Don't include '...' to empty-dimensional matrices (#174)

* Don't include '...' to empty-dimensional matrices

* regression tests

* flip which dimension is tested

* msising ')'

* stronger test

* similar test in the no-colnames case

* use expect_no* matchers

* requires more recent testthat (2022)

* simplify regexes by using expect_match()+expect_no_match()

* symmetric comment

Author: MichaelChirico

DESCRIPTION

@@ -31,7 +31,7 @@ Suggests:
     highr,
     Cairo,
     stringr,
-    testthat (>= 3.0.0),
+    testthat (>= 3.1.5),
     leaflet,
     withr
 Enhances:

R/repr_matrix_df.r

@@ -153,8 +153,8 @@ arr_part_format <- function(part) {
 arr_parts_combine <- function(parts, rownms, colnms) {
 	omit <- attr(parts, 'omit')
 	mat <- switch(omit,
-		rows = rbind(parts$upper, chars$ellip_v, parts$lower, deparse.level = 0L),
-		cols = cbind(parts$left,  chars$ellip_h, parts$right, deparse.level = 0L),
+		rows = rbind(parts$upper, if (ncol(parts$upper)) chars$ellip_v, parts$lower, deparse.level = 0L),
+		cols = cbind(parts$left,  if (nrow(parts$left)) chars$ellip_h, parts$right, deparse.level = 0L),
 		none = parts$full,
 		both = rbind(
 			cbind(parts$ul, chars$ellip_h, parts$ur, deparse.level = 0L),

tests/testthat/test_repr_array_df.r

@@ -249,3 +249,21 @@ test_that('data.table elision works in 1-column and 1-row edge cases', {
 	DF <- data.frame(a = 1:3, b = 4:6, c = 7:9)
 	expect_identical(repr_text(DF), repr_text(data.table::as.data.table(DF)))
 })
+
+test_that("partially-empty matrices requiring elision can be displayed", {
+  withr::local_options(list(
+    repr.matrix.max.rows = 8L,
+    repr.matrix.max.cols = 8L
+  ))
+  m <- matrix(nrow = 0L, ncol = 10L)
+  # all on one line
+  expect_no_warning(expect_no_match(repr(m), "\n", fixed = TRUE))
+  # always [n,] with nothing after it
+  expect_no_warning(expect_no_match(repr(t(m)), "\\][^\n]"))
+
+  colnames(m) <- sprintf("A%02d", 1:10)
+  # gap from A04 to A07 with \cdots, then only A0n, no newline
+  expect_no_warning(expect_no_match(expect_match(repr(m), "A04[^A]*A07"), "\n", fixed = TRUE))
+  # gap from A04 to A07 with \vdots, all A0n followed by newline
+  expect_no_warning(expect_no_match(expect_match(repr(t(m)), "A04[^A]*A07"), "A0[1-9][^\n]"))
+})