Desugaring

Certain Ruby language features are implemented using syntactic sugar. For example, supposing that ``x`` is an object with an attribute ``foo``, the assignment::

is desugared to code similar to::

In other words, there is effectively a call to the SetterMethodCall_ ``foo=`` on ``x`` with argument ``__synth_0 = y``, followed by a read of the ``__synth_0`` variable.

In CodeQL, this is implemented by syntheisizing AstNode_ instances corresponding to this desugared version of the code.

Note that both the original AssignExpr_ and the desugared SetterMethodCall_ versions are both available to CodeQL queries, and it is usually not necessary to be aware of any desugaring that may take place. However, if a codebase explicitly uses ``x.foo=(y)`` SetterMethodCall_ syntax, then this will not be found by a query for AssignExpr_ instances.

Other synthesized AstNode_ instances exist, see the isSynthesized_ and getDesugared_ predicates for details.

.. _isSynthesized: https://codeql.github.com/codeql-standard-libraries/ruby/codeql/ruby/AST.qll/predicate.AST$AstNode$isSynthesized.0.html

.. _getDesugared: https://codeql.github.com/codeql-standard-libraries/ruby/codeql/ruby/AST.qll/predicate.AST$AstNode$getDesugared.0.html