diff --git a/cmd/gopls/main.go b/cmd/gopls/main.go
index 26d32d06fd..dcd108d9fa 100644
--- a/cmd/gopls/main.go
+++ b/cmd/gopls/main.go
@@ -17,5 +17,5 @@ import (
 )
 
 func main() {
-	tool.Main(context.Background(), cmd.New(nil), os.Args[1:])
+	tool.Main(context.Background(), cmd.New("", nil), os.Args[1:])
 }
diff --git a/internal/lsp/cache/cache.go b/internal/lsp/cache/cache.go
index 71db06b638..4f0e3e68d0 100644
--- a/internal/lsp/cache/cache.go
+++ b/internal/lsp/cache/cache.go
@@ -5,20 +5,31 @@
 package cache
 
 import (
+	"go/token"
+
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/lsp/xlog"
+	"golang.org/x/tools/internal/span"
 )
 
 func New() source.Cache {
-	return &cache{}
+	return &cache{
+		fset: token.NewFileSet(),
+	}
 }
 
 type cache struct {
+	fset *token.FileSet
 }
 
 func (c *cache) NewSession(log xlog.Logger) source.Session {
 	return &session{
-		cache: c,
-		log:   log,
+		cache:    c,
+		log:      log,
+		overlays: make(map[span.URI][]byte),
 	}
 }
+
+func (c *cache) FileSet() *token.FileSet {
+	return c.fset
+}
diff --git a/internal/lsp/cache/check.go b/internal/lsp/cache/check.go
index b2d12526d1..a81f6902e3 100644
--- a/internal/lsp/cache/check.go
+++ b/internal/lsp/cache/check.go
@@ -10,6 +10,7 @@ import (
 	"go/ast"
 	"go/parser"
 	"go/scanner"
+	"go/token"
 	"go/types"
 
 	"golang.org/x/tools/go/analysis"
@@ -49,6 +50,7 @@ func (v *view) parse(ctx context.Context, file source.File) ([]packages.Error, e
 		view: v,
 		seen: make(map[string]struct{}),
 		ctx:  ctx,
+		fset: f.FileSet(),
 	}
 	// Start prefetching direct imports.
 	for importPath := range f.meta.children {
@@ -69,12 +71,11 @@ func (v *view) parse(ctx context.Context, file source.File) ([]packages.Error, e
 
 func (v *view) checkMetadata(ctx context.Context, f *goFile) ([]packages.Error, error) {
 	if v.reparseImports(ctx, f, f.filename()) {
-		cfg := v.config
-		cfg.Mode = packages.LoadImports | packages.NeedTypesSizes
-		pkgs, err := packages.Load(&cfg, fmt.Sprintf("file=%s", f.filename()))
+		cfg := v.buildConfig()
+		pkgs, err := packages.Load(cfg, fmt.Sprintf("file=%s", f.filename()))
 		if len(pkgs) == 0 {
 			if err == nil {
-				err = fmt.Errorf("no packages found for %s", f.filename())
+				err = fmt.Errorf("%s: no packages found", f.filename())
 			}
 			// Return this error as a diagnostic to the user.
 			return []packages.Error{
@@ -104,7 +105,7 @@ func (v *view) reparseImports(ctx context.Context, f *goFile, filename string) b
 	}
 	// Get file content in case we don't already have it?
 	f.read(ctx)
-	parsed, _ := parser.ParseFile(v.config.Fset, filename, f.content, parser.ImportsOnly)
+	parsed, _ := parser.ParseFile(f.FileSet(), filename, f.content, parser.ImportsOnly)
 	if parsed == nil {
 		return true
 	}
@@ -173,7 +174,8 @@ type importer struct {
 	// If we have seen a package that is already in this map, we have a circular import.
 	seen map[string]struct{}
 
-	ctx context.Context
+	ctx  context.Context
+	fset *token.FileSet
 }
 
 func (imp *importer) Import(pkgPath string) (*types.Package, error) {
@@ -255,9 +257,10 @@ func (imp *importer) typeCheck(pkgPath string) (*pkg, error) {
 			view: imp.view,
 			seen: seen,
 			ctx:  imp.ctx,
+			fset: imp.fset,
 		},
 	}
-	check := types.NewChecker(cfg, imp.view.config.Fset, pkg.types, pkg.typesInfo)
+	check := types.NewChecker(cfg, imp.fset, pkg.types, pkg.typesInfo)
 	check.Files(pkg.syntax)
 
 	// Add every file in this package to our cache.
@@ -273,7 +276,7 @@ func (v *view) cachePackage(ctx context.Context, pkg *pkg, meta *metadata) {
 			v.Session().Logger().Errorf(ctx, "invalid position for file %v", file.Name)
 			continue
 		}
-		tok := v.config.Fset.File(file.Pos())
+		tok := v.Session().Cache().FileSet().File(file.Pos())
 		if tok == nil {
 			v.Session().Logger().Errorf(ctx, "no token.File for %v", file.Name)
 			continue
@@ -341,7 +344,7 @@ func (v *view) appendPkgError(pkg *pkg, err error) {
 		}
 	case types.Error:
 		errs = append(errs, packages.Error{
-			Pos:  v.config.Fset.Position(err.Pos).String(),
+			Pos:  v.Session().Cache().FileSet().Position(err.Pos).String(),
 			Msg:  err.Msg,
 			Kind: packages.TypeError,
 		})
diff --git a/internal/lsp/cache/file.go b/internal/lsp/cache/file.go
index 14bb7f54e8..5b69dec1d7 100644
--- a/internal/lsp/cache/file.go
+++ b/internal/lsp/cache/file.go
@@ -80,8 +80,8 @@ func (f *fileBase) GetContent(ctx context.Context) []byte {
 	return f.content
 }
 
