Fix print output for #7099

Author: skitsy24

NEWS.md

@@ -30,6 +30,8 @@
 
 5. `tables()` can now optionally report `data.table` objects stored one level deep inside list objects when `depth=1L`, [#2606](https://github.com/Rdatatable/data.table/issues/2606). Thanks @MichaelChirico for the report and @manmita for the PR
 
+6. `yearqtr()` and `yearmon()` now gain an optional format specifier [#7694](https://github.com/Rdatatable/data.table/issues/7694). 'numeric' is the default, which preserves the original behavior, but 'character' formats `yearqtr()` as YYYYQ# (e.g. 2025Q2) and `yearmon()` as YYYYM## (e.g. 2025M02, 2025M10). Thanks to @jan-swissre for the report and @LunaticSage218 for the implementation.
+
 ### BUG FIXES
 
 1. `fread()` with `skip=0` and `(header=TRUE|FALSE)` no longer skips the first row when it has fewer fields than subsequent rows, [#7463](https://github.com/Rdatatable/data.table/issues/7463). Thanks @emayerhofer for the report and @ben-schwen for the fix.
@@ -40,17 +42,15 @@
 
 4. `rowwiseDT()` now provides a helpful error message when a complex object that is not a list (e.g., a function) is provided as a cell value, instructing the user to wrap it in `list()`, [#7219](https://github.com/Rdatatable/data.table/issues/7219). Thanks @kylebutts for the report and @venom1204 for the fix.
 
-5. Non-equi joins combining an equality condition with two inequality conditions on the same column (e.g., `on = .(id == id, val >= lo, val <= hi)`) no longer error, [#7641](https://github.com/Rdatatable/data.table/issues/7641). The internal `chmatchdup` remapping of duplicate `rightcols` was overwriting the original column indices, causing downstream code to reference non-existent columns. Thanks @tarun-t for the report and fix, and @aitap for the diagnosis.
-
-6. By-reference sub-assignments of strings to factor columns now _actually_ match the levels in UTF-8 when required and now don't result in invalid factors being created, [#7648](https://github.com/Rdatatable/data.table/issues/7648), amending a previous incomplete fix to [#6886](https://github.com/Rdatatable/data.table/issues/6886) in v1.17.2. Thanks @BASS-JN for the report and @aitap for the fix.
+5. `fread()` can now read from connections directly by spilling to a temporary file first, [#561](https://github.com/Rdatatable/data.table/issues/561). For the best throughput, point `tmpdir=` (or the global temp directory) to fast storage like an SSD or RAM. Thanks to Chris Neff for the report and @ben-schwen for the implementation.
 
-7. `fread()` can now read from connections directly by spilling to a temporary file first, [#561](https://github.com/Rdatatable/data.table/issues/561). For the best throughput, point `tmpdir=` (or the global temp directory) to fast storage like an SSD or RAM. Thanks to Chris Neff for the report and @ben-schwen for the implementation.
+6. `fread()` no longer replaces a literal header column name `"NA"` with an auto-generated `Vn` name when `na.strings` includes `"NA"`, [#5124](https://github.com/Rdatatable/data.table/issues/5124). Data rows still continue to parse `"NA"` as missing. Thanks @Mashin6 for the report and @shrektan for the fix.
 
-8. `frollapply()` no longer produces output longer than the input when the window length is also longer than the input [#7646](https://github.com/Rdatatable/data.table/issues/7646). Thanks to @hadley-johnson for reporting and @jangorecki for the fix.
+7. `fread()` would not give a warning when every second line of input was empty, [#3339](https://github.com/Rdatatable/data.table/issues/3339). Now, a warning message 'The rows in this file appear to be separated by blank lines.' is given and suggests to set `blank.lines.skip` to `TRUE`. Thanks to @Henrik-P for the report and @Asa-Henry for the fix.
 
