internal/lsp: add a Version constant

This change will allow users in $GOPATH mode to have some
semblance of a gopls version.

Change-Id: I1b490d18fdf7550c54d56653ae500dc4dc25ee3b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/181238
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/lsp/debug/info.1.11.go

@@ -12,5 +12,5 @@ import (
 )
 
 func printBuildInfo(w io.Writer, verbose bool, mode PrintMode) {
-	fmt.Fprintf(w, "no module information, gopls not built with go 1.11 or earlier\n")
+	fmt.Fprintf(w, "version %s, built in $GOPATH mode", Version)
 }

internal/lsp/debug/info.1.12.go

@@ -14,15 +14,15 @@ import (
 
 func printBuildInfo(w io.Writer, verbose bool, mode PrintMode) {
 	if info, ok := debug.ReadBuildInfo(); ok {
-		fmt.Fprintf(w, "%v\n", info.Path)
+		fmt.Fprintf(w, "%v %v\n", info.Path, Version)
 		printModuleInfo(w, &info.Main, mode)
 		if verbose {
 			for _, dep := range info.Deps {
 				printModuleInfo(w, dep, mode)
 			}
 		}
 	} else {
-		fmt.Fprintf(w, "no module information, gopls not built in module mode\n")
+		fmt.Fprintf(w, "version %s, built in $GOPATH mode", Version)
 	}
 }
 

internal/lsp/debug/info.go

@@ -19,6 +19,9 @@ const (
 	HTML
 )
 
+// Version is a manually-updated mechanism for tracking versions.
+const Version = "v0.0.1-20190607+alpha"
+
 // This writes the version and environment information to a writer.
 func PrintVersionInfo(w io.Writer, verbose bool, mode PrintMode) {
 	if !verbose {