Catch any os.Stat error

[spenserblack]

tl;dr I discovered some weird Windows behavior where an invalid path causes scc.exe to panic. Surprisingly, the error is not a "does not exist" error. After some thought it seemed better to exit on any non-nil error.

In PowerShell, I tried to run scc.exe *.go, and to my surprise I got a panic. PowerShell did not expand the glob -- that's not scc's fault, although potentially glob expansion can be added as a feature if that's reasonable. But the issue is that, on Windows, apparently this does not raise a "does not exist" error. So os.Stat() returns nil, err where err is not nil. So the call to s.IsDir() raises a nil pointer dereference error.

I did some playing around using the code below:

package main

import "os"
import "path/filepath"
import "fmt"
import "io/fs"

func main() {
	arg := "."
	if len(os.Args) > 1 {
		arg = os.Args[1]
	}
	arg = filepath.Clean(arg)
	fmt.Println("statting", arg)
	s, err := os.Stat(arg)
	fmt.Printf("s = %v, err = %v\n", s, err)

	checks := []struct {
		name  string
		check func(err error) bool
	}{
		{
			name:  "IsNotExist",
			check: os.IsNotExist,
		},
		{
			name:  "IsExist",
			check: os.IsExist,
		},
		{
			name:  "IsPermission",
			check: os.IsPermission,
		},
	}

	for _, c := range checks {
		fmt.Println(c.name, c.check(err))
	}

	if err, ok := err.(*fs.PathError); ok {
		fmt.Println("err.Op =", err.Op)
	}
}

And here's the result of go run .\main.go "?":

statting ?
s = <nil>, err = CreateFile ?: The filename, directory name, or volume label syntax is incorrect.
IsNotExist false
IsExist false
IsPermission false
err.Op = CreateFile

Perhaps unexpectedly, filepath.Clean does not clean the invalid character ?. Also, CreateFile is not the op that I would expect 🤔

At first I wanted to narrow down to exactly the error type, but then I figured that it should be fine to treat any os.Stat error the same, especially with more unusual errors like these.

[boyter]

Now that is a doozy. Thanks so much for the investigation. No idea what I was thinking there, you would have thought I would have caught all errors after checking, but apparently not. Thanks for this and it will make it into the next release.

[spenserblack]

To be fair it's pretty hard to find if you don't have a Windows machine. I honestly don't know how I'd trigger it on Linux, since AFAIK any character is valid in a path name, even if it's not valid in a filename. And it's perfectly reasonable to assume that filepath.Clean would return a valid path 😅