fix(shared): preserve final quoted empty CSV records

packages/shared/src/delimitedPreview.test.ts

@@ -21,6 +21,35 @@ describe("delimited file previews", () => {
       ["", "three"],
     ]);
   });
+  describe.each([",", "\t"] as const)("with delimiter %j", (delimiter) => {
+    it("preserves a final quoted empty record without requiring a line ending", () => {
+      for (const ending of ["", "\n", "\r\n"]) {
+        expect(parseDelimitedPreview(`name\r\nAlice\r\n""${ending}`, delimiter)).toEqual({
+          rows: [["name"], ["Alice"], [""]],
+          truncated: false,
+        });
+      }
+      expect(parseDelimitedPreview('""', delimiter)).toEqual({
+        rows: [[""]],
+        truncated: false,
+      });
+    });
+    it("does not invent records for empty input or a trailing line ending", () => {
+      for (const prefix of ["", "\ufeff"]) {
+        expect(parseDelimitedPreview(prefix, delimiter).rows).toEqual([]);
+        expect(parseDelimitedPreview(`${prefix}name\r\n`, delimiter).rows).toEqual([["name"]]);
+        expect(parseDelimitedPreview(`${prefix}""`, delimiter).rows).toEqual([[""]]);
+      }
+    });
+    it("keeps a quoted empty record at the row limit", () => {
+      const text = `${"name\n".repeat(99)}""`;
+      const preview = parseDelimitedPreview(text, delimiter);
+      expect(preview.rows).toHaveLength(100);
+      expect(preview.rows.at(-1)).toEqual([""]);
+      expect(preview.truncated).toBe(false);
+      expect(parseDelimitedPreview(`${text}\nextra`, delimiter).truncated).toBe(true);
+    });
+  });
   it("bounds rows, columns and cell length and reports partial content", () => {
     const table = parseDelimitedPreview(
       Array.from({ length: 101 }, () =>

packages/shared/src/delimitedPreview.ts

@@ -16,12 +16,13 @@ export function parseDelimitedPreview(text: string, delimiter: "," | "\t") {
   let cell = "";
   let quoted = false;
   let truncated = false;
+  let rowStart = text.charCodeAt(0) === 0xfeff ? 1 : 0;
   const endCell = () => {
     if (row.length < 30) row.push(cell);
     else truncated = true;
     cell = "";
   };
-  for (let index = text.charCodeAt(0) === 0xfeff ? 1 : 0; index < text.length; index++) {
+  for (let index = rowStart; index < text.length; index++) {
     const char = text[index];
     if (char === '"') {
       if (quoted && text[index + 1] === '"') {
@@ -41,12 +42,13 @@ export function parseDelimitedPreview(text: string, delimiter: "," | "\t") {
         rows.push(row);
         row = [];
         if (char === "\r" && text[index + 1] === "\n") index++;
+        rowStart = index + 1;
         if (rows.length === 100) return { rows, truncated: truncated || index < text.length - 1 };
       }
     } else if (cell.length < 2000) cell += char;
     else truncated = true;
   }
-  if (cell.length || row.length) {
+  if (rowStart < text.length) {
     endCell();
     rows.push(row);
   }