code review 5711044: os: diagnose chdir error during StartProcess

src/pkg/os/exec_posix.go

 // Copyright 2009 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.
 
 // +build darwin freebsd linux netbsd openbsd windows
 
 package os
 
 import (
         "syscall"
 )
 
 // StartProcess starts a new process with the program, arguments and attributes
 // specified by name, argv and attr.
 //
 // StartProcess is a low-level interface. The os/exec package provides
 // higher-level interfaces.
 //
 // If there is an error, it will be of type *PathError.
 func StartProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
+        // Double-check existence of the directory we want
+        // to chdir into.  We can make the error clearer this way.
+        if attr != nil && attr.Dir != "" {
+                if _, err := Stat(attr.Dir); err != nil {
+                        pe := err.(*PathError)
+                        pe.Op = "chdir"
+                        return nil, pe
+                }
+        }
+
         sysattr := &syscall.ProcAttr{
                 Dir: attr.Dir,
                 Env: attr.Env,
                 Sys: attr.Sys,
         }
         if sysattr.Env == nil {
                 sysattr.Env = Environ()
         }
         for _, f := range attr.Files {
                 sysattr.Files = append(sysattr.Files, f.Fd())
@@ skipping 92 matching lines @@
                         res += " (trap " + itod(status.TrapCause()) + ")"
                 }
         case status.Continued():
                 res = "continued"
         }
         if status.CoreDump() {
                 res += " (core dumped)"
         }
         return res
 }