cmd/go: go test does not parse -overlay files for test functions

[eandre]

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

$ go version
go version go1.16 darwin/arm64

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
GO111MODULE="on"
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/eandre/Library/Caches/go-build"
GOENV="/Users/eandre/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/eandre/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/eandre"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/homebrew/Cellar/go/1.16/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.16/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.16"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/hc/w9bwjfwd69dd6_6thw6xqmkw0000gn/T/go-build1638807139=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Consider this txtar:

-- go.mod --
module test.pkg
-- foo/foo_test.go --
package foo

import "testing"

func TestFoo(t *testing.T) { }
-- tmp/bar_test.go --
package foo

import "testing"

func TestBar(t *testing.T) {
	t.Fatal("dummy failure")
}
-- foo/overlay.json --
{"Replace": {"bar_test.go": "../tmp/bar_test.go"}}

Running go test -overlay=overlay.json in the foo folder should result in TestBar running.

What did you expect to see?

cd foo
go test -overlay=overlay.json .
--- FAIL: TestBar (0.00s)
    bar_test.go:5: dummy failure
FAIL
FAIL	test.app	0.138s
FAIL

What did you see instead?

# test.pkg
open /Users/eandre/tmp/foo/bar_test.go: no such file or directory
FAIL	test.app [setup failed]
FAIL

The issue is because https://github.com/golang/go/blob/master/src/cmd/go/internal/load/test.go#L579 implicitly reads from the filesystem instead of using the overlay file data (due to src == nil).

[eandre]

Making this change fixes the issue for me: https://gist.github.com/eandre/45f5a554faff3b23f6f5d92f794a222b

[jayconrod]

cc @matloob

[matloob]

@eandre Your change looks reasonable. Do you want to contribute it? If not I can make a change myself.

[eandre]

@matloob great! Either way, up to you. I can get around to doing it sometime next week.

[matloob]

Go for it! I look forward to your CL!

[gopherbot]

Change https://golang.org/cl/305071 mentions this issue: cmd/go/internal/load/test: parse overlay files for test functions