Adding upstream version 0.0~git20250501.cd50c6a.

Signed-off-by: Daniel Baumann <daniel@debian.org>

join.go

@@ -0,0 +1,44 @@
+package errors
+
+import "unsafe"
+
+func Join(errs ...error) error {
+	n := 0
+	for _, err := range errs {
+		if err != nil {
+			n++
+		}
+	}
+	if n == 0 {
+		return nil
+	}
+	e := &joinError{
+		errs: make([]error, 0, n),
+	}
+	for _, err := range errs {
+		if err != nil {
+			e.errs = append(e.errs, err)
+		}
+	}
+	return e
+}
+
+type joinError struct {
+	errs []error
+}
+
+func (e *joinError) Error() string {
+	// Since Join returns nil if every value in errs is nil,
+	// e.errs cannot be empty.
+	if len(e.errs) == 1 {
+		return e.errs[0].Error()
+	}
+
+	b := []byte(e.errs[0].Error())
+	for _, err := range e.errs[1:] {
+		b = append(b, ':', ' ')
+		b = append(b, err.Error()...)
+	}
+	// At this point, b has at least one byte '\n'.
+	return unsafe.String(&b[0], len(b))
+}