cmd/go,x/mod/module: missing exclusion for COM0, LPT0 for embedded file names

[cookiengineer]

Go version

go version go1.22.1 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/cookiengineer/.cache/go-build'
GOENV='/home/cookiengineer/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/cookiengineer/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/cookiengineer/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/lib/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/lib/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.1'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/cookiengineer/whatever/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2124737729=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I tried to embed a file called aux.json.gz on GNU/Linux:

//go:embed ./subfolder/aux.json.gz
var embedded_bytes []byte

What did you see happen?

Trying to embed files on GNU/Linux systems that have aux, (or con, nul, prn, com*, lpt*) as a basename of the file cannot be embedded via go:embed.

The reason is a call to isBadEmbedName() in the resolveEmbed() method in go/internal/load/pkg.go.

The isBadEmbedName() method leads to module.CheckFilePath(name) which compares the basename of the file to the badWindowsNames slice in module/module.go.

My questions are now the following:

• Why is this the case on GNU/Linux systems?
• Why does go:embed need valid filenames for go modules?
• Why does go:embed need valid filenames for Windows? Is it unpacked temporarily when the binary is executed later, similar to squashfs, behind the scenes? Why is this not behind a host-specific tag?
• If the decision is to keep the reserved basenames, COM0 and LPT0 are missing from that list. See the linked article from the module.go file.

What did you expect to see?

I expected to be able to embed filenames when they conform to the POSIX filesystem requirements, so I think it should be possible to embed filenames with the basename of con, prn, aux, nul, com*, lpt* etc.

[seankhliao]

we expect modules to be usable cross platform, so file name restrictions apply everywhere

[gopherbot]

Change https://go.dev/cl/583836 mentions this issue: module: add COM0 and LPT0 to badWindowsNames

[gopherbot]

Change https://go.dev/cl/584335 mentions this issue: cmd: vendor golang.org/x/mod@6686f41

[matloob]

Because it's not clear if those filenames were intender to be excluded in the Microsoft documentation, I will revert this change in x/mod and revendor x/mod. If we get more conclusive evidence that the filenames are indeed excluded, we'll redo for 1.24.