-func (f *fileBase) GetFileSet(ctx context.Context) *token.FileSet {
-	return f.view.config.Fset
+func (f *fileBase) FileSet() *token.FileSet {
+	return f.view.Session().Cache().FileSet()
 }
 
 func (f *goFile) GetToken(ctx context.Context) *token.File {
@@ -144,7 +144,9 @@ func (f *fileBase) read(ctx context.Context) {
 		}
 	}
 	// We might have the content saved in an overlay.
-	if content, ok := f.view.config.Overlay[f.filename()]; ok {
+	f.view.session.overlayMu.Lock()
+	defer f.view.session.overlayMu.Unlock()
+	if content, ok := f.view.session.overlays[f.URI()]; ok {
 		f.content = content
 		return
 	}
diff --git a/internal/lsp/cache/parse.go b/internal/lsp/cache/parse.go
index c9876ba6cb..d8329ffb37 100644
--- a/internal/lsp/cache/parse.go
+++ b/internal/lsp/cache/parse.go
@@ -11,7 +11,6 @@ import (
 	"go/parser"
 	"go/scanner"
 	"go/token"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -20,6 +19,10 @@ import (
 	"golang.org/x/tools/internal/span"
 )
 
+func parseFile(fset *token.FileSet, filename string, src []byte) (*ast.File, error) {
+	return parser.ParseFile(fset, filename, src, parser.AllErrors|parser.ParseComments)
+}
+
 // We use a counting semaphore to limit
 // the number of parallel I/O calls per process.
 var ioLimit = make(chan bool, 20)
@@ -37,53 +40,43 @@ func (imp *importer) parseFiles(filenames []string) ([]*ast.File, []error) {
 	parsed := make([]*ast.File, n)
 	errors := make([]error, n)
 	for i, filename := range filenames {
-		if imp.view.config.Context.Err() != nil {
+		if imp.ctx.Err() != nil {
 			parsed[i] = nil
-			errors[i] = imp.view.config.Context.Err()
+			errors[i] = imp.ctx.Err()
 			continue
 		}
 
 		// First, check if we have already cached an AST for this file.
 		f, err := imp.view.findFile(span.FileURI(filename))
-		if err != nil {
+		if err != nil || f == nil {
 			parsed[i], errors[i] = nil, err
+			continue
 		}
-		var fAST *ast.File
-		if f != nil {
-			if gof, ok := f.(*goFile); ok {
-				fAST = gof.ast
-			}
+		gof, ok := f.(*goFile)
+		if !ok {
+			parsed[i], errors[i] = nil, fmt.Errorf("Non go file in parse call: %v", filename)
+			continue
 		}
 
 		wg.Add(1)
 		go func(i int, filename string) {
 			ioLimit <- true // wait
 
-			if fAST != nil {
-				parsed[i], errors[i] = fAST, nil
+			if gof.ast != nil {
+				parsed[i], errors[i] = gof.ast, nil
 			} else {
 				// We don't have a cached AST for this file.
-				var src []byte
-				// Check for an available overlay.
-				for f, contents := range imp.view.config.Overlay {
-					if sameFile(f, filename) {
-						src = contents
-					}
-				}
-				var err error
-				// We don't have an overlay, so we must read the file's contents.
+				gof.read(imp.ctx)
+				src := gof.content
 				if src == nil {
-					src, err = ioutil.ReadFile(filename)
-				}
-				if err != nil {
-					parsed[i], errors[i] = nil, err
+					parsed[i], errors[i] = nil, fmt.Errorf("No source for %v", filename)
 				} else {
 					// ParseFile may return both an AST and an error.
-					parsed[i], errors[i] = imp.view.config.ParseFile(imp.view.config.Fset, filename, src)
+					parsed[i], errors[i] = parseFile(imp.fset, filename, src)
 
 					// Fix any badly parsed parts of the AST.
 					if file := parsed[i]; file != nil {
-						tok := imp.view.config.Fset.File(file.Pos())
+						tok := imp.fset.File(file.Pos())
 						imp.view.fix(imp.ctx, parsed[i], tok, src)
 					}
 				}
diff --git a/internal/lsp/cache/session.go b/internal/lsp/cache/session.go
index 4ebe57eceb..c4c7a9b978 100644
--- a/internal/lsp/cache/session.go
+++ b/internal/lsp/cache/session.go
@@ -10,7 +10,6 @@ import (
 	"strings"
 	"sync"
 
-	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/lsp/xlog"
 	"golang.org/x/tools/internal/span"
@@ -24,6 +23,9 @@ type session struct {
 	viewMu  sync.Mutex
 	views   []*view
 	viewMap map[span.URI]source.View
+
+	overlayMu sync.Mutex
+	overlays  map[span.URI][]byte
 }
 
 func (s *session) Shutdown(ctx context.Context) {
@@ -40,7 +42,7 @@ func (s *session) Cache() source.Cache {
 	return s.cache
 }
 
-func (s *session) NewView(name string, folder span.URI, config *packages.Config) source.View {
+func (s *session) NewView(name string, folder span.URI) source.View {
 	s.viewMu.Lock()
 	defer s.viewMu.Unlock()
 	ctx := context.Background()
@@ -49,9 +51,7 @@ func (s *session) NewView(name string, folder span.URI, config *packages.Config)
 		session:        s,
 		baseCtx:        ctx,
 		backgroundCtx:  backgroundCtx,
-		builtinPkg:     builtinPkg(*config),
 		cancel:         cancel,
-		config:         *config,
 		name:           name,
 		folder:         folder,
 		filesByURI:     make(map[span.URI]viewFile),
@@ -65,9 +65,6 @@ func (s *session) NewView(name string, folder span.URI, config *packages.Config)
 		},
 		ignoredURIs: make(map[span.URI]struct{}),
 	}
-	for filename := range v.builtinPkg.Files {
-		v.ignoredURIs[span.NewURI(filename)] = struct{}{}
-	}
 	s.views = append(s.views, v)
 	// we always need to drop the view map
 	s.viewMap = make(map[span.URI]source.View)
@@ -155,3 +152,26 @@ func (s *session) removeView(ctx context.Context, view *view) error {
 func (s *session) Logger() xlog.Logger {
 	return s.log
 }
+
+func (s *session) setOverlay(uri span.URI, content []byte) {
+	s.overlayMu.Lock()
+	defer s.overlayMu.Unlock()
+	//TODO: we also need to invalidate anything that depended on this "file"
+	if content == nil {
+		delete(s.overlays, uri)
+		return
+	}
+	s.overlays[uri] = content
+}
+
+func (s *session) buildOverlay() map[string][]byte {
+	s.overlayMu.Lock()
+	defer s.overlayMu.Unlock()
+	overlay := make(map[string][]byte)
+	for uri, content := range s.overlays {
+		if filename, err := uri.Filename(); err == nil {
+			overlay[filename] = content
+		}
+	}
+	return overlay
+}
diff --git a/internal/lsp/cache/view.go b/internal/lsp/cache/view.go
index f64f7a3712..f2573605a4 100644
--- a/internal/lsp/cache/view.go
+++ b/internal/lsp/cache/view.go
@@ -8,7 +8,6 @@ import (
 	"context"
 	"go/ast"
 	"go/parser"
-	"go/token"
 	"go/types"
 	"os"
 	"sync"
@@ -42,9 +41,8 @@ type view struct {
 	// Folder is the root of this view.
 	folder span.URI
 
