feat: custom error codes (#1114)

errors/errors.go

@@ -0,0 +1,40 @@
+package errors
+
+import "errors"
+
+// General exit codes
+const (
+	CodeOk      int = iota // Used when the program exits without errors
+	CodeUnknown            // Used when no other exit code is appropriate
+)
+
+// Taskfile related exit codes
+const (
+	CodeTaskfileNotFound int = iota + 100
+	CodeTaskfileAlreadyExists
+	CodeTaskfileInvalid
+)
+
+// Task related exit codes
+const (
+	CodeTaskNotFound int = iota + 200
+	CodeTaskRunError
+	CodeTaskInternal
+	CodeTaskNameConflict
+	CodeTaskCalledTooManyTimes
+)
+
+// TaskError extends the standard error interface with a Code method. This code will
+// be used as the exit code of the program which allows the user to distinguish
+// between different types of errors.
+type TaskError interface {
+	error
+	Code() int
+}
+
+// New returns an error that formats as the given text. Each call to New returns
+// a distinct error value even if the text is identical. This wraps the standard
+// errors.New function so that we don't need to alias that package.
+func New(text string) error {
+	return errors.New(text)
+}