cmd/go: "go generate" appears to be a silent no-op when given a missing package

[mvdan]

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

$ go version
go version devel go1.21-8d5065ce6e Tue May 9 01:28:10 2023 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes; appears to happen with 1.20.4 as well.

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

go env Output

$ go env
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/mvdan/.cache/go-build'
GOENV='/home/mvdan/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/mvdan/go/pkg/mod'
GONOPROXY='github.com/cue-unity'
GONOSUMDB='github.com/cue-unity'
GOOS='linux'
GOPATH='/home/mvdan/go'
GOPRIVATE='github.com/cue-unity'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/mvdan/tip'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLDIR='/home/mvdan/tip/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='devel go1.21-8d5065ce6e Tue May 9 01:28:10 2023 +0000'
GCCGO='gccgo'
GOAMD64='v3'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/mvdan/tip/src/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-build1520120181=/tmp/go-build -gno-record-gcc-switches'

What did you do?

$ cd $(go env GOROOT)/src
$ go list ./cmd/missing
stat /home/mvdan/tip/src/cmd/missing: directory not found
$ go generate ./cmd/missing
$ echo $?
0

What did you expect to see?

Both commands should fail on a missing package.

What did you see instead?

go generate appears to happily do nothing.

It could be due to its nature of working with broken packages, for example if the generated files are required for the package to typecheck but they are missing. However, if the package can't be located at all, that should clearly be an error. I had a weird issue at work where I thought my generator wasn't working, simply because I was making a typo when writing go generate ./some/pkg.

[cherrymui]

cc @bcmills @matloob

[bcmills]

Agreed, go generate should error out if any argument pattern fails to match at least one package.

It may be as simple as adding an error check in this loop:
https://cs.opensource.google/go/go/+/master:src/cmd/go/internal/generate/generate.go;l=204;drc=93d9035c9e8b129578d3a177fd90eb308e44a597

[gopherbot]

Change https://go.dev/cl/494836 mentions this issue: cmd/go/internal/generate: error if failed to find a package

[katexochen]

@g4s8 Maybe this change in behavior should be documented in the release notes?

[matloob]

I don't think this is a big enough change in behavior to merit a release note

[katexochen]

@matloob It is a breaking changes in an API that breaks use cases downstream (nixpkgs in my case). How can that not be enough to be mentioned in the release notes?

[matloob]

Hi @katexochen, sorry about the long delay in response. I'm curious about your use case: I'm assuming that go generate is being run by a tool with packages whose existence is not known at the time of running generate? If that is the case then we should probably mention it...