Warn at launch on development (dev branch) builds

Common/FeatureFlags.swift

@@ -39,6 +39,7 @@ struct FeatureFlagConfiguration: Decodable {
     let profileExpirationSettingsViewEnabled: Bool
     let missedMealNotifications: Bool
     let allowAlgorithmExperiments: Bool
+    let devBranchWarningEnabled: Bool
 
 
     fileprivate init() {
@@ -232,6 +233,13 @@ struct FeatureFlagConfiguration: Decodable {
         #else
         self.allowAlgorithmExperiments = false
         #endif
+
+        // Swift compiler config is inverse, since the default state is enabled.
+        #if DEV_BRANCH_WARNING_DISABLED
+        self.devBranchWarningEnabled = false
+        #else
+        self.devBranchWarningEnabled = true
+        #endif
     }
 }
 
@@ -267,6 +275,7 @@ extension FeatureFlagConfiguration : CustomDebugStringConvertible {
             "* profileExpirationSettingsViewEnabled: \(profileExpirationSettingsViewEnabled)",
             "* missedMealNotifications: \(missedMealNotifications)",
             "* allowAlgorithmExperiments: \(allowAlgorithmExperiments)",
+            "* devBranchWarningEnabled: \(devBranchWarningEnabled)",
             "* allowExperimentalFeatures: \(allowExperimentalFeatures)"
         ].joined(separator: "\n")
     }

Loop.xcodeproj/project.pbxproj

@@ -497,6 +497,7 @@
 		C1F00C60285A802A006302C5 /* SwiftCharts in Frameworks */ = {isa = PBXBuildFile; productRef = C1F00C5F285A802A006302C5 /* SwiftCharts */; };
 		C1F00C78285A8256006302C5 /* SwiftCharts in Embed Frameworks */ = {isa = PBXBuildFile; productRef = C1F00C5F285A802A006302C5 /* SwiftCharts */; settings = {ATTRIBUTES = (CodeSignOnCopy, ); }; };
 		C1F2075C26D6F9B0007AB7EB /* AppExpirationAlerter.swift in Sources */ = {isa = PBXBuildFile; fileRef = C1F2075B26D6F9B0007AB7EB /* AppExpirationAlerter.swift */; };
+		FADE0001000000000000DE02 /* DevelopmentBranchAlerter.swift in Sources */ = {isa = PBXBuildFile; fileRef = FADE0001000000000000DE01 /* DevelopmentBranchAlerter.swift */; };
 		C1F7822627CC056900C0919A /* SettingsManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = C1F7822527CC056900C0919A /* SettingsManager.swift */; };
 		C1F8B243223E73FD00DD66CF /* BolusProgressTableViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = C1F8B1D122375E4200DD66CF /* BolusProgressTableViewCell.swift */; };
 		C1FB428C217806A400FAB378 /* StateColorPalette.swift in Sources */ = {isa = PBXBuildFile; fileRef = C1FB428B217806A300FAB378 /* StateColorPalette.swift */; };
@@ -1316,6 +1317,7 @@
 		C1EE9E802A38D0FB0064784A /* BuildDetails.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = BuildDetails.plist; sourceTree = "<group>"; };
 		C1EF747128D6A44A00C8C083 /* CrashRecoveryManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CrashRecoveryManager.swift; sourceTree = "<group>"; };
 		C1F2075B26D6F9B0007AB7EB /* AppExpirationAlerter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppExpirationAlerter.swift; sourceTree = "<group>"; };
+		FADE0001000000000000DE01 /* DevelopmentBranchAlerter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DevelopmentBranchAlerter.swift; sourceTree = "<group>"; };
 		C1F48FF62995821600C8BD69 /* pl */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = pl; path = pl.lproj/InfoPlist.strings; sourceTree = "<group>"; };
 		C1F7822527CC056900C0919A /* SettingsManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SettingsManager.swift; sourceTree = "<group>"; };
 		C1F8B1D122375E4200DD66CF /* BolusProgressTableViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BolusProgressTableViewCell.swift; sourceTree = "<group>"; };
@@ -2037,6 +2039,7 @@
 				E9B355232935906B0076AB04 /* Missed Meal Detection */,
 				3ED319902EB65A2D00820BCF /* Live Activity */,
 				C1F2075B26D6F9B0007AB7EB /* AppExpirationAlerter.swift */,
+				FADE0001000000000000DE01 /* DevelopmentBranchAlerter.swift */,
 				A96DAC2B2838F31200D94E38 /* SharedLogging.swift */,
 				7E69CFFB2A16A77E00203CBD /* ResetLoopManager.swift */,
 				84AA81E42A4A3981000B658B /* DeeplinkManager.swift */,
@@ -3391,6 +3394,7 @@
 				3ED319992EB65A6900820BCF /* LiveActivityManagementView.swift in Sources */,
 				3ED3199A2EB65A6900820BCF /* LiveActivityBottomRowManagerView.swift in Sources */,
 				C1F2075C26D6F9B0007AB7EB /* AppExpirationAlerter.swift in Sources */,
+				FADE0001000000000000DE02 /* DevelopmentBranchAlerter.swift in Sources */,
 				B4FEEF7D24B8A71F00A8DF9B /* DeviceDataManager+DeviceStatus.swift in Sources */,
 				142CB7592A60BF2E0075748A /* EditMode.swift in Sources */,
 				E95D380324EADF36005E2F50 /* CarbStoreProtocol.swift in Sources */,

