From 30642927b077eb994f561b6576e9c61e8f65ffb0 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard@metafoo.co.uk>
Date: Wed, 18 May 2022 16:27:58 -0700
Subject: [PATCH] Fix type of a choice value to be the choice type, not the
 type-of-choice type. (#1276)

---
 explorer/interpreter/type_checker.cpp        | 16 +++++++---------
 explorer/testdata/basic_syntax/choice.carbon |  6 +++---
 2 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/explorer/interpreter/type_checker.cpp b/explorer/interpreter/type_checker.cpp
index bb93d554165f..2a52ce39cb0a 100644
--- a/explorer/interpreter/type_checker.cpp
+++ b/explorer/interpreter/type_checker.cpp
@@ -952,8 +952,7 @@ auto TypeChecker::TypeCheckExp(Nonnull<Expression*> e,
                    << " does not have a field named " << access.field();
           }
           access.set_static_type(arena_->New<FunctionType>(
-              *parameter_types, llvm::None, &aggregate_type, llvm::None,
-              llvm::None));
+              *parameter_types, llvm::None, &choice, llvm::None, llvm::None));
           access.set_value_category(ValueCategory::Let);
           return Success();
         }
@@ -1740,17 +1739,16 @@ auto TypeChecker::TypeCheckPattern(
         return CompilationError(alternative.source_loc())
                << "alternative pattern does not name a choice type.";
       }
-      if (expected) {
-        CARBON_RETURN_IF_ERROR(ExpectExactType(
-            alternative.source_loc(), "alternative pattern", *expected,
-            &alternative.choice_type().static_type()));
-      }
       const ChoiceType& choice_type =
           cast<TypeOfChoiceType>(alternative.choice_type().static_type())
               .choice_type();
+      if (expected) {
+        CARBON_RETURN_IF_ERROR(ExpectType(alternative.source_loc(),
+                                          "alternative pattern", &choice_type,
+                                          *expected));
+      }
       std::optional<Nonnull<const Value*>> parameter_types =
-          cast<ChoiceType>(choice_type)
-              .FindAlternative(alternative.alternative_name());
+          choice_type.FindAlternative(alternative.alternative_name());
       if (parameter_types == std::nullopt) {
         return CompilationError(alternative.source_loc())
                << "'" << alternative.alternative_name()
diff --git a/explorer/testdata/basic_syntax/choice.carbon b/explorer/testdata/basic_syntax/choice.carbon
index 4ee9c3ae32ef..0a0a5ab8e484 100644
--- a/explorer/testdata/basic_syntax/choice.carbon
+++ b/explorer/testdata/basic_syntax/choice.carbon
@@ -18,9 +18,9 @@ choice Ints {
 }
 
 fn Main() -> i32 {
-  var x: auto = Ints.None();
-  var y: auto = Ints.One(42);
-  var n: auto = 0;
+  var x: Ints = Ints.None();
+  var y: Ints = Ints.One(42);
+  var n: i32 = 0;
   match (y) {
     case Ints.None =>
       n = n + 2;