Check if iOS 14 is available in SwiftUI body

Code Block 
struct StyledList: ViewModifier {
		func body(content: Content) -> some View {
				if #available(iOS 14.0, *) {
						return content
								.listStyle(InsetGroupedListStyle())
				} else {
						return content
								.listStyle(DefaultListStyle())
					 }
				}
		}
}

Code Block 
extension View {
		public func styledList() -> some View {
				if #available(iOS 14.0, *) {
						return self.listStyle(InsetGroupedListStyle())
				} else {
						return self
				}
		}
}

• Give it a title that summarizes the aspects that you think are most likely to be important to figure out the bug. For this bug, I'd say these are (1) it's a crash, (2) it's in SwiftUI code, (2) it happens on an iOS 13 device, and (3) you're using an iOS 14-only API, so something like "iOS 13 crashes when running iOS 14 SwiftUI code" might be a good title.

• Always state explicitly the steps the engineer should follow to trigger the bug, what you expected them to do, and what actually happened instead. Those last two are often easy for crashing bugs—you expected it to not crash, and instead it crashed 😉—but it's good to be in the habit, because for some bugs it may not be clear what exactly is wrong about the result.

• Mention the versions of the software involved, ideally including the build number (the parenthesized alphanumeric identifier after the version number). For example: "I built this with Xcode 12 beta 1 (12A6159). It ran correctly on iOS 14 beta 1 (18A5301v), but crashed on iOS 13.6 beta 2 (17G5045c)."

• For bugs you see in your own apps, ideally you should attach an Xcode project which can be used to reproduce it. It's actually best if this isn't your entire real project, but instead is a small sample that fails in the same way. However, if you can't spare the time or can't share all of the code involved, give us what you can and we'll do our best.

• Also think about what else you can attach that might help engineers quickly understand the bug.

• Crashes: Try to include a crash report file. You can retrieve crash reports for crashes on your Mac from Console.app, and you can retrieve them for crashes on your iOS devices with the Xcode "Devices and Simulators" window.

• Build failures: Export a build log from Xcode. You should also check if there are any related crash reports on your Mac and, if so, include them.

• UI glitches: A screenshot or screen recording is often worth a thousand words.

• Processes hanging on your Mac: A sample or spindump is often helpful. (A sample basically repeatedly records backtraces in one process; a spindump does the same thing, but for all processes.) You can use Activity Monitor to collect these.

• Miscellaneous: A sysdiagnose is never a bad thing to include and is particularly important for "weirdness" like poor battery life or difficulty connecting to a network. Sysdiagnoses include a wide range of logs and diagnostic files. The Feedback Assistant website has instructions for collecting sysdiagnoses from various devices.

1. Running macOS 10.15.5

2. Generated a new test project in Xcode 11 ( to set deployment target to iOS 13.5 )

3. Opened it in Xcode 12 beta

4. Run and get a crash in simulator and on a real device until I remove the conditional or change LazyHStack/LazyVStack to HStack/VStack/Text..etc

Code Block import SwiftUI
struct ContentView: View {
  var body: some View {
    VStack {
      Text("Hello, World!")
       
      if #available(iOS 14.0, *) {
        LazyVStack {
          Text("ios14 1")
          Text("ios14 2")
        }
      } else {
        HStack {
          Text("ios13 1")
          Text("ios13 2")
        }
      }
    }
     
  }
}
struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

Code Block swift
struct ContentView: View {
	 var body: some View {
     Group {
            if #available(iOS 14.0, *) {
                ScrollView {
                    AnyView(LazyVStack { content.padding(.horizontal, 15) })
                }
            } else {
                List { content }
            }
        }
    }
}

Code Block struct CustomView: View {
    var body: some View {
        someView()
    }
    func someView() -> AnyView {
        if #available(iOS 14.0, *) {
            return AnyView(Text("iOS 14"))
        } else {
            return AnyView(Text("iOS 13"))
        }
    }
}

Code Block 
	@ViewBuilder
    private var textImageView: some View {
        if #available(iOS 14.0, *) {
            AnyView(Label {
                text
            } icon: {
                image
            })
        } else {
            HStack {
                image
                text
            }
        }
    }

Also running into this issue:

extension View {
 func listRow() -> some View {
  let view = self
   .frame(maxWidth: .infinity, minHeight: 0, maxHeight: .infinity, alignment: .leading)
   
  if #available(iOS 15, *) {
   return AnyView(view.listRowSeparatorVisibility(.hidden).listRowInsets(EdgeInsets(top: 0, leading: 0, bottom: 0, trailing: 0)))
  }
   
  return AnyView(view.listRowInsets(EdgeInsets(top: -1, leading: 0, bottom: -1, trailing: 0)))
 }
}

This crashes, among other approaches as well

it seems working in Xcode 12.5 but we do have a WORSE case.

Suppose You need to write something like that:

struct InfoSheetView: View {

    if #available(iOS 15, *) {
    } else {
    }

var body: some View {
     .....
 }
}

even if an EMPTY if # I got:

Expected declaration

on if #..

I would like to write ..

    if #available(iOS 15, *) {
            @Environment(\.dismiss) var dismiss
    } else {
            @Environment(\.presentationMode) var presentationMode
    }

see original example at: https://www.hackingwithswift.com/quick-start/swiftui/how-to-present-a-new-view-using-sheets and try to conditionally use

@Environment(\.dismiss) var dismiss

OR

    @Environment(.presentationMode) var presentationMode

I am experiencing this issue in Xcode 13.2.1 on an iOS 14.8.1 device. Take this simple custom ViewModifier which applies the appropriate non-deprecated capitalization modifier based on the OS.

struct CapitalizationModifier: ViewModifier {
  let shouldCapitalize: Bool
   
  func body(content: Content) -> some View {
    if #available(iOS 15.0, *) {
      content.textInputAutocapitalization(shouldCapitalize ? .words : .never)
    } else {
      content.autocapitalization(shouldCapitalize ? .words : .none)
    }
  }
}

I found that the crash only happens when built in the release configuration, but not debug. Changing the Optimization Level in the Swift Compiler - Code Generation section of the target's Build Settings prevents the crash.

Having a similar issue on Xcode 13.2.1 and iOS 14 devices only. Error:

protocol witness for ViewModifier.body(content:) in conformance *** + 43700770729 
SwiftUI ModifierBodyAccessor.body(of:)