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fix auto-print detection on R 3.4/3.5 where sys.calls() returns a promise #7727

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fix auto-print detection on R 3.4/3.5 where sys.calls() returns a promise #7727

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2d02ffa
added check for promise to autoprint for R3.5
skitsy24 Apr 25, 2026
af7736d
adjusted comment on change
skitsy24 Apr 25, 2026
194ef2b
added nocov for R 3.4/5 fix and TODO
skitsy24 Apr 26, 2026
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22 changes: 21 additions & 1 deletion R/print.data.table.R
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
stopifnot(isTRUEorFALSE(class))
if (col.names == "none" && class)
warningf("Column classes will be suppressed when col.names is 'none'")

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file=R/print.data.table.R,line=25,col=1,[trailing_whitespace_linter] Remove trailing whitespace.
if (!shouldPrint(x)) {
# := in [.data.table sets .global$print=address(x) to suppress the next print i.e., like <- does. See FAQ 2.22 and README item in v1.9.5
# The issue is distinguishing "> DT" (after a previous := in a function) from "> DT[,foo:=1]". To print.data.table(), there
Expand All @@ -31,7 +32,26 @@
# Other options investigated (could revisit): Cstack_info(), .Last.value gets set first before autoprint, history(), sys.status(),
# topenv(), inspecting next statement in caller, using clock() at C level to timeout suppression after some number of cycles
SYS = sys.calls()
if (identical(SYS[[1L]][[1L]], print) || # this is what auto-print looks like, i.e. '> DT' and '> DT[, a:=b]' in the terminal; see #3029.

# TODO(R>=3.6): Remove this branch once the minimal supported R version is raised. No need for is_print_call. Just
# identical(SYS[[1L]][[1L]], print)

# is_print_call detects whether print() was called either explicitly or through autoprint,
# is wrapped in a promise or not to account for R 3.4/3.5.
is_print_call = FALSE
if (identical(SYS[[1L]][[1L]], print)) {
is_print_call = TRUE
}

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file=R/print.data.table.R,line=44,col=6,[trailing_whitespace_linter] Remove trailing whitespace.
# nocov start

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file=R/print.data.table.R,line=45,col=20,[trailing_whitespace_linter] Remove trailing whitespace.
else if (typeof(SYS[[1L]][[1L]]) == "promise") {
# in R 3.4 and R 3.5, auto-print uses a promise to reference base::print due to lazy loading
# safely evaluate promise to get the actual function
evaluated = tryCatch(eval(SYS[[1L]][[1L]]), error = function(e) NULL)
if (identical(evaluated, print)) {
is_print_call = TRUE
}
} # nocov end
if (is_print_call || # this is what auto-print looks like, i.e. '> DT' and '> DT[, a:=b]' in the terminal; see #3029.
( length(SYS) >= 3L && is.symbol(thisSYS <- SYS[[length(SYS)-2L]][[1L]]) &&
as.character(thisSYS) == 'source') ) { # suppress printing from source(echo = TRUE) calls, #2369
return(invisible(x))
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