testing: no way to get a snapshot of current coverage data accumulator

[straightdave]

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

$ go version
go version go1.12.7 darwin/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
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/wei.wu/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/wei.wu/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/wei.wu/repos/go/src/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/t0/zqt5zk8152n89780p5_qvb9r0000gn/T/go-build258050164=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Tried to find a way to get value of coverage data accumulator.

What did you expect to see?

There's a way to register a coverage data accumulator. Hence there should be a way to get value of coverage data accumulator.

What did you see instead?

Found no way to get the value of a package level non-exposing variable cover.

[toothrot]

Hi @straightdave,

Can you please add more detail about what you're trying to do? Does testing.RegisterCover(c) do what you want?

https://godoc.org/testing#RegisterCover

[straightdave]

Hi @toothrot
Thanks for the reply 😃

I am trying to upload the line coverage data periodically while the binary code is running. I've tried to use RegisterCover to inject mine Cover instance but failed to get any data other than zero value from it. Meanwhile the hack function GetCover could always return the data no matter when and where I call it.

So the working way (and it's convenient) I found so far is to add this GetCover function to return the package level variable cover in src/testing/cover.go:

var cover Cover

// hack function
func GetCover() Cover {
    return cover
}

Any ideas?

[toothrot]

@straightdave Thanks for following up!

The Cover struct is documented as such:

NOTE: This struct is internal to the testing infrastructure and may change. It is not covered (yet) by the Go 1 compatibility guidelines.

Many parts of the testing library predate "internal" packages, and were exported for internal usage only. I think there's a single example in the Go codebase of how to use RegisterCover, but again, it could break in the future and we have no promises to support it externally.

Finally, I don't think we will be adding a new API to something that ought to have been internal in the first place, so I am going to close this issue.

I don't know the best way to help you do what you want, but a better place to ask this kind of question is golang-nuts. See https://golang.org/wiki/Questions. It'll reach a wider audience of people who may have tried something similar.

[straightdave]

🤔Makes sense. Thanks @toothrot