cmd/gofmt: go fmt not working when go:embed file is missing

[mewmew]

What version of Go are you using (go version)?

$ go version
go version devel +2ff33f5e44 Thu Dec 17 16:03:19 2020 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/u/.cache/go-build"
GOENV="/home/u/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/u/goget/pkg/mod"
GOOS="linux"
GOPATH="/home/u/goget"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/u/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/u/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="devel +2ff33f5e44 Thu Dec 17 16:03:19 2020 +0000"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3114393024=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Repository to reproduce issue: https://github.com/mewspring/embed-test

I tried to use go fmt to format main.go.

The main.go source file contains a go:embed directive reading the text file version.txt. This text file is generated by the gen_version.sh script.

Trying to run go fmt prior to generating the version.txt file fails, with the error message pattern version.txt: no matching files found.

$ git clone https://github.com/mewspring/embed-test
$ cd embed-test
$ go fmt
# Outputs: pattern version.txt: no matching files found

Generating version.txt using ./gen_version.sh and then running go fmt succeeds.

$ git clone https://github.com/mewspring/embed-test
$ cd embed-test
$ ./gen_version.sh
$ go fmt
# Outputs: main.go (as it was successfully formatted)

What did you expect to see?

Go fmt successfully formatting the source code (even if files or directives listed in go:embed directive are missing).

The contents of go:embed directives should only matter for the compilation step, not source code formatting.

Note: a warning may still be issued by go fmt if preferable, but this should not interrupt the formatting of the source file.

What did you see instead?

Trying to run go fmt prior to generating the version.txt file fails, with the error message pattern version.txt: no matching files found.

[dmitshur]

CC @rsc.

[bcmills]

CC @jayconrod @matloob

[bcmills]

This may be (fairly closely) related to #39442, but this particular issue is specific to the go:embed feature that is new in 1.16, so marking as release-blocker for 1.16.

[gopherbot]

Change https://golang.org/cl/280452 mentions this issue: cmd/go: remove check of existence of embed files

[iwdgo]

There does not seem to be any reason to expect embedded files to be present when go fmt is used.
The error message would be emitted during go build.

$ goissue fmt
main.go

$ goissue build
# github.com/mewspring/embed-test
.\main.go:11:5: go:embed cannot find file

$ goissue generate

$ goissue build

$ ls
embed-test.exe*  gen_version.sh*  go.mod  main.go  version.txt  version_date.txt  version_tag_and_commit.txt

[cagedmantis]

Friendly ping as this is a release blocker and the release is approaching.

[bcmills]

@cagedmantis, this was blocked on #43632. (There is current activity on https://golang.org/cl/280452.)

[cagedmantis]

Thanks for the update!