Go: x/tools/go/analysis/passes/nilness: no position information with error

[reillywatson]

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

$ go version
1.12

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/reilly/Library/Caches/go-build"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="darwin"

GOOS="darwin"

GOPATH="/Users/reilly/league/services:/Users/reilly/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/gz/4ytqr0r12q1fbx8ct_w3k_880000gn/T/go-build175674008=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Ran the nilness analyzer on this (simplified) package:

package foo

import (
    "fmt"
)

func Foo() {
    var x []int
    for _, a := range x {
        fmt.Println(a)
    }
}

What did you expect to see?

Ideally: a different error about how you're iterating over a nil slice
Less ideally: the same error, but with information telling me where the error is

What did you see instead?

-: nil dereference in index operation

This kind of error is pretty hard to track down if I'm running the analyzer over a large codebase, because it doesn't say which file or package is failing.

[julieqiu]

/cc @matloob

[acestronautical]

This is a major problem that deserves attention. I work for a medium sized tech company looking to adopt golangci-lint and this issue is holding me back.

[gopherbot]

Change https://golang.org/cl/208599 mentions this issue: go/ssa: add position data in indexed range loops

[findleyr]

@vovapi's CL above adds position information to the error message, but I think to improve this further we'd have alter the way go/ssa tracks position information. Something similar was done for staticcheck: https://github.com/dominikh/go-tools/commit/c14c261fd1fd7dec2e23b44bbf8c7b49cbd4e239