craft-docx: a file with no default table style gives its tables no cell margins

Port of storytold/wordcraft#3821, whose reader code moved here with storytold/wordcraft#6603. Word's 0.08" cell margin comes from the Normal Table default table style; without a default table style a table that sets no margins (and whose style sets none) has zero margins. The zeros are kept as the table's own, also for the old properties of a tblPrChange, so they survive saving. w:default="on" now marks a default style too.

crates/docx/src/read.rs

@@ -119,6 +119,10 @@ pub(crate) struct Reader<'p> {
     pub theme_fills: shape_style::ThemeFills,
     /// The fill of the group being read (what its members' `a:grpFill` stands for).
     pub group_fill: Option<craft_wordmodel::fill::Fill>,
+    /// The package has no default table style (no styles part, or none marked `w:default`):
+    /// Word then gives tables no cell margins rather than its Normal Table's 0.08". Set by
+    /// `read_styles`, which runs before any story with tables is read.
+    pub no_default_table_style: bool,
 }
 
 /// The package path that internal relationship `id` points at, if it has type `kind` (an `rt`
@@ -193,6 +197,7 @@ fn read_opened_in(pkg: &Package, chunks: ChunkState) -> Result<(Document, usize,
         theme_fills: Default::default(),
         group_fill: None,
         chunks,
+        no_default_table_style: true,
     };
     r.doc.missing_pictures.main = main.clone();
     r.pc.major_font = r.doc.settings.major_font.clone();

crates/docx/src/read/story/blocks.rs

@@ -314,15 +314,32 @@ impl Reader<'_> {
 
     // ---- tables ----
 
+    /// Word gives a table no cell margins when the file has no default table style and neither the
+    /// table nor its style sets them; saving may write a default Normal Table, so the zeros are
+    /// kept as the table's own. shortcut: they stay direct formatting (a table style applied later
+    /// keeps them), until the model knows the file's default table style. A `w:tblCellMar` that sets
+    /// only some sides keeps them: only the sides it omits become 0.
+    fn no_default_margins(&self, props: &mut craft_wordmodel::props::TableProps) {
+        if self.no_default_table_style
+            && props.cell_margins.is_none()
+            && props.style.as_deref().and_then(|id| self.doc.styles.table_style(id)).is_none_or(|s| s.parts.cell_margins.is_none())
+        {
+            props.cell_margins = Some([0.0; 4]);
+        }
+    }
+
     fn read_table(&mut self, sc: &mut StoryCtx, t: &El, rels: &Rels, depth: usize) -> Option<Table> {
         let mut table = Table::default();
         if let Some(p) = t.child("w:tblPr") {
             table.props = self.pc.tblpr(p);
             if let Some(ch) = p.child("w:tblPrChange") {
-                let old = ch.child("w:tblPr").map(|o| self.pc.tblpr(o)).unwrap_or_default();
+                let mut old = ch.child("w:tblPr").map(|o| self.pc.tblpr(o)).unwrap_or_default();
+                // Rejecting the change brings back these properties: with the same margins.
+                self.no_default_margins(&mut old);
                 table.props.fmt_change = PropChange::boxed(self.revision(RevisionKind::Format, ch), old);
             }
         }
+        self.no_default_margins(&mut table.props);
         if let Some(g) = t.child("w:tblGrid") {
             table.grid = g
                 .children("w:gridCol")

crates/docx/src/read/styles.rs

@@ -64,6 +64,20 @@ fn builtin_heading_level(name: &str) -> Option<u8> {
 }
 
 impl Reader<'_> {
+    /// Whether a style's kept (last) definition is a default table style.
+    fn has_default_table_style(&self, root: &El) -> bool {
+        let mut defaults: Vec<String> = Vec::new();
+        for s in root.children("w:style").take(10_000) {
+            let Some(raw_id) = s.attr("w:styleId").filter(|i| !i.is_empty()) else { continue };
+            let id = self.pc.style_id(raw_id);
+            defaults.retain(|d| *d != id);
+            if s.attr("w:type") == Some("table") && style_is_default(s) {
+                defaults.push(id);
+            }
+        }
+        !defaults.is_empty()
+    }
+
     pub(super) fn read_styles(&mut self, path: &str) -> Result<(), DocxError> {
         /// Largest `w:latentStyles` kept (Word's has ~380 exceptions, ~40 KB).
         const MAX_LATENT_STYLES_XML: usize = 1 << 20;
@@ -207,6 +221,7 @@ impl Reader<'_> {
                 None => sheet.styles.push(st),
             }
         }
+        self.no_default_table_style = !self.has_default_table_style(&root);
         // Styles that give only a list level take the list from the style they are based on
         // (Heading 3: level 3 of Heading 2's outline list).
         let fixed: Vec<Option<craft_wordmodel::props::NumRef>> = sheet

