x/tools/gopls: SEGV in types.Type.Underlying

[adonovan]

#!stacks
"sigpanic" && "go/types.under:+4"

Issue created by stacks.

This stack 3WhcMA was reported by telemetry:

• crash/crash
• runtime.gopanic:+69,+0x167
• runtime.panicmem:=262,+0x358
• runtime.sigpanic:+19,+0x328
• go/types.under:+4,+0x35
• go/types.isBytesOrRunes:+2,+0x3b
• go/types.(*operand).convertibleTo:+47,+0x3bc
• go/types.ConvertibleTo:=46,+0x1ea
• golang.org/x/tools/gopls/internal/golang/completion.convertibleTo:+6,+0x1eb
• golang.org/x/tools/gopls/internal/golang/completion.considerTypeConversion:+12,+0x7c
• golang.org/x/tools/gopls/internal/golang/completion.(*candidateInference).candTypeMatches.func1:+27,+0x231
• golang.org/x/tools/gopls/internal/golang/completion.(*candidate).anyCandType.func1:+1,+0x5e
• golang.org/x/tools/gopls/internal/golang/completion.(*candidate).anyCandType:+28,+0xd9
• golang.org/x/tools/gopls/internal/golang/completion.(*candidateInference).candTypeMatches:+14,+0x13b
• golang.org/x/tools/gopls/internal/golang/completion.(*completer).matchingCandidate:+17,+0xc4
• golang.org/x/tools/gopls/internal/golang/completion.(*completer).addCandidate:+2,+0x5b
• golang.org/x/tools/gopls/internal/golang/completion.(*completer).deepSearch:+71,+0x4de
• golang.org/x/tools/gopls/internal/golang/completion.Completion:+165,+0x13a5
• golang.org/x/tools/gopls/internal/server.(*server).Completion:+19,+0x357

golang.org/x/tools/[email protected] go1.24.4 linux/amd64 vscode (1)

Dups: dumPAQ