Crash: `ForEach(0...num-1)` produces invalid Range when `num == 0` (ConfettiSwiftUI.swift:168)

[mikeini]

Summary

ConfettiContainer.body crashes with Swift runtime failure: Range requires lowerBound <= upperBound whenever a ConfettiCannon is mounted with num: 0. The crash fires during view-body evaluation, so it's a hard SIGTRAP that kills the app — not catchable.

The offending line:

// Sources/ConfettiSwiftUI.swift, line 168
ForEach(0...confettiConfig.num-1, id:\.self) { _ in
    ConfettiView(confettiConfig: confettiConfig)
}

When num == 0, the closed range expands to 0...-1, which is invalid. Closed ranges require lowerBound <= upperBound.

Why this matters in practice

The natural pattern for honoring @Environment(\.accessibilityReduceMotion) is to set num to 0 (or some small number) when the system flag is on:

@Environment(\.accessibilityReduceMotion) var reduceMotion

SomeView()
    .confettiCannon(
        trigger: $trigger,
        num: reduceMotion ? 0 : 60,
        // ...
    )

This is a documented, common SwiftUI accessibility pattern (Apple's HIG explicitly recommends suppressing decorative motion when Reduce Motion is on). Anyone using ConfettiSwiftUI in a shippable, accessibility-aware app will hit this.

We caught it via a TestFlight crash report on iOS 26.4.2 from a tester who had Reduce Motion enabled. The app crashed every time they performed the action that triggered the cannon. Workaround applied on our side: we pinned num to a non-zero value and gated Reduce Motion at the trigger site instead — but library users shouldn't have to know about this footgun.

Reproduction

Minimum repro (~10 lines):

import SwiftUI
import ConfettiSwiftUI

struct CrashRepro: View {
    @State private var trigger = 0
    var body: some View {
        Button("Fire") { trigger += 1 }
            .confettiCannon(
                trigger: $trigger,
                num: 0   // ← crashes the app on first render
            )
    }
}

Run on simulator or device. App crashes on initial render of the view tree, before trigger is even bumped.

Crash signature

Exception Type:  EXC_BREAKPOINT (SIGTRAP)
Termination Reason: SIGNAL 5 Trace/BPT trap: 5

Thread 0 Crashed:
0   MyApp  Swift runtime failure: Range requires lowerBound <= upperBound + 0
1   MyApp  closure #1 in ConfettiContainer.body.getter + 352 (ConfettiSwiftUI.swift:168)
2   MyApp  specialized closure #1 in ZStack.init(alignment:content:) + 8
3   MyApp  ConfettiContainer.body.getter + 44 (ConfettiSwiftUI.swift:166)

Suggested fix

Two equivalent one-line patches — either works.

Option A — half-open range (preferred, no edge-case math):

ForEach(0..<confettiConfig.num, id:\.self) { _ in
    ConfettiView(confettiConfig: confettiConfig)
}

0..<0 is a valid empty range. ForEach with 0 iterations is a no-op.

Option B — guard the existing closed range:

if confettiConfig.num > 0 {
    ForEach(0...confettiConfig.num-1, id:\.self) { _ in
        ConfettiView(confettiConfig: confettiConfig)
    }
}

Option A is cleaner and matches the idiom used elsewhere in SwiftUI for "render N copies".

Environment

• ConfettiSwiftUI: 3.0.0 (9ae5bc2)
• Xcode: 26.4.1
• iOS: 26.4.2 (also reproduces on iOS 18 simulator)
• Swift: 5/6 strict concurrency

Happy to send a PR if it'd help.