internal/lsp: check for invalid URIs in definition

URI.Filename() panics on non-file URIs. Just pass UnknownKind to
beginFileRequest to allow handling template files.

Fixes golang/go#49223

Change-Id: Ic2add49d3d0c04855bf25583712102a50fb425ed
Reviewed-on: https://go-review.googlesource.com/c/tools/+/359734
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

Author: findleyr

gopls/internal/regtest/misc/definition_test.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 	"testing"
 
+	"golang.org/x/tools/internal/lsp/protocol"
 	. "golang.org/x/tools/internal/lsp/regtest"
 	"golang.org/x/tools/internal/testenv"
 
@@ -277,3 +278,14 @@ package client
 		env.GoToDefinition("client/client_role_test.go", env.RegexpSearch("client/client_role_test.go", "RoleSetup"))
 	})
 }
+
+// This test exercises a crashing pattern from golang/go#49223.
+func TestGoToCrashingDefinition_Issue49223(t *testing.T) {
+	Run(t, "", func(t *testing.T, env *Env) {
+		params := &protocol.DefinitionParams{}
+		params.TextDocument.URI = protocol.DocumentURI("fugitive%3A///Users/user/src/mm/ems/.git//0/pkg/domain/treasury/provider.go")
+		params.Position.Character = 18
+		params.Position.Line = 0
+		env.Editor.Server.Definition(env.Ctx, params)
+	})
+}

internal/lsp/definition.go

@@ -13,8 +13,7 @@ import (
 )
 
 func (s *Server) definition(ctx context.Context, params *protocol.DefinitionParams) ([]protocol.Location, error) {
-	kind := source.DetectLanguage("", params.TextDocument.URI.SpanURI().Filename())
-	snapshot, fh, ok, release, err := s.beginFileRequest(ctx, params.TextDocument.URI, kind)
+	snapshot, fh, ok, release, err := s.beginFileRequest(ctx, params.TextDocument.URI, source.UnknownKind)
 	defer release()
 	if !ok {
 		return nil, err