Loop/Managers/DevelopmentBranchAlerter.swift

@@ -0,0 +1,50 @@
+//
+//  DevelopmentBranchAlerter.swift
+//  Loop
+//
+//  Copyright © 2026 LoopKit Authors. All rights reserved.
+//
+
+import UIKit
+
+enum DevelopmentBranchAlerter {
+
+    // The LoopWorkspace superproject branch this warning applies to.
+    private static let developmentBranchName = "dev"
+
+    private static let switchToMainURL = URL(string: "https://loopkit.github.io/loopdocs/browser/build-dev-browser/#build-development-version")!
+
+    /// Presents a blocking warning when this is a build from the development branch.
+    /// Shown on every launch; the alert can only be dismissed by an explicit choice.
+    static func alertIfNeeded(viewControllerToPresentFrom: UIViewController) {
+        guard FeatureFlags.devBranchWarningEnabled else {
+            return
+        }
+
+        guard BuildDetails.default.workspaceGitBranch == developmentBranchName else {
+            return
+        }
+
+        let alert = UIAlertController(
+            title: NSLocalizedString("Warning", comment: "Title of the warning shown at launch on development builds"),
+            message: NSLocalizedString("This is the development version of Loop, built from the dev branch. Any updates on this branch may contain new, untested features, and may be unsafe. If you are not a tester, please do not use this branch, and switch to main.", comment: "Body of the warning shown at launch on development builds"),
+            preferredStyle: .alert
+        )
+
+        alert.addAction(UIAlertAction(
+            title: NSLocalizedString("I'm a tester", comment: "Button that dismisses the development build warning"),
+            style: .default,
+            handler: nil
+        ))
+
+        alert.addAction(UIAlertAction(
+            title: NSLocalizedString("Switch to main", comment: "Button on the development build warning that opens documentation about switching branches"),
+            style: .default,
+            handler: { _ in
+                UIApplication.shared.open(switchToMainURL)
+            }
+        ))
+
+        viewControllerToPresentFrom.present(alert, animated: true)
+    }
+}

Loop/Managers/LoopAppManager.swift

@@ -315,6 +315,10 @@ class LoopAppManager: NSObject {
         self.state = state.next
 
         alertManager.playbackAlertsFromPersistence()
+
+        if let rootViewController = rootViewController {
+            DevelopmentBranchAlerter.alertIfNeeded(viewControllerToPresentFrom: rootViewController)
+        }
     }
 
     // MARK: - Life Cycle