go/types: SEGV in typeWriter.typ

[adonovan]

#!stacks
"sigpanic" && "(*typeWriter).typ"

Issue created by stacks.

This stack z3SQZg 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.(*typeWriter).typ:+185,+0x124
• go/types.(*typeWriter).typ:+235,+0xb23
• go/types.(*typeWriter).signature:+23,+0x1b3
• go/types.(*typeWriter).typ:+81,+0x483
• go/types.(*typeWriter).typ:+235,+0xb23
• go/types.(*typeWriter).signature:+23,+0x1b3
• go/types.(*typeWriter).typ:+81,+0x483
• go/types.(*typeWriter).typ:+235,+0xb23
• go/types.(*typeWriter).tuple:+31,+0x18f
• go/types.(*typeWriter).signature:+12,+0x10f
• go/types.(*typeWriter).typ:+81,+0x483

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:

    func TestIssue80276(t *testing.T) {
        pkg := NewPackage("p", "p")
        tname := NewTypeName(token.NoPos, pkg, "A", nil)

        var nilNamed *Named
        alias := NewAlias(tname, nilNamed)

        ctxt := NewContext()
        Instantiate(ctxt, alias, []Type{Typ[Int]}, false)
    }

[gabyhelp]

Related Issues

• go/types: SEGV in (*Named).TypeArgs due to invalid receiver #80275
• 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 while preprinting TypeAssertionError in panicdottypeE #79918 (closed)
• x/tools/gopls: SEGV in go/types due to invalid pointer in BinaryExpr.Y #76238 (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)
• go/types: alias TypeName has nil typ #77321

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