gopls/internal/settings: add a hidden option to disable zero config

Fixes golang/go#65515

Change-Id: If9786c00eb7629ec8d488cf8483144514d28786b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/562856
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

gopls/internal/cache/session.go

@@ -480,7 +480,7 @@ func selectViewDefs(ctx context.Context, fs file.Source, folders []*Folder, open
 checkFiles:
 	for _, uri := range openFiles {
 		folder := folderForFile(uri)
-		if folder == nil {
+		if folder == nil || !folder.Options.ZeroConfig {
 			continue // only guess views for open files
 		}
 		fh, err := fs.ReadFile(ctx, uri)

gopls/internal/settings/default.go

@@ -116,6 +116,7 @@ func DefaultOptions(overrides ...func(*Options)) *Options {
 				TelemetryPrompt:             false,
 				LinkifyShowMessage:          false,
 				IncludeReplaceInWorkspace:   true,
+				ZeroConfig:                  true,
 			},
 			Hooks: Hooks{
 				URLRegexp:            urlRegexp(),

gopls/internal/settings/settings.go

@@ -559,6 +559,11 @@ type InternalOptions struct {
 	// Or in other words, if a go.mod file with local replaces behaves like a
 	// go.work file.
 	IncludeReplaceInWorkspace bool
+
+	// ZeroConfig enables the zero-config algorithm for workspace layout,
+	// dynamically creating build configurations for different modules,
+	// directories, and GOOS/GOARCH combinations to cover open files.
+	ZeroConfig bool
 }
 
 type SubdirWatchPatterns string
@@ -1159,6 +1164,9 @@ func (o *Options) set(name string, value interface{}, seen map[string]struct{})
 	case "includeReplaceInWorkspace":
 		result.setBool(&o.IncludeReplaceInWorkspace)
 
+	case "zeroConfig":
+		result.setBool(&o.ZeroConfig)
+
 	// Replaced settings.
 	case "experimentalDisabledAnalyses":
 		result.deprecated("analyses")

gopls/internal/test/integration/workspace/zero_config_test.go

@@ -234,3 +234,37 @@ const B = 1
 		})
 	}
 }
+
+func TestDisableZeroConfig(t *testing.T) {
+	// This test checks that we treat locally replaced modules as workspace
+	// modules, according to the "includeReplaceInWorkspace" setting.
+	const files = `
+-- moda/go.mod --
+module golang.org/a
+
+go 1.20
+
+-- moda/a.go --
+package a
+
+-- modb/go.mod --
+module golang.org/b
+
+go 1.20
+
+-- modb/b.go --
+package b
+
+`
+
+	WithOptions(
+		Settings{"zeroConfig": false},
+	).Run(t, files, func(t *testing.T, env *Env) {
+		env.OpenFile("moda/a.go")
+		env.OpenFile("modb/b.go")
+		env.AfterChange()
+		if got := env.Views(); len(got) != 1 || got[0].Type != cache.AdHocView.String() {
+			t.Errorf("Views: got %v, want one adhoc view", got)
+		}
+	})
+}