go/types: failed genericType assertion in Checker.instantiatedType

[adonovan]

#!stacks
"runtime.typeAssert" && "go/types.(*Checker).instantiatedType:+38"

Issue created by stacks.

func (check *Checker) instantiatedType(ix *indexedExpr, def *TypeName) (res Type) {
...
	// create instance
	// The instance is not generic anymore as it has type arguments, but it still
	// satisfies the genericType interface because it has type parameters, too.
	inst := check.instance(ix.Pos(), gtyp, targs, nil, check.context()).(genericType)

This stack aEVlDg was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Checker).handleBailout:+7
• go/types.(*Checker).Files.deferwrap1:+0
• runtime.gopanic:+50
• runtime.getitab:+58
• runtime.typeAssert:+7
• go/types.(*Checker).instantiatedType:+38
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).varType:+1
• go/types.(*Checker).varDecl:+5
• go/types.(*Checker).declStmt.func1:+56
• go/types.(*Checker).walkDecl:+27
• go/types.(*Checker).declStmt:+3
• go/types.(*Checker).stmt:+23
• go/types.(*Checker).stmtList:+9

golang.org/x/tools/[email protected] go1.24rc1 linux/amd64 vscode (10)

cc: @griesemer @findleyr

Dups: HNc-0g sRb2ZQ caAKMA ubM70w f0cr5w -B6Zow

[adonovan]

This stack HNc-0g was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Checker).handleBailout:+7
• go/types.(*Checker).Files.deferwrap1:+0
• runtime.gopanic:+50
• runtime.getitab:+58
• runtime.typeAssert:+7
• go/types.(*Checker).instantiatedType:+38
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).varType:+1
• go/types.(*Checker).typeList:+3
• go/types.(*Checker).instantiatedType:+30
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).varType:+1
• go/types.(*Checker).varDecl:+5

golang.org/x/tools/[email protected] go1.24rc1 linux/amd64 vscode (5)

This stack sRb2ZQ was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Checker).handleBailout:+7
• go/types.(*Checker).Files.deferwrap1:+0
• runtime.gopanic:+50
• runtime.getitab:+58
• runtime.typeAssert:+7
• go/types.(*Checker).instantiatedType:+38
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).typ:=151
• go/types.(*Checker).bound:+20
• go/types.(*Checker).collectTypeParams:+36
• go/types.(*Checker).typeDecl:+90
• go/types.(*Checker).objDecl:+139
• go/types.(*Checker).ident:+54
• go/types.(*Checker).typInternal:+26
• go/types.(*Checker).genericType:+1

golang.org/x/tools/[email protected] go1.24rc1 linux/amd64 vscode (13)

This stack caAKMA was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Checker).handleBailout:+7
• go/types.(*Checker).Files.deferwrap1:+0
• runtime.gopanic:+50
• runtime.getitab:+58
• runtime.typeAssert:+7
• go/types.(*Checker).instantiatedType:+38
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).typ:=151
• go/types.(*Checker).bound:+20
• go/types.(*Checker).collectTypeParams:+36
• go/types.(*Checker).typeDecl:+52
• go/types.(*Checker).objDecl:+139
• go/types.(*Checker).packageObjects:+61
• go/types.(*Checker).checkFiles:+29
• go/types.(*Checker).Files:+13

golang.org/x/tools/[email protected] go1.24rc1 linux/amd64 vscode (2)

This stack ubM70w was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Checker).handleBailout:+7
• go/types.(*Checker).Files.deferwrap1:+0
• runtime.gopanic:+50
• runtime.getitab:+58
• runtime.typeAssert:+7
• go/types.(*Checker).instantiatedType:+38
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).typeDecl:+55
• go/types.(*Checker).objDecl:+139
• go/types.(*Checker).packageObjects:+61
• go/types.(*Checker).checkFiles:+29
• go/types.(*Checker).Files:+13
• golang.org/x/tools/gopls/internal/cache.(*typeCheckBatch).checkPackage:+73
• golang.org/x/tools/gopls/internal/cache.(*typeCheckBatch).getPackage.func1:+49

golang.org/x/tools/[email protected] go1.24rc1 linux/amd64 vscode (5)

This stack f0cr5w was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Checker).handleBailout:+7
• go/types.(*Checker).Files.deferwrap1:+0
• runtime.gopanic:+50
• runtime.getitab:+58
• runtime.typeAssert:+7
• go/types.(*Checker).instantiatedType:+38
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).typ:=151
• go/types.(*Checker).bound:+20
• go/types.(*Checker).collectTypeParams:+36
• go/types.(*Checker).funcType:+29
• go/types.(*Checker).funcDecl:+18
• go/types.(*Checker).objDecl:+143
• go/types.(*Checker).packageObjects:+65
• go/types.(*Checker).checkFiles:+29

golang.org/x/tools/[email protected] go1.24rc1 linux/amd64 vscode (19)

This stack -B6Zow was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• go/types.(*Checker).handleBailout:+7
• go/types.(*Checker).Files.deferwrap1:+0
• runtime.gopanic:+50
• runtime.getitab:+58
• runtime.typeAssert:+7
• go/types.(*Checker).instantiatedType:+38
• go/types.(*Checker).typInternal:+61
• go/types.(*Checker).definedType:+1
• go/types.(*Checker).typ:=151
• go/types.(*Checker).bound:+20
• go/types.(*Checker).collectTypeParams:+36
• go/types.(*Checker).typeDecl:+90
• go/types.(*Checker).objDecl:+139
• go/types.(*Checker).packageObjects:+53
• go/types.(*Checker).checkFiles:+29
• go/types.(*Checker).Files:+13

golang.org/x/tools/[email protected] go1.24rc1 linux/amd64 vscode (42)

[findleyr]

The bug is that Checker.instance can return a Typ[Invalid], which is not a generic type.

All crashes are with the rc1, indicating that this is a regression. Marking as a release blocker.

CC @griesemer

[findleyr]

Repro: https://go.dev/play/p/77Rx2onG7rT?v=gotip

package main

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

const src = `
package p

type I[T any] = interface {
}

func F[T I[int, string]]() {
}
`

func main() {
	fset := token.NewFileSet()
	f, _ := parser.ParseFile(fset, "p.go", src, 0)
	conf := types.Config{Error: func(error) {}}
	conf.Check("p", fset, []*ast.File{f}, nil)
}

[gabyhelp]

Related Issues

• go/types: panic("t.fromRHS = %s, typ = %s") in setDefType #71029
• go.tools/go/types assertion failure in recordTypeAndValue #8169 (closed)
• go/types: assertion failed #11347 (closed)
• cmd/compile/internal/types2: panic when type function selector is not instantiated #48048 (closed)
• x/tools/gopls: types.IsInterface "Named.check == nil but type is incomplete" panic in methodsets.EnsurePointer #69537 (closed)
• x/tools/gopls: completion: failed type assertion in inferExpectedTypeArg #70889 (closed)
• go/types, types2: crash in typesSummary (which assumes well-typedness) #70526 (closed)
• x/tools/gopls: Completion: failed type assertion in completer.item #71044
• dev.go2go: assertion fails when type parameter is specified for non-generic function call #42319 (closed)
• go/types: panic "assertion failed" when autocompleting generic test code #47923 (closed)

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

[griesemer]

I will take this one on. Thanks for reporting.

[gopherbot]

Change https://go.dev/cl/641857 mentions this issue: go/types, types2: don't panic when instantiating generic alias with wrong number of type arguments