diff --git a/gopls/internal/regtest/codelens_test.go b/gopls/internal/regtest/codelens_test.go
index e4c90bde9b..8402e9b84c 100644
--- a/gopls/internal/regtest/codelens_test.go
+++ b/gopls/internal/regtest/codelens_test.go
@@ -68,7 +68,7 @@ func TestUpdateCodelens(t *testing.T) {
 -- golang.org/x/hello@v1.3.3/go.mod --
 module golang.org/x/hello
 
-go 1.14
+go 1.12
 -- golang.org/x/hello@v1.3.3/hi/hi.go --
 package hi
 
@@ -76,7 +76,7 @@ var Goodbye error
 	-- golang.org/x/hello@v1.2.3/go.mod --
 module golang.org/x/hello
 
-go 1.14
+go 1.12
 -- golang.org/x/hello@v1.2.3/hi/hi.go --
 package hi
 
@@ -87,9 +87,12 @@ var Goodbye error
 -- go.mod --
 module mod.com
 
-go 1.14
+go 1.12
 
 require golang.org/x/hello v1.2.3
+-- go.sum --
+golang.org/x/hello v1.2.3 h1:jOtNXLsiCuLzU6KM3wRHidpc29IxcKpofHZiOW1hYKA=
+golang.org/x/hello v1.2.3/go.mod h1:X79D30QqR94cGK8aIhQNhCZLq4mIr5Gimj5qekF08rY=
 -- main.go --
 package main
 
@@ -123,7 +126,7 @@ func main() {
 		got := env.ReadWorkspaceFile("go.mod")
 		const wantGoMod = `module mod.com
 
-go 1.14
+go 1.12
 
 require golang.org/x/hello v1.3.3
 `
diff --git a/gopls/internal/regtest/diagnostics_test.go b/gopls/internal/regtest/diagnostics_test.go
index fac3f712b3..50ae251fba 100644
--- a/gopls/internal/regtest/diagnostics_test.go
+++ b/gopls/internal/regtest/diagnostics_test.go
@@ -408,7 +408,7 @@ func TestResolveDiagnosticWithDownload(t *testing.T) {
 func TestMissingDependency(t *testing.T) {
 	runner.Run(t, testPackageWithRequire, func(t *testing.T, env *Env) {
 		env.OpenFile("print.go")
-		env.Await(LogMatching(protocol.Error, "initial workspace load failed"))
+		env.Await(LogMatching(protocol.Error, "initial workspace load failed", 1))
 	})
 }
 
@@ -1278,7 +1278,7 @@ func main() {
 // Test some secondary diagnostics
 func TestSecondaryDiagnostics(t *testing.T) {
 	const dir = `
--- mod --
+-- go.mod --
 module mod.com
 -- main.go --
 package main
@@ -1295,16 +1295,19 @@ func main() {}
 		env.OpenFile("other.go")
 		env.Await(CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromInitialWorkspaceLoad), 1))
 		x := env.DiagnosticsFor("main.go")
+		if x == nil {
+			t.Fatalf("expected 1 diagnostic, got none")
+		}
 		if len(x.Diagnostics) != 1 {
-			t.Errorf("main.go, got %d diagnostics, expected 1", len(x.Diagnostics))
+			t.Fatalf("main.go, got %d diagnostics, expected 1", len(x.Diagnostics))
 		}
 		keep := x.Diagnostics[0]
 		y := env.DiagnosticsFor("other.go")
 		if len(y.Diagnostics) != 1 {
-			t.Errorf("other.go: got %d diagnostics, expected 1", len(y.Diagnostics))
+			t.Fatalf("other.go: got %d diagnostics, expected 1", len(y.Diagnostics))
 		}
 		if len(y.Diagnostics[0].RelatedInformation) != 1 {
-			t.Errorf("got %d RelatedInformations, expected 1", len(y.Diagnostics[0].RelatedInformation))
+			t.Fatalf("got %d RelatedInformations, expected 1", len(y.Diagnostics[0].RelatedInformation))
 		}
 		// check that the RelatedInformation matches the error from main.go
 		c := y.Diagnostics[0].RelatedInformation[0]
@@ -1315,6 +1318,9 @@ func main() {}
 }
 
 func TestNotifyOrphanedFiles(t *testing.T) {
+	// Need GO111MODULE=on for this test to work with Go 1.12.
+	testenv.NeedsGo1Point(t, 13)
+
 	const files = `
 -- go.mod --
 module mod.com
diff --git a/gopls/internal/regtest/env.go b/gopls/internal/regtest/env.go
index 6bcfd5c4e6..356fbb521b 100644
--- a/gopls/internal/regtest/env.go
+++ b/gopls/internal/regtest/env.go
@@ -471,17 +471,21 @@ func NoErrorLogs() LogExpectation {
 
