internal/lsp/source: allow opt-out from -mod=readonly, GOPROXY=off

The changes to require more explicit dependency management and network
access are very user-facing, and we may not fully understand their
implications. Allow users to roll them back with options for the moment.
Ideally we'll be able to remove them in a few months after things
stabilize.

Change-Id: I5a5ff7c9f3afa490b9945604109c4e3bd9bd7844
Reviewed-on: https://go-review.googlesource.com/c/tools/+/274532
Trust: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/doc/settings.md

@@ -240,6 +240,19 @@ comprehensively test.
 
 
 Default: `true`.
+### **allowModfileModifications** *bool*
+allowModfileModifications disables -mod=readonly, allowing imports from
+out-of-scope modules. This option will eventually be removed.
+
+
+Default: `false`.
+### **allowImplicitNetworkAccess** *bool*
+allowImplicitNetworkAccess disables GOPROXY=off, allowing implicit module
+downloads rather than requiring user action. This option will eventually
+be removed.
+
+
+Default: `false`.
 <!-- END Experimental: DO NOT MANUALLY EDIT THIS SECTION -->
 
 ## Debugging

internal/lsp/cache/snapshot.go

@@ -249,6 +249,8 @@ func (s *snapshot) RunGoCommandPiped(ctx context.Context, mode source.Invocation
 
 func (s *snapshot) goCommandInvocation(ctx context.Context, flags source.InvocationFlags, inv *gocommand.Invocation) (tmpURI span.URI, updatedInv *gocommand.Invocation, cleanup func(), err error) {
 	s.view.optionsMu.Lock()
+	allowModfileModificationOption := s.view.options.AllowModfileModifications
+	allowNetworkOption := s.view.options.AllowImplicitNetworkAccess
 	inv.Env = append(append(append(os.Environ(), s.view.options.EnvSlice()...), inv.Env...), "GO111MODULE="+s.view.go111module)
 	inv.BuildFlags = append([]string{}, s.view.options.BuildFlags...)
 	s.view.optionsMu.Unlock()
@@ -260,7 +262,7 @@ func (s *snapshot) goCommandInvocation(ctx context.Context, flags source.Invocat
 	}
 
 	mode, allowNetwork := flags.Mode(), flags.AllowNetwork()
-	if !allowNetwork {
+	if !allowNetwork && !allowNetworkOption {
 		inv.Env = append(inv.Env, "GOPROXY=off")
 	}
 
@@ -314,7 +316,7 @@ func (s *snapshot) goCommandInvocation(ctx context.Context, flags source.Invocat
 	case source.LoadWorkspace, source.Normal:
 		if vendorEnabled {
 			inv.ModFlag = "vendor"
-		} else if s.workspaceMode()&usesWorkspaceModule == 0 {
+		} else if s.workspaceMode()&usesWorkspaceModule == 0 && !allowModfileModificationOption {
 			inv.ModFlag = "readonly"
 		} else {
 			// Temporarily allow updates for multi-module workspace mode:

internal/lsp/source/options.go

@@ -350,6 +350,15 @@ type ExperimentalOptions struct {
 	// by an experiment because caching behavior is subtle and difficult to
 	// comprehensively test.
 	ExperimentalPackageCacheKey bool
+
+	// AllowModfileModifications disables -mod=readonly, allowing imports from
+	// out-of-scope modules. This option will eventually be removed.
+	AllowModfileModifications bool
+
+	// AllowImplicitNetworkAccess disables GOPROXY=off, allowing implicit module
+	// downloads rather than requiring user action. This option will eventually
+	// be removed.
+	AllowImplicitNetworkAccess bool
 }
 
 // DebuggingOptions should not affect the logical execution of Gopls, but may