12,7 +12,7 @@ use hir_expand::name::Name;
 use test_utils::tested_by;
 
 use super::{BindingMode, InferenceContext};
-use crate::{db::HirDatabase, utils::variant_data, Substs, Ty, TypeCtor, ApplicationTy};
+use crate::{db::HirDatabase, utils::variant_data, Substs, Ty, TypeCtor};
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn infer_tuple_struct_pat(
@@ -186,17 +186,21 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 return inner_ty;
             }
             Pat::Slice { prefix, slice: _slice, suffix } => {
-                let ty = if let Ty::Apply(ApplicationTy { ctor: TypeCtor::Slice, parameters }) = expected {
-                    for pat_id in prefix.iter().chain(suffix) {
-                        self.infer_pat(*pat_id, parameters.as_single(), default_bm);
-                    }
-
-                    parameters.as_single().clone()
-                } else {
-                    Ty::Unknown
+                let (container_ty, elem_ty) = match &expected {
+                    ty_app!(TypeCtor::Array, st) => {
+                        (TypeCtor::Array, st.as_single().clone())
+                    },
+                    ty_app!(TypeCtor::Slice, st) => {
+                        (TypeCtor::Slice, st.as_single().clone())
+                    },
+                    _ => (TypeCtor::Slice, Ty::Unknown),
                 };
 
-                Ty::apply_one(TypeCtor::Slice, ty)
+                for pat_id in prefix.iter().chain(suffix) {
+                    self.infer_pat(*pat_id, &elem_ty, default_bm);
+                }
+
+                Ty::apply_one(container_ty, elem_ty)
             }
             _ => Ty::Unknown,
         };

crates/ra_hir_ty/src/tests/patterns.rs

@@ -54,6 +54,7 @@ fn test(x: &i32) {
     [144; 145) 'e': {unknown}
     [158; 205) 'if let...     }': ()
     [165; 170) '[val]': [{unknown}]
+    [166; 169) 'val': {unknown}
     [173; 176) 'opt': [{unknown}]
     [177; 205) '{     ...     }': ()
     [191; 192) 'h': {unknown}
@@ -184,6 +185,46 @@ fn test() {
     );
 }
 
+#[test]
+fn infer_pattern_match_arr() {
+    assert_snapshot!(
+        infer(r#"
+fn test() {
+    let arr: [f64; 2] = [0.0, 1.0];
+    match arr {
+        [1.0, a] => {
+            a;
+        },
+        [b, c] => {
+            b;
+            c;
+        }
+    }
+}
+"#),
+    @r###"
+    [11; 180) '{     ...   } }': ()
+    [21; 24) 'arr': [f64; _]
+    [37; 47) '[0.0, 1.0]': [f64; _]
+    [38; 41) '0.0': f64
+    [43; 46) '1.0': f64
+    [53; 178) 'match ...     }': ()
+    [59; 62) 'arr': [f64; _]
+    [73; 81) '[1.0, a]': [f64; _]
+    [74; 77) '1.0': f64
+    [79; 80) 'a': f64
+    [85; 111) '{     ...     }': ()
+    [99; 100) 'a': f64
+    [121; 127) '[b, c]': [f64; _]
+    [122; 123) 'b': f64
+    [125; 126) 'c': f64
+    [131; 172) '{     ...     }': ()
+    [145; 146) 'b': f64
+    [160; 161) 'c': f64
+    "###
+    );
+}
+
 #[test]
 fn infer_adt_pattern() {
     assert_snapshot!(