exec: introduce ExitError

The existing code uses *os.Waitmsg as an os.Error,
but *os.Waitmsg is really just a stringer.

Introduce an explicit error type for the real error.

Not to be submitted until just before error goes in;
the gofix for error updates type assertions
        err.(*os.Waitmsg)
to
        err.(*exec.ExitError)

The seemingly redundant String method will become
an Error method when error goes in, and will no longer
be redundant.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5331044

diff --git a/src/pkg/exec/exec.go b/src/pkg/exec/exec.go
index aaad50846ea7d88b4a67b52eab185c682fa38643..3b818c2f659be3577730e3292eb5c46ca8f1e303 100644 (file)
--- a/src/pkg/exec/exec.go
+++ b/src/pkg/exec/exec.go
@@ -203,7 +203,7 @@ func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err os.Error) {
 // status.
 //
 // If the command fails to run or doesn't complete successfully, the
-// error is of type *os.Waitmsg. Other error types may be
+// error is of type *ExitError. Other error types may be
 // returned for I/O problems.
 func (c *Cmd) Run() os.Error {
        if err := c.Start(); err != nil {
@@ -256,6 +256,15 @@ func (c *Cmd) Start() os.Error {
        return nil
 }
 
+// An ExitError reports an unsuccessful exit by a command.
+type ExitError struct {
+       *os.Waitmsg
+}
+
+func (e *ExitError) String() string {
+       return e.Waitmsg.String()
+}
+
 // Wait waits for the command to exit.
 // It must have been started by Start.
 //
@@ -264,7 +273,7 @@ func (c *Cmd) Start() os.Error {
 // status.
 //
 // If the command fails to run or doesn't complete successfully, the
-// error is of type *os.Waitmsg. Other error types may be
+// error is of type *ExitError. Other error types may be
 // returned for I/O problems.
 func (c *Cmd) Wait() os.Error {
        if c.Process == nil {
@@ -290,7 +299,7 @@ func (c *Cmd) Wait() os.Error {
        if err != nil {
                return err
        } else if !msg.Exited() || msg.ExitStatus() != 0 {
-               return msg
+               return &ExitError{msg}
        }
 
        return copyError

diff --git a/src/pkg/exec/exec_test.go b/src/pkg/exec/exec_test.go
index 2b36e2535a4def27c788d6664ccf4b58aa3d5431..3183919f673e2ca11f37291a2462227da23d92e3 100644 (file)
--- a/src/pkg/exec/exec_test.go
+++ b/src/pkg/exec/exec_test.go
@@ -53,8 +53,8 @@ func TestCatStdin(t *testing.T) {
 func TestCatGoodAndBadFile(t *testing.T) {
        // Testing combined output and error values.
        bs, err := helperCommand("cat", "/bogus/file.foo", "exec_test.go").CombinedOutput()
-       if _, ok := err.(*os.Waitmsg); !ok {
-               t.Errorf("expected Waitmsg from cat combined; got %T: %v", err, err)
+       if _, ok := err.(*ExitError); !ok {
+               t.Errorf("expected *ExitError from cat combined; got %T: %v", err, err)
        }
        s := string(bs)
        sp := strings.SplitN(s, "\n", 2)
@@ -81,12 +81,12 @@ func TestNoExistBinary(t *testing.T) {
 func TestExitStatus(t *testing.T) {
        // Test that exit values are returned correctly
        err := helperCommand("exit", "42").Run()
-       if werr, ok := err.(*os.Waitmsg); ok {
+       if werr, ok := err.(*ExitError); ok {
                if s, e := werr.String(), "exit status 42"; s != e {
                        t.Errorf("from exit 42 got exit %q, want %q", s, e)
                }
        } else {
-               t.Fatalf("expected Waitmsg from exit 42; got %T: %v", err, err)
+               t.Fatalf("expected *ExitError from exit 42; got %T: %v", err, err)
        }
 }