Migrate to GOPLS

.gitmodules

@@ -13,14 +13,6 @@
 [submodule "third_party/requests"]
 	path = third_party/requests_deps/requests
 	url = https://github.com/requests/requests
-[submodule "third_party/go/src/github.com/mdempsky/gocode"]
-	path = third_party/go/src/github.com/mdempsky/gocode
-	url = https://github.com/mdempsky/gocode
-	ignore = dirty
-[submodule "third_party/go/src/github.com/rogpeppe/godef"]
-	path = third_party/go/src/github.com/rogpeppe/godef
-	url = https://github.com/rogpeppe/godef
-	ignore = dirty
 [submodule "third_party/jedi"]
 	path = third_party/jedi_deps/jedi
 	url = https://github.com/davidhalter/jedi
@@ -48,3 +40,6 @@
 [submodule "third_party/idna"]
 	path = third_party/requests_deps/idna
 	url = https://github.com/kjd/idna
+[submodule "third_party/go/src/golang.org/x/tools"]
+	path = third_party/go/src/golang.org/x/tools
+	url = https://go.googlesource.com/tools

build.py

@@ -682,18 +682,11 @@ def EnableGoCompleter( args ):
   go = FindExecutableOrDie( 'go', 'go is required to build gocode.' )
 
   go_dir = p.join( DIR_OF_THIS_SCRIPT, 'third_party', 'go' )
-  os.chdir( p.join( go_dir, 'src', 'github.com', 'mdempsky', 'gocode' ) )
-  new_env = os.environ.copy()
-  new_env[ 'GOPATH' ] = go_dir
+  os.chdir( p.join(
+    go_dir, 'src', 'golang.org', 'x', 'tools', 'cmd', 'gopls' ) )
   CheckCall( [ go, 'build' ],
-             env = new_env,
-             quiet = args.quiet,
-             status_message = 'Building gocode for go completion' )
-  os.chdir( p.join( go_dir, 'src', 'github.com', 'rogpeppe', 'godef' ) )
-  CheckCall( [ go, 'build' ],
-             env = new_env,
              quiet = args.quiet,
-             status_message = 'Building godef for go definition' )
+             status_message = 'Building gopls for go completion' )
 
 
 def WriteToolchainVersion( version ):

run_tests.py

@@ -72,7 +72,8 @@ def RunFlake8():
 #  - no aliases.
 SIMPLE_COMPLETERS = [
   'clangd',
-  'rust'
+  'rust',
+  'go',
 ]
 
 # More complex or legacy cases can specify all of:
@@ -95,11 +96,6 @@ def RunFlake8():
     'test': [ '--exclude-dir=ycmd/tests/tern' ],
     'aliases': [ 'js', 'tern' ]
   },
-  'go': {
-    'build': [ '--go-completer' ],
-    'test': [ '--exclude-dir=ycmd/tests/go' ],
-    'aliases': [ 'gocode' ]
-  },
   'typescript': {
     'build': [ '--ts-completer' ],
     'test': [ '--exclude-dir=ycmd/tests/javascript',