testing: exclude unreachable code in test coverage

[santhosh-tekuri]

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

$ go version
go version go1.12.1 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/santhosh/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/santhosh/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=""
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/v5/44ncgqws3dg3pmjnktpt_l2w0000gq/T/go-build063045597=/tmp/go-build -gno-record-gcc-switches -fno-common"

i have code like this in my project:

const trace = false

func doSomething() {
    if trace {
        fmt.Println("some information")
    }
}

because trace is false, the coverage reports the tracing code as not covered
can such code be shown as "not tracked"

I enable trace if we are debugging some issue in our code using build tags
I can enable trace during coverage generation, but tracing output is large and it takes significant time.

I have seen types package from stdlib also uses if trace
so may be this can be taken as enhancement

[bcmills]

Flagging statically-unreachable code seems like a useful signal to me, and whether the compiler is able to determine statically that it is unreachable is an implementation detail.

100% code coverage is usually not an appropriate goal for Go projects. Can you give some more detail as to why this particular behavior is important?

[santhosh-tekuri]

I am not targeting for 100% coverage. the code coverage numbers does not reflect expected ones. the html report generated shows all tracing code as red. so when seeing reports, I have to mentally discard all those tracing lines of code highlighted in red.

currently I am doing a workaround of enable trace variable but do not generate any trace during tests suing build tags. this keeps code coverage track those lines.

[sam-github]

I was looking for a similar feature, not so much to reach 100% coverage, but because when reviewing coverage to determine if uncovered lines should be covered, its useful to have an annotation that says "not reachable, expected to be red". I guess I could literally put such a comment in my code, but I think it'd be pretty nice to get a report that said "92% covered, 6%uncovered, and 2% marked unreachable".

I think of uncovered code a bit like lint output or compiler warnings. Developers shouldn't have to reevaluate every time they checkout a project and run lint if the output is relevant. If its been decided that it is irrelevant, its handy to suppress it with in-line markup, and then nobody has to see the output again and then go look to see if its valid.