HOW TO: Debug a Windows Installer custom action

Prerequisites:

Determine the name of the custom action you want to debug
Ensure you have the source code and debug symbols for your custom action

Steps

Set the MsiBreak environment variable (user or system) to the name of the custom action. For example, if your custom action is called MyCustomAction:

Microsoft.Playwright.PlaywrightException: Error: The language "cmd" has no grammar.
    at Object.highlight (http://127.0.0.1:41899/main.js:3978:11)
    at eval (eval at evaluate (:226:30), :2:18)
    at UtilityScript.evaluate (:233:19)
    at UtilityScript. (:1:44)
   at Microsoft.Playwright.Transport.Connection.InnerSendMessageToServerAsync[T](ChannelOwnerBase object, String method, Dictionary`2 dictionary, Boolean keepNulls) in /_/src/Playwright/Transport/Connection.cs:line 209
   at Microsoft.Playwright.Transport.Connection.WrapApiCallAsync[T](Func`1 action, Boolean isInternal) in /_/src/Playwright/Transport/Connection.cs:line 535
   at Microsoft.Playwright.Core.Frame.EvaluateAsync[T](String script, Object arg) in /_/src/Playwright/Core/Frame.cs:line 548
   at SiteGen.Extensions.Markdown.Prism.PrismHost.Highlight(String source, String language)
   at SiteGen.Extensions.Markdown.Prism.PrismCodeBlockRenderer.Write(HtmlRenderer renderer, PrismCodeBlock obj)

Run your installer and wait for the message box prompt

Details

When your custom action is about to execute, you should get this message box prompt:

Debugging Custom Actions

Now you can use Visual Studio or another debugger such as WinDBG to attach to the specified process.

References:

Debugging Custom Actions @ msdn.microsoft.com