 // LogMatching asserts that the client has received a log message
 // of type typ matching the regexp re.
-func LogMatching(typ protocol.MessageType, re string) LogExpectation {
+func LogMatching(typ protocol.MessageType, re string, count int) LogExpectation {
 	rec, err := regexp.Compile(re)
 	if err != nil {
 		panic(err)
 	}
 	check := func(msgs []*protocol.LogMessageParams) (Verdict, interface{}) {
+		var found int
 		for _, msg := range msgs {
 			if msg.Type == typ && rec.Match([]byte(msg.Message)) {
-				return Met, msg
+				found++
 			}
 		}
+		if found == count {
+			return Met, nil
+		}
 		return Unmet, nil
 	}
 	return LogExpectation{
diff --git a/gopls/internal/regtest/watch_test.go b/gopls/internal/regtest/watch_test.go
index f42006097a..6e6919bcd0 100644
--- a/gopls/internal/regtest/watch_test.go
+++ b/gopls/internal/regtest/watch_test.go
@@ -386,7 +386,12 @@ package a
 		runner.Run(t, pkg, func(t *testing.T, env *Env) {
 			env.OpenFile("a/a.go")
 			env.OpenFile("a/a_unneeded.go")
-			env.Await(CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidOpen), 2))
+			env.Await(
+				OnceMet(
+					CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidOpen), 2),
+					LogMatching(protocol.Info, "a_unneeded.go", 1),
+				),
+			)
 
 			// Close and delete the open file, mimicking what an editor would do.
 			env.CloseBuffer("a/a_unneeded.go")
@@ -397,7 +402,13 @@ package a
 			)
 			env.SaveBuffer("a/a.go")
 			env.Await(
-				NoLogMatching(protocol.Info, "a_unneeded.go"),
+				OnceMet(
+					CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidSave), 1),
+					// There should only be one log message containing
+					// a_unneeded.go, from the initial workspace load, which we
+					// check for earlier. If there are more, there's a bug.
+					LogMatching(protocol.Info, "a_unneeded.go", 1),
+				),
 				EmptyDiagnostics("a/a.go"),
 			)
 		})
@@ -407,18 +418,29 @@ package a
 		runner.Run(t, pkg, func(t *testing.T, env *Env) {
 			env.OpenFile("a/a.go")
 			env.OpenFile("a/a_unneeded.go")
-			env.Await(CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidOpen), 2))
+			env.Await(
+				OnceMet(
+					CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidOpen), 2),
+					LogMatching(protocol.Info, "a_unneeded.go", 1),
+				),
+			)
 
 			// Delete and then close the file.
-			env.CloseBuffer("a/a_unneeded.go")
 			env.RemoveWorkspaceFile("a/a_unneeded.go")
+			env.CloseBuffer("a/a_unneeded.go")
 			env.RegexpReplace("a/a.go", "var _ int", "fmt.Println(\"\")")
 			env.Await(
 				env.DiagnosticAtRegexp("a/a.go", "fmt"),
 			)
 			env.SaveBuffer("a/a.go")
 			env.Await(
-				NoLogMatching(protocol.Info, "a_unneeded.go"),
+				OnceMet(
+					CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidSave), 1),
+					// There should only be one log message containing
+					// a_unneeded.go, from the initial workspace load, which we
+					// check for earlier. If there are more, there's a bug.
+					LogMatching(protocol.Info, "a_unneeded.go", 1),
+				),
 				EmptyDiagnostics("a/a.go"),
 			)
 		})
diff --git a/gopls/internal/regtest/workspace_test.go b/gopls/internal/regtest/workspace_test.go
index 7b997aee0a..63bcdea40c 100644
--- a/gopls/internal/regtest/workspace_test.go
+++ b/gopls/internal/regtest/workspace_test.go
@@ -9,7 +9,6 @@ import (
 	"testing"
 
