defer() run immediately when used inside Rmd

[hadley]

withr::defer(print("Hi!"))
#> Setting deferred event(s) on global environment.
#>   * Will be run automatically when session ends
#>   * Execute (and clear) with `withr::deferred_run()`.
#>   * Clear (without executing) with `withr::deferred_clear()`.
#> [1] "Hi!"
1
#> [1] 1
2
#> [1] 2

^{Created on 2022-01-03 by the reprex package (v2.0.1)}

[hadley]

Reprex that's more amenable for interactive exploration and that maybe hints at the underlying root cause:

evaluate::replay(evaluate::evaluate("
  withr::defer(print('Hi!'))
  1
"))
#> > 
#> >   withr::defer(print('Hi!'))
#> Setting deferred event(s) on global environment.
#>   * Will be run automatically when session ends
#>   * Execute (and clear) with `withr::deferred_run()`.
#>   * Clear (without executing) with `withr::deferred_clear()`.
#> [1] "Hi!"
#> >   1
#> [1] 1

^{Created on 2022-01-03 by the reprex package (v2.0.1)}

No, that doesn't really illustrate the problem as the handlers are still run once you actually terminate the global environment.