[elastic] Try invoke 'go list ...' again if we get nothing from the previous 'go list ...' invoke (#85)

The original 'go list ...' invoke has strict limitations about the load
mode, once 'go list ...' failed, we will get nothing about the packages.

For this case, try to invoke 'go list ...' with weaker limitations, like
without any dependency related information query. Although the
information we get is limited to the current file, it is better than
nothing.

Author: Henry Wong

go/packages/golist.go

@@ -653,6 +653,11 @@ func golistDriverLRUCached(cfg *Config, rootsDirs func() *goInfo, words ...strin
 	h.Write([]byte(cfg.Dir))
 	h.Write([]byte(words[len(words)-1]))
 	hashKey := h.Sum32()
+	// If this is a temporary `go list ...` invoke, i.e. without deps information query. Don't entangle it with the go
+	// list cache.
+	if cfg.Mode&(NeedImports|NeedTypes|NeedSyntax|NeedTypesInfo) == 0 {
+		return golistDriver(cfg, rootsDirs, words...)
+	}
 	if val, ok := goListLRUCache.Get(hashKey); ok {
 		res := val.(goListResult)
 		return res.response, res.err

internal/lsp/cache/load.go

@@ -86,6 +86,16 @@ func (v *view) checkMetadata(ctx context.Context, f *goFile) (map[packageID]*met
 	ctx, done := trace.StartSpan(ctx, "packages.Load", telemetry.File.Of(f.filename()))
 	defer done()
 	pkgs, err := packages.Load(v.Config(ctx), fmt.Sprintf("file=%s", f.filename()))
+	// Give another try with loose mode to load the packages for current file.
+	if len(pkgs) == 0 {
+		cfg := v.Config(ctx)
+		cfg.Tests = false
+		// Remove any dependency require mode.
+		cfg.Mode = packages.NeedName |
+			packages.NeedFiles |
+			packages.NeedCompiledGoFiles
+		pkgs, err = packages.Load(cfg, fmt.Sprintf("file=%s", f.filename()))
+	}
 	if len(pkgs) == 0 {
 		if err == nil {
 			err = errors.Errorf("go/packages.Load: no packages found for %s", f.filename())