cmd/go: go:embed errors attributed to the wrong file

[zombiezen]

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

$ go version
go version go1.16beta1 linux/amd64

Does this issue reproduce with the latest release?

Haven't tried on tip.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/light/.cache/go-build"
GOENV="/home/light/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/light/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/light"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/light/sdk/go1.16beta1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/light/sdk/go1.16beta1/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16beta1"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/light/src/foo/go.mod"
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-build4010338713=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Run go build on:

https://play.golang.org/p/HR-SdE2vE8c

What did you expect to see?

bar/bar.go:5:1: pattern xxx.txt: no matching files found

What did you see instead?

The line number is for the import of the package with the go:embed directive:

foo.go:5:2: pattern xxx.txt: no matching files found

[zombiezen]

Further, running go build ./bar outputs no line numbers:

pattern xxx.txt: no matching files found

I would expect to see the same output as what I expected above.

[toothrot]

/cc @rsc @bcmills @jayconrod @matloob

[bcmills]

Looks like there are no cmd/go tests for the no matching files found and invalid pattern syntax error messages, and the existing tests for the adjacent pattern …: cannot embed … errors lack anchors — so they aren't testing for the correct file or line numbers. 😞

[bcmills]

This is a release blocker for 1.16: go:embed is new in 1.16, and misattributing the file may mean that we're also misattributing the module, which could get very confusing for transitive errors in modules deep in the module cache.

[gopherbot]

Change https://golang.org/cl/280452 mentions this issue: cmd/go: allow go fmt to complete when embedded file is missing

[jayconrod]

The fix for this looks pretty small. We just need to resolve embeds a little lower in Package.load, after we push the path onto the import stack. That distinguishes errors in the importing and imported packages.

I'll wait a bit to send a fix until we decide how to resolve #43632, since that will affect tests.

[gopherbot]

Change https://golang.org/cl/283638 mentions this issue: cmd/go/internal/load: report positions for embed errors