gopls/internal/protocol: PublishDiagnosticsParams.version omitempty

This CL reverts the status of the PublishDiagnostics.version field
to omitempty. This status was removed by CL 73501, causing some
clients (e.g. coc.nvim) to treat the zero version (meaning "missing"
to gopls' file.Handle) as an actual version in the past.

Unfortunately it is not possible to reproduce the regression using
gopls' JSON encoding structures, hence the lack of a test.

Fixes golang/go#73501
Updates golang/go#71489

Change-Id: Ia116f948e13782610c9de8d2d7ffd99bdb377d3e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/678095
Commit-Queue: Alan Donovan <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: adonovan

gopls/internal/cmd/cmd.go

@@ -641,6 +641,10 @@ func updateFile(filename string, old, new []byte, edits []diff.Edit, flags *Edit
 
 func (c *cmdClient) PublishDiagnostics(ctx context.Context, p *protocol.PublishDiagnosticsParams) error {
 	// Don't worry about diagnostics without versions.
+	//
+	// (Note: the representation of PublishDiagnosticsParams
+	// cannot distinguish a missing Version from v0, but the
+	// server never sends back an explicit zero.)
 	if p.Version == 0 {
 		return nil
 	}

gopls/internal/protocol/generate/tables.go

@@ -34,7 +34,7 @@ var goplsStar = map[prop]int{
 	{"CompletionItem", "kind"}:                         wantOpt, // need temporary variables
 	{"CompletionParams", "context"}:                    wantOpt, // needs nil checks
 
-	{"Diagnostic", "severity"}:            wantOpt,     // nil checks or more careful thought
+	{"Diagnostic", "severity"}:            wantOpt,     // needs nil checks or more careful thought
 	{"DidSaveTextDocumentParams", "text"}: wantOptStar, // capabilities_test.go:112 logic
 	{"DocumentHighlight", "kind"}:         wantOpt,     // need temporary variables
 
@@ -46,6 +46,7 @@ var goplsStar = map[prop]int{
 	{"Hover", "range"}:    wantOpt, // complex expressions
 	{"InlayHint", "kind"}: wantOpt, // temporary variables
 
+	{"PublishDiagnosticsParams", "version"}:                   wantOpt,     // zero => missing (#73501)
 	{"TextDocumentClientCapabilities", "codeAction"}:          wantOpt,     // A.B.C.D
 	{"TextDocumentClientCapabilities", "completion"}:          wantOpt,     // A.B.C.D
 	{"TextDocumentClientCapabilities", "documentSymbol"}:      wantOpt,     // A.B.C.D

gopls/internal/protocol/tsprotocol.go

@@ -904,7 +904,7 @@ func (s *server) publishFileDiagnosticsLocked(ctx context.Context, views viewSet
 		if err := s.client.PublishDiagnostics(ctx, &protocol.PublishDiagnosticsParams{
 			Diagnostics: toProtocolDiagnostics(unique),
 			URI:         uri,
-			Version:     version,
+			Version:     version, // 0 ("on disk") => omitted from JSON encoding
 		}); err != nil {
 			return err
 		}