From 523426657dc402b1c629f63a2c9f9df5c356a7ce Mon Sep 17 00:00:00 2001
From: Max Desiatov <max@desiatov.com>
Date: Mon, 22 Jun 2020 10:18:47 +0100
Subject: [PATCH] Remove default `Never` body, refine error messages

Resolve #110.
---
 Sources/Tokamak/Views/AnyView.swift     |  4 ++++
 Sources/Tokamak/Views/Button.swift      |  4 ++++
 Sources/Tokamak/Views/HStack.swift      |  4 ++++
 Sources/Tokamak/Views/Text.swift        |  4 ++++
 Sources/Tokamak/Views/TupleView.swift   |  4 ++++
 Sources/Tokamak/Views/VStack.swift      |  4 ++++
 Sources/Tokamak/Views/View.swift        | 13 ++++++++-----
 Sources/Tokamak/Views/ViewBuilder.swift |  8 ++++++++
 Sources/TokamakDOM/Views/HTML.swift     |  4 ++++
 9 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/Sources/Tokamak/Views/AnyView.swift b/Sources/Tokamak/Views/AnyView.swift
index 5ed6762e1..d3e5af6f1 100644
--- a/Sources/Tokamak/Views/AnyView.swift
+++ b/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? {
diff --git a/Sources/Tokamak/Views/Button.swift b/Sources/Tokamak/Views/Button.swift
index 39ad366d2..17ec6c58c 100644
--- a/Sources/Tokamak/Views/Button.swift
+++ b/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 {
diff --git a/Sources/Tokamak/Views/HStack.swift b/Sources/Tokamak/Views/HStack.swift
index 540d5b676..83769f2b5 100644
--- a/Sources/Tokamak/Views/HStack.swift
+++ b/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 {
diff --git a/Sources/Tokamak/Views/Text.swift b/Sources/Tokamak/Views/Text.swift
index 346e9e95e..f1c0522ce 100644
--- a/Sources/Tokamak/Views/Text.swift
+++ b/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 {
diff --git a/Sources/Tokamak/Views/TupleView.swift b/Sources/Tokamak/Views/TupleView.swift
index 26152f753..2dfcd7620 100644
--- a/Sources/Tokamak/Views/TupleView.swift
+++ b/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
diff --git a/Sources/Tokamak/Views/VStack.swift b/Sources/Tokamak/Views/VStack.swift
index e18618cfe..0db9f0f93 100644
--- a/Sources/Tokamak/Views/VStack.swift
+++ b/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 {
diff --git a/Sources/Tokamak/Views/View.swift b/Sources/Tokamak/Views/View.swift
index 9b1f1e24b..1990770cf 100644
--- a/Sources/Tokamak/Views/View.swift
+++ b/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`.")
+}
diff --git a/Sources/Tokamak/Views/ViewBuilder.swift b/Sources/Tokamak/Views/ViewBuilder.swift
index 825ee9b1a..e34ee18e8 100644
--- a/Sources/Tokamak/Views/ViewBuilder.swift
+++ b/Sources/Tokamak/Views/ViewBuilder.swift
@@ -17,6 +17,10 @@
 
 public struct EmptyView: View {
   @inlinable public init() {}
+
+  public var body: Never {
+    neverBody("EmptyView")
+  }
 }
 
 // swiftlint:disable:next type_name
@@ -24,6 +28,10 @@ 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 {
diff --git a/Sources/TokamakDOM/Views/HTML.swift b/Sources/TokamakDOM/Views/HTML.swift
index f1a5b10f2..0673acd18 100644
--- a/Sources/TokamakDOM/Views/HTML.swift
+++ b/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 {