gopls: deprecate "tempModfile" and "expandWorkspaceToModule" settings

These settings deeply affect gopls' behavior, and can't work well when
set to a non-default value. More rationale is provided in the attached
issues.

The features controlled by these settings are not yet removed. For the
v0.14.0 release, we will simply warn users who have them set.

Fixes golang/go#57514
Fixes golang/go#61970

Change-Id: Ica631dcb8980eeeace9ceaec159218e6306831ae
Reviewed-on: https://go-review.googlesource.com/c/tools/+/534919
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>

Author: findleyr

gopls/internal/lsp/source/options.go

@@ -1181,6 +1181,7 @@ func (o *Options) set(name string, value interface{}, seen map[string]struct{})
 		result.setBool(&o.VerboseWorkDoneProgress)
 
 	case "tempModfile":
+		result.softErrorf("gopls setting \"tempModfile\" is deprecated.\nPlease comment on https://go.dev/issue/63537 if this impacts your workflow.")
 		result.setBool(&o.TempModfile)
 
 	case "showBugReports":
@@ -1207,6 +1208,7 @@ func (o *Options) set(name string, value interface{}, seen map[string]struct{})
 		result.setBool(&o.NoSemanticNumber)
 
 	case "expandWorkspaceToModule":
+		result.softErrorf("gopls setting \"expandWorkspaceToModule\" is deprecated.\nPlease comment on https://go.dev/issue/63536 if this impacts your workflow.")
 		result.setBool(&o.ExpandWorkspaceToModule)
 
 	case "experimentalPostfixCompletions":
@@ -1356,6 +1358,11 @@ func (r *OptionResult) deprecated(replacement string) {
 	r.Error = &SoftError{msg}
 }
 
+// softErrorf reports a soft error related to the current option.
+func (r *OptionResult) softErrorf(format string, args ...any) {
+	r.Error = &SoftError{fmt.Sprintf(format, args...)}
+}
+
 // unexpected reports that the current setting is not known to gopls.
 func (r *OptionResult) unexpected() {
 	r.Error = fmt.Errorf("unexpected gopls setting %q", r.Name)

gopls/internal/regtest/misc/configuration_test.go

@@ -141,13 +141,17 @@ func TestDeprecatedSettings(t *testing.T) {
 			"experimentalUseInvalidMetadata": true,
 			"experimentalWatchedFileDelay":   "1s",
 			"experimentalWorkspaceModule":    true,
+			"tempModfile":                    true,
+			"expandWorkspaceToModule":        false,
 		},
 	).Run(t, "", func(t *testing.T, env *Env) {
 		env.OnceMet(
 			InitialWorkspaceLoad,
 			ShownMessage("experimentalWorkspaceModule"),
 			ShownMessage("experimentalUseInvalidMetadata"),
 			ShownMessage("experimentalWatchedFileDelay"),
+			ShownMessage("https://go.dev/issue/63537"), // issue to remove tempModfile
+			ShownMessage("https://go.dev/issue/63536"), // issue to remove expandWorkspaceToModule
 		)
 	})
 }