Please answer these questions before submitting your issue. Thanks!

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

1.10

Does this issue reproduce with the latest release?

Yes

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

GOBIN=""
GOCACHE="/home/frew/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/frew/go"
GORACE=""
GOROOT="/home/frew/go"
GOTMPDIR=""
GOTOOLDIR="/home/frew/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
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"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/run/shm/go-build797590454=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://play.golang.org/p/ZU-Ys77Q766

Basically, I have run into many variations of:

			if _, ok := found[x]; ok {
				found[x] += y
			} else {
				found[x] = y
			}

and even surprised some people who have been writing Go for years, when pointing out that thanks to zero values the above is totally superfluous, and that the following is totally sufficient. (Or at least I can't think of a type where it is not.)

			found[x] += y

Note that I think = 1 and ++ should be detected, but presumably as a special case, unless ++ desugars to += 1.

What did you expect to see?

A warning from go vet that the pattern should be corrected.

What did you see instead?

Nothing