Paul Berry
cb0eb28cba
With one exception (noted below), the shared analysis logic uses the convention that the expressions passed to flow analysis are the original (pre-lowered) expressions, whereas the expressions passed to flow analysis by the CFE are the lowered expressions. This difference caused two problems: - If a boolean expression appeared on the right hand side of a pattern assignment or pattern variable declaration, and it was lowered, the flow analysis implications of that boolean expression would be lost. - If a boolean expression appeared in a `when` clause, and it was lowered, the flow analysis implications of that boolean expression would be lost. Exception: for switch statements, the shared analysis logic has been passing lowered expressions to flow analysis, so this problem didn't occur for `when` clauses in switch statements. Notably, when compiling for the VM, the CFE lowers expressions like `x != null` to something more like `!(x == null)`. Fortunately, the first of these two situations shouldn't cause problems very often, since typically if the right hand side of an assignment or variable declaration is a boolean expression, there is no need for the left hand side to involve patterns. As for the second of these two situations, it's also not too likely to cause problems, since typically null checks occur inside patterns rather than in `when` clauses. As a short term fix, we remove the exception noted above, and we account for the difference in conventions by adding a call to `FlowAnalysis.forwardExpression` to the CFE's implementation of `dispatchExpression`, so that when transitioning between CFE logic and shared logic, flow analysis will be informed how to match up the lowered expressions to their pre-lowered counterparts. Longer term, I would like to switch everything to the convention of using the original (pre-lowered) expressions; this will bring the analyzer and CFE into better alignment with each other and should eliminate a class of subtle bugs. This long term goal is tracked in https://github.com/dart-