fix(tsql): skip gap-fill on descending bucket order

A bucket-led ORDER BY DESC combined with fillGaps emitted an ascending WITH FILL (positive step, ascending bounds), which produces invalid or empty fills. Skip the gap-fill rewrite for descending orders and let the plain descending query stand. Adds a DESC fillGaps test.

Author: ericallam

internal-packages/tsql/src/query/printer.test.ts

@@ -3971,4 +3971,14 @@ describe("timeBucket() fillGaps", () => {
     expect(sql).not.toContain("WITH FILL");
     expect(sql).not.toContain("INTERPOLATE");
   });
+
+  it("bucket-led ORDER BY DESC: fill is skipped (ascending fill would be invalid)", () => {
+    const query =
+      "SELECT timeBucket(), count() AS runs FROM metrics GROUP BY timeBucket ORDER BY timeBucket DESC";
+    const { sql } = run(query, true);
+    expect(sql).not.toContain("WITH FILL");
+    expect(sql).not.toContain("INTERPOLATE");
+    // The plain descending order still stands.
+    expect(sql).toContain("ORDER BY timebucket DESC");
+  });
 });

internal-packages/tsql/src/query/printer.ts

@@ -652,16 +652,24 @@ export class ClickHousePrinter {
     // js/polynomial-redos). endsWith + slice is linear.
     const trimmedLead = leadTerm.trim();
     const upperLead = trimmedLead.toUpperCase();
+    const isDescending = upperLead.endsWith(" DESC");
     const leadExpr = upperLead.endsWith(" ASC")
       ? trimmedLead.slice(0, -4).trimEnd()
-      : upperLead.endsWith(" DESC")
+      : isDescending
         ? trimmedLead.slice(0, -5).trimEnd()
         : trimmedLead;
     const matchesBucket = (expr: string): boolean =>
       expr.toLowerCase() === bucketAlias!.toLowerCase() || expr === bucketSql;
     if (!matchesBucket(leadExpr)) {
       return null;
     }
+    // WITH FILL is emitted with ascending bounds and a positive STEP, which is
+    // only valid for an ascending bucket order. A descending order would need
+    // swapped bounds and a negative step (newer ClickHouse only), so skip the
+    // gap-fill rewrite and let the plain descending ORDER BY stand.
+    if (isDescending) {
+      return null;
+    }
 
     // Group dims = GROUP BY expressions that are NOT the timeBucket column.
     const groupDims = (groupBy ?? []).filter((g) => !matchesBucket(g.trim()));