cmd: relocate cmd/go/internal/script to cmd/internal/script

Relocate cmd/go's internal/script package up a level into
cmd/internal/script, so as to enable the use of script tests in
other cmd packages.  No change in functionality.

Updates #68606.

Change-Id: I3974b0bf59c76e0f459184c9f3090d6077dd5d91
Reviewed-on: https://go-review.googlesource.com/c/go/+/601358
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 64 insertions, 0 deletions

diff --git a/src/cmd/internal/script/errors.go b/src/cmd/internal/script/errors.go
new file mode 100644
index 0000000000..7f43e72888
--- /dev/null
+++ b/src/cmd/internal/script/errors.go
@@ -0,0 +1,64 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package script
+
+import (
+	"errors"
+	"fmt"
+)
+
+// ErrUnexpectedSuccess indicates that a script command that was expected to
+// fail (as indicated by a "!" prefix) instead completed successfully.
+var ErrUnexpectedSuccess = errors.New("unexpected success")
+
+// A CommandError describes an error resulting from attempting to execute a
+// specific command.
+type CommandError struct {
+	File string
+	Line int
+	Op   string
+	Args []string
+	Err  error
+}
+
+func cmdError(cmd *command, err error) *CommandError {
+	return &CommandError{
+		File: cmd.file,
+		Line: cmd.line,
+		Op:   cmd.name,
+		Args: cmd.args,
+		Err:  err,
+	}
+}
+
+func (e *CommandError) Error() string {
+	if len(e.Args) == 0 {
+		return fmt.Sprintf("%s:%d: %s: %v", e.File, e.Line, e.Op, e.Err)
+	}
+	return fmt.Sprintf("%s:%d: %s %s: %v", e.File, e.Line, e.Op, quoteArgs(e.Args), e.Err)
+}
+
+func (e *CommandError) Unwrap() error { return e.Err }
+
+// A UsageError reports the valid arguments for a command.
+//
+// It may be returned in response to invalid arguments.
+type UsageError struct {
+	Name    string
+	Command Cmd
+}
+
+func (e *UsageError) Error() string {
+	usage := e.Command.Usage()
+	suffix := ""
+	if usage.Async {
+		suffix = " [&]"
+	}
+	return fmt.Sprintf("usage: %s %s%s", e.Name, usage.Args, suffix)
+}
+
+// ErrUsage may be returned by a Command to indicate that it was called with
+// invalid arguments; its Usage method may be called to obtain details.
+var ErrUsage = errors.New("invalid usage")