948f11b8a8
When unifying two types A and B where one or both of them are interfaces, consider the shared method signatures in unification. 1) If a defined interface (an interface with a type name) is unified with another (defined) interface, currently they must originate in the same type declaration (same origin) for unification to succeed. This is more restrictive than necessary for assignments: when interfaces are assigned to each other, corresponding methods must match, but the interfaces don't have to be identical. In unification, we don't know which direction the assignment is happening (or if we have an assignment in the first place), but in any case one interface must implement the other. Thus, we check that one interface has a subset of the methods of the other and that corresponding method signatures unify. The assignment or instantiation may still not be possible but that will be checked when instantiation and parameter passing is checked. If two interfaces are compared as part of another type during unification, the types must be equal. If they are not, unifying a method subset may still succeed (and possibly produce more type arguments), but that is ok: again, subsequent instantiation and assignment will fail if the types are indeed not identical. 2) In a non-interface type is unified with an interface, currently unification fails. If this unification is a consequence of an assignment (parameter passing), this is again too restrictive: the non-interface type must only implement the interface (possibly among other type set requirements). In any case, all methods of the interface type must be present in the non-interface type and unify with the corresponding interface methods. If they don't, unification will fail either way. If they do, we may infer additional type arguments. Again, the resulting types may still not be correct but that will be determined by the instantiation and parameter passing or assignment checks. If the non-interface type and the interface type appear as component of another type, unification may now produce additional type arguments. But that is again ok because the respective types won't pass instantiation or assignment checks since they are different types. This CL introduces a new unifier flag, enableInterfaceInference, to enable this new behavior. It is currently disabled. For #60353. For #41176. For #57192. Change-Id: I983d0ad5f043c7fe9d377dbb95f6b9342f36f45f Reviewed-on: https://go-review.googlesource.com/c/go/+/497656 TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com> Run-TryBot: Robert Griesemer <gri@google.com> Auto-Submit: Robert Griesemer <gri@google.com> |
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