-	// Config is the configuration used for the view's interaction with the
-	// go/packages API. It is shared across all views.
-	config packages.Config
+	// env is the environment to use when invoking underlying tools.
+	env []string
 
 	// keep track of files by uri and by basename, a single file may be mapped
 	// to multiple uris, and the same basename may map to multiple files
@@ -110,12 +108,40 @@ func (v *view) Folder() span.URI {
 
 // Config returns the configuration used for the view's interaction with the
 // go/packages API. It is shared across all views.
-func (v *view) Config() packages.Config {
-	return v.config
+func (v *view) buildConfig() *packages.Config {
+	//TODO:should we cache the config and/or overlay somewhere?
+	folderPath, err := v.folder.Filename()
+	if err != nil {
+		folderPath = ""
+	}
+	return &packages.Config{
+		Context: v.backgroundCtx,
+		Dir:     folderPath,
+		Env:     v.env,
+		Mode: packages.NeedName |
+			packages.NeedFiles |
+			packages.NeedCompiledGoFiles |
+			packages.NeedImports |
+			packages.NeedDeps |
+			packages.NeedTypesSizes,
+		Fset:      v.session.cache.fset,
+		Overlay:   v.session.buildOverlay(),
+		ParseFile: parseFile,
+		Tests:     true,
+	}
+}
+
+func (v *view) Env() []string {
+	v.mu.Lock()
+	defer v.mu.Unlock()
+	return v.env
 }
 
 func (v *view) SetEnv(env []string) {
-	v.config.Env = env
+	v.mu.Lock()
+	defer v.mu.Unlock()
+	//TODO: this should invalidate the entire view
+	v.env = env
 }
 
 func (v *view) Shutdown(ctx context.Context) {
@@ -139,33 +165,33 @@ func (v *view) BackgroundContext() context.Context {
 }
 
 func (v *view) BuiltinPackage() *ast.Package {
+	if v.builtinPkg == nil {
+		v.buildBuiltinPkg()
+	}
 	return v.builtinPkg
 }
 
-func builtinPkg(cfg packages.Config) *ast.Package {
-	var bpkg *ast.Package
-	cfg.Mode = packages.LoadFiles
+func (v *view) buildBuiltinPkg() {
+	v.mu.Lock()
+	defer v.mu.Unlock()
+	cfg := *v.buildConfig()
 	pkgs, _ := packages.Load(&cfg, "builtin")
 	if len(pkgs) != 1 {
-		bpkg, _ = ast.NewPackage(cfg.Fset, nil, nil, nil)
-		return bpkg
+		v.builtinPkg, _ = ast.NewPackage(cfg.Fset, nil, nil, nil)
+		return
 	}
 	pkg := pkgs[0]
 	files := make(map[string]*ast.File)
 	for _, filename := range pkg.GoFiles {
 		file, err := parser.ParseFile(cfg.Fset, filename, nil, parser.ParseComments)
 		if err != nil {
-			bpkg, _ = ast.NewPackage(cfg.Fset, nil, nil, nil)
-			return bpkg
+			v.builtinPkg, _ = ast.NewPackage(cfg.Fset, nil, nil, nil)
+			return
 		}
 		files[filename] = file
+		v.ignoredURIs[span.NewURI(filename)] = struct{}{}
 	}
-	bpkg, _ = ast.NewPackage(cfg.Fset, files, nil, nil)
-	return bpkg
-}
-
-func (v *view) FileSet() *token.FileSet {
-	return v.config.Fset
+	v.builtinPkg, _ = ast.NewPackage(cfg.Fset, files, nil, nil)
 }
 
 // SetContent sets the overlay contents for a file.
@@ -230,12 +256,12 @@ func (f *goFile) setContent(content []byte) {
 	case f.active && content == nil:
 		// The file was active, so we need to forget its content.
 		f.active = false
-		delete(f.view.config.Overlay, f.filename())
+		f.view.session.setOverlay(f.URI(), nil)
 		f.content = nil
 	case content != nil:
 		// This is an active overlay, so we update the map.
 		f.active = true
-		f.view.config.Overlay[f.filename()] = f.content
+		f.view.session.setOverlay(f.URI(), f.content)
 	}
 }
 
diff --git a/internal/lsp/cmd/cmd.go b/internal/lsp/cmd/cmd.go
index 6c9ab2d8cb..b66039c5d8 100644
--- a/internal/lsp/cmd/cmd.go
+++ b/internal/lsp/cmd/cmd.go
@@ -11,8 +11,6 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	"go/ast"
-	"go/parser"
 	"go/token"
 	"io/ioutil"
 	"log"
@@ -21,7 +19,6 @@ import (
 	"strings"
 	"sync"
 
