Runtime Warning: Publishing from within view updates

[Smail]

I am receiving multiple "Publishing changes from within view updates is not allowed, this will cause undefined behavior" warning in iOS 18.3.1. This happens for example when a LaTeX view is conditionally displayed, e.g.:

@State private var isDisplayed = false

var body: some View {
    if isDisplayed {
        LaTeX("Hello World")
    }
    Button("Click Me") { isDisplayed.toggle() }
}

The issue is the renderSync function, specifically where variables are set:

@MainActor func renderSync(
    latex: String,
    unencodeHTML: Bool,
    parsingMode: LaTeX.ParsingMode,
    processEscapes: Bool,
    errorMode: LaTeX.ErrorMode,
    font: Font,
    displayScale: CGFloat,
    renderingMode: SwiftUI.Image.TemplateRenderingMode
  ) -> [ComponentBlock] {
  guard !isRendering else {
    return []
  }
  guard !rendered else {
    return blocks
  }
  isRendering = true // <-- HERE
  
  let texOptions = TeXInputProcessorOptions(processEscapes: processEscapes, errorMode: errorMode)
  let renderedBlocks = render(
    blocks: parseBlocks(latex: latex, unencodeHTML: unencodeHTML, parsingMode: parsingMode),
    font: font,
    displayScale: displayScale,
    renderingMode: renderingMode,
    texOptions: texOptions)
  
  blocks = renderedBlocks  // <-- HERE
  isRendering = false      // <-- HERE
  rendered = true          // <-- HERE
  return blocks
}

I found a solution, but I am not sure if it captures the essence of the renderSync function:

@MainActor func renderSync(
  latex: String,
  unencodeHTML: Bool,
  parsingMode: LaTeX.ParsingMode,
  processEscapes: Bool,
  errorMode: LaTeX.ErrorMode,
  font: Font,
  displayScale: CGFloat,
  renderingMode: SwiftUI.Image.TemplateRenderingMode
) -> [ComponentBlock] {
  guard !isRendering else {
    return []
  }
  guard !rendered else {
    return blocks
  }
  
  let texOptions = TeXInputProcessorOptions(processEscapes: processEscapes, errorMode: errorMode)
  let renderedBlocks = render(
    blocks: parseBlocks(latex: latex, unencodeHTML: unencodeHTML, parsingMode: parsingMode),
    font: font,
    displayScale: displayScale,
    renderingMode: renderingMode,
    texOptions: texOptions)
  
  // Schedule updates for the next view cycle on the main actor outside the current view update
  Task {
    await MainActor.run {
      isRendering = true
      blocks = renderedBlocks
      isRendering = false
      rendered = true
    }
  }
  
  return renderedBlocks
}

Now, it still computes and returns the new renderedBlocks synchronously, but they are only registered for the next view cycle in the UI (I believe).
I tried the .wait rendering method with my approach, and it still seems to block the UI, just like the first version did. But I am obviously unsure if this is the way to go and if I should create a PR.

[ddwty]

I'm facing the same issue.