[Result Builders] When inferring result builder attributes on value witnesses,

always map type parameters into context.

For result builders applied to function/variable/subscript bodies, the builder
type will only be used for calls to `buildBlock` and friends inside the body,
for which we always want the contextual type of the builder, not the interface
type.

Author: hborla

lib/Sema/TypeCheckRequestFunctions.cpp

@@ -298,11 +298,16 @@ static Type inferResultBuilderType(ValueDecl *decl)  {
           continue;
 
         // Substitute Self and associated type witnesses into the
-        // result builder type.
+        // result builder type. Then, map all type parameters from
+        // the conforming type into context. We don't want type
+        // parameters to appear in the result builder type, because
+        // the result builder type will only be used inside the body
+        // of this decl; it's not part of the interface type.
         auto subs = SubstitutionMap::getProtocolSubstitutions(
-            protocol, dc->getSelfTypeInContext(),
+            protocol, dc->getSelfInterfaceType(),
             ProtocolConformanceRef(conformance));
-        Type subResultBuilderType = resultBuilderType.subst(subs);
+        Type subResultBuilderType = dc->mapTypeIntoContext(
+            resultBuilderType.subst(subs));
 
         matches.push_back(
             Match::forConformance(

test/Constraints/result_builder_generic_infer.swift

@@ -17,15 +17,41 @@ enum Builder<T> {
 
 struct S {}
 
-// CHECK: struct_decl{{.*}}TestGenericBuilderInference
-struct TestGenericBuilderInference: P {
+// CHECK: struct_decl{{.*}}ProtocolSubstitution
+struct ProtocolSubstitution: P {
   typealias A = Int
 
   // CHECK: var_decl{{.*}}x1
   // CHECK: Builder.buildBlock{{.*}}(substitution_map generic_signature=<T> (substitution T -> Int))
   var x1: [S] { S() }
 
   // CHECK: var_decl{{.*}}x2
-  // CHECK: Builder.buildBlock{{.*}}(substitution_map generic_signature=<T> (substitution T -> TestGenericBuilderInference))
+  // CHECK: Builder.buildBlock{{.*}}(substitution_map generic_signature=<T> (substitution T -> ProtocolSubstitution))
+  var x2: [S] { S() }
+}
+
+// CHECK: struct_decl{{.*}}ArchetypeSubstitution
+struct ArchetypeSubstitution<A>: P {
+  // CHECK: var_decl{{.*}}x1
+  // CHECK: Builder.buildBlock{{.*}}(substitution_map generic_signature=<T> (substitution T -> A))
+  var x1: [S] { S() }
+
+  // CHECK: var_decl{{.*}}x2
+  // CHECK: Builder.buildBlock{{.*}}(substitution_map generic_signature=<T> (substitution T -> ArchetypeSubstitution<A>))
+  var x2: [S] { S() }
+}
+
+// CHECK: struct_decl{{.*}}ConcreteTypeSubstitution
+struct ConcreteTypeSubstitution<Value> {}
+
+extension ConcreteTypeSubstitution: P where Value == Int {
+  typealias A = Value
+
+  // CHECK: var_decl{{.*}}x1
+  // CHECK: Builder.buildBlock{{.*}}(substitution_map generic_signature=<T> (substitution T -> Int))
+  var x1: [S] { S() }
+
+  // CHECK: var_decl{{.*}}x2
+  // CHECK: Builder.buildBlock{{.*}}(substitution_map generic_signature=<T> (substitution T -> ConcreteTypeSubstitution<Int>))
   var x2: [S] { S() }
 }