Remove default Never body, refine error messages

Resolve #110.

Sources/Tokamak/Views/AnyView.swift

@@ -55,6 +55,10 @@ public struct AnyView: View {
       }
     }
   }
+
+  public var body: Never {
+    neverBody("AnyView")
+  }
 }
 
 public func mapAnyView<T, V>(_ anyView: AnyView, transform: (V) -> T) -> T? {

Sources/Tokamak/Views/Button.swift

@@ -25,6 +25,10 @@ public struct Button<Label>: View where Label: View {
     self.label = label()
     self.action = action
   }
+
+  public var body: Never {
+    neverBody("Text")
+  }
 }
 
 extension Button where Label == Text {

Sources/Tokamak/Views/HStack.swift

@@ -35,6 +35,10 @@ public struct HStack<Content>: View where Content: View {
     self.spacing = spacing
     self.content = content()
   }
+
+  public var body: Never {
+    neverBody("HStack")
+  }
 }
 
 extension HStack: ParentView {

Sources/Tokamak/Views/Text.swift

@@ -25,6 +25,10 @@ public struct Text: View {
   public init<S>(_ content: S) where S: StringProtocol {
     self.content = String(content)
   }
+
+  public var body: Never {
+    neverBody("Text")
+  }
 }
 
 public func textContent(_ text: Text) -> String {

Sources/Tokamak/Views/TupleView.swift

@@ -16,6 +16,10 @@
 //
 
 public struct TupleView<T>: View {
+  public var body: Never {
+    neverBody("TupleView")
+  }
+
   public let value: T
 
   // FIXME: should not be public

Sources/Tokamak/Views/VStack.swift

@@ -32,6 +32,10 @@ public struct VStack<Content>: View where Content: View {
     self.spacing = spacing
     self.content = content()
   }
+
+  public var body: Never {
+    neverBody("VStack")
+  }
 }
 
 extension VStack: ParentView {

Sources/Tokamak/Views/View.swift

@@ -22,11 +22,9 @@ public protocol View {
 }
 
 extension Never: View {
-  public typealias Body = Never
-}
-
-public extension View where Body == Never {
-  var body: Never { fatalError() }
+  public var body: Never {
+    neverBody("Never")
+  }
 }
 
 /// A `View` type that renders with subviews, usually specified in the `Content` type argument
@@ -40,3 +38,8 @@ protocol GroupView: ParentView {}
 public protocol ViewDeferredToRenderer {
   var deferredBody: AnyView { get }
 }
+
+/// Calls `fatalError` with an explanation that a given `type` is a primitive `View`
+public func neverBody(_ type: String) -> Never {
+  fatalError("\(type) is a primitive `View`, you're not supposed to access its `body`.")
+}

Sources/Tokamak/Views/ViewBuilder.swift

@@ -17,13 +17,21 @@
 
 public struct EmptyView: View {
   @inlinable public init() {}
+
+  public var body: Never {
+    neverBody("EmptyView")
+  }
 }
 
 // swiftlint:disable:next type_name
 public enum _ConditionalContent<TrueBranch, FalseBranch>: View
   where TrueBranch: View, FalseBranch: View {
   case trueBranch(TrueBranch)
   case falseBranch(FalseBranch)
+
+  public var body: Never {
+    neverBody("_ConditionalContent")
+  }
 }
 
 @_functionBuilder public struct ViewBuilder {

Sources/TokamakDOM/Views/HTML.swift

@@ -68,6 +68,10 @@ public struct HTML<Content>: View, AnyHTML where Content: View {
   }
 
   var innerHTML: String? { nil }
+
+  public var body: Never {
+    neverBody("HTML")
+  }
 }
 
 extension HTML where Content == EmptyView {