-	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/jsonrpc2"
 	"golang.org/x/tools/internal/lsp"
 	"golang.org/x/tools/internal/lsp/cache"
@@ -44,11 +41,14 @@ type Application struct {
 	// TODO: Remove this when we stop allowing the serve verb by default.
 	Serve Serve
 
-	// An initial, common go/packages configuration
-	Config packages.Config
-
 	// The base cache to use for sessions from this application.
-	Cache source.Cache
+	cache source.Cache
+
+	// The working directory to run commands in.
+	wd string
+
+	// The environment variables to use.
+	env []string
 
 	// Support for remote lsp server
 	Remote string `flag:"remote" help:"*EXPERIMENTAL* - forward all commands to a remote lsp"`
@@ -58,12 +58,14 @@ type Application struct {
 }
 
 // Returns a new Application ready to run.
-func New(config *packages.Config) *Application {
-	app := &Application{
-		Cache: cache.New(),
+func New(wd string, env []string) *Application {
+	if wd == "" {
+		wd, _ = os.Getwd()
 	}
-	if config != nil {
-		app.Config = *config
+	app := &Application{
+		cache: cache.New(),
+		wd:    wd,
+		env:   env,
 	}
 	return app
 }
@@ -104,20 +106,6 @@ func (app *Application) Run(ctx context.Context, args ...string) error {
 		tool.Main(ctx, &app.Serve, args)
 		return nil
 	}
-	if app.Config.Dir == "" {
-		if wd, err := os.Getwd(); err == nil {
-			app.Config.Dir = wd
-		}
-	}
-	app.Config.Mode = packages.LoadSyntax
-	app.Config.Tests = true
-	if app.Config.Fset == nil {
-		app.Config.Fset = token.NewFileSet()
-	}
-	app.Config.Context = ctx
-	app.Config.ParseFile = func(fset *token.FileSet, filename string, src []byte) (*ast.File, error) {
-		return parser.ParseFile(fset, filename, src, parser.AllErrors|parser.ParseComments)
-	}
 	command, args := args[0], args[1:]
 	for _, c := range app.commands() {
 		if c.Name() == command {
@@ -151,12 +139,12 @@ func (app *Application) connect(ctx context.Context) (*connection, error) {
 	switch app.Remote {
 	case "":
 		connection := newConnection(app)
-		connection.Server = lsp.NewClientServer(app.Cache, connection.Client)
+		connection.Server = lsp.NewClientServer(app.cache, connection.Client)
 		return connection, connection.initialize(ctx)
 	case "internal":
 		internalMu.Lock()
 		defer internalMu.Unlock()
-		if c := internalConnections[app.Config.Dir]; c != nil {
+		if c := internalConnections[app.wd]; c != nil {
 			return c, nil
 		}
 		connection := newConnection(app)
@@ -166,11 +154,11 @@ func (app *Application) connect(ctx context.Context) (*connection, error) {
 		var jc *jsonrpc2.Conn
 		jc, connection.Server, _ = protocol.NewClient(jsonrpc2.NewHeaderStream(cr, cw), connection.Client)
 		go jc.Run(ctx)
-		go lsp.NewServer(app.Cache, jsonrpc2.NewHeaderStream(sr, sw)).Run(ctx)
+		go lsp.NewServer(app.cache, jsonrpc2.NewHeaderStream(sr, sw)).Run(ctx)
 		if err := connection.initialize(ctx); err != nil {
 			return nil, err
 		}
-		internalConnections[app.Config.Dir] = connection
+		internalConnections[app.wd] = connection
 		return connection, nil
 	default:
 		connection := newConnection(app)
@@ -188,7 +176,7 @@ func (app *Application) connect(ctx context.Context) (*connection, error) {
 
 func (c *connection) initialize(ctx context.Context) error {
 	params := &protocol.InitializeParams{}
-	params.RootURI = string(span.FileURI(c.Client.app.Config.Dir))
+	params.RootURI = string(span.FileURI(c.Client.app.wd))
 	params.Capabilities.Workspace.Configuration = true
 	params.Capabilities.TextDocument.Hover.ContentFormat = []protocol.MarkupKind{protocol.PlainText}
 	if _, err := c.Server.Initialize(ctx, params); err != nil {
@@ -283,7 +271,7 @@ func (c *cmdClient) Configuration(ctx context.Context, p *protocol.Configuration
 			continue
 		}
 		env := map[string]interface{}{}
-		for _, value := range c.app.Config.Env {
+		for _, value := range c.app.env {
 			l := strings.SplitN(value, "=", 2)
 			if len(l) != 2 {
 				continue
diff --git a/internal/lsp/cmd/cmd_test.go b/internal/lsp/cmd/cmd_test.go
index 5b8b4c5086..611d78a825 100644
--- a/internal/lsp/cmd/cmd_test.go
+++ b/internal/lsp/cmd/cmd_test.go
@@ -37,7 +37,7 @@ func testCommandLine(t *testing.T, exporter packagestest.Exporter) {
 	r := &runner{
 		exporter: exporter,
 		data:     data,
-		app:      cmd.New(data.Exported.Config),
+		app:      cmd.New(data.Config.Dir, data.Exported.Config.Env),
 	}
 	tests.Run(t, r, data)
 }
diff --git a/internal/lsp/cmd/definition_test.go b/internal/lsp/cmd/definition_test.go
index 6eacc18d9f..36b61eff5c 100644
--- a/internal/lsp/cmd/definition_test.go
+++ b/internal/lsp/cmd/definition_test.go
@@ -54,7 +54,7 @@ func TestDefinitionHelpExample(t *testing.T) {
 		fmt.Sprintf("%v:#%v", thisFile, cmd.ExampleOffset)} {
 		args := append(baseArgs, query)
 		got := captureStdOut(t, func() {
-			tool.Main(context.Background(), cmd.New(nil), args)
+			tool.Main(context.Background(), cmd.New("", nil), args)
 		})
 		if !expect.MatchString(got) {
 			t.Errorf("test with %v\nexpected:\n%s\ngot:\n%s", args, expect, got)
diff --git a/internal/lsp/cmd/format_test.go b/internal/lsp/cmd/format_test.go
index 981ebdb60c..3e83d8d70f 100644
--- a/internal/lsp/cmd/format_test.go
+++ b/internal/lsp/cmd/format_test.go
@@ -41,8 +41,7 @@ func (r *runner) Format(t *testing.T, data tests.Formats) {
 				//TODO: our error handling differs, for now just skip unformattable files
 				continue
 			}
-			app := cmd.New(nil)
-			app.Config = r.data.Config
+			app := cmd.New(r.data.Config.Dir, r.data.Config.Env)
 			got := captureStdOut(t, func() {
 				tool.Main(context.Background(), app, append([]string{"-remote=internal", "format"}, args...))
 			})
diff --git a/internal/lsp/cmd/serve.go b/internal/lsp/cmd/serve.go
index ddac3568ab..28b7398f3a 100644
--- a/internal/lsp/cmd/serve.go
+++ b/internal/lsp/cmd/serve.go
@@ -79,13 +79,13 @@ func (s *Serve) Run(ctx context.Context, args ...string) error {
 		go srv.Conn.Run(ctx)
 	}
 	if s.Address != "" {
-		return lsp.RunServerOnAddress(ctx, s.app.Cache, s.Address, run)
+		return lsp.RunServerOnAddress(ctx, s.app.cache, s.Address, run)
 	}
 	if s.Port != 0 {
-		return lsp.RunServerOnPort(ctx, s.app.Cache, s.Port, run)
+		return lsp.RunServerOnPort(ctx, s.app.cache, s.Port, run)
 	}
 	stream := jsonrpc2.NewHeaderStream(os.Stdin, os.Stdout)
-	srv := lsp.NewServer(s.app.Cache, stream)
+	srv := lsp.NewServer(s.app.cache, stream)
 	srv.Conn.Logger = logger(s.Trace, out)
 	return srv.Conn.Run(ctx)
 }
diff --git a/internal/lsp/general.go b/internal/lsp/general.go
index 78d14f1517..6091519a68 100644
--- a/internal/lsp/general.go
+++ b/internal/lsp/general.go
@@ -10,7 +10,6 @@ import (
 	"fmt"
 	"os"
 	"path"
-	"strings"
 
