exec: use custom error for LookPath

Make the error message and the needed action more obvious
when a command isn't found to obtain the source code
of a project.  Users seem to strugle with the existing
wording in practice.

R=rsc
CC=golang-dev
https://golang.org/cl/4058047

1 files changed, 11 insertions, 0 deletions

diff --git a/src/pkg/exec/exec.go b/src/pkg/exec/exec.go
index ba9bd2472a..4f4c8c7770 100644
--- a/src/pkg/exec/exec.go
+++ b/src/pkg/exec/exec.go
@@ -7,6 +7,7 @@ package exec
 
 import (
 	"os"
+	"strconv"
 )
 
 // Arguments to Run.
@@ -29,6 +30,16 @@ type Cmd struct {
 	Pid    int
 }
 
+// PathError records the name of a binary that was not
+// found on the current $PATH.
+type PathError struct {
+	Name string
+}
+
+func (e *PathError) String() string {
+	return "command " + strconv.Quote(e.Name) + " not found in $PATH"
+}
+
 // Given mode (DevNull, etc), return file for child
 // and file to record in Cmd structure.
 func modeToFiles(mode, fd int) (*os.File, *os.File, os.Error) {