refactor: Change all Needs Waitgroup errors into static errors.

 #lint

internal/exporter/export.go

@@ -83,13 +83,18 @@ func DisableExport() Option {
 	}
 }
 
+var (
+	ErrNeedsStore     = errors.New("exporter needs a Store")
+	ErrNeedsWaitgroup = errors.New("exporter needs a WaitGroup")
+)
+
 // New creates a new Exporter.
 func New(ctx context.Context, wg *sync.WaitGroup, store *metrics.Store, options ...Option) (*Exporter, error) {
 	if store == nil {
-		return nil, errors.New("exporter needs a Store")
+		return nil, ErrNeedsStore
 	}
 	if wg == nil {
-		return nil, errors.New("exporter needs a WaitGroup")
+		return nil, ErrNeedsWaitgroup
 	}
 	e := &Exporter{
 		ctx:      ctx,

internal/mtail/exec_integration_test.go

@@ -31,7 +31,9 @@ func TestExecMtail(t *testing.T) {
 		t.Skip()
 	}
 
-	cs := []string{"-progs", "../../examples",
+	cs := []string{
+		"-progs",
+		"../../examples",
 		"-logs", "testdata/rsyncd.log",
 		"-one_shot",
 		"-one_shot_format=prometheus",

internal/runtime/runtime.go

@@ -241,13 +241,18 @@ type Runtime struct {
 	signalQuit chan struct{} // When closed stops the signal handler goroutine.
 }
 
+var (
+	ErrNeedsStore     = errors.New("loader needs a store")
+	ErrNeedsWaitgroup = errors.New("loader needs a WaitGroup")
+)
+
 // New creates a new program loader that reads programs from programPath.
 func New(lines <-chan *logline.LogLine, wg *sync.WaitGroup, programPath string, store *metrics.Store, options ...Option) (*Runtime, error) {
 	if store == nil {
-		return nil, errors.New("loader needs a store")
+		return nil, ErrNeedsStore
 	}
 	if wg == nil {
-		return nil, errors.New("loader needs a WaitGroup")
+		return nil, ErrNeedsWaitgroup
 	}
 	r := &Runtime{
 		ms:            store,

internal/tailer/logstream/logstream.go

@@ -46,6 +46,7 @@ var (
 	ErrUnsupportedURLScheme = errors.New("unsupported URL scheme")
 	ErrUnsupportedFileType  = errors.New("unsupported file type")
 	ErrEmptySocketAddress   = errors.New("socket address cannot be empty, please provide a unix domain socket filename or host:port")
+	ErrNeedsWaitgroup       = errors.New("logstream needs a waitgroup")
 )
 
 // New creates a LogStream from the file object located at the absolute path
@@ -55,7 +56,7 @@ var (
 // files that can be seeked.
 func New(ctx context.Context, wg *sync.WaitGroup, waker waker.Waker, pathname string, lines chan<- *logline.LogLine, oneShot bool) (LogStream, error) {
 	if wg == nil {
-		return nil, errors.New("logstream needs a WaitGroup")
+		return nil, ErrNeedsWaitgroup
 	}
 	u, err := url.Parse(pathname)
 	if err != nil {

internal/tailer/tail.go

@@ -127,15 +127,18 @@ func (opt logstreamPollWaker) apply(t *Tailer) error {
 	return nil
 }
 
-var ErrNoLinesChannel = errors.New("Tailer needs a lines channel")
+var (
+	ErrNoLinesChannel = errors.New("Tailer needs a lines channel")
+	ErrNeedsWaitgroup = errors.New("tailer needs a WaitGroup")
+)
 
 // New creates a new Tailer.
 func New(ctx context.Context, wg *sync.WaitGroup, lines chan<- *logline.LogLine, options ...Option) (*Tailer, error) {
 	if lines == nil {
 		return nil, ErrNoLinesChannel
 	}
 	if wg == nil {
-		return nil, errors.New("tailer needs a WaitGroup")
+		return nil, ErrNeedsWaitgroup
 	}
 	t := &Tailer{
 		ctx:          ctx,