cmd/go: go test -cover loses coverage of some inlined functions

[soniakeys]

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

Bisected to ci ee4fbbc, "stop creating nested temp directory trees". Reproduces at tip as of Jan 2.

Does this issue reproduce with the latest release?

with 1.9.2, No.

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

linux/amd64

What did you do?

go get -t github.com/soniakeys/unit
go test -cover github.com/soniakeys/unit

(The issue happens on this package of mine, github.com/soniakeys/unit. I'm very sorry I don't have a small test case at the moment. I wanted to file the issue anyway to see if the information here was enough to spark some idea of the problem.)

What did you expect to see?

With 1.9.2, or up to the ci noted above,
ok github.com/soniakeys/unit 0.003s coverage: 100.0% of statements

What did you see instead?

From the noted ci or later built in ~/pt,
$ ~/pt/bin/go test -cover github.com/soniakeys/unit
ok github.com/soniakeys/unit 0.003s coverage: 63.4% of statements

The coverprofile showed the missing statements were one-liners, likely inlined. Sure enough, with '-l':
$ ~/pt/bin/go test -cover -gcflags=-l github.com/soniakeys/unit
ok github.com/soniakeys/unit 0.003s coverage: 100.0% of statements

[agnivade]

/cc @rsc

[namusyaka]

Couldn't reproduce the issue in my local (osx) or linux/amd64.

go version:

$ go version
go version go1.9.2 linux/amd64

go env:

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/namusyaka/go"
GORACE=""
GOROOT="/home/namusyaka/.goenv/versions/1.9.2"
GOTOOLDIR="/home/namusyaka/.goenv/versions/1.9.2/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build842395550=/tmp/go-build"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

$ go test -cover github.com/soniakeys/unit
ok  	github.com/soniakeys/unit	0.009s	coverage: 100.0% of statements

Hope that helps.

[soniakeys]

Right. It shows 100% with 1.9.2, but try it with tip and it shows 63%.

[mvdan]

Conservatively marking for 1.10, unless it is proven to not be a regression.

[agnivade]

Tried with 1.10beta and master. 63% with both and 100% with 1.9.2. Seems like a regression to me.

[gopherbot]

Change https://golang.org/cl/86237 mentions this issue: cmd/go: fix coverage rebuild corner case