 	"golang.org/x/tools/internal/jsonrpc2"
 	"golang.org/x/tools/internal/lsp/protocol"
@@ -161,9 +160,11 @@ func (s *Server) processConfig(view source.View, config interface{}) error {
 		if !ok {
 			return fmt.Errorf("invalid config gopls.env type %T", env)
 		}
+		env := view.Env()
 		for k, v := range menv {
-			view.SetEnv(applyEnv(view.Config().Env, k, v))
+			env = append(env, fmt.Sprintf("%s=%s", k, v))
 		}
+		view.SetEnv(env)
 	}
 	// Check if placeholders are enabled.
 	if usePlaceholders, ok := c["usePlaceholders"].(bool); ok {
@@ -176,18 +177,6 @@ func (s *Server) processConfig(view source.View, config interface{}) error {
 	return nil
 }
 
-func applyEnv(env []string, k string, v interface{}) []string {
-	prefix := k + "="
-	value := prefix + fmt.Sprint(v)
-	for i, s := range env {
-		if strings.HasPrefix(s, prefix) {
-			env[i] = value
-			return env
-		}
-	}
-	return append(env, value)
-}
-
 func (s *Server) shutdown(ctx context.Context) error {
 	s.initializedMu.Lock()
 	defer s.initializedMu.Unlock()
diff --git a/internal/lsp/link.go b/internal/lsp/link.go
index 155787ff93..e5ab123f02 100644
--- a/internal/lsp/link.go
+++ b/internal/lsp/link.go
@@ -27,7 +27,7 @@ func (s *Server) documentLink(ctx context.Context, params *protocol.DocumentLink
 	// Add a Godoc link for each imported package.
 	var result []protocol.DocumentLink
 	for _, imp := range file.Imports {
-		spn, err := span.NewRange(f.GetFileSet(ctx), imp.Pos(), imp.End()).Span()
+		spn, err := span.NewRange(f.FileSet(), imp.Pos(), imp.End()).Span()
 		if err != nil {
 			return nil, err
 		}
diff --git a/internal/lsp/lsp_test.go b/internal/lsp/lsp_test.go
index e6cffa075c..7d20a5d300 100644
--- a/internal/lsp/lsp_test.go
+++ b/internal/lsp/lsp_test.go
@@ -36,13 +36,18 @@ type runner struct {
 const viewName = "lsp_test"
 
 func testLSP(t *testing.T, exporter packagestest.Exporter) {
+	ctx := context.Background()
 	data := tests.Load(t, exporter, "testdata")
 	defer data.Exported.Cleanup()
 
 	log := xlog.New(xlog.StdSink{})
 	cache := cache.New()
 	session := cache.NewSession(log)
-	session.NewView(viewName, span.FileURI(data.Config.Dir), &data.Config)
+	view := session.NewView(viewName, span.FileURI(data.Config.Dir))
+	view.SetEnv(data.Config.Env)
+	for filename, content := range data.Config.Overlay {
+		view.SetContent(ctx, span.FileURI(filename), content)
+	}
 	r := &runner{
 		server: &Server{
 			session:     session,
diff --git a/internal/lsp/source/analysis.go b/internal/lsp/source/analysis.go
index a1bb2e3b06..f7021b20b1 100644
--- a/internal/lsp/source/analysis.go
+++ b/internal/lsp/source/analysis.go
@@ -42,7 +42,7 @@ func analyze(ctx context.Context, v View, pkgs []Package, analyzers []*analysis.
 	}
 
