Merge pull request ole#6 from ole/duplicate-label-warnings

Runtime warnings for duplicate view labels

Author: ole

DebugLayout/Sources/DebugLayout/DebugLayout.swift

@@ -15,10 +15,17 @@ extension View {
     }
 
     /// Monitor the layout proposals and responses for this view and add them to the log.
-    public func debugLayout(_ label: String) -> some View {
+    public func debugLayout(
+        _ label: String,
+        file: StaticString = #fileID,
+        line: UInt = #line
+    ) -> some View {
         DebugLayout(label: label) {
             self
         }
+        .onAppear {
+            LogStore.shared.registerViewLabelAndWarnIfNotUnique(label, file: file, line: line)
+        }
         .modifier(DebugLayoutSelectionHighlight(viewID: label))
     }
 }

DebugLayout/Sources/DebugLayout/DebugLayoutLog.swift

@@ -45,6 +45,7 @@ struct ClearDebugLayoutLog: Layout {
         assert(subviews.count == 1)
         DispatchQueue.main.async {
             LogStore.shared.log.removeAll()
+            LogStore.shared.viewLabels.removeAll()
         }
         return subviews[0].sizeThatFits(proposal)
     }
@@ -59,6 +60,17 @@ public final class LogStore: ObservableObject {
     public static let shared: LogStore = .init()
 
     @Published var log: [LogEntry] = []
+    var viewLabels: Set<String> = []
+
+    func registerViewLabelAndWarnIfNotUnique(_ label: String, file: StaticString, line: UInt) {
+        DispatchQueue.main.async {
+            if self.viewLabels.contains(label) {
+                let message: StaticString = "Duplicate view label '%s' detected. Use unique labels in debugLayout() calls"
+                runtimeWarning(message, [label], file: file, line: line)
+            }
+            self.viewLabels.insert(label)
+        }
+    }
 }
 
 struct LogEntry: Identifiable {

DebugLayout/Sources/DebugLayout/RuntimeWarnings.swift

@@ -0,0 +1,51 @@
+// Source: Point-Free, Swift Composable Architecture, RuntimeWarnings.swift
+// https://github.com/pointfreeco/swift-composable-architecture/blob/399bc83dcfc7bdcee99f7f6cc0a687ca29e8494b/Sources/ComposableArchitecture/Internal/RuntimeWarnings.swift
+//
+// Based on: Point-Free, Unobtrusive runtime warnings for libraries (2022-01-03)
+// https://www.pointfree.co/blog/posts/70-unobtrusive-runtime-warnings-for-libraries
+//
+// Slightly modified by Ole Begemann
+
+#if DEBUG
+    import os
+
+    // NB: Xcode runtime warnings offer a much better experience than traditional assertions and
+    //     breakpoints, but Apple provides no means of creating custom runtime warnings ourselves.
+    //     To work around this, we hook into SwiftUI's runtime issue delivery mechanism, instead.
+    //
+    // Feedback filed: https://gist.github.com/stephencelis/a8d06383ed6ccde3e5ef5d1b3ad52bbc
+    private let rw = (
+        dso: { () -> UnsafeMutableRawPointer in
+            let count = _dyld_image_count()
+            for i in 0..<count {
+                if let name = _dyld_get_image_name(i) {
+                    let swiftString = String(cString: name)
+                    if swiftString.hasSuffix("/SwiftUI") {
+                        if let header = _dyld_get_image_header(i) {
+                            return UnsafeMutableRawPointer(mutating: UnsafeRawPointer(header))
+                        }
+                    }
+                }
+            }
+            return UnsafeMutableRawPointer(mutating: #dsohandle)
+        }(),
+        log: OSLog(subsystem: "com.apple.runtime-issues", category: "DebugLayout")
+    )
+#endif
+
+@_transparent
+@inline(__always)
+func runtimeWarning(
+    _ message: @autoclosure () -> StaticString,
+    _ args: @autoclosure () -> [CVarArg] = [],
+    file: StaticString? = nil,
+    line: UInt? = nil
+) {
+    #if DEBUG
+        let message = message()
+        unsafeBitCast(
+            os_log as (OSLogType, UnsafeRawPointer, OSLog, StaticString, CVarArg...) -> Void,
+            to: ((OSLogType, UnsafeRawPointer, OSLog, StaticString, [CVarArg]) -> Void).self
+        )(.fault, rw.dso, rw.log, message, args())
+    #endif
+}