-9. `fread()` no longer replaces a literal header column name `"NA"` with an auto-generated `Vn` name when `na.strings` includes `"NA"`, [#5124](https://github.com/Rdatatable/data.table/issues/5124). Data rows still continue to parse `"NA"` as missing. Thanks @Mashin6 for the report and @shrektan for the fix.
+8. `test()` now reports multiple expected warnings more clearly when `warning=` has length greater than 1L, instead of printing a collapsed or repeated mismatch summary after messages like `Test 1 produced 1 warnings but expected 2`, [#7092](https://github.com/Rdatatable/data.table/issues/7092). Expected and observed warnings are now printed on separate aligned lines, making small differences easier to spot. Thanks @MichaelChirico for the report, @ben-schwen for assistance, and @lucaslarson25, @tjdavis51, @D3VTHSTVR, and @car723 for the fix.
 
-10. `fread()` no longer misreads dates with negative years, [#7704](https://github.com/Rdatatable/data.table/issues/7704). Thanks to @kevinushey for the report and @aitap for the fix.
+11. `fread()` now correctly preserves empty trailing fields when `fill=TRUE` is used with irregular rows, [#7099](https://github.com/Rdatatable/data.table/issues/7099). Thanks to @aitap for the report and @skitsy24 for the fix.
 
 ### Notes
 
@@ -66,6 +66,20 @@
 
 6. Enhanced tests for OpenMP support, detecting incompatibilities such as R-bundled runtime _vs._ newer Xcode and testing for a manually installed runtime from <https://mac.r-project.org/openmp>, [#6622](https://github.com/Rdatatable/data.table/issues/6622). Thanks to @dvg-p4 for initial report and testing, @twitched for the pointers, @tdhock and @aitap for the fix.
 
+7. Verbose outputs from `frolladaptivefun()` and `frollfun()` are now clearer and more user friendly [#7021](https://github.com/Rdatatable/data.table/issues/7021). Thanks to @Omartech312, @aidengseay, @kkarissa, and @heb229 for the implementation, to @ben-schwen for the review, and to @jangorecki for the extensive guidance and review.
+
+## data.table [v1.18.4](https://github.com/Rdatatable/data.table/milestone/45) (6 May 2026)
+
+### BUG FIXES
+
+1. Non-equi joins combining an equality condition with two inequality conditions on the same column (e.g., `on = .(id == id, val >= lo, val <= hi)`) no longer error, [#7641](https://github.com/Rdatatable/data.table/issues/7641). The internal `chmatchdup` remapping of duplicate `rightcols` was overwriting the original column indices, causing downstream code to reference non-existent columns. Thanks @tarun-t for the report and fix, and @aitap for the diagnosis.
+
+2. By-reference sub-assignments of strings to factor columns now _actually_ match the levels in UTF-8 when required and now don't result in invalid factors being created, [#7648](https://github.com/Rdatatable/data.table/issues/7648), amending a previous incomplete fix to [#6886](https://github.com/Rdatatable/data.table/issues/6886) in v1.17.2. Thanks @BASS-JN for the report and @aitap for the fix.
+
+3. `fread()` no longer misreads dates with negative years, [#7704](https://github.com/Rdatatable/data.table/issues/7704). Thanks to @kevinushey for the report and @aitap for the fix.
+
+4. `frollapply()` no longer produces output longer than the input when the window length is also longer than the input [#7646](https://github.com/Rdatatable/data.table/issues/7646). Thanks to @hadley-johnson for reporting and @jangorecki for the fix.
+
 ## data.table [v1.18.2.1](https://github.com/Rdatatable/data.table/milestone/44?closed=1)  (22 January 2026)
 
 ### BUG FIXES

R/print.data.table.R

@@ -22,6 +22,7 @@ print.data.table = function(x, topn=getOption("datatable.print.topn"),
   stopifnot(isTRUEorFALSE(class))
   if (col.names == "none" && class)
     warningf("Column classes will be suppressed when col.names is 'none'")
+
   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
@@ -31,7 +32,26 @@ print.data.table = function(x, topn=getOption("datatable.print.topn"),
     # 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
+    }
+      # nocov start
+      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))