 	"golang.org/x/tools/internal/lsp"
-	"golang.org/x/tools/internal/lsp/fake"
 )
 
 const workspaceProxy = `
@@ -199,7 +198,6 @@ func Hello() int {
 `
 	withOptions(
 		WithProxyFiles(workspaceModuleProxy),
-		WithEditorConfig(fake.EditorConfig{ExperimentalWorkspaceModule: true}),
 	).run(t, multiModule, func(t *testing.T, env *Env) {
 		env.Await(
 			CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromInitialWorkspaceLoad), 1),
diff --git a/gopls/test/gopls_test.go b/gopls/test/gopls_test.go
index 5f43202ace..f4754d4af9 100644
--- a/gopls/test/gopls_test.go
+++ b/gopls/test/gopls_test.go
@@ -12,6 +12,7 @@ import (
 	"golang.org/x/tools/gopls/internal/hooks"
 	cmdtest "golang.org/x/tools/internal/lsp/cmd/test"
 	"golang.org/x/tools/internal/lsp/source"
+	"golang.org/x/tools/internal/lsp/tests"
 	"golang.org/x/tools/internal/testenv"
 )
 
@@ -32,5 +33,6 @@ func TestCommandLine(t *testing.T) {
 func commandLineOptions(options *source.Options) {
 	options.Staticcheck = true
 	options.GoDiff = false
+	tests.DefaultOptions(options)
 	hooks.Options(options)
 }
diff --git a/internal/lsp/cache/check.go b/internal/lsp/cache/check.go
index 8311416c82..48b09124ba 100644
--- a/internal/lsp/cache/check.go
+++ b/internal/lsp/cache/check.go
@@ -15,6 +15,7 @@ import (
 	"strings"
 	"sync"
 
+	"golang.org/x/mod/module"
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/lsp/debug/tag"
@@ -256,7 +257,6 @@ func typeCheck(ctx context.Context, snapshot *snapshot, m *metadata, mode source
 		mode:            mode,
 		goFiles:         make([]*source.ParsedGoFile, len(m.goFiles)),
 		compiledGoFiles: make([]*source.ParsedGoFile, len(m.compiledGoFiles)),
-		module:          m.module,
 		imports:         make(map[packagePath]*pkg),
 		typesSizes:      m.typesSizes,
 		typesInfo: &types.Info{
@@ -268,6 +268,18 @@ func typeCheck(ctx context.Context, snapshot *snapshot, m *metadata, mode source
 			Scopes:     make(map[ast.Node]*types.Scope),
 		},
 	}
+	// If this is a replaced module in the workspace, the version is
+	// meaningless, and we don't want clients to access it.
+	if m.module != nil {
+		version := m.module.Version
+		if version == source.WorkspaceModuleVersion {
+			version = ""
+		}
+		pkg.version = &module.Version{
+			Path:    m.module.Path,
+			Version: version,
+		}
+	}
 	var (
 		files        = make([]*ast.File, len(m.compiledGoFiles))
 		parseErrors  = make([]error, len(m.compiledGoFiles))
diff --git a/internal/lsp/cache/mod.go b/internal/lsp/cache/mod.go
index c689e2cd21..d21257041f 100644
--- a/internal/lsp/cache/mod.go
+++ b/internal/lsp/cache/mod.go
@@ -233,7 +233,7 @@ func (s *snapshot) ModWhy(ctx context.Context, fh source.FileHandle) (map[string
 		for _, req := range pm.File.Require {
 			args = append(args, req.Mod.Path)
 		}
-		stdout, err := snapshot.RunGoCommand(ctx, "mod", args)
+		stdout, err := snapshot.runGoCommandWithConfig(ctx, cfg, "mod", args)
 		if err != nil {
 			return &modWhyData{err: err}
 		}
@@ -329,7 +329,7 @@ func (s *snapshot) ModUpgrade(ctx context.Context, fh source.FileHandle) (map[st
 			// (see golang/go#38711).
 			args = append([]string{"-mod", "readonly"}, args...)
 		}
-		stdout, err := snapshot.RunGoCommand(ctx, "list", args)
+		stdout, err := snapshot.runGoCommandWithConfig(ctx, cfg, "list", args)
 		if err != nil {
 			return &modUpgradeData{err: err}
 		}
diff --git a/internal/lsp/cache/pkg.go b/internal/lsp/cache/pkg.go
index b29eb27b33..faa0b29e75 100644
--- a/internal/lsp/cache/pkg.go
+++ b/internal/lsp/cache/pkg.go
@@ -8,7 +8,7 @@ import (
 	"go/ast"
 	"go/types"
 
