internal/lsp: warn users who have built gopls with go-diff v1.2.0

I considered having gopls not initialize at all, but VS Code Go
intercepts those error messages and they get buried. We should probably
fix that in VS Code Go, but for now just show a warning.

Updates golang/go#45732

Change-Id: I214974e5a96231c96b1583af8ac245de03cea5d8
Reviewed-on: https://go-review.googlesource.com/c/tools/+/315852
Trust: Rebecca Stambler <[email protected]>
Run-TryBot: Rebecca Stambler <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: stamblerre

internal/lsp/general.go

@@ -96,7 +96,24 @@ func (s *Server) initialize(ctx context.Context, params *protocol.ParamInitializ
 		}
 	}
 
-	goplsVersion, err := json.Marshal(debug.VersionInfo())
+	versionInfo := debug.VersionInfo()
+
+	// golang/go#45732: Warn users who've installed sergi/[email protected], since
+	// it will corrupt the formatting of their files.
+	for _, dep := range versionInfo.Deps {
+		if dep.Path == "github.com/sergi/go-diff" && dep.Version == "v1.2.0" {
+			if err := s.eventuallyShowMessage(ctx, &protocol.ShowMessageParams{
+				Message: `It looks like you have a bad gopls installation.
+Please reinstall gopls by running 'GO111MODULE=on go get golang.org/x/tools/gopls@latest'.
+See https://github.com/golang/go/issues/45732 for more information.`,
+				Type: protocol.Error,
+			}); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	goplsVersion, err := json.Marshal(versionInfo)
 	if err != nil {
 		return nil, err
 	}