x/tools/gopls: impossible nil deref in reflect package

[adonovan]

#!stacks
"sigpanic" && "reflect.(*rtype).common" && "reflect.(*rtype).Implements"

Issue created by stacks.

func (t *rtype) Implements(u Type) bool {
	if u == nil {
		panic("reflect: nil type passed to Type.Implements")
	}
	if u.Kind() != Interface {
		panic("reflect: non-interface type passed to Type.Implements")
	}
	return implements(u.common(), t.common()) // <--- panics because u is nil (or SP is corrupt), but u cannot be nil
}

func (t *rtype) common() *abi.Type {
	return &t.t // <--- panic
}

This stack 2veB9A was reported by telemetry:

• crash/crash
• runtime.throw:+9,+0x37
• runtime.sigpanic:+33,+0x223
• reflect.(*rtype).common:=324,+0x58
• reflect.(*rtype).Implements:+7,+0x44
• encoding/json.newTypeEncoder:+5,+0x73
• encoding/json.typeEncoder:+23,+0x15b
• encoding/json.typeFields:+206,+0x567
• encoding/json.cachedTypeFields:+4,+0xdb
• encoding/json.(*decodeState).object:+48,+0x20f
• encoding/json.(*decodeState).value:+17,+0x3f
• encoding/json.(*decodeState).unmarshal:+10,+0xff
• encoding/json.(*Decoder).Decode:+24,+0x117
• golang.org/x/tools/go/packages.(*golistState).createDriverResponse:+32,+0x227
• golang.org/x/tools/go/packages.goListDriver:+71,+0x6c3
• golang.org/x/tools/go/packages.defaultDriver.func1:+1,+0x43
• golang.org/x/tools/go/packages.callDriverOnChunks.func1:+1,+0x5f
• golang.org/x/sync/errgroup.(*Group).add.func1:+32,+0x87

golang.org/x/tools/gopls@v0.19.1 go1.24.4 darwin/arm64 other,vscode (1)

[gabyhelp]

Related Issues

• x/tools/gopls: impossible nil panic in reflect.ValueOf #73853
• x/tools/gopls: Implementation (by signatures): nil panic in dynamicFuncCallType #74305 (closed)
• x/tools/gopls: Inline call: panic in reflect.Value.Set #74653
• x/tools/gopls: nil *types.Package panic in testKind #73096 (closed)
• x/tools/gopls: Package.Path called on nil Package in AddTestForFunc #73687 (closed)
• x/tools/gopls: Hover: invalid nil entry in types.Defs map #69362 (closed)
• x/tools/gopls: Hover: nil deref in typeDeclContent #74056 (closed)
• x/tools/gopls: Completion: nil deref in expectedCompositeLiteralType #72136 (closed)
• x/tools/gopls: nil Signature (?) deref in Completion #70634 (closed)
• go/types: panic("t.fromRHS = %s, typ = %s") in setDefType #71029 (closed)

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

[jba]

Not a gopls bug?

[adonovan]

The presumption is that gopls has a data race that causes random failures anywhere in the address space. See #71425, and the "memory corruption" label.