 	// Execute the graph in parallel.
-	if err := execAll(ctx, v.FileSet(), roots); err != nil {
+	if err := execAll(ctx, v.Session().Cache().FileSet(), roots); err != nil {
 		return nil, err
 	}
 	return roots, nil
diff --git a/internal/lsp/source/completion.go b/internal/lsp/source/completion.go
index e1d03dcb3b..990cfdd352 100644
--- a/internal/lsp/source/completion.go
+++ b/internal/lsp/source/completion.go
@@ -189,7 +189,7 @@ func (c *completer) setSurrounding(ident *ast.Ident) {
 
 	c.surrounding = &Selection{
 		Content: ident.Name,
-		Range:   span.NewRange(c.view.FileSet(), ident.Pos(), ident.End()),
+		Range:   span.NewRange(c.view.Session().Cache().FileSet(), ident.Pos(), ident.End()),
 		Cursor:  c.pos,
 	}
 }
diff --git a/internal/lsp/source/completion_format.go b/internal/lsp/source/completion_format.go
index e5d069863e..c399afdc0a 100644
--- a/internal/lsp/source/completion_format.go
+++ b/internal/lsp/source/completion_format.go
@@ -143,7 +143,7 @@ func formatFieldList(ctx context.Context, v View, list *ast.FieldList) ([]string
 		p := list.List[i]
 		cfg := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 4}
 		b := &bytes.Buffer{}
-		if err := cfg.Fprint(b, v.FileSet(), p.Type); err != nil {
+		if err := cfg.Fprint(b, v.Session().Cache().FileSet(), p.Type); err != nil {
 			v.Session().Logger().Errorf(ctx, "unable to print type %v", p.Type)
 			continue
 		}
diff --git a/internal/lsp/source/completion_snippet.go b/internal/lsp/source/completion_snippet.go
index 8ac4fab3a1..9b1841fe6e 100644
--- a/internal/lsp/source/completion_snippet.go
+++ b/internal/lsp/source/completion_snippet.go
@@ -46,7 +46,7 @@ func (c *completer) structFieldSnippets(label, detail string) (*snippet.Builder,
 
 	// If the cursor position is on a different line from the literal's opening brace,
 	// we are in a multiline literal.
-	if c.view.FileSet().Position(c.pos).Line != c.view.FileSet().Position(clInfo.cl.Lbrace).Line {
+	if c.view.Session().Cache().FileSet().Position(c.pos).Line != c.view.Session().Cache().FileSet().Position(clInfo.cl.Lbrace).Line {
 		plain.WriteText(",")
 		placeholder.WriteText(",")
 	}
diff --git a/internal/lsp/source/diagnostics.go b/internal/lsp/source/diagnostics.go
index f66e278637..5cbea3ccbd 100644
--- a/internal/lsp/source/diagnostics.go
+++ b/internal/lsp/source/diagnostics.go
@@ -141,7 +141,7 @@ func diagnostics(ctx context.Context, v View, pkg Package, reports map[span.URI]
 func analyses(ctx context.Context, v View, pkg Package, reports map[span.URI][]Diagnostic) error {
 	// Type checking and parsing succeeded. Run analyses.
 	if err := runAnalyses(ctx, v, pkg, func(a *analysis.Analyzer, diag analysis.Diagnostic) error {
-		r := span.NewRange(v.FileSet(), diag.Pos, 0)
+		r := span.NewRange(v.Session().Cache().FileSet(), diag.Pos, 0)
 		s, err := r.Span()
 		if err != nil {
 			// The diagnostic has an invalid position, so we don't have a valid span.
@@ -209,7 +209,7 @@ func pointToSpan(ctx context.Context, v View, spn span.Span) span.Span {
 		v.Session().Logger().Errorf(ctx, "Could not find content for diagnostic: %v", spn.URI())
 		return spn
 	}
-	c := span.NewTokenConverter(diagFile.GetFileSet(ctx), tok)
+	c := span.NewTokenConverter(diagFile.FileSet(), tok)
 	s, err := spn.WithOffset(c)
 	//we just don't bother producing an error if this failed
 	if err != nil {
diff --git a/internal/lsp/source/format.go b/internal/lsp/source/format.go
index ba85ff52fb..ed26bee734 100644
--- a/internal/lsp/source/format.go
+++ b/internal/lsp/source/format.go
@@ -37,7 +37,7 @@ func Format(ctx context.Context, f GoFile, rng span.Range) ([]TextEdit, error) {
 	// of Go used to build the LSP server will determine how it formats code.
 	// This should be acceptable for all users, who likely be prompted to rebuild
 	// the LSP server on each Go release.
-	fset := f.GetFileSet(ctx)
+	fset := f.FileSet()
 	buf := &bytes.Buffer{}
 	if err := format.Node(buf, fset, node); err != nil {
 		return nil, err
diff --git a/internal/lsp/source/highlight.go b/internal/lsp/source/highlight.go
index bf3cb46f68..f8db00fba5 100644
--- a/internal/lsp/source/highlight.go
+++ b/internal/lsp/source/highlight.go
@@ -18,7 +18,7 @@ func Highlight(ctx context.Context, f GoFile, pos token.Pos) []span.Span {
 	if file == nil {
 		return nil
 	}
-	fset := f.GetFileSet(ctx)
+	fset := f.FileSet()
 	path, _ := astutil.PathEnclosingInterval(file, pos, pos)
 	if len(path) == 0 {
 		return nil
diff --git a/internal/lsp/source/hover.go b/internal/lsp/source/hover.go
index d4bb08ecd9..4d00527a85 100644
--- a/internal/lsp/source/hover.go
+++ b/internal/lsp/source/hover.go
@@ -29,7 +29,7 @@ func (i *IdentifierInfo) Hover(ctx context.Context, qf types.Qualifier, markdown
 		if !wantComments {
 			c = nil
 		}
-		return writeHover(x, i.File.GetFileSet(ctx), &b, c, markdownSupported, qf)
+		return writeHover(x, i.File.FileSet(), &b, c, markdownSupported, qf)
 	}
 	obj := i.Declaration.Object
 	switch node := i.Declaration.Node.(type) {
diff --git a/internal/lsp/source/identifier.go b/internal/lsp/source/identifier.go
index 763494ff7a..affa130998 100644
--- a/internal/lsp/source/identifier.go
+++ b/internal/lsp/source/identifier.go
@@ -90,7 +90,7 @@ func identifier(ctx context.Context, v View, f GoFile, pos token.Pos) (*Identifi
 		}
 	}
 	result.Name = result.ident.Name
-	result.Range = span.NewRange(v.FileSet(), result.ident.Pos(), result.ident.End())
+	result.Range = span.NewRange(f.FileSet(), result.ident.Pos(), result.ident.End())
 	result.Declaration.Object = pkg.GetTypesInfo().ObjectOf(result.ident)
 	if result.Declaration.Object == nil {
 		return nil, fmt.Errorf("no object for ident %v", result.Name)
@@ -105,7 +105,7 @@ func identifier(ctx context.Context, v View, f GoFile, pos token.Pos) (*Identifi
 			return nil, fmt.Errorf("no declaration for %s", result.Name)
 		}
 		result.Declaration.Node = decl
-		if result.Declaration.Range, err = posToRange(ctx, v.FileSet(), result.Name, decl.Pos()); err != nil {
+		if result.Declaration.Range, err = posToRange(ctx, f.FileSet(), result.Name, decl.Pos()); err != nil {
 			return nil, err
 		}
 		return result, nil
@@ -121,7 +121,7 @@ func identifier(ctx context.Context, v View, f GoFile, pos token.Pos) (*Identifi
 		}
 	}
 
