How does one handle the $container property while manually rewriting the AST?

[soft-guy]

Context:

Some parser rules of the grammar of a language I am developing represent syntactic sugar. Instead of writing additional generation code for the AST nodes resulting from these rules, I want to rewrite the AST to eliminate the syntactic sugar.

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Workaround

To achieve this, I need to create a new object of a specific type whose properties are to reference objects accessible through the properties of the original syntactic sugar node. After creating this new object, I would substitute it for the syntactic sugar node in the AST. However, I have some challenges with the $container property.

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1. The Problem with $container:

• I can assign $container property of a new object while creating it.
• However, the objects used to construct this new object retain their $container property values, which are now incorrect since they refer to the old syntactic sugar node, which is no longer in the AST.
• Since the $container property is read-only, I cannot directly update it to reflect the new AST structure.

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2. Possible Workarounds:

• Creating new objects that replicate the properties of the existing nodes but assign the correct $container values manually while creating.
• However, this approach requires recursively updating all related nodes down to the leaves, which seems cumbersome and inelegant.
• Alternatively, I could ignore handling $container property, at least occasionally, but this might cause issues in other parts that depend on its correctness.

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Question:

Is there an established, recommended, or conventional way in Langium to handle $container updates when manually modifying the AST? Alternatively, how critical is the $container property for AST consistency, and can it be safely ignored in some scenarios?

[msujew]

Hey @soft-guy,

we have a utility function AstUtils.linkContentToContainer that you can use for this exact purpose. During the AST construction, you can just ignore the $container property (for example, by setting it to undefined!), and then use the linked function to let the framework take over the assignment.