fix: a table aligned to the margins fills the text width

ODF's table:align="margins" means the table spans between its own margins, and
style:width is then the width the producing page had. Read as a left-aligned
table, the undeclared right margin was derived from that width against ours and
the table came out narrow — measured 12.4cm on a 14.7cm text width, its column
rule 10.4mm left of where LibreOffice draws it.

src/lib/import/odt.ts

@@ -2881,8 +2881,12 @@ function tableMargins(el: Element, ctx: Ctx): { marginLeft?: number; marginRight
 
   let left = lengthToCm(props['fo:margin-left']);
   let right = lengthToCm(props['fo:margin-right']);
+  const align = props['table:align'];
+  // "margins" is ODF for a table filling the space between its own: the side it does
+  // not declare is 0, and style:width is the width the producer's page had, not one to
+  // measure a margin against.
+  if (align === 'margins') { left ??= 0; right ??= 0; }
   if (left == null && width != null) {
-    const align = props['table:align'];
     left = align === 'center' ? (content - width) / 2 : align === 'right' ? content - width : 0;
   }
   left = left ?? 0; // negative is real: a table may hang into the page margin

tests/unit/table-align-margins.test.ts

@@ -0,0 +1,56 @@
+import { describe, it, expect } from 'vitest';
+import { zipSync, strToU8 } from 'fflate';
+import { importOdt } from '../../src/lib/import/odt';
+
+// table:align="margins" is a table stretched between the text margins. Its style:width
+// is the width the producing page had, so deriving a margin from it against ours leaves
+// the table narrow — measured 12.4cm on a 14.7cm text width.
+const NS =
+  'xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0" ' +
+  'xmlns:style="urn:oasis:names:tc:opendocument:xmlns:style:1.0" ' +
+  'xmlns:fo="urn:oasis:names:tc:opendocument:xmlns:xsl-fo-compatible:1.0" ' +
+  'xmlns:table="urn:oasis:names:tc:opendocument:xmlns:table:1.0" ' +
+  'xmlns:text="urn:oasis:names:tc:opendocument:xmlns:text:1.0"';
+
+function odtWithTable(tableProps: string): Uint8Array {
+  const styles = `<?xml version="1.0"?><office:document-styles ${NS}><office:styles>
+   <style:style style:name="Standard" style:family="paragraph"/>
+  </office:styles><office:automatic-styles>
+   <style:page-layout style:name="pm1"><style:page-layout-properties
+     fo:page-width="21cm" fo:page-height="29.7cm" fo:margin-left="3.6cm" fo:margin-right="2.7cm"/></style:page-layout>
+  </office:automatic-styles><office:master-styles>
+   <style:master-page style:name="Standard" style:page-layout-name="pm1"/>
+  </office:master-styles></office:document-styles>`;
+  const content = `<?xml version="1.0"?><office:document-content ${NS}><office:automatic-styles>
+   <style:style style:name="T1" style:family="table"><style:table-properties ${tableProps}/></style:style>
+  </office:automatic-styles><office:body><office:text>
+   <table:table table:name="T" table:style-name="T1">
+    <table:table-column/>
+    <table:table-row><table:table-cell><text:p text:style-name="Standard">a</text:p></table:table-cell></table:table-row>
+   </table:table>
+  </office:text></office:body></office:document-content>`;
+  return zipSync({ 'content.xml': strToU8(content), 'styles.xml': strToU8(styles) });
+}
+
+const attrsOf = (tableProps: string) =>
+  (importOdt(odtWithTable(tableProps)).content.content?.[0] as { attrs?: Record<string, unknown> }).attrs ?? {};
+
+describe('a table aligned to the margins', () => {
+  it('keeps the full text width whatever width the producer wrote', () => {
+    const attrs = attrsOf('style:width="14.7cm" table:align="margins"');
+    expect(attrs.marginLeft).toBeUndefined();
+    expect(attrs.marginRight).toBeUndefined();
+  });
+
+  it('still honours the margins the file declares itself', () => {
+    const attrs = attrsOf('style:width="12cm" table:align="margins" fo:margin-left="1.5cm"');
+    expect(attrs.marginLeft).toBe(1.5);
+    expect(attrs.marginRight).toBeUndefined();
+  });
+
+  it('leaves a centred table centred', () => {
+    const attrs = attrsOf('style:width="10.7cm" table:align="center"');
+    expect(attrs.marginLeft).toBe(2);
+    expect(attrs.marginRight).toBe(2);
+  });
+});