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Motivation:
* fix known bugs and limitations of for-generators
* improve code health by removing complex workarounds
Changes:
* simplify AstBuilder code related to for-generators
* track for-generators via `SymbolTable.enterForGenerator()`
* add `RestoreForBindingsNode` during initial AST construction
instead of calling `MemberNode.replaceBody()` later on
* simplify some unnecessarily complex code
* remove workarounds and band-aids such as:
* `isInIterable`
* `executeAndSetEagerly`
* adding dummy slots in `AmendFunctionNode`
* overhaul implementation of for-generators
* store keys and values of for-generator iterations in regular instead of auxiliary frame slots
* set them via `TypeNode.executeAndSet()`
* `ResolveVariableNode` no longer needs to search auxiliary slots
* `Read(Enclosing)AuxiliarySlot` is no longer needed
* at the start of each for-generator iteration, create a new `VirtualFrame`
that is a copy of the current frame (arguments + slots)
and stores the iteration key and value in additional slots.
* execute for-generator iteration with the newly created frame
* `childNode.execute(newFrame)`
* Pkl objects created during the iteration will materialize this frame
* store newly created frames in `owner.extraStorage`
if their for-generator slots may be accessed when a generated member is executed
* resolving variable names to for-generator variables at parse time would make this analysis more precise
* when a generated member is executed,
* retrieve the corresponding frame stored in `owner.extraStorage`
* copy the retrieved frame's for-generator slots into slots of the current frame
Result:
* for-generators are implemented in a correct, reasonably simple, and reasonably efficient way
* complexity is fully contained within package `generator` and `AstBuilder`
* for-generator keys and values can be accessed from all nested scopes:
* key and value expressions of generated members
* condition expressions of nested when-generators
* iterable expressions of nested for-generators
* for-generator keys and values can be accessed from within objects created by the expressions listed above
* sibling for-generators can use the same key/value variable names
* parent/child for-generators can use the same key/value variable names
* fixes https://github.com/apple/pkl/issues/741
Core implementation of the Pkl language. Includes Java APIs for embedding the language into JVM applications, and for building libraries and tools on top of the language.