internal/lsp/lsprpc: add an LSP forwarder and regtest environment

Add a new Forwarder type to the lsprpc package, which implements the
jsonrpc2.StreamServer interface. This will be used to establish some
parity in the implementation of shared and singleton gopls servers.

Much more testing is needed, as is handling for the many edge cases
around forwarding the LSP, but since this is functionally equivalent to
TCP forwarding (and the -remote flag was already broken), I went ahead
and used the Forwarder to replace the forward method in the serve
command. This means that we can now use the combination of -listen and
-remote to chain together gopls servers... not that there's any reason
to do this.

Also, wrap the new regression tests with a focus on expressiveness when
testing the happy path, as well as parameterizing them so that they can
be run against different client/server execution environments. This
started to be sizable enough to warrant moving them to a separate
regtest package. The lsprpc package tests will instead focus on unit
testing the client-server binding logic.

Updates golang/go#36879
Updates golang/go#34111

Change-Id: Ib98131a58aabc69299845d2ecefceccfc1199574
Reviewed-on: https://go-review.googlesource.com/c/tools/+/218698
Run-TryBot: Robert Findley <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>

Author: findleyr

Diff for: internal/lsp/cmd/serve.go

@@ -8,8 +8,6 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	"io"
-	"net"
 	"os"
 
 	"golang.org/x/tools/internal/jsonrpc2"
@@ -64,11 +62,13 @@ func (s *Serve) Run(ctx context.Context, args ...string) error {
 	s.app.debug.Serve(ctx)
 	s.app.debug.MonitorMemory(ctx)
 
+	var ss jsonrpc2.StreamServer
 	if s.app.Remote != "" {
-		return s.forward()
+		ss = lsprpc.NewForwarder(s.app.Remote, true)
+	} else {
+		ss = lsprpc.NewStreamServer(cache.New(s.app.options), true)
 	}
 
-	ss := lsprpc.NewStreamServer(cache.New(s.app.options), true)
 	if s.Address != "" {
 		return jsonrpc2.ListenAndServe(ctx, s.Address, ss)
 	}
@@ -82,23 +82,3 @@ func (s *Serve) Run(ctx context.Context, args ...string) error {
 	}
 	return ss.ServeStream(ctx, stream)
 }
-
-func (s *Serve) forward() error {
-	conn, err := net.Dial("tcp", s.app.Remote)
-	if err != nil {
-		return err
-	}
-	errc := make(chan error)
-
-	go func(conn net.Conn) {
-		_, err := io.Copy(conn, os.Stdin)
-		errc <- err
-	}(conn)
-
-	go func(conn net.Conn) {
-		_, err := io.Copy(os.Stdout, conn)
-		errc <- err
-	}(conn)
-
-	return <-errc
-}

Diff for: internal/lsp/fake/edit.go

@@ -36,6 +36,16 @@ type Edit struct {
 	Text       string
 }
 
+// NewEdit creates an edit replacing all content between
+// (startLine, startColumn) and (endLine, endColumn) with text.
+func NewEdit(startLine, startColumn, endLine, endColumn int, text string) Edit {
+	return Edit{
+		Start: Pos{Line: startLine, Column: startColumn},
+		End:   Pos{Line: endLine, Column: endColumn},
+		Text:  text,
+	}
+}
+
 func (e Edit) toProtocolChangeEvent() protocol.TextDocumentContentChangeEvent {
 	return protocol.TextDocumentContentChangeEvent{
 		Range: &protocol.Range{