-	"golang.org/x/tools/go/packages"
+	"golang.org/x/mod/module"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/span"
 	errors "golang.org/x/xerrors"
@@ -22,7 +22,7 @@ type pkg struct {
 	compiledGoFiles []*source.ParsedGoFile
 	errors          []*source.Error
 	imports         map[packagePath]*pkg
-	module          *packages.Module
+	version         *module.Version
 	typeErrors      []types.Error
 	types           *types.Package
 	typesInfo       *types.Info
@@ -133,6 +133,6 @@ func (p *pkg) Imports() []source.Package {
 	return result
 }
 
-func (p *pkg) Module() *packages.Module {
-	return p.module
+func (p *pkg) Version() *module.Version {
+	return p.version
 }
diff --git a/internal/lsp/cache/session.go b/internal/lsp/cache/session.go
index d2c2611da3..141fc27d70 100644
--- a/internal/lsp/cache/session.go
+++ b/internal/lsp/cache/session.go
@@ -173,7 +173,7 @@ func (s *Session) createView(ctx context.Context, name string, folder span.URI,
 		name:               name,
 		folder:             folder,
 		root:               folder,
-		modules:            make(map[span.URI]*module),
+		modules:            make(map[span.URI]*moduleRoot),
 		filesByURI:         make(map[span.URI]*fileBase),
 		filesByBase:        make(map[string][]*fileBase),
 	}
@@ -206,7 +206,7 @@ func (s *Session) createView(ctx context.Context, name string, folder span.URI,
 	}
 
 	// Find all of the modules in the workspace.
-	if err := v.findAndBuildWorkspaceModule(ctx, options); err != nil {
+	if err := v.findWorkspaceModules(ctx, options); err != nil {
 		return nil, nil, func() {}, err
 	}
 
@@ -214,6 +214,13 @@ func (s *Session) createView(ctx context.Context, name string, folder span.URI,
 	// check if the view has a valid build configuration.
 	v.setBuildConfiguration()
 
+	// Build the workspace module, if needed.
+	if options.ExperimentalWorkspaceModule {
+		if err := v.buildWorkspaceModule(ctx); err != nil {
+			return nil, nil, func() {}, err
+		}
+	}
+
 	// We have v.goEnv now.
 	v.processEnv = &imports.ProcessEnv{
 		GocmdRunner: s.gocmdRunner,
@@ -240,13 +247,13 @@ func (s *Session) createView(ctx context.Context, name string, folder span.URI,
 	return v, v.snapshot, v.snapshot.generation.Acquire(ctx), nil
 }
 
-// findAndBuildWorkspaceModule walks the view's root folder, looking for go.mod
-// files. Any that are found are added to the view's set of modules, which are
-// then used to construct the workspace module.
+// findWorkspaceModules walks the view's root folder, looking for go.mod files.
+// Any that are found are added to the view's set of modules, which are then
+// used to construct the workspace module.
 //
 // It assumes that the caller has not yet created the view, and therefore does
 // not lock any of the internal data structures before accessing them.
-func (v *View) findAndBuildWorkspaceModule(ctx context.Context, options source.Options) error {
+func (v *View) findWorkspaceModules(ctx context.Context, options source.Options) error {
 	// If the user is intentionally limiting their workspace scope, add their
 	// folder to the roots and return early.
 	if !options.ExpandWorkspaceToModule {
@@ -257,11 +264,9 @@ func (v *View) findAndBuildWorkspaceModule(ctx context.Context, options source.O
 		return nil
 	}
 
