fix(xlsx): let fitToWidth / fitToHeight imply fitToPage

src/_types.ts

@@ -474,8 +474,15 @@ export type PaperSizeName =
 export interface PageSetup {
   paperSize?: PaperSize
   orientation?: "portrait" | "landscape"
+  /**
+   * Scale the sheet to fit `fitToWidth` × `fitToHeight` pages instead of
+   * printing at `scale`. The writer turns this on when either count is
+   * set; pass `false` to keep the counts out of the file.
+   */
   fitToPage?: boolean
+  /** Pages wide to fit the sheet to. `0` means as many as needed. Implies `fitToPage`. */
   fitToWidth?: number
+  /** Pages tall to fit the sheet to. `0` means as many as needed. Implies `fitToPage`. */
   fitToHeight?: number
   scale?: number
   margins?: PageMargins

src/xlsx/worksheet-writer.ts

@@ -332,8 +332,9 @@ export function writeWorksheetXml(
     // `<pageSetup fitToWidth>` alone does nothing in Excel — the scaling
     // mode is switched by this flag, and the fit counts are read only
     // once it is on. It also carries `fitToPage: true` on its own, which
-    // previously emitted no XML whatsoever. See #407.
-    if (sheet.pageSetup?.fitToPage) {
+    // previously emitted no XML whatsoever. See #407. Either count also
+    // implies the flag; see `isFitToPage` (#596).
+    if (sheet.pageSetup && isFitToPage(sheet.pageSetup)) {
       sheetPrChildren.push(xmlSelfClose("pageSetUpPr", { fitToPage: 1 }))
     }
     if (sheetPrChildren.length > 0) {
@@ -1398,6 +1399,17 @@ function serializePrintOptions(ps: PageSetup | undefined): string {
 
 // ── Page Setup Serialization ─────────────────────────────────────────
 
+/**
+ * Whether the sheet prints in fit-to-page mode. The page counts do nothing
+ * without the mode, so writing them without it would be a field that looks
+ * set and prints at 100% — the counts imply the mode unless the caller
+ * says otherwise. The reader already treats either count as turning it on.
+ * See #596.
+ */
+function isFitToPage(ps: PageSetup): boolean {
+  return ps.fitToPage ?? (ps.fitToWidth !== undefined || ps.fitToHeight !== undefined)
+}
+
 function serializePageSetup(ps: PageSetup): string {
   const attrs: Record<string, string | number> = {}
 
@@ -1416,7 +1428,7 @@ function serializePageSetup(ps: PageSetup): string {
     attrs["scale"] = ps.scale
   }
 
-  if (ps.fitToPage) {
+  if (isFitToPage(ps)) {
     if (ps.fitToWidth !== undefined) {
       attrs["fitToWidth"] = ps.fitToWidth
     }

test/print-settings.test.ts

@@ -151,6 +151,49 @@ describe("page setup — writing", () => {
     expect(findChild(sheetPr, "pageSetUpPr").attrs["fitToPage"]).toBe("1")
   })
 
+  it("turns on fit to page when only the page counts are given", () => {
+    // The counts used to be dropped without `fitToPage: true`, so the
+    // sheet printed at 100%. See #596.
+    const doc = parseSheet(
+      writeXml({ name: "Test", rows: [["Data"]], pageSetup: { fitToWidth: 1, fitToHeight: 0 } }),
+    )
+
+    const ps = findChild(doc, "pageSetup")
+    expect(ps).toBeDefined()
+    expect(ps.attrs["fitToWidth"]).toBe("1")
+    expect(ps.attrs["fitToHeight"]).toBe("0")
+    const sheetPr = findChild(doc, "sheetPr")
+    expect(sheetPr).toBeDefined()
+    expect(findChild(sheetPr, "pageSetUpPr").attrs["fitToPage"]).toBe("1")
+  })
+
+  it("turns on fit to page when only fitToHeight is given", () => {
+    const doc = parseSheet(
+      writeXml({ name: "Test", rows: [["Data"]], pageSetup: { fitToHeight: 2 } }),
+    )
+
+    const ps = findChild(doc, "pageSetup")
+    expect(ps).toBeDefined()
+    expect(ps.attrs["fitToHeight"]).toBe("2")
+    expect(ps.attrs["fitToWidth"]).toBeUndefined()
+    const sheetPr = findChild(doc, "sheetPr")
+    expect(sheetPr).toBeDefined()
+    expect(findChild(sheetPr, "pageSetUpPr").attrs["fitToPage"]).toBe("1")
+  })
+
+  it("lets an explicit fitToPage: false override the page counts", () => {
+    const doc = parseSheet(
+      writeXml({
+        name: "Test",
+        rows: [["Data"]],
+        pageSetup: { fitToPage: false, fitToWidth: 1, fitToHeight: 0 },
+      }),
+    )
+
+    expect(findChild(doc, "sheetPr")).toBeUndefined()
+    expect(findChild(doc, "pageSetup")).toBeUndefined()
+  })
+
   it("writes all paper sizes correctly", () => {
     const paperSizes: Array<[string, string]> = [
       ["letter", "1"],
@@ -458,6 +501,17 @@ describe("page setup — round-trip", () => {
     expect(ps!.fitToHeight).toBeUndefined()
   })
 
+  it("round-trips the page counts without fitToPage (#596)", async () => {
+    const data = await writeXlsx({
+      sheets: [{ name: "Sheet1", rows: [["Data"]], pageSetup: { fitToWidth: 1, fitToHeight: 0 } }],
+    })
+
+    const ps = (await readXlsx(data)).sheets[0].pageSetup
+    expect(ps!.fitToPage).toBe(true)
+    expect(ps!.fitToWidth).toBe(1)
+    expect(ps!.fitToHeight).toBe(0)
+  })
+
   it("round-trips all paper sizes", async () => {
     const sizes = ["letter", "legal", "a3", "a4", "a5", "b4", "b5", "executive", "tabloid"] as const