gopls: support jump to definition for field links in comments

I don't know why we didn't support this, but it was trivial to enable.

Fixes golang/go#75038

Change-Id: Ia41953aadb1fcf459db16049c1e3bef56cd7882c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/696435
Auto-Submit: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

Author: findleyr

gopls/internal/golang/comment.go

@@ -181,8 +181,8 @@ func lookupDocLinkSymbol(pkg *cache.Package, pgf *parsego.File, name string) typ
 	// that define the symbol but are not directly imported;
 	// see https://github.com/golang/go/issues/61677
 
-	// Type.Method?
-	recv, method, ok := strings.Cut(name, ".")
+	// Field or sel?
+	recv, sel, ok := strings.Cut(name, ".")
 	if ok {
 		obj := scope.Lookup(recv) // package scope
 		if obj == nil {
@@ -192,11 +192,8 @@ func lookupDocLinkSymbol(pkg *cache.Package, pgf *parsego.File, name string) typ
 		if !ok {
 			return nil
 		}
-		m, _, _ := types.LookupFieldOrMethod(obj.Type(), true, obj.Pkg(), method)
-		if is[*types.Func](m) {
-			return m
-		}
-		return nil
+		m, _, _ := types.LookupFieldOrMethod(obj.Type(), true, obj.Pkg(), sel)
+		return m
 	}
 
 	if obj := scope.Lookup(name); obj != nil {

gopls/internal/test/marker/testdata/definition/comment.txt

@@ -27,9 +27,18 @@ func Conv(s string) int { //@loc(Conv, "Conv")
 	return int(i)
 }
 
+type T struct {
+	Field int //@ loc(Field, "Field")
+}
+
+func (T) Method() {} //@ loc(Method, "Method")
+
 // The declared and imported names of the package both work:
 // [path.Join]    //@ def("Join", Join)
 // [pathpkg.Join] //@ def("Join", Join)
+//
+// Also, both [T.Field] and //@ def("Field", Field)
+// [T.Method] are supported. //@ def("Method", Method)
 func _() {
 	pathpkg.Join()
 }