x/tools/gopls: bug in Codec[...].Encode

[adonovan]

#!stacks
"sigpanic" && "reflect.Value.lenNonSlice:+11"

Issue created by stacks.

Crash while loading the length word of a string in an interface value: must be memory corruption.

This stack 2Tlc6w was reported by telemetry:

• crash/crash
• runtime.throw:+9,+0x47
• runtime.sigpanic:+33,+0x26b
• reflect.Value.lenNonSlice:+11,+0x175
• reflect.Value.Len:=1828,+0x1385
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+85,+0x1376
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+93,+0x15a7
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+81,+0x10d7
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+60,+0x162b
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+93,+0x15a7
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+81,+0x10d7
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+60,+0x162b
• golang.org/x/tools/gopls/internal/util/frob.(*frob).encode:+93,+0x15a7
• golang.org/x/tools/gopls/internal/util/frob.(*frob).Encode:+7,+0x17e
• golang.org/x/tools/gopls/internal/util/frob.Codec[...].Encode:=51,+0x1ab
• golang.org/x/tools/gopls/internal/cache/methodsets.(*Index).Encode:=79,+0x14d
• golang.org/x/tools/gopls/internal/cache.storePackageResults:+3,+0x13c
• golang.org/x/tools/gopls/internal/cache.(*typeCheckBatch).getPackage.func1.gowrap1:+0,+0x2b
• runtime.goexit:+0,+0x0

golang.org/x/tools/gopls@v0.20.0 go1.25.2 linux/amd64 gopls.client=other,vscode (1)

Use this command to reproduce the executable:
(HOME=$(mktemp -d); GOOS=linux GOARCH=amd64 GOTOOLCHAIN=go1.25.2 go install golang.org/x/tools/gopls@v0.20.0 && find $HOME/go/bin -type f)
To disassemble: go tool objdump exe | less

[gabyhelp]

Related Issues

• x/tools/gopls: SEGV accessing g in function prolog (R28 is nil or invalid) #76158
• x/tools/gopls: SEGV in json.Marshal #75740
• x/tools/gopls: SEGV in string comparison in mapaccess #76159
• x/tools/gopls: impossible crash in strings.HasPrefix #76627
• x/tools/gopls: impossible panic reading rtype.hash in type assertion #76328
• x/tools/gopls: impossible crash in (*types.Checker).basicLit #76329
• x/tools/gopls: out-of-bounds slice panic in bug in frob.(*reader).bytes #71244
• x/tools/gopls: impossible nil panic in reflect.ValueOf #73853
• x/tools/gopls: impossible panic in BlockStmt.End (type checking IfStmt with nil Body) #76327
• x/tools/gopls: growslice crashes while zeroing #74932

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