x/tools/go/ssa: panic: T

[iangudger]

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

$ go version
go version go1.19 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

I'm using v0.34 of bazelbuild/rules_go's nogo functionality. This includes v0.1.11 of golang.org/x/tools. When I use either golang.org/x/tools/go/analysis/passes/nilness or golang.org/x/tools/go/analysis/passes/unusedwrite, I get a panic. I looked through all of the commits since v0.1.11 and none of them look like they would fix the issue. It would be difficult for me to test a newer version though.

Sample nilness panic

compilepkg: panic: T

goroutine 36 [running]:
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0002d09c0, {0x726a98?, 0xc000263c20?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:237 +0x5b9
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0002d09c0, {0x726a70?, 0xc000295c68?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:233 +0x710
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0002d09c0, {0x7269d0?, 0xc000277a50?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:182 +0x1d3
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0002d09c0, {0x726980?, 0xc000292a10?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:215 +0x565
golang.org/x/tools/go/ssa.(*Program).needMethodsOf(0xc0002d09c0, {0x726980?, 0xc000292a10?})
        external/org_golang_x_tools/go/ssa/methods.go:145 +0x70
golang.org/x/tools/go/ssa.(*Package).build(0xc0002df320)
        external/org_golang_x_tools/go/ssa/builder.go:2284 +0x111
sync.(*Once).doSlow(0xc0002d09c0?, 0xc0000f2e10?)
        GOROOT/src/sync/once.go:74 +0xc2
sync.(*Once).Do(...)
        GOROOT/src/sync/once.go:65
golang.org/x/tools/go/ssa.(*Package).Build(...)
        external/org_golang_x_tools/go/ssa/builder.go:2272
golang.org/x/tools/go/analysis/passes/buildssa.run(0xc0002d08f0)
        external/org_golang_x_tools/go/analysis/passes/buildssa/buildssa.go:72 +0x2ee
main.(*action).execOnce(0xc0000bd440)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:301 +0x842
sync.(*Once).doSlow(0x0?, 0x0?)
        GOROOT/src/sync/once.go:74 +0xc2
sync.(*Once).Do(...)
        GOROOT/src/sync/once.go:65
main.(*action).exec(0x0?)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:245 +0x3d
main.execAll.func1(0x0?)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:239 +0x54
created by main.execAll
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:237 +0x47
panic: interface conversion: interface {} is nil, not *buildssa.SSA

goroutine 35 [running]:
golang.org/x/tools/go/analysis/passes/nilness.run(0xc0004020d0)
        external/org_golang_x_tools/go/analysis/passes/nilness/nilness.go:64 +0xad
main.(*action).execOnce(0xc0000bd3b0)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:301 +0x842
sync.(*Once).doSlow(0x0?, 0x0?)
        GOROOT/src/sync/once.go:74 +0xc2
sync.(*Once).Do(...)
        GOROOT/src/sync/once.go:65
main.(*action).exec(0x0?)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:245 +0x3d
main.execAll.func1(0x0?)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:239 +0x54
created by main.execAll
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:237 +0x47

Sample unusedwrite panic

compilepkg: panic: E

goroutine 79 [running]:
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0000c5110, {0x724488?, 0xc00023c8a0?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:237 +0x5b9
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0000c5110, {0x724410?, 0xc000236e20?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:196 +0x33a
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0000c5110, {0x724460?, 0xc00023ee28?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:233 +0x710
golang.org/x/tools/go/ssa.(*Program).needMethods(0xc0000c5110, {0x7243e8?, 0xc00027c080?}, 0x0)
        external/org_golang_x_tools/go/ssa/methods.go:209 +0x2e5
golang.org/x/tools/go/ssa.(*Program).needMethodsOf(0xc0000c5110, {0x7243e8?, 0xc00027c080?})
        external/org_golang_x_tools/go/ssa/methods.go:145 +0x70
golang.org/x/tools/go/ssa.(*Package).build(0xc0000e2c60)
        external/org_golang_x_tools/go/ssa/builder.go:2284 +0x111
sync.(*Once).doSlow(0xc0000c5110?, 0xc000239400?)
        GOROOT/src/sync/once.go:74 +0xc2
sync.(*Once).Do(...)
        GOROOT/src/sync/once.go:65
golang.org/x/tools/go/ssa.(*Package).Build(...)
        external/org_golang_x_tools/go/ssa/builder.go:2272
golang.org/x/tools/go/analysis/passes/buildssa.run(0xc0000c5040)
        external/org_golang_x_tools/go/analysis/passes/buildssa/buildssa.go:72 +0x2ee
main.(*action).execOnce(0xc000161440)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:301 +0x842
sync.(*Once).doSlow(0x0?, 0x0?)
        GOROOT/src/sync/once.go:74 +0xc2
sync.(*Once).Do(...)
        GOROOT/src/sync/once.go:65
main.(*action).exec(0x0?)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:245 +0x3d
main.execAll.func1(0x0?)
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:239 +0x54
created by main.execAll
        external/io_bazel_rules_go/go/tools/builders/nogo_main.go:237 +0x47

[dmitshur]

CC @timothy-king, @findleyr.

[timothy-king]

What is the output of go list -m golang.org/x/tools for the tool you are using to build the nilness check? I know you mentioned v0.1.11 but sometimes folks refer to things like v0.1.11-0.20220316014157-77aa08bb151a as v0.1.11.

