From edb82bfb7654b882802446e20eac90a44e7bd991 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=A0t=C4=9Bp=C3=A1n=20Hor=C3=A1=C4=8Dek?=
 <xhorace2@fi.muni.cz>
Date: Sat, 7 May 2022 22:21:33 +0200
Subject: [PATCH] Make ValuePattern non-exhaustive
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Changes behaviour of PatternChecker so that ValuePattern does not cover
the entire type since it can catch only a single value.

Signed-off-by: Štěpán Horáček <xhorace2@fi.muni.cz>
---
 mypy/checkpattern.py                |  4 +++-
 test-data/unit/check-python310.test | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/mypy/checkpattern.py b/mypy/checkpattern.py
index 6a8a0196306c..978b03b342f5 100644
--- a/mypy/checkpattern.py
+++ b/mypy/checkpattern.py
@@ -23,7 +23,7 @@
 from mypy.typeops import try_getting_str_literals_from_type, make_simplified_union, \
     coerce_to_literal
 from mypy.types import (
-    ProperType, AnyType, TypeOfAny, Instance, Type, UninhabitedType, get_proper_type,
+    LiteralType, ProperType, AnyType, TypeOfAny, Instance, Type, UninhabitedType, get_proper_type,
     TypedDictType, TupleType, NoneType, UnionType
 )
 from mypy.typevars import fill_typevars
@@ -183,6 +183,8 @@ def visit_value_pattern(self, o: ValuePattern) -> PatternType:
             o,
             default=current_type
         )
+        if not isinstance(get_proper_type(narrowed_type), (LiteralType, UninhabitedType)):
+            return PatternType(narrowed_type, UnionType.make_union([narrowed_type, rest_type]), {})
         return PatternType(narrowed_type, rest_type, {})
 
     def visit_singleton_pattern(self, o: SingletonPattern) -> PatternType:
diff --git a/test-data/unit/check-python310.test b/test-data/unit/check-python310.test
index cb39a519a146..818981238b3b 100644
--- a/test-data/unit/check-python310.test
+++ b/test-data/unit/check-python310.test
@@ -1576,3 +1576,18 @@ def f(x: AST) -> None:
             reveal_type(b)  # N: Revealed type is "builtins.int"
             reveal_type(c)  # N: Revealed type is "builtins.str"
 [builtins fixtures/tuple.pyi]
+
+[case testMatchReachableDottedNames]
+# flags: --warn-unreachable
+class Consts:
+    BLANK = ""
+    SPECIAL = "asdf"
+
+def test_func(test_str: str) -> str:
+    match test_str:
+        case Consts.BLANK:
+            return "blank"
+        case Consts.SPECIAL:
+            return "special"
+        case _:
+            return "other"