go/types: SEGV in (*Named).TypeArgs due to invalid receiver

[adonovan]

#!stacks
"sigpanic" && "(*Named).TypeArgs:=404"

Issue created by stacks.

This stack EmUwAQ was reported by telemetry:

• crash/crash
• runtime.gopanic:+70,+0x15b
• go/types.(*Checker).handleBailout:+25,+0x93
• go/types.(*Checker).Files.deferwrap1:+0,+0x1f
• runtime.gopanic:+51,+0x12b
• runtime.panicmem:=336,+0x2ef
• runtime.sigpanic:+19,+0x2c0
• go/types.(*Named).TypeArgs:=404,+0xd4c
• go/types.(*comparer).identical:+225,+0xd58
• go/types.(*comparer).identical:+70,+0x763
• go/types.(*comparer).identical:+129,+0x7df
• go/types.(*comparer).identical:+70,+0x763
• go/types.(*comparer).identical:+129,+0x7df
• go/types.Identical:=90,+0x17f
• go/types.(*operand).assignableTo:+10,+0x180
• go/types.(*Checker).assignment:+87,+0x693
• go/types.(*Checker).initVar:+25,+0x377
• go/types.(*Checker).initVars:+55,+0x18f
• go/types.(*Checker).stmt:+154,+0x4e7
• go/types.(*Checker).stmtList:+9,+0x7f

golang.org/x/tools/gopls@v0.22.0 go1.26.4 darwin/arm64 gopls.client=other (1)

Use this command to reproduce the executable:
(HOME=$(mktemp -d); GOOS=darwin GOARCH=arm64 GOTOOLCHAIN=go1.26.4 go install golang.org/x/tools/gopls@v0.22.0 && find $HOME/go/bin -type f)
To disassemble: go tool objdump exe | less

[adonovan]

Gemini claims this is a repro:

package main

import (
	"go/token"
	"go/types"
)

func main() {
	var nilNamed *types.Named

	pkg := types.NewPackage("p", "p")
	tname := types.NewTypeName(token.NoPos, pkg, "T", nil)
	validNamed := types.NewNamed(tname, types.Typ[types.Int], nil)

	// Causes SEGV at (*Named).TypeArgs:+0xd4c inside (*comparer).identical:+0xd58
	types.Identical(nilNamed, validNamed)
}

Executing this with GOWORK=off GOTOOLCHAIN=go1.26.4 go run repro.go yields the exact telemetry panic signature:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x18 pc=0x10502f42c]

goroutine 1 [running]:
go/types.(*Named).TypeArgs(...)
	/.../src/go/types/named.go:404
go/types.(*comparer).identical(0x1d0436f8ef1e, {0x105150128?, 0x0?}, {0x105150128?, 0x1d0437022100?}, 0x0)
	/.../src/go/types/predicates.go:477 +0xd4c

[gabyhelp]

Related Issues

• go/types: SEGV in typeWriter.typ #80276
• x/tools/gopls: types.isString crashes in MOV reg,reg instruction #77920 (closed)
• go/types: SEGV in tpWalker.isParameterized, case Signature #79772
• x/tools/gopls: SEGV in (*types.*Checker).Ident due to nil or invalid *ast.Ident in syntax tree #77078 (closed)
• x/tools/gopls: impossible panic reading rtype.hash in type assertion #76328 (closed)
• x/tools/gopls: SEGV loading m.used field from non-nil map pointer (in types.Scope.elems map) #76979 (closed)
• x/tools/gopls: impossible crash in (*types.Checker).basicLit #76329 (closed)
• x/tools/gopls: SEGV in go/types due to invalid pointer in BinaryExpr.Y #76238 (closed)
• x/tools/gopls: failed assertion in go/types.validType0 #78042
• x/tools/gopls: impossible panic in BlockStmt.End (type checking IfStmt with nil Body) #76327 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}