x/tools/gopls: Hover: nil deref using zero types.Selection

[adonovan]

#!stacks
"sigpanic" && "types.(*Selection).Index" && "golang.hover:+188"

Issue created by stacks.

	// When hovering over a reference to a promoted struct field,
	// show the implicitly selected intervening fields.
	cur, ok := pgf.Cursor.FindByPos(pos, pos)
	if !ok {
		return protocol.Range{}, nil, fmt.Errorf("Invalid hover position, failed to get cursor")
	}
	if obj, ok := obj.(*types.Var); ok && obj.IsField() {
		if selExpr, ok := cur.Parent().Node().(*ast.SelectorExpr); ok {
			sel := pkg.TypesInfo().Selections[selExpr]
			if len(sel.Index()) > 1 { <----- panics is sel is zero

@madelinekalil

This stack j9Y3kA was reported by telemetry:

• crash/crash
• runtime.gopanic:+69,+0x167
• runtime.panicmem:=262,+0x197
• runtime.sigpanic:+9,+0x167
• go/types.(*Selection).Index:=137,+0xf4e
• golang.org/x/tools/gopls/internal/golang.hover:+188,+0xf53
• golang.org/x/tools/gopls/internal/golang.Hover:+4,+0xbe
• golang.org/x/tools/gopls/internal/server.(*server).Hover:+30,+0x3aa
• golang.org/x/tools/gopls/internal/protocol.serverDispatch:+335,+0xe99
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.ServerHandler.func4:+5,+0x84
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.handshaker.func5:+52,+0x908
• golang.org/x/tools/gopls/internal/protocol.Handlers.MustReplyHandler.func1:+2,+0xc5
• golang.org/x/tools/gopls/internal/protocol.Handlers.AsyncHandler.func2.2:+3,+0x95
• runtime.goexit:+0,+0x0

golang.org/x/tools/gopls@v0.19.0-pre.2 go1.24.3 windows/amd64 vscode (1)

Dups: nagHbw cJUhUw

[adonovan]

Let's cherrypick a fix for this into rc3.

[adonovan]

This stack nagHbw was reported by telemetry:

• crash/crash
• runtime.gopanic:+69,+0x153
• runtime.panicmem:=262,+0x2ff
• runtime.sigpanic:+19,+0x2cc
• go/types.(*Selection).Index:=137,+0xc60
• golang.org/x/tools/gopls/internal/golang.hover:+188,+0xc64
• golang.org/x/tools/gopls/internal/golang.Hover:+4,+0x8b
• golang.org/x/tools/gopls/internal/server.(*server).Hover:+30,+0x29b
• golang.org/x/tools/gopls/internal/protocol.serverDispatch:+335,+0xc57
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.ServerHandler.func4:+5,+0x73
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.handshaker.func5:+52,+0x68f
• golang.org/x/tools/gopls/internal/protocol.Handlers.MustReplyHandler.func1:+2,+0xbf
• golang.org/x/tools/gopls/internal/protocol.Handlers.AsyncHandler.func2.2:+3,+0x8f
• runtime.goexit:+0,+0x3

golang.org/x/tools/gopls@v0.19.0-pre.1 go1.24.3 darwin/arm64 other (1)

[gopherbot]

Change https://go.dev/cl/680257 mentions this issue: gopls/internal/golang: add missing ,ok check

[gabyhelp]

Related Issues

• x/tools/gopls: Hover: nil deref in parseDocLink #70635 (closed)
• x/tools/gopls: Hover: nil deref in golang.StdSymbolOf #70969 (closed)
• x/tools/gopls: Hover: invalid nil entry in types.Defs map #69362 (closed)
• x/tools/gopls: Hover: nil deref in typeDeclContent #74056
• x/tools/gopls: panic in hover #52211 (closed)
• x/tools/gopls: nil deref in x/telemetry/internal/counter.(*Counter).add #73890
• x/tools/gopls: "type name %q without type spec" bug in Hover (via telemetry) #64241
• x/tools/gopls: "type name %q without type spec" bug in Hover(reported by telemetry) #66314 (closed)
• x/tools/gopls: panic in mod.hoverOnModuleStatement #59077 (closed)
• x/tools/gopls: crash in work.Hover #60821 (closed)

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

[adonovan]

This stack cJUhUw was reported by telemetry:

• crash/crash
• runtime.gopanic:+69,+0x167
• runtime.panicmem:=262,+0x358
• runtime.sigpanic:+19,+0x328
• go/types.(*Selection).Index:=137,+0xf4e
• golang.org/x/tools/gopls/internal/golang.hover:+188,+0xf53
• golang.org/x/tools/gopls/internal/golang.Hover:+4,+0xbe
• golang.org/x/tools/gopls/internal/server.(*server).Hover:+30,+0x3aa
• golang.org/x/tools/gopls/internal/protocol.serverDispatch:+335,+0xe99
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.ServerHandler.func4:+5,+0x84
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.handshaker.func5:+52,+0x908
• golang.org/x/tools/gopls/internal/protocol.Handlers.MustReplyHandler.func1:+2,+0xc5
• golang.org/x/tools/gopls/internal/protocol.Handlers.AsyncHandler.func2.2:+3,+0x95
• runtime.goexit:+0,+0x0

golang.org/x/tools/gopls@v0.19.0-pre.2 go1.24.4 linux/amd64 vscode (1)