cmd/compile: internal compiler error when processing invalid recursive type

[rhysh]

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

$ go version
go version devel go1.18-02e5913406 Mon Nov 1 22:55:50 2021 +0000 darwin/amd64

Does this issue reproduce with the latest release?

This is new in tip. It is not present in go1.17.2.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/rhys/Library/Caches/go-build"
GOENV="/Users/rhys/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/rhys/go/pkg/mod"
GONOPROXY="*"
GONOSUMDB="*"
GOOS="darwin"
GOPATH="/Users/rhys/go"
GOPRIVATE="*"
GOPROXY="direct"
GOROOT="/usr/local/go"
GOSUMDB="off"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="devel go1.18-02e5913406 Mon Nov 1 22:55:50 2021 +0000"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
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 x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/49/zmds5zsn75z1283vtzxyfr5hj7yjq4/T/go-build3896010661=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

$ cat ./repro.go
package repro

import "unsafe"

type a struct {
	_ [42 - unsafe.Sizeof(a{})]byte
}

$ go install

What did you expect to see?

$ go1.17 version
go version go1.17.2 darwin/amd64

$ go1.17 install
# bug.repro
./repro.go:6:25: invalid composite literal type a

What did you see instead?

$ go version
go version devel go1.18-02e5913406 Mon Nov 1 22:55:50 2021 +0000 darwin/amd64

$ go install
# bug.repro
./repro.go:6:23: internal compiler error: got 0 from types2, but want 42

goroutine 1 [running]:
runtime/debug.Stack()
        /usr/local/go/src/runtime/debug/stack.go:24 +0x65
cmd/compile/internal/base.FatalfAt({0x128300?, 0xc0?}, {0x191cd35, 0x1f}, {0xc000118f18, 0x2, 0x2})
        /usr/local/go/src/cmd/compile/internal/base/print.go:227 +0x1ca
cmd/compile/internal/noder.(*irgen).validateBuiltin(0xc000128300, {0xc000027088, 0x6}, 0xc0000317c0)
        /usr/local/go/src/cmd/compile/internal/noder/validate.go:100 +0x2bf
cmd/compile/internal/noder.(*irgen).validate(0xc000128300, {0x1a76680?, 0xc0000317c0})
        /usr/local/go/src/cmd/compile/internal/noder/validate.go:70 +0x157
cmd/compile/internal/noder.(*irgen).generate.func1({0x1a76680?, 0xc0000317c0?})
        /usr/local/go/src/cmd/compile/internal/noder/irgen.go:297 +0x30
cmd/compile/internal/syntax.Crawl.func1({0x1a76680?, 0xc0000317c0?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:41 +0x30
cmd/compile/internal/syntax.inspector.Visit(0xc000060cf0, {0x1a76680?, 0xc0000317c0?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:24 +0x31
cmd/compile/internal/syntax.walker.node({{0x1a76300?, 0xc000060cf0?}}, {0x1a76680, 0xc0000317c0?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:76 +0x6b
cmd/compile/internal/syntax.walker.node({{0x1a76300?, 0xc000060cf0?}}, {0x1a76a90, 0xc000031780?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:179 +0x13ad
cmd/compile/internal/syntax.walker.node({{0x1a76300?, 0xc000060cf0?}}, {0x1a76568, 0xc0003d1080?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:192 +0x845
cmd/compile/internal/syntax.walker.node({{0x1a76300?, 0xc000060cf0?}}, {0x1a76838, 0xc0003d10b0?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:214 +0xf7d
cmd/compile/internal/syntax.walker.fieldList({{0x1a76300?, 0xc000060cf0?}}, {0xc00000e490, 0x1, 0x1f73840?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:360 +0x4b
cmd/compile/internal/syntax.walker.node({{0x1a76300?, 0xc000060cf0?}}, {0x1a76bf8, 0xc000031740?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:203 +0x39e
cmd/compile/internal/syntax.walker.node({{0x1a76300?, 0xc000060cf0?}}, {0x1a76c48, 0xc00010bb00?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:106 +0x1287
cmd/compile/internal/syntax.walker.declList({{0x1a76300?, 0xc000060cf0?}}, {0xc0003d9de0?, 0x2, 0xc0001196a0?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:336 +0x91
cmd/compile/internal/syntax.walker.node({{0x1a76300?, 0xc000060cf0?}}, {0x1a76860, 0xc0003fdcc0?})
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:85 +0xfee
cmd/compile/internal/syntax.Walk(...)
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:57
cmd/compile/internal/syntax.Inspect(...)
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:18
cmd/compile/internal/syntax.Crawl({0x1a76860?, 0xc0003fdcc0?}, 0xc000060ce0?)
        /usr/local/go/src/cmd/compile/internal/syntax/walk.go:40 +0x75
cmd/compile/internal/noder.(*irgen).generate(0xc000128300, {0xc00000e478, 0x1, 0x203000?})
        /usr/local/go/src/cmd/compile/internal/noder/irgen.go:296 +0x2d3
cmd/compile/internal/noder.check2({0xc00000e478, 0x1, 0x1})
        /usr/local/go/src/cmd/compile/internal/noder/irgen.go:92 +0x16d
cmd/compile/internal/noder.LoadPackage({0xc00001e220, 0x1, 0x0?})
        /usr/local/go/src/cmd/compile/internal/noder/noder.go:90 +0x335
cmd/compile/internal/gc.Main(0x1937480)
        /usr/local/go/src/cmd/compile/internal/gc/main.go:191 +0xb13
main.main()
        /usr/local/go/src/cmd/compile/main.go:55 +0xdd

[danscales]

cc @griesemer

[griesemer]

Should be fixed but not a release blocker, and also not urgent. This is pretty pathological code.

[rhysh]

Pathological, yes. For context, I ran into this via a typo / copy-paste error. Not urgent, not a blocker, a better error message would be nice.

[griesemer]

Investigated a bit. The Checker.validType function currently doesn't walk array length expressions and thus doesn't flag the above struct as an invalid type. Separately, the size computation determines the size of the struct eagerly, before it's fully set up. Fixing the first would suffice for this case.

[edit] validType cannot do this check because the array length expression is gone at that point. This cycle should perhaps be detected as part of the type cycle detection mechanism. Not clear why it's not.

[griesemer]

Another fun test case:

package p

import "unsafe"

type a struct { f *[unsafe.Sizeof(a{})]int }

[gopherbot]

Change https://golang.org/cl/361412 mentions this issue: cmd/compile/internal/types2: report error for incomplete struct composite literal type