-	if result.Declaration.Range, err = objToRange(ctx, v.FileSet(), result.Declaration.Object); err != nil {
+	if result.Declaration.Range, err = objToRange(ctx, f.FileSet(), result.Declaration.Object); err != nil {
 		return nil, err
 	}
 	if result.Declaration.Node, err = objToNode(ctx, v, result.Declaration.Object, result.Declaration.Range); err != nil {
@@ -137,7 +137,7 @@ func identifier(ctx context.Context, v View, f GoFile, pos token.Pos) (*Identifi
 		if hasErrorType(result.Type.Object) {
 			return result, nil
 		}
-		if result.Type.Range, err = objToRange(ctx, v.FileSet(), result.Type.Object); err != nil {
+		if result.Type.Range, err = objToRange(ctx, f.FileSet(), result.Type.Object); err != nil {
 			return nil, err
 		}
 	}
@@ -219,7 +219,7 @@ func importSpec(f GoFile, fAST *ast.File, pkg Package, pos token.Pos) (*Identifi
 		result := &IdentifierInfo{
 			File:  f,
 			Name:  importPath,
-			Range: span.NewRange(f.View().FileSet(), imp.Pos(), imp.End()),
+			Range: span.NewRange(f.FileSet(), imp.Pos(), imp.End()),
 		}
 		// Consider the "declaration" of an import spec to be the imported package.
 		importedPkg := pkg.GetImport(importPath)
@@ -239,7 +239,7 @@ func importSpec(f GoFile, fAST *ast.File, pkg Package, pos token.Pos) (*Identifi
 		if dest == nil {
 			return nil, fmt.Errorf("package %q has no files", importPath)
 		}
-		result.Declaration.Range = span.NewRange(f.View().FileSet(), dest.Name.Pos(), dest.Name.End())
+		result.Declaration.Range = span.NewRange(f.FileSet(), dest.Name.Pos(), dest.Name.End())
 		return result, nil
 	}
 	return nil, nil
diff --git a/internal/lsp/source/source_test.go b/internal/lsp/source/source_test.go
index 475d9ace8e..dd979ef050 100644
--- a/internal/lsp/source/source_test.go
+++ b/internal/lsp/source/source_test.go
@@ -32,6 +32,7 @@ type runner struct {
 }
 
 func testSource(t *testing.T, exporter packagestest.Exporter) {
+	ctx := context.Background()
 	data := tests.Load(t, exporter, "../testdata")
 	defer data.Exported.Cleanup()
 
@@ -39,9 +40,13 @@ func testSource(t *testing.T, exporter packagestest.Exporter) {
 	cache := cache.New()
 	session := cache.NewSession(log)
 	r := &runner{
-		view: session.NewView("source_test", span.FileURI(data.Config.Dir), &data.Config),
+		view: session.NewView("source_test", span.FileURI(data.Config.Dir)),
 		data: data,
 	}
+	r.view.SetEnv(data.Config.Env)
+	for filename, content := range data.Config.Overlay {
+		r.view.SetContent(ctx, span.FileURI(filename), content)
+	}
 	tests.Run(t, r, data)
 }
 
@@ -134,6 +139,9 @@ func (r *runner) Completion(t *testing.T, data tests.Completions, snippets tests
 			t.Fatalf("failed for %v: %v", src, err)
 		}
 		tok := f.(source.GoFile).GetToken(ctx)
+		if tok == nil {
+			t.Fatalf("failed to get token for %v", src)
+		}
 		pos := tok.Pos(src.Start().Offset())
 		list, surrounding, err := source.Completion(ctx, f.(source.GoFile), pos)
 		if err != nil {
@@ -273,7 +281,7 @@ func (r *runner) Format(t *testing.T, data tests.Formats) {
 		if err != nil {
 			t.Fatalf("failed for %v: %v", spn, err)
 		}
-		rng, err := spn.Range(span.NewTokenConverter(f.GetFileSet(ctx), f.GetToken(ctx)))
+		rng, err := spn.Range(span.NewTokenConverter(f.FileSet(), f.GetToken(ctx)))
 		if err != nil {
 			t.Fatalf("failed for %v: %v", spn, err)
 		}
diff --git a/internal/lsp/source/symbols.go b/internal/lsp/source/symbols.go
index aba8f81466..bb765cd649 100644
--- a/internal/lsp/source/symbols.go
+++ b/internal/lsp/source/symbols.go
@@ -41,7 +41,7 @@ type Symbol struct {
 }
 
 func DocumentSymbols(ctx context.Context, f GoFile) []Symbol {
-	fset := f.GetFileSet(ctx)
+	fset := f.FileSet()
 	file := f.GetAST(ctx)
 	if file == nil {
 		return nil
diff --git a/internal/lsp/source/view.go b/internal/lsp/source/view.go
index f9802c1703..cef3011c64 100644
--- a/internal/lsp/source/view.go
+++ b/internal/lsp/source/view.go
@@ -28,6 +28,9 @@ import (
 type Cache interface {
 	// NewSession creates a new Session manager and returns it.
 	NewSession(log xlog.Logger) Session
+
+	// FileSet returns the shared fileset used by all files in the system.
+	FileSet() *token.FileSet
 }
 
