(core) Showing censored values as a grey cell

Test Plan: Block read access to column A based on the condition rec.B == 1. Then setting B = 1 in a row makes the cell under A grey.

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: paulfitz, dsagal

Differential Revision: https://phab.getgrist.com/D2828

app/client/components/viewCommon.css

@@ -78,6 +78,27 @@
   background-color: unset;
 }
 
+.field_clip.invalid.field-error-C {
+  background-color: unset;
+  color: var(--grist-color-dark-grey);
+  padding-left: 18px;
+}
+
+.field_clip.invalid.field-error-C::before {
+  /* based on standard icon styles */
+  content: "";
+  position: absolute;
+  top: 4px;
+  left: 2px;
+  width: 14px;
+  height: 14px;
+  background-color: var(--grist-color-dark-grey);
+  -webkit-mask-repeat: no-repeat;
+  -webkit-mask-position: center;
+  -webkit-mask-size: contain;
+  -webkit-mask-image: var(--icon-Lock);
+}
+
 .field_clip.field-error-U {
   color: #6363a2;
   background-color: unset;

app/client/widgets/FieldEditor.ts

@@ -152,7 +152,19 @@ export class FieldEditor extends Disposable {
 
     const column = this._field.column();
     const cellCurrentValue = this._editRow.cells[this._field.colId()].peek();
-    const cellValue = column.isFormula() ? column.formula() : cellCurrentValue;
+    let cellValue: CellValue;
+    if (column.isFormula()) {
+      cellValue = column.formula();
+    } else if (Array.isArray(cellCurrentValue) && cellCurrentValue[0] === 'C') {
+      // This cell value is censored by access control rules
+      // Really the rules should also block editing, but in case they don't, show a blank value
+      // rather than a 'C'. However if the user tries to edit the cell and then clicks away
+      // without typing anything the empty string is saved, deleting what was there.
+      // We should probably just automatically block updates where reading is not allowed.
+      cellValue = '';
+    } else {
+      cellValue = cellCurrentValue;
+    }
 
     // Enter formula-editing mode (e.g. click-on-column inserts its ID) only if we are opening the
     // editor by typing into it (and overriding previous formula). In other cases (e.g. double-click),