[write] allow shared formulas without A1 cell reference

NEWS.md

@@ -1,3 +1,12 @@
+# openxlsx2 (development version)
+
+## Fixes
+
+* Formulas that do not have a `A1` cell reference to increase, are now shareable too. `wb_add_formula(x = "1", dims = "A1:A2", shared = TRUE)`
+
+
+***************************************************************************
+
 # openxlsx2 1.12
 
 ## New features

R/write.R

@@ -520,7 +520,7 @@ write_data2 <- function(
     cc$f_t              <- "shared"
     cc[1, "f_ref"]      <- dims
     cc[2:nrow(cc), "f"] <- ""
-    cc$f_si             <- max(int_si) + 1L
+    cc$f_si             <- max(int_si, 0) + 1L
   }
 
   if (is.null(wb$worksheets[[sheetno]]$sheet_data$cc)) {

tests/testthat/test-formulas.R

@@ -187,6 +187,13 @@ test_that("writing shared formulas works", {
   got <- unique(cc$f_si)
   expect_equal(exp, got)
 
+  wb <- wb_workbook()$add_worksheet()
+  wb$add_formula(x = "1", dims = "A1:B1", shared = TRUE)
+
+  exp <- "shared"
+  got <- unique(wb$worksheets[[1]]$sheet_data$cc$f_t)
+  expect_equal(exp, got)
+
 })
 
 test_that("increase formula dims if required", {