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Mypy doesn't recognize access to a named tuple defined in another module within an import cycle, if the other module is processed later than the module that contains the reference to the named tuple.
The same is true for TypedDicts and probably for all other "made-up" TypoInfos created during the second pass (not during the first, like for normal classes).
Forward references didn't work with anything apart from classes, for example
this didn't work:
```
x: A
A = NamedTuple('A', [('x', int)])
```
The same situation was with `TypedDict`, `NewType`, and type aliases. The
root problem is that these synthetic types are neither detected in first pass,
nor fixed in third pass. In certain cases this can lead to crashes (first six issues
below are various crash scenarios). This fixes these crashes by applying some
additional patches after third pass.
Here is the summary of the PR:
* New simple wrapper type `ForwardRef` with only one field `link` is introduced
(with updates to type visitors)
* When an unknown type is found in second pass, the corresponding
`UnboundType` is wrapped in `ForwardRef`, it is given a "second chance" in
third pass.
* After third pass I record the "suspicious" nodes, where forward references and
synthetic types have been encountered and append patches (callbacks) to fix
them after third pass. Patches use the new visitor `TypeReplacer` (which is the
core of this PR).
Fixes#3340Fixes#3419Fixes#3674Fixes#3685Fixes#3799Fixes#3836Fixes#3881Fixes#867Fixes#2241Fixes#2399Fixes#1701Fixes#3016Fixes#3054Fixes#2762Fixes#3575Fixes#3990
Mypy doesn't recognize access to a named tuple defined in another module within an import cycle, if the other module is processed later than the module that contains the reference to the named tuple.
Example:
A potential fix is to process references to types in a later phase of semantic analysis than type definitions.
This is related to #3016.
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