internal/lsp/regtest: simpler way to invert options

This is an alternative to CL 241739, preserving the exiting variadic
options pattern and just adding a helper method to put the options up
front.

All things considered, I think this is better. CL 241739 was too
complicated, and being able to reuse "curried" runners isn't actually
important.

Updates golang/go#39384

Change-Id: I7ecd80d310cac879520b2d1feebcf5bd5e96e89b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/243057
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

internal/lsp/regtest/modfile_test.go

@@ -39,7 +39,7 @@ import "example.com/blah"
 func main() {
 	fmt.Println(blah.Name)
 }`
-	runner.Run(t, untidyModule, func(t *testing.T, env *Env) {
+	withOptions(WithProxy(proxy)).run(t, untidyModule, func(t *testing.T, env *Env) {
 		// Open the file and make sure that the initial workspace load does not
 		// modify the go.mod file.
 		goModContent := env.ReadWorkspaceFile("go.mod")
@@ -59,7 +59,7 @@ func main() {
 		if got := env.ReadWorkspaceFile("go.mod"); got != goModContent {
 			t.Fatalf("go.mod changed on disk:\n%s", tests.Diff(goModContent, got))
 		}
-	}, WithProxy(proxy))
+	})
 }
 
 func TestIndirectDependencyFix(t *testing.T) {

internal/lsp/regtest/reg_test.go

@@ -27,6 +27,22 @@ var (
 
 var runner *Runner
 
+func run(t *testing.T, files string, f TestFunc) {
+	runner.Run(t, files, f)
+}
+
+func withOptions(opts ...RunOption) configuredRunner {
+	return configuredRunner{opts: opts}
+}
+
+type configuredRunner struct {
+	opts []RunOption
+}
+
+func (r configuredRunner) run(t *testing.T, files string, f TestFunc) {
+	runner.Run(t, files, f, r.opts...)
+}
+
 func TestMain(m *testing.M) {
 	flag.Parse()
 	if os.Getenv("_GOPLS_TEST_BINARY_RUN_AS_GOPLS") == "true" {

internal/lsp/regtest/runner.go

@@ -140,10 +140,12 @@ func InGOPATH() RunOption {
 	})
 }
 
+type TestFunc func(t *testing.T, env *Env)
+
 // Run executes the test function in the default configured gopls execution
 // modes. For each a test run, a new workspace is created containing the
 // un-txtared files specified by filedata.
-func (r *Runner) Run(t *testing.T, filedata string, test func(t *testing.T, e *Env), opts ...RunOption) {
+func (r *Runner) Run(t *testing.T, filedata string, test TestFunc, opts ...RunOption) {
 	t.Helper()
 	config := r.defaultConfig()
 	for _, opt := range opts {