XTypeRecovery

Based on a flow-insensitive static single-assignment symbol-table-style approach. This pass aims to be fast and deterministic and does not try to converge to some fixed point but rather iterates a fixed number of times. This will help recover:

• Imported call signatures from external dependencies
• Dynamic type hints for mutable variables in a compilation unit.

The algorithm flows roughly as follows:

• Scan for method signatures of methods for each compilation unit, either by internally defined methods or by reading import signatures. This includes looking for aliases, e.g. import foo as bar.
• (Optionally) Prune these method signatures by checking their validity against the CPG.
• Visit assignments to populate where variables are assigned a value to extrapolate its type. Store these values in a local symbol table. If a field is assigned a value, store this in the global table
• Find instances of where these fields and variables are used and update their type information.
• If this variable is the receiver of a call, make sure to set the type of the call accordingly.

The symbol tables use the SymbolTable class to track possible type information.
Note: Local symbols are cleared once a compilation unit is complete. This is to keep memory usage down while maximizing concurrency.