internal/lsp: check InRange before calling token.Offset

This shows up every now and then--maybe we need a wrapper function
around token.Offset to check the range.

Updates golang/go#48249

Change-Id: I9c60bc7cc61fcfb2f4e8c6963586d8b8fbb21835
Reviewed-on: https://go-review.googlesource.com/c/tools/+/348429
Trust: Rebecca Stambler <[email protected]>
Run-TryBot: Rebecca Stambler <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>
(cherry picked from commit 0a6f080)
Reviewed-on: https://go-review.googlesource.com/c/tools/+/348530

Author: stamblerre

internal/lsp/source/hover.go

@@ -341,7 +341,9 @@ func HoverInfo(ctx context.Context, s Snapshot, pkg Package, obj types.Object, p
 			tok2 := s.FileSet().File(node.Pos())
 			var spec ast.Spec
 			for _, s := range node.Specs {
-				if tok2.Offset(s.Pos()) <= offset && offset <= tok2.Offset(s.End()) {
+				// Avoid panics by guarding the calls to token.Offset (golang/go#48249).
+				// TODO(rstambler): Investigate this further and adjust if needed.
+				if InRange(tok2, s.Pos()) && InRange(tok2, s.End()) && tok2.Offset(s.Pos()) <= offset && offset <= tok2.Offset(s.End()) {
 					spec = s
 					break
 				}