crates/docx/tests/it/cell_margin_inheritance.rs

@@ -28,3 +28,73 @@ fn partial_margin_stays_partial() {
     assert!(!margins.contains("<w:bottom"));
     assert!(!margins.contains("<w:right"));
 }
+
+/// A package with this body and, if given, this styles part.
+fn package(body: &str, styles: Option<&str>) -> Vec<u8> {
+    const W: &str = "http://schemas.openxmlformats.org/wordprocessingml/2006/main";
+    let mut zip = zip::ZipWriter::new(Cursor::new(Vec::new()));
+    let mut add = |name: &str, xml: &str| {
+        zip.start_file(name, zip::write::SimpleFileOptions::default()).unwrap();
+        zip.write_all(xml.as_bytes()).unwrap();
+    };
+    add("word/document.xml", &format!(r#"<w:document xmlns:w="{W}"><w:body>{body}</w:body></w:document>"#));
+    if let Some(styles) = styles {
+        add("word/styles.xml", &format!(r#"<w:styles xmlns:w="{W}">{styles}</w:styles>"#));
+        add(
+            "word/_rels/document.xml.rels",
+            r#"<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/styles" Target="styles.xml"/></Relationships>"#,
+        );
+    }
+    zip.finish().unwrap().into_inner()
+}
+
+/// Without a default table style (no styles part, or none marked `w:default`) Word gives a table
+/// no cell margins: a cell that sets only its right margin has none on its other sides.
+#[test]
+fn no_default_table_style_means_no_cell_margins() {
+    let body = r#"<w:tbl><w:tblPr><w:tblW w:w="6000" w:type="dxa"/></w:tblPr><w:tblGrid><w:gridCol w:w="3000"/></w:tblGrid><w:tr><w:tc><w:tcPr><w:tcMar><w:right w:w="108" w:type="dxa"/></w:tcMar></w:tcPr><w:p/></w:tc></w:tr></w:tbl>"#;
+    let normal_table = r#"<w:style w:type="table" w:default="1" w:styleId="TableNormal"><w:name w:val="Normal Table"/><w:tblPr><w:tblCellMar><w:left w:w="108" w:type="dxa"/><w:right w:w="108" w:type="dxa"/></w:tblCellMar></w:tblPr></w:style>"#;
+    let margins = |styles: Option<&str>| {
+        let doc = craft_docx::read(&package(body, styles)).unwrap();
+        let table = doc.body[0].as_table().unwrap();
+        (table.props.cell_margins, table.rows[0].cells[0].props.resolved_margins(table.props.cell_margins.unwrap_or([0.0, 5.4, 0.0, 5.4])))
+    };
+    assert_eq!(margins(None), (Some([0.0; 4]), [0.0, 0.0, 0.0, 5.4]));
+    assert_eq!(margins(Some(r#"<w:docDefaults/>"#)), (Some([0.0; 4]), [0.0, 0.0, 0.0, 5.4]));
+    // With Word's usual Normal Table the table keeps no margins of its own (the defaults apply).
+    assert_eq!(margins(Some(normal_table)).0, None);
+    // A style defined twice is its last definition: a default one redefined as not default leaves none.
+    let redefined = format!(r#"{normal_table}<w:style w:type="table" w:styleId="TableNormal"><w:name w:val="Normal Table"/></w:style>"#);
+    assert_eq!(margins(Some(&redefined)).0, Some([0.0; 4]));
+    // A custom default table style marked `on` is a default too, also after saving and reopening.
+    let plain = r#"<w:style w:type="table" w:default="on" w:customStyle="1" w:styleId="Plain"><w:name w:val="Plain"/></w:style>"#;
+    let doc = craft_docx::read(&package(body, Some(plain))).unwrap();
+    assert_eq!(doc.body[0].as_table().unwrap().props.cell_margins, None);
+    let reopened = craft_docx::read(&craft_docx::write(&doc).unwrap()).unwrap();
+    assert_eq!(reopened.body[0].as_table().unwrap().props.cell_margins, None);
+    // A table that sets only some sides keeps them; the sides it omits are 0.
+    let partial = body.replace("<w:tblPr>", r#"<w:tblPr><w:tblCellMar><w:left w:w="144" w:type="dxa"/></w:tblCellMar>"#);
+    let doc = craft_docx::read(&package(&partial, None)).unwrap();
+    assert_eq!(doc.body[0].as_table().unwrap().props.cell_margins, Some([0.0, 7.2, 0.0, 0.0]));
+    // Rejecting a tracked change to the table's properties brings back the same zero margins.
+    let tracked = body.replace(
+        "</w:tblPr>",
+        r#"<w:tblPrChange w:id="1" w:author="A" w:date="2026-11-13T00:00:00Z"><w:tblPr><w:tblW w:w="5000" w:type="dxa"/></w:tblPr></w:tblPrChange></w:tblPr>"#,
+    );
+    let doc = craft_docx::read(&package(&tracked, None)).unwrap();
+    let change = doc.body[0].as_table().unwrap().props.fmt_change.as_deref().expect("a tracked table change");
+    assert_eq!(change.old.cell_margins, Some([0.0; 4]));
+    // A table whose own style gives margins keeps them.
+    let styled = body.replace("<w:tblPr>", r#"<w:tblPr><w:tblStyle w:val="Boxed"/>"#);
+    let boxed = r#"<w:style w:type="table" w:styleId="Boxed"><w:name w:val="Boxed"/><w:tblPr><w:tblCellMar><w:left w:w="144" w:type="dxa"/></w:tblCellMar></w:tblPr></w:style>"#;
+    let doc = craft_docx::read(&package(&styled, Some(boxed))).unwrap();
+    assert_eq!(doc.body[0].as_table().unwrap().props.cell_margins, None);
+    // The zeros survive saving, which writes a default Normal Table.
+    let doc = craft_docx::read(&package(body, None)).unwrap();
+    let bytes = craft_docx::write(&doc).unwrap();
+    let mut xml = String::new();
+    zip::ZipArchive::new(Cursor::new(bytes.clone())).unwrap().by_name("word/document.xml").unwrap().read_to_string(&mut xml).unwrap();
+    assert!(xml.contains("<w:tblCellMar>"), "{xml}");
+    let reopened = craft_docx::read(&bytes).unwrap();
+    assert_eq!(reopened.body[0].as_table().unwrap().props.cell_margins, Some([0.0; 4]));
+}