 // Session represents a single connection from a client.
@@ -36,7 +39,7 @@ type Cache interface {
 // A session may have many active views at any given time.
 type Session interface {
 	// NewView creates a new View and returns it.
-	NewView(name string, folder span.URI, config *packages.Config) View
+	NewView(name string, folder span.URI) View
 
 	// Cache returns the cache that created this session.
 	Cache() Cache
@@ -44,10 +47,16 @@ type Session interface {
 	// Returns the logger in use for this session.
 	Logger() xlog.Logger
 
+	// View returns a view with a mathing name, if the session has one.
 	View(name string) View
+
+	// ViewOf returns a view corresponding to the given URI.
 	ViewOf(uri span.URI) View
+
+	// Views returns the set of active views built by this session.
 	Views() []View
 
+	// Shutdown the session and all views it has created.
 	Shutdown(ctx context.Context)
 }
 
@@ -57,16 +66,36 @@ type Session interface {
 type View interface {
 	// Session returns the session that created this view.
 	Session() Session
+
+	// Name returns the name this view was constructed with.
 	Name() string
+
+	// Folder returns the root folder for this view.
 	Folder() span.URI
-	FileSet() *token.FileSet
+
+	// BuiltinPackage returns the ast for the special "builtin" package.
 	BuiltinPackage() *ast.Package
+
+	// GetFile returns the file object for a given uri.
 	GetFile(ctx context.Context, uri span.URI) (File, error)
+
+	// Called to set the effective contents of a file from this view.
 	SetContent(ctx context.Context, uri span.URI, content []byte) error
+
+	// BackgroundContext returns a context used for all background processing
+	// on behalf of this view.
 	BackgroundContext() context.Context
-	Config() packages.Config
+
+	// Env returns the current set of environment overrides on this view.
+	Env() []string
+
+	// SetEnv is used to adjust the environment applied to the view.
 	SetEnv([]string)
+
+	// Shutdown closes this view, and detaches it from it's session.
 	Shutdown(ctx context.Context)
+
+	// Ignore returns true if this file should be ignored by this view.
 	Ignore(span.URI) bool
 }
 
@@ -75,7 +104,7 @@ type File interface {
 	URI() span.URI
 	View() View
 	GetContent(ctx context.Context) []byte
-	GetFileSet(ctx context.Context) *token.FileSet
+	FileSet() *token.FileSet
 	GetToken(ctx context.Context) *token.File
 }
 
diff --git a/internal/lsp/text_synchronization.go b/internal/lsp/text_synchronization.go
index 20a0ffa963..e273cd3b70 100644
--- a/internal/lsp/text_synchronization.go
+++ b/internal/lsp/text_synchronization.go
@@ -69,7 +69,7 @@ func (s *Server) applyChanges(ctx context.Context, params *protocol.DidChangeTex
 	if err != nil {
 		return "", jsonrpc2.NewErrorf(jsonrpc2.CodeInternalError, "file not found")
 	}
-	fset := f.GetFileSet(ctx)
+	fset := f.FileSet()
 	filename, err := f.URI().Filename()
 	if err != nil {
 		return "", jsonrpc2.NewErrorf(jsonrpc2.CodeInternalError, "no filename for %s", uri)
diff --git a/internal/lsp/util.go b/internal/lsp/util.go
index a41ba56516..5955882561 100644
--- a/internal/lsp/util.go
+++ b/internal/lsp/util.go
@@ -55,7 +55,7 @@ func getSourceFile(ctx context.Context, v source.View, uri span.URI) (source.Fil
 	if err != nil {
 		return nil, nil, err
 	}
-	m := protocol.NewColumnMapper(f.URI(), filename, f.GetFileSet(ctx), f.GetToken(ctx), f.GetContent(ctx))
+	m := protocol.NewColumnMapper(f.URI(), filename, f.FileSet(), f.GetToken(ctx), f.GetContent(ctx))
 
 	return f, m, nil
 }
diff --git a/internal/lsp/workspace.go b/internal/lsp/workspace.go
index 687e2c8f69..4c761b48f1 100644
--- a/internal/lsp/workspace.go
+++ b/internal/lsp/workspace.go
@@ -7,12 +7,7 @@ package lsp
 import (
 	"context"
 	"fmt"
-	"go/ast"
-	"go/parser"
-	"go/token"
-	"os"
 
-	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/span"
 )
@@ -36,25 +31,6 @@ func (s *Server) changeFolders(ctx context.Context, event protocol.WorkspaceFold
 }
 
 func (s *Server) addView(ctx context.Context, name string, uri span.URI) error {
-	// We need a "detached" context so it does not get timeout cancelled.
-	// TODO(iancottrell): Do we need to copy any values across?
-	viewContext := context.Background()
-	folderPath, err := uri.Filename()
-	if err != nil {
-		return err
-	}
-	s.session.NewView(name, uri, &packages.Config{
-		Context: viewContext,
-		Dir:     folderPath,
-		Env:     os.Environ(),
-		Mode:    packages.LoadImports,
-		Fset:    token.NewFileSet(),
-		Overlay: make(map[string][]byte),
-		ParseFile: func(fset *token.FileSet, filename string, src []byte) (*ast.File, error) {
-			return parser.ParseFile(fset, filename, src, parser.AllErrors|parser.ParseComments)
-		},
-		Tests: true,
-	})
-
+	s.session.NewView(name, uri)
 	return nil
 }