And: add accessor to get the primary from a secondary Package.
This change documents a surprising fact about the current
go/types resolver implementation, namely that each ast.ImportSpec
import "fmt"
creates a new ("secondary") Package object for fmt with the
same String, Name, Path and Scope as the canonical ("primary")
fmt package, but with a different identity.
This change also adds an accessor Package.Primary() that
returns the primary package associated with a secondary
package object, if any.
IMHO the current design is wrong, and the resolver should not
create secondary packages at all. Even if a package is
imported under a non-default name, as in
import f "fmt"
...
f.Print
we should just regard f as a reference to the existing package
"fmt", not as the defining identifier for a secondary package.
What we would lose by such a change (the connection of the two
f's in 'f.Print' and 'import f "fmt"') seems a small price to
pay.
This CL is thus just a minimal change to permit clients to
make progress under the status quo.
R=r, gri, crawshaw
CC=golang-dev
https://golang.org/cl/13626043
9a9fb35468