[timothy-king]

As you are on bazel the previous request for go list -m golang.org/x/tools might not make sense. Can you confirm more precisely what version the nilness is being built against?

I suspect you are compiling against a too old version. This is very similar to #54086

[iangudger]

It is the version in https://github.com/golang/tools/archive/refs/tags/v0.1.11.zip.

https://github.com/bazelbuild/rules_go/blob/28e7e33ca1dd7adfd8371c7f5d9a6fd18f386fa1/go/private/repositories.bzl#L66-L73

[timothy-king]

I am not able to reproduce this. Without being able to reproduce this my suspicion is still that your nogo binary has not been built using an up to date golang.org/x/tools (such as v0.1.11) FWIW. Are you sure it is up to date? (Also how are you sure? This might help me.)

Here is what I have tried so far. I bootstrapped bazel, created a blaze workspace with nogo analysis (using v0.34 of rules_go), created a mildly custom analyzer to inspect the ssa, created an example with features that should tickle this, and ran nogo on the example.

$BAZEL build //:hello gives the expected output: no crashes, there are generic methods called, generic types that flow into interfaces (so needsMethods should be called), and the ssa looks post v.01.11. The example is single directory containing the following: code under analysis (hello.go), the blaze + nogo setup (WORKSPACE, BUILD.bazel), and some extra analysis to dump buildssa (printbuildinfo.go). Included at the bottom.

I think I need more specific reproduction instructions at this point. Code under analysis? Blaze+nogo setup?

--- hello.go

package main

import "fmt"

type S[T any] struct{}

func (s S[T]) Foo() {}

func main() {
	fmt.Println("calling an fmt function")

	var s S[int]
	var i interface{ Foo() } = s
	i.Foo()

	var n *int
	if n == nil {
		println("expect a nilness complaint")
	}
}

--- WORKSPACE

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "io_bazel_rules_go",
    sha256 = "16e9fca53ed6bd4ff4ad76facc9b7b651a89db1689a2877d6fd7b82aa824e366",
    urls = [
        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.34.0/rules_go-v0.34.0.zip",
        "https://github.com/bazelbuild/rules_go/releases/download/v0.34.0/rules_go-v0.34.0.zip",
    ],
)

load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_dependencies")

go_rules_dependencies()

go_register_toolchains(version = "1.18.3", nogo = "@//:my_nogo")

--- BUILD.bazel

load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")

load("@io_bazel_rules_go//go:def.bzl", "nogo")

nogo(
    name = "my_nogo",
    deps = [
        ":printbuildinfo",
        "@org_golang_x_tools//go/analysis/passes/nilness:go_default_library",
    ],
    visibility = ["//visibility:public"], # must have public visibility
)

go_library(
    name = "printbuildinfo",
    srcs = ["printbuildinfo.go"],
    importpath = "printbuildinfo",
    deps = [
      "@org_golang_x_tools//go/analysis:go_default_library",
      "@org_golang_x_tools//go/analysis/passes/buildssa:go_default_library",
      "@org_golang_x_tools//go/ssa:go_default_library",
    ],
    visibility = ["//visibility:public"],
)

go_binary(
    name = "hello",
    srcs = ["hello.go"],
)

--- printbuildinfo.go

package printdebuginfo

import (
	"bytes"
	"go/token"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/analysis/passes/buildssa"
	"golang.org/x/tools/go/ssa"
)

var Analyzer = &analysis.Analyzer{
	Name:     "printdebuginfo",
	Doc:      "...",
	Run:      run,
	Requires: []*analysis.Analyzer{buildssa.Analyzer},
}

func run(pass *analysis.Pass) (interface{}, error) {
	ssainput := pass.ResultOf[buildssa.Analyzer].(*buildssa.SSA)

	for fn := range AllFunctions(ssainput.Pkg.Prog) {
		var buf bytes.Buffer
		ssa.WriteFunction(&buf, fn)
		pass.Reportf(token.NoPos, "Function %s: %s", fn.String(), buf.String())
	}
	return nil, nil
}

func AllFunctions(prog *ssa.Program) map[*ssa.Function]bool {
	visit := visitor{
		prog: prog,
		seen: make(map[*ssa.Function]bool),
	}
	visit.program()
	return visit.seen
}

type visitor struct {
	prog *ssa.Program
	seen map[*ssa.Function]bool
}

func (visit *visitor) program() {
	for _, pkg := range visit.prog.AllPackages() {
		for _, mem := range pkg.Members {
			if fn, ok := mem.(*ssa.Function); ok {
				visit.function(fn)
			}
		}
	}
	for _, T := range visit.prog.RuntimeTypes() {
		mset := visit.prog.MethodSets.MethodSet(T)
		for i, n := 0, mset.Len(); i < n; i++ {
			visit.function(visit.prog.MethodValue(mset.At(i)))
		}
	}
}

func (visit *visitor) function(fn *ssa.Function) {
	if !visit.seen[fn] {
		visit.seen[fn] = true
		var buf [10]*ssa.Value // avoid alloc in common case
		for _, b := range fn.Blocks {
			for _, instr := range b.Instrs {
				for _, op := range instr.Operands(buf[:0]) {
					if fn, ok := (*op).(*ssa.Function); ok {
						visit.function(fn)
					}
				}
			}
		}
	}
}

FWIW

$ $BAZEL --version
bazel 6.0.0-pre.20220720.3- (@non-git)

[iangudger]

@timothy-king you were right. My other Bazel config was downgrading golang.org/x/tools below the required version.