[write] protect against overwriting a shared formula reference

R/helper-functions.R

@@ -1339,3 +1339,39 @@ wb_upd_custom_pid <- function(wb) {
     xml_children = out
   )
 }
+
+#' replace shared formulas with single cell formulas
+#' @param cc the full frame
+#' @param cc_shared a subset of the full frame with shared formulas
+#' @noRd
+shared_as_fml <- function(cc, cc_shared) {
+    cc_shared <- cc_shared[order(as.integer(cc_shared$f_si)), ]
+
+    # carry forward the shared formula
+    cc_shared$f    <- ave2(cc_shared$f, cc_shared$f_si, carry_forward)
+
+    # calculate differences from the formula cell, to the shared cells
+    cc_shared$cols <- ave2(col2int(cc_shared$c_r), cc_shared$f_si, calc_distance)
+    cc_shared$rows <- ave2(as.integer(cc_shared$row_r), cc_shared$f_si, calc_distance)
+
+    # begin updating the formulas. find a1 notion, get the next cell, update formula
+    cells <- find_a1_notation(cc_shared$f)
+    repls <- vector("list", length = length(cells))
+
+    for (i in seq_along(cells)) {
+      repls[[i]] <- next_cell(cells[[i]], cc_shared$cols[i], cc_shared$rows[i])
+    }
+
+    cc_shared$f     <- replace_a1_notation(cc_shared$f, repls)
+    cc_shared$cols  <- NULL
+    cc_shared$rows  <- NULL
+    cc_shared$f_t   <- ""
+    cc_shared$f_si  <- ""
+    cc_shared$f_ref <- ""
+
+    # reduce and assign
+    cc_shared <- cc_shared[which(cc_shared$r %in% cc$r), ]
+
+    cc[match(cc_shared$r, cc$r), ] <- cc_shared
+    cc
+}

R/read.R

@@ -438,37 +438,12 @@ wb_to_df <- function(
   if (show_formula) {
 
     if (any(cc$f_t == "shared")) {
-
       # depending on the sheet, this might require updates to many cells
       # TODO reduce this to cells, that are part of `cc`. Currently we
       # might waste time, updating cells that are not visible to the user
       cc_shared <- wb$worksheets[[sheet]]$sheet_data$cc
       cc_shared <- cc_shared[cc_shared$f_t == "shared", ]
-      cc_shared <- cc_shared[order(as.integer(cc_shared$f_si)), ]
-
-      # carry forward the shared formula
-      cc_shared$f    <- ave2(cc_shared$f, cc_shared$f_si, carry_forward)
-
-      # calculate differences from the formula cell, to the shared cells
-      cc_shared$cols <- ave2(col2int(cc_shared$c_r), cc_shared$f_si, calc_distance)
-      cc_shared$rows <- ave2(as.integer(cc_shared$row_r), cc_shared$f_si, calc_distance)
-
-      # begin updating the formulas. find a1 notion, get the next cell, update formula
-      cells <- find_a1_notation(cc_shared$f)
-      repls <- vector("list", length = length(cells))
-
-      for (i in seq_along(cells)) {
-        repls[[i]] <- next_cell(cells[[i]], cc_shared$cols[i], cc_shared$rows[i])
-      }
-
-      cc_shared$f    <- replace_a1_notation(cc_shared$f, repls)
-      cc_shared$cols <- NULL
-      cc_shared$rows <- NULL
-
-      # reduce and assign
-      cc_shared <- cc_shared[which(cc_shared$r %in% cc$r), ]
-      cc[match(cc_shared$r, cc$r), ] <- cc_shared
-
+      cc <- shared_as_fml(cc, cc_shared)
     }
 
     sel <- cc$f != ""

R/write.R

@@ -100,6 +100,28 @@ inner_update <- function(
                    "f", "f_t", "f_ref", "f_ca", "f_si", "is", "typ")
 
   sel <- match(x$r, cc$r)
+
+  # to avoid bricking the worksheet, we make sure that we do not overwrite the
+  # reference cell of a shared formula. To be on the save side, we replace all
+  # values with the formula. If the entire cc is replaced with x, we can skip.
+  if (length(sf <- cc$f_si[sel & cc$f_t[sel] == "shared" & cc$f_ref[sel] != ""]) && !all(cc$r %in% x$r)) {
+
+    # collect all the shared formulas that we have to convert
+    sel_fsi <- cc$f_si %in% unique(sf)
+
+    cc_shared <- cc[sel_fsi, , drop = FALSE]
+
+    cc <- shared_as_fml(cc, cc_shared)
+
+    msg <- paste0(
+      "A shared formula reference cell was overwritten. To protect the",
+      " spreadsheet formulas, the impacted cells were converted from shared",
+      " formulas to normal formulas."
+    )
+    warning(msg, call. = FALSE)
+
+  }
+
   cc[sel, replacement] <- x[replacement]
 
   # avoid missings in cc

tests/testthat/test-write.R

@@ -1476,3 +1476,20 @@ test_that("writing list with sep works", {
   expect_equal(exp, got)
 
 })
+
+test_that("guarding against overwriting shared formula reference works", {
+
+  wb <- wb_workbook()$add_worksheet()$
+    add_data(x = 1)$
+    add_formula(dims = "B1:D1", x = "A1 + 1", shared = TRUE)
+
+  expect_warning(
+    wb$add_data(x = 2, dims = "B1"),
+    "A shared formula reference cell was overwritten."
+  )
+
+  exp <- c("1", "2", "B1 + 1", "C1 + 1")
+  got <- unname(unlist(wb$to_df(show_formula = TRUE, col_names = FALSE)))
+  expect_equal(exp, got)
+
+})