Add some ASTGen tests

Author: Azoy

lib/Macros/Sources/SwiftMacros/DistributedResolvableMacro.swift

@@ -151,7 +151,11 @@ extension DistributedResolvableMacro {
             isGenericStub = false
 
           case .expr:
-            fatalError("Expression type not supported for distributed actor")
+            throw DiagnosticsError(
+              syntax: sameTypeReq.rightType,
+              message: "Expression type not supported for distributed actor",
+              id: .invalidGenericArgument
+            )
           }
 
         default:
@@ -277,6 +281,7 @@ struct DistributedResolvableMacroDiagnostic: DiagnosticMessage {
   enum ID: String {
     case invalidApplication = "invalid type"
     case missingInitializer = "missing initializer"
+    case invalidGenericArgument = "invalid generic argument"
   }
 
   var message: String

test/ASTGen/decls.swift

@@ -291,3 +291,12 @@ struct ValueStruct<let N: Int> {}
 func genericTest1<T>(_: T) {}
 func genericTest2<each T>(_: repeat each T) {}
 func genericTest4<let T: Int>(_: ValueStruct<T>) {}
+
+func concreteValueTest1(_: ValueStruct<123>) {}
+func concreteValueTest2(_: ValueStruct<-123>) {}
+
+extension ValueStruct where N == 123 {}
+extension ValueStruct where 123 == N {}
+extension ValueStruct where N == -123 {}
+extension ValueStruct where -123 == N {}
+