doc

Summary:
A bit of clarification in the hack schema to address user questions.

The "override" semantics isn't properly specified. There's no documentation where we can point to.

The indexer uses this [method](https://www.internalfb.com/code/fbsource/[b35bdae4ad9f]/fbcode/hphp/hack/src/providers/decl_provider.mli?lines=68). There are some edge cases, for instance, a trait method can override an interface method, but a class method doesn't.   See also D63282603.

Reviewed By: josefs

Differential Revision: D63415167

fbshipit-source-id: e65363239e08f584d1bf9f930fd18fbfdecb3137

glean/schema/source/hack.angle

@@ -290,6 +290,9 @@ predicate MemberCluster :
     members : [Declaration]
   }
 
+# All declarations in a container coming from a parent class (recursively)
+# or a trait. Doesn't include the declarations that directly defined
+# in the container. Members are grouped in clusters for storage efficiency.
 predicate InheritedMembers :
   {
     container : ContainerDeclaration,
@@ -769,8 +772,10 @@ predicate ModuleChild:
     decl : hack.Declaration
   } stored { Module, Decl } where hack.ModuleParent { Decl, Module }
 
-# Class methods implementation of an interface aren't considered as override.
-# However, the methods introduced by `use T` can override interface methods.
+#  Generally, method "derived" overrides "base", if "derived" would have been inherited
+#  in case where "base" wasn't defined.
+#  Note that class methods implementing interface aren't considered as override, but
+#  trait methods can override interface methods.
 predicate MethodOverrides :
   {
     derived : MethodDeclaration,