internal/lsp/cache: set a 15 minute deadline on calls to packages.Load

We've recently noticed multiple instances of `go list` hanging
indefinitely during an initial workspace load. Heschi suggested setting
a 5 minute deadline on the IWL, but it seems reasonable to set this
deadline on all calls to packages.Load since that calls `go list`.

I also started with a 15 minute deadline to be a little more careful.
Do you think this is risky enough to merit an experimental setting?

Fixes golang/go#42132

Change-Id: I0a38741f3d99b6a38c46c3e663daf61f2cb45581
Reviewed-on: https://go-review.googlesource.com/c/tools/+/266478
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

internal/lsp/cache/load.go

@@ -13,6 +13,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"time"
 
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/event"
@@ -98,6 +99,13 @@ func (s *snapshot) load(ctx context.Context, scopes ...interface{}) error {
 	if err != nil {
 		return err
 	}
+
+	// Set a last resort deadline on packages.Load since it calls the go
+	// command, which may hang indefinitely if it has a bug. golang/go#42132
+	// and golang/go#42255 have more context.
+	ctx, cancel := context.WithTimeout(ctx, 15*time.Minute)
+	defer cancel()
+
 	cfg := s.config(ctx, inv)
 	pkgs, err := packages.Load(cfg, query...)
 	cleanup()