-	v.workspaceMode |= usesWorkspaceModule | moduleMode
-
 	// Walk the view's folder to find all modules in the view.
 	root := v.root.Filename()
-	if err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
+	return filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err
 		}
@@ -284,15 +289,39 @@ func (v *View) findAndBuildWorkspaceModule(ctx context.Context, options source.O
 		// so add it to the view.
 		modURI := span.URIFromPath(path)
 		rootURI := span.URIFromPath(filepath.Dir(path))
-		v.modules[rootURI] = &module{
+		v.modules[rootURI] = &moduleRoot{
 			rootURI: rootURI,
 			modURI:  modURI,
 			sumURI:  span.URIFromPath(sumFilename(modURI)),
 		}
 		return nil
-	}); err != nil {
-		return err
+	})
+}
+
+func (v *View) buildWorkspaceModule(ctx context.Context) error {
+	// If the view has an invalid configuration, don't build the workspace
+	// module.
+	if !v.hasValidBuildConfiguration {
+		return nil
 	}
+	// If the view is not in a module and contains no modules, but still has a
+	// valid workspace configuration, do not create the workspace module.
+	// It could be using GOPATH or a different build system entirely.
+	if v.modURI == "" && len(v.modules) == 0 && v.hasValidBuildConfiguration {
+		return nil
+	}
+	v.workspaceMode |= moduleMode
+
+	// Don't default to multi-workspace mode if one of the modules contains a
+	// vendor directory. We still have to decide how to handle vendoring.
+	for _, mod := range v.modules {
+		if info, _ := os.Stat(filepath.Join(mod.rootURI.Filename(), "vendor")); info != nil {
+			return nil
+		}
+	}
+
+	v.workspaceMode |= usesWorkspaceModule
+
 	// If the user does not have a gopls.mod, we need to create one, based on
 	// modules we found in the user's workspace.
 	var err error
diff --git a/internal/lsp/cache/snapshot.go b/internal/lsp/cache/snapshot.go
index 45054901ef..81d5fc93d1 100644
--- a/internal/lsp/cache/snapshot.go
+++ b/internal/lsp/cache/snapshot.go
@@ -181,6 +181,10 @@ func (s *snapshot) RunGoCommandDirect(ctx context.Context, verb string, args []s
 
 func (s *snapshot) RunGoCommand(ctx context.Context, verb string, args []string) (*bytes.Buffer, error) {
 	cfg := s.config(ctx)
+	return s.runGoCommandWithConfig(ctx, cfg, verb, args)
+}
+
+func (s *snapshot) runGoCommandWithConfig(ctx context.Context, cfg *packages.Config, verb string, args []string) (*bytes.Buffer, error) {
 	_, runner, inv, cleanup, err := s.goCommandInvocation(ctx, cfg, true, verb, args)
 	if err != nil {
 		return nil, err
@@ -1248,15 +1252,13 @@ func (s *snapshot) buildBuiltinPackage(ctx context.Context, goFiles []string) er
 	return nil
 }
 
-const workspaceModuleVersion = "v0.0.0-00010101000000-000000000000"
-
 // buildWorkspaceModule generates a workspace module given the modules in the
 // the workspace.
 func (s *snapshot) buildWorkspaceModule(ctx context.Context) (*modfile.File, error) {
 	file := &modfile.File{}
 	file.AddModuleStmt("gopls-workspace")
 
-	paths := make(map[string]*module)
+	paths := make(map[string]*moduleRoot)
 	for _, mod := range s.view.modules {
 		fh, err := s.view.snapshot.GetFile(ctx, mod.modURI)
 		if err != nil {
@@ -1266,9 +1268,12 @@ func (s *snapshot) buildWorkspaceModule(ctx context.Context) (*modfile.File, err
 		if err != nil {
 			return nil, err
 		}
+		if parsed.File.Module == nil {
+			return nil, fmt.Errorf("no module declaration for %s", mod.modURI)
+		}
 		path := parsed.File.Module.Mod.Path
 		paths[path] = mod
-		file.AddNewRequire(path, workspaceModuleVersion, false)
+		file.AddNewRequire(path, source.WorkspaceModuleVersion, false)
 		if err := file.AddReplace(path, "", mod.rootURI.Filename(), ""); err != nil {
 			return nil, err
 		}
diff --git a/internal/lsp/cache/view.go b/internal/lsp/cache/view.go
index 5011a36fa4..91d537d913 100644
--- a/internal/lsp/cache/view.go
+++ b/internal/lsp/cache/view.go
@@ -72,7 +72,7 @@ type View struct {
 	// the snapshot and invalidated on file changes.
 
