[elastic] Move the deps download into 'intialize' request handle

The original implementation relies on 'go list' to download the deps.
And 'go list' will be called by the request handler indirectly.
This approach is unpredictable and 'go list' is black box to us. So it's
better download the deps manually in 'ManageDeps', i.e. inside
'initialize' request handler.

For security, set 'GO111MODULE=off' by default, once we set
'GO111MODULE=off', we pass option to `-mod=vendor` to any `go list`
command, so we can resolve packages from `vendor` folder. And we can
jump to the `vendor` folder.

Author: Henry Wong

go/packages/golist.go

@@ -861,6 +861,31 @@ func invokeGo(cfg *Config, args ...string) (*bytes.Buffer, error) {
 		cfg.Logf("%s for %v, stderr: <<%s>>\n", time.Since(start), cmdDebugStr(cmd, args...), stderr)
 	}(time.Now())
 
+	enableVendor := func(cfg *Config) bool {
+		l := len(cfg.Env)
+		for i := range cfg.Env {
+			if cfg.Env[l-i-1] == "GO111MODULE=off" {
+				return true
+			}
+		}
+		return false
+	}(cfg)
+	for i := range cmd.Args {
+		if cmd.Args[i] == "list" && len(cmd.Args) != i {
+			if enableVendor {
+				l := len(cmd.Env)
+				for j := range cmd.Env {
+					if cmd.Env[l-j-1] == "GO111MODULE=off" {
+						cmd.Env[l-j-1] = "GO111MODULE=on"
+						cmd.Args = append(cmd.Args[:i+1], append([]string{"-mod=vendor"}, cmd.Args[i+1:]...)...)
+						break
+					}
+				}
+				break
+			}
+		}
+	}
+
 	if err := cmd.Run(); err != nil {
 		// Check for 'go' executable not being found.
 		if ee, ok := err.(*exec.Error); ok && ee.Err == exec.ErrNotFound {

internal/lsp/cache/session.go

@@ -93,6 +93,8 @@ func (s *session) NewView(ctx context.Context, name string, folder span.URI) sou
 		},
 		ignoredURIs: make(map[span.URI]struct{}),
 	}
+	// Disable 'GO111MODULE' by default, 'GO111MODULE=off' will disallow the deps download for the repos under mod mode
+	disableGoModule(v)
 	// Preemptively build the builtin package,
 	// so we immediately add builtin.go to the list of ignored files.
 	v.buildBuiltinPkg(ctx)
@@ -382,3 +384,13 @@ func (s debugSession) File(hash string) *debug.File {
 		Hash:    hash,
 	}
 }
+
+func disableGoModule(v *view) {
+	for _, ev := range v.env {
+		if ev == "GO111MODULE=off" {
+			return
+		}
+	}
+	// TODO(henrywong) Use 'GOPROXY=off' to disable the network access
+	v.env = append(v.env, "GO111MODULE=off")
+}

internal/lsp/elasticserver.go

@@ -189,10 +189,8 @@ type WorkspaceFolderMeta struct {
 // manageDeps will try its best to convert the folders to modules. The core functions, like deps downloading and deps
 // management, will be implemented in the package 'cache'.
 func (s ElasticServer) ManageDeps(folders *[]protocol.WorkspaceFolder) error {
-	// Note: For the upstream go langserver, granularity of the workspace folders is repository. But for the elastic go
-	// language server, there are repositories contain multiple modules. In order to handle the modules separately, we
-	// consider different modules as different workspace folders, so we can manage the dependency of different modules
-	// separately.
+	// In order to handle the modules separately, we consider different modules as different workspace folders, so we
+	// can manage the dependency of different modules separately.
 	for _, folder := range *folders {
 		metadata := &WorkspaceFolderMeta{}
 		if folder.URI != "" {

internal/lsp/general.go

@@ -38,6 +38,9 @@ func (s *Server) initialize(ctx context.Context, params *protocol.InitializePara
 		if opt, ok := opts["noIncrementalSync"].(bool); ok && opt {
 			s.textDocumentSyncKind = protocol.Full
 		}
+		if opt, ok := opts["installGoDependency"].(bool); ok && opt {
+			s.installGoDependency = true
+		}
 	}
 
 	// Default to using synopsis as a default for hover information.

internal/lsp/server.go

@@ -88,6 +88,7 @@ type Server struct {
 	preferredContentFormat        protocol.MarkupKind
 	disabledAnalyses              map[string]struct{}
 	wantSuggestedFixes            bool
+	installGoDependency           bool
 
 	supportedCodeActions map[source.FileKind]map[protocol.CodeActionKind]bool
 

internal/lsp/workspace.go

@@ -8,8 +8,10 @@ import (
 	"context"
 
 	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/lsp/telemetry/log"
 	"golang.org/x/tools/internal/span"
 	errors "golang.org/x/xerrors"
+	"os/exec"
 )
 
 func (s *Server) changeFolders(ctx context.Context, event protocol.WorkspaceFoldersChangeEvent) error {
@@ -31,6 +33,13 @@ func (s *Server) changeFolders(ctx context.Context, event protocol.WorkspaceFold
 }
 
 func (s *Server) addView(ctx context.Context, name string, uri span.URI) error {
+	if s.installGoDependency {
+		cmd := exec.Command("go", "mod", "download")
+		cmd.Dir = uri.Filename()
+		if err := cmd.Run(); err != nil {
+			log.Error(ctx, "failed to download the dependencies", err)
+		}
+	}
 	view := s.session.NewView(ctx, name, uri)
 	s.stateMu.Lock()
 	state := s.state