Don't "force unhandled errors" as a matter of course

cc @lionel-

R/reprex.R

@@ -15,7 +15,7 @@
 #' reprex can also be used for syntax highlighting (with or without rendering);
 #' see below for more.
 #'
-#' @section Details:
+#' @details
 #' The usual "code + commented output" is returned invisibly, put on the
 #' clipboard, and written to file. An HTML preview displays in RStudio's Viewer
 #' pane, if available, or in the default browser, otherwise. Leading `"> "`
@@ -48,6 +48,17 @@
 #' discussed in [an
 #' article](https://reprex.tidyverse.org/articles/articles/rtf.html)
 #'
+#' @section Backtraces:
+#' The functions `rlang::last_error()` and `rlang::last_trace()` do not work the
+#' same inside `reprex()` as they do in an interactive session. This is outside
+#' the scope of the reprex package and should get resolved by future changes in
+#' the evaluate package. In the meantime, enable these functions in a specific
+#' reprex by setting an rlang option *in the code snippet* you are reprexing:
+#'
+#' ```
+#' options("rlang:::force_unhandled_error" = TRUE)
+#' ````
+#'
 #' @param x An expression. If not given, `reprex()` looks for code in
 #'   `input` or on the clipboard, in that order.
 #' @param input Character. If has length one and lacks a terminating newline,

R/reprex_render.R

@@ -84,7 +84,9 @@ reprex_render_impl <- function(input,
   opts <- list(
     keep.source = TRUE,
     rlang_trace_top_env = globalenv(),
-    `rlang:::force_unhandled_error` = TRUE,
+    # https://github.com/tidyverse/reprex/issues/320
+    # TL;DR Inline this, as needed. Real fix needs to happen in evaluate.
+    #`rlang:::force_unhandled_error` = TRUE,
     rlang_backtrace_on_error = "full",
     crayon.enabled = FALSE
   )

tests/testthat/test-reprex.R

@@ -35,10 +35,11 @@ test_that("rmarkdown::render() context is trimmed from rlang backtrace", {
   expect_false(any(grepl("rmarkdown::render", ret)))
 })
 
-test_that("rlang::last_error() and last_trace() work", {
+test_that("rlang::last_error() and last_trace() can work", {
   skip_on_cran()
 
   input <- c(
+    "options('rlang:::force_unhandled_error' = TRUE)",
     "f <- function() rlang::abort('foo')",
     "f()",
     "rlang::last_error()",