idml: explicit zero cell edge weights hide the default table border (#1623)

crates/idml/src/import.rs

@@ -2170,9 +2170,12 @@ impl<'r> Importer<'r> {
         }
         // Table-local options override the named table style. Cell styles are already
         // materialized independently, so their edges retain their higher precedence.
+        let mut border_unset = style.border.is_none() && style.borders.iter().all(|b| b.is_empty());
         let mut borders = std::array::from_fn::<_, 4, _>(|i| t.options.border_for(i).clone());
         for (side, border) in ["TopBorder", "LeftBorder", "BottomBorder", "RightBorder"].iter().zip(&mut borders) {
-            self.cell_stroke_attrs(e, side).apply_to(border);
+            let attrs = self.cell_stroke_attrs(e, side);
+            border_unset &= attrs.is_empty();
+            attrs.apply_to(border);
         }
         t.options.border = borders[0].clone();
         t.options.borders = borders.map(Some);
@@ -2243,6 +2246,10 @@ impl<'r> Importer<'r> {
                 cell.stroke_priorities[i] = priority;
                 // Preserve style-defined edges and #102's positive-priority local overrides.
                 cell.border_overrides[i] |= priority > 0;
+                // No table or table style border is given anywhere, so the built-in 1 pt default must not
+                // draw over an outer edge the cell explicitly hides (weight 0 or the None swatch), as InDesign draws nothing.
+                let hidden = attrs.weight == Some(0.0) || attrs.color.as_deref() == Some(swatch::NONE);
+                cell.border_overrides[i] |= border_unset && hidden;
             }
             if let Some(slot) = t.cell_mut(r, c) {
                 *slot = cell;

crates/idml/src/tests.rs

@@ -1100,6 +1100,35 @@ fn imports_and_round_trips_explicit_cell_border_overrides() {
     assert_eq!(roundtrip.cell(0, 1).unwrap().border_overrides, [false; 4]);
 }
 
+#[test]
+fn explicitly_hidden_cell_edges_hide_the_default_table_border() {
+    // No table border or table style is given, and every cell edge is explicitly hidden (issue #1623):
+    // the first cell by weight 0, the second by the None swatch.
+    let cell = |name: &str, attr: &str, value: &str| {
+        format!(
+            r#"<Cell Name="{name}" LeftEdge{attr}="{value}" RightEdge{attr}="{value}" TopEdge{attr}="{value}" BottomEdge{attr}="{value}">
+    <ParagraphStyleRange><CharacterStyleRange><Content>X</Content></CharacterStyleRange></ParagraphStyleRange></Cell>"#
+        )
+    };
+    let story = format!(
+        r#"<idPkg:Story xmlns:idPkg="http://ns.adobe.com/AdobeInDesign/idml/1.0/packaging">
+<Story Self="s1"><ParagraphStyleRange><CharacterStyleRange>
+<Table HeaderRowCount="0" FooterRowCount="0">
+  <Row Name="0" MinimumHeight="24"/>
+  <Column Name="0" SingleColumnWidth="60"/><Column Name="1" SingleColumnWidth="60"/>
+  {}{}
+</Table></CharacterStyleRange></ParagraphStyleRange></Story></idPkg:Story>"#,
+        cell("0:0", "StrokeWeight", "0"),
+        cell("1:0", "StrokeColor", "Swatch/None")
+    );
+    let d = import_idml(&fixture_with_story(&story)).unwrap();
+    d.check().unwrap();
+    let table = d.stories.values().flat_map(|s| s.tables.values()).next().unwrap();
+    for c in 0..2 {
+        assert_eq!(table.cell(0, c).unwrap().border_overrides, [true; 4], "cell {c} suppresses the table border");
+    }
+}
+
 #[test]
 fn round_trips_footnotes_and_options() {
     let mut d = Document::new(&NewDocument::default());