q.Check and q.CheckE

The error-only bubble — for functions that return just error (file.Close, db.Ping, validate(input)).

Signatures

func Check(err error)
func CheckE(err error) CheckResult

Both return nothing. Consequence: q.Check(...) and q.CheckE(...) only make sense as expression statements — v := q.Check(...) is a Go type error, caught by the compiler before the rewriter runs. That's deliberate: q only accepts what gopls accepts.

What q.Check does

q.Check(db.Ping())

rewrites to:

_qErr1 := db.Ping()
if _qErr1 != nil {
    return /* zeros */, _qErr1
}

The enclosing function's last result must be error for the bubble to land anywhere.

Chain methods on q.CheckE

All methods return void. Every one of them maps to the same shape as the q.TryE counterpart, minus the value.

Method	Bubbled error
.Err(replacement error)	replacement
.ErrF(fn func(error) error)	fn(capturedErr)
.Wrap(msg string)	fmt.Errorf("<msg>: %w", capturedErr)
.Wrapf(format string, args ...any)	fmt.Errorf("<format>: %w", args..., capturedErr)
.Catch(fn func(error) error)	fn(err) — nil suppresses the bubble, non-nil bubbles that error in place of the original

The .Catch signature is func(error) error (not func(error) (T, error) as in TryE) because there is no T to recover. Returning nil is the "swallow this" shape:

q.CheckE(file.Close()).Catch(func(e error) error {
    if errors.Is(e, os.ErrClosed) {
        return nil                    // already closed — not an error we care about
    }
    return e                          // bubble everything else
})

Examples

func shutdown(db *sql.DB, file *os.File) error {
    q.Check(db.Ping())                          // bubble db.Ping's err unchanged
    q.CheckE(file.Close()).Wrap("closing log")  // wrap with message + %w
    q.Check(db.Close())
    return nil
}

Not supported

• v := q.Check(...) — Check returns (); this is a Go type error.
• return q.Check(...), 0, nil — same reason, can't use void in a return tuple.
• q.Check as a return-position or hoist argument — both require a value.

See also

• q.Try — for (T, error) values