Slava Pestov d0e4ba38b8 Serialization: Use nested type lookup table for cross-module references also ...

Fixes a class of deserialization issues in the merge-modules
step.

The setup was the following:

- File A defines a typealias A whose underlying type is a nested
  type S of a type T, defined in a different module.

- File B defines an extension of T, and the extension member's
  type references A.

When deserializing A, we would proceed to deserialize the
underlying type, which references T.S. This would first deserialize
T and perform a name lookup to find S, which would deserialize all
members, including pulling in extensions. Deserialization of the
extension defined in file B would then fail, because the declaration
for A is not yet available.

We had a previous fix for these problems in the single-module case;
a per-file lookup table mapping mangled nested type names to
declarations, allowing a nested type to be deserialized without
pulling in all members and extensions of its parent type.

This patch generalizes the nested type lookup table allowing it to
be used to resolve cross-module references as well. Also, we were
only writing out the nested type table when serializing a partial
swiftmodule corresponding to a source file. Removing this check
allows the nested type table to be serialized for modules built
with WMO enabled as well, such as the standard library.

Fixes <rdar://problem/30976604> and
<https://bugs.swift.org/browse/SR-4208>.

2017-05-16 19:06:26 -07:00

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