 	// modules is the set of modules currently in this workspace.
-	modules map[span.URI]*module
+	modules map[span.URI]*moduleRoot
 
 	// workspaceModule is an in-memory representation of the go.mod file for
 	// the workspace module.
@@ -177,7 +177,8 @@ type builtinPackageData struct {
 	parsed *source.BuiltinPackage
 	err    error
 }
-type module struct {
+
+type moduleRoot struct {
 	rootURI        span.URI
 	modURI, sumURI span.URI
 }
diff --git a/internal/lsp/cmd/cmd_test.go b/internal/lsp/cmd/cmd_test.go
index be054954a2..81e20f2052 100644
--- a/internal/lsp/cmd/cmd_test.go
+++ b/internal/lsp/cmd/cmd_test.go
@@ -28,7 +28,7 @@ func TestCommandLine(t *testing.T) {
 	packagestest.TestAll(t,
 		cmdtest.TestCommandLine(
 			"../testdata",
-			nil,
+			tests.DefaultOptions,
 		),
 	)
 }
diff --git a/internal/lsp/fake/editor.go b/internal/lsp/fake/editor.go
index d5cd277904..892774c7e2 100644
--- a/internal/lsp/fake/editor.go
+++ b/internal/lsp/fake/editor.go
@@ -84,10 +84,6 @@ type EditorConfig struct {
 
 	// EnableStaticcheck enables staticcheck analyzers.
 	EnableStaticcheck bool
-
-	// ExperimentalWorkspaceModule enables the experimental support for
-	// multi-module workspaces.
-	ExperimentalWorkspaceModule bool
 }
 
 // NewEditor Creates a new Editor.
@@ -196,9 +192,8 @@ func (e *Editor) configuration() map[string]interface{} {
 	if e.Config.EnableStaticcheck {
 		config["staticcheck"] = true
 	}
-	if e.Config.ExperimentalWorkspaceModule {
-		config["experimentalWorkspaceModule"] = true
-	}
+	// Default to using the experimental workspace module mode.
+	config["experimentalWorkspaceModule"] = true
 
 	return config
 }
diff --git a/internal/lsp/link.go b/internal/lsp/link.go
index 6c0b561fb6..adacc3aff4 100644
--- a/internal/lsp/link.go
+++ b/internal/lsp/link.go
@@ -179,10 +179,10 @@ func moduleAtVersion(ctx context.Context, snapshot source.Snapshot, target strin
 	if err != nil {
 		return "", "", false
 	}
-	if impPkg.Module() == nil {
+	if impPkg.Version() == nil {
 		return "", "", false
 	}
-	version, modpath := impPkg.Module().Version, impPkg.Module().Path
+	version, modpath := impPkg.Version().Version, impPkg.Version().Path
 	if modpath == "" || version == "" {
 		return "", "", false
 	}
diff --git a/internal/lsp/lsp_test.go b/internal/lsp/lsp_test.go
index 20459f11ef..eccc56ba85 100644
--- a/internal/lsp/lsp_test.go
+++ b/internal/lsp/lsp_test.go
@@ -50,7 +50,8 @@ func testLSP(t *testing.T, exporter packagestest.Exporter) {
 
 		cache := cache.New(ctx, nil)
 		session := cache.NewSession(ctx)
-		options := tests.DefaultOptions()
+		options := source.DefaultOptions()
+		tests.DefaultOptions(&options)
 		session.SetOptions(options)
 		options.Env = datum.Config.Env
 		view, _, release, err := session.NewView(ctx, datum.Config.Dir, span.URIFromPath(datum.Config.Dir), options)
diff --git a/internal/lsp/mod/diagnostics.go b/internal/lsp/mod/diagnostics.go
index af01caec9c..7c85022669 100644
--- a/internal/lsp/mod/diagnostics.go
+++ b/internal/lsp/mod/diagnostics.go
@@ -89,11 +89,17 @@ func ExtractGoCommandError(ctx context.Context, snapshot source.Snapshot, fh sou
 		if match == nil || len(match) < 3 {
 			continue
 		}
-		v.Path = match[1]
-		v.Version = match[2]
-		if err := module.Check(v.Path, v.Version); err == nil {
-			break
+		path, version := match[1], match[2]
+		// Any module versions that come from the workspace module should not
+		// be shown to the user.
+		if version == source.WorkspaceModuleVersion {
+			continue
 		}
+		if err := module.Check(path, version); err != nil {
+			continue
+		}
+		v.Path, v.Version = path, version
+		break
 	}
 	pm, err := snapshot.ParseMod(ctx, fh)
 	if err != nil {
diff --git a/internal/lsp/mod/mod_test.go b/internal/lsp/mod/mod_test.go
index 4c17deceb7..1103cd87e2 100644
--- a/internal/lsp/mod/mod_test.go
+++ b/internal/lsp/mod/mod_test.go
@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"golang.org/x/tools/internal/lsp/cache"
+	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/lsp/tests"
 	"golang.org/x/tools/internal/span"
 	"golang.org/x/tools/internal/testenv"
@@ -27,7 +28,8 @@ func TestModfileRemainsUnchanged(t *testing.T) {
 	ctx := tests.Context(t)
 	cache := cache.New(ctx, nil)
 	session := cache.NewSession(ctx)
-	options := tests.DefaultOptions()
+	options := source.DefaultOptions()
+	tests.DefaultOptions(&options)
 	options.TempModfile = true
 	options.Env = []string{"GOPACKAGESDRIVER=off", "GOROOT="}
 
diff --git a/internal/lsp/source/hover.go b/internal/lsp/source/hover.go
index d331e72f2e..7e4a10c809 100644
--- a/internal/lsp/source/hover.go
+++ b/internal/lsp/source/hover.go
@@ -201,10 +201,10 @@ func moduleAtVersion(path string, i *IdentifierInfo) (string, string, bool) {
 	if err != nil {
 		return "", "", false
 	}
-	if impPkg.Module() == nil {
+	if impPkg.Version() == nil {
 		return "", "", false
 	}
-	version, modpath := impPkg.Module().Version, impPkg.Module().Path
+	version, modpath := impPkg.Version().Version, impPkg.Version().Path
 	if modpath == "" || version == "" {
 		return "", "", false
 	}
diff --git a/internal/lsp/source/source_test.go b/internal/lsp/source/source_test.go
index c35e9160fb..60081a09b8 100644
--- a/internal/lsp/source/source_test.go
+++ b/internal/lsp/source/source_test.go
@@ -52,7 +52,8 @@ func testSource(t *testing.T, exporter packagestest.Exporter) {
 
 		cache := cache.New(ctx, nil)
 		session := cache.NewSession(ctx)
-		options := tests.DefaultOptions()
+		options := source.DefaultOptions()
+		tests.DefaultOptions(&options)
 		options.Env = datum.Config.Env
 		view, _, release, err := session.NewView(ctx, "source_test", span.URIFromPath(datum.Config.Dir), options)
 		release()
diff --git a/internal/lsp/source/view.go b/internal/lsp/source/view.go
index 099d87014e..20ee4b5786 100644
--- a/internal/lsp/source/view.go
+++ b/internal/lsp/source/view.go
@@ -14,8 +14,8 @@ import (
 	"io"
 
 	"golang.org/x/mod/modfile"
+	"golang.org/x/mod/module"
 	"golang.org/x/tools/go/analysis"
-	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/imports"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/span"
@@ -473,7 +473,7 @@ type Package interface {
 	GetImport(pkgPath string) (Package, error)
 	MissingDependencies() []string
 	Imports() []Package
-	Module() *packages.Module
+	Version() *module.Version
 }
 
 type Error struct {
@@ -508,3 +508,9 @@ var (
 	InconsistentVendoring = errors.New("inconsistent vendoring")
 	PackagesLoadError     = errors.New("packages.Load error")
 )
+
+// WorkspaceModuleVersion is the nonexistent pseudoversion used in the
+// construction of the workspace module. It is exported so that we can make
+// sure not to show this version to end users in error messages, to avoid
+// confusion.
+const WorkspaceModuleVersion = "v0.0.0-goplsworkspace"
diff --git a/internal/lsp/tests/tests.go b/internal/lsp/tests/tests.go
index 7a9d582a2f..65a3a48c21 100644
--- a/internal/lsp/tests/tests.go
+++ b/internal/lsp/tests/tests.go
@@ -221,8 +221,7 @@ func Context(t testing.TB) context.Context {
 	return context.Background()
 }
 
-func DefaultOptions() source.Options {
-	o := source.DefaultOptions()
+func DefaultOptions(o *source.Options) {
 	o.SupportedCodeActions = map[source.FileKind]map[protocol.CodeActionKind]bool{
 		source.Go: {
 			protocol.SourceOrganizeImports: true,
@@ -241,7 +240,7 @@ func DefaultOptions() source.Options {
 	o.InsertTextFormat = protocol.SnippetTextFormat
 	o.CompletionBudget = time.Minute
 	o.HierarchicalDocumentSymbolSupport = true
-	return o
+	o.ExperimentalWorkspaceModule = true
 }
 
 var (