text/template: inconsistency when accessing a field of an interface field

[nodirt]

In a pipeline {{.Foo.Bar}} where Foo field is declared as of type interface I and points to a struct S that implements I and has Bar field:

• Bar can be resolved if I is interface{}
• Bar cannot be resolved if I is a non-empty interface

http://play.golang.org/p/Knps5C6aaL

I think this is inconsistent, Bar should be resolvable with non-empty I.
This wasn't catched by tests because there is a test for interface{}, but not for a non-empty interface.

I'd like to work on this.

[adg]

This does seem inconsistent. It also seems like a bad thing to rely on. Happy to review a fix.

[gopherbot]

CL https://golang.org/cl/15809 mentions this issue.

[nodirt]

While reading the code, discovered one more case
http://play.golang.org/p/eM7lrc1lIM

I think we have to support this because templates are inherently dynamically-typed.

[nodirt]

Same thing with len http://play.golang.org/p/qXOU4I5Vyj

[nodirt]

And with range