rodaine-table/PR.md

fix: pad short rows in SetRows to the number of columns

Problem

SetRows does not pad rows that have fewer cells than the table has columns. As a result, short rows render fmt's missing-argument verb, and an empty row combined with a first-column formatter panics:

tbl := table.New("A", "B", "C").WithPadding(1)
tbl.SetRows([][]string{{"x", "y"}})
tbl.Print()
// A B C
// x y %!s(MISSING)

tbl := table.New("A", "B").
	WithFirstColumnFormatter(func(f string, v ...interface{}) string { return fmt.Sprintf(f, v...) })
tbl.SetRows([][]string{{}})
tbl.Print() // panic: runtime error: index out of range [0] with length 0

AddRow already handles this: it allocates make([]string, len(t.header)) per row, so short input renders the remaining columns empty. The documented behaviour ("Rows can have less cells than the total number of columns; subsequent cells will be rendered empty.") is not honored by SetRows.

Root cause

table.go, SetRows:

for _, row := range rows {
	if len(row) > headerLength {
		t.rows = append(t.rows, row[:headerLength])
	} else {
		t.rows = append(t.rows, row) // short rows stored as-is
	}
}

Short rows are stored unchanged. Later, printRow builds one value per cell of the row and passes them to fmt.Fprintf with a format string containing len(t.header) verbs, so missing cells become %!s(MISSING). With a first-column formatter, printRow also indexes vals[0], which panics for an empty row.

Fix

Pad short rows to the number of columns, mirroring AddRow:

switch {
case len(row) > headerLength:
	t.rows = append(t.rows, row[:headerLength])
case len(row) < headerLength:
	// pad short rows so every column is rendered, matching AddRow
	padded := make([]string, headerLength)
	copy(padded, row)
	t.rows = append(t.rows, padded)
default:
	t.rows = append(t.rows, row)
}

Test

Added TestSetRowsShortRowsPadded (asserts no MISSING verb and the exact padded output) and TestSetRowsEmptyRowWithFirstColumnFormatter (asserts no panic).

• Gate (GOTOOLCHAIN=go1.25.10): go test ./... -> ok (PASS, exit 0)
• go vet ./... -> exit 0
• go build ./... -> exit 0

Counterfactual: reverting SetRows makes TestSetRowsShortRowsPadded fail with output contains missing-arg verb: "A B C \nx y %!s(MISSING)\n".

Note: gofmt -l table.go reports the file, but this is pre-existing (the Print() block near line 258 is space-indented on the base commit) and unrelated to this change; the modified region is gofmt-clean, so unrelated lines were intentionally left untouched.