Session watcher never attaches on R >= 4.6 — startup no longer calls the globalenv .First.sys override armed by init.R (plots silently fall back to Rplots.pdf)

[davidkane9]

Summary

vscode-R's session watcher attaches via R/session/init.R, which assigns a .First.sys shadow into the global environment during profile loading and relies on R's startup invoking it after default packages load (init_first → assign(".First.sys", init_last, envir = globalenv())). On R 4.6.x, R's startup no longer calls a globalenv .First.sys override — the shadow is armed but never invoked — so the watcher never attaches, options(device=...) is never set, and every plot() in the R terminal silently writes Rplots.pdf. No error appears anywhere, which makes this brutal to diagnose in teaching environments.

Verified empirically with a minimal profile (no extension involved):

cat > /tmp/profile.R <<'PROF'
first_sys_orig <- .First.sys
.First.sys <- function() {
    first_sys_orig()
    writeLines("fired", "/tmp/fired")
}
PROF
rm -f /tmp/fired
R_PROFILE_USER=/tmp/profile.R R -q --no-save -e 'invisible(NULL)'
ls /tmp/fired

• R 4.5.3 (macOS): marker created — shadow honored.
• R 4.6.1 (Linux, rocker image): marker never created — shadow bypassed.

Same result across consoles (plain R and custom front ends alike), since the change is in R's own startup, not any front end. We could not find the change documented in the R 4.6.0/4.6.1 NEWS; it may be a side effect of internal startup refactoring.

Observed in the wild

vscode-R 2.8.8 + GitHub Codespaces + R 4.6.1: after startup, exists(".First.sys", envir=globalenv(), inherits=FALSE) is TRUE (armed, unfired), "tools:vscode" %in% search() is FALSE, plot() → Rplots.pdf. Manually calling .First.sys() attaches the watcher and everything works from then on — only the startup invocation is missing.

Workaround we ship (site profile)

.First <- function() {
    fs <- globalenv()$.First.sys
    if (is.function(fs)) fs()
}

R still honors the documented .First() user hook after all profiles, so this fires the armed shadow; it's a no-op outside vscode-R sessions. Works on R 4.6.1 (CI-tested). The extension could adopt something equivalent in profile.R/init.R (e.g., arrange the deferred init via .First, or a top-level task callback) rather than relying on the .First.sys override that R >= 4.6 ignores.

Happy to test a fix — we ship vscode-R to a large intro data-science course.

[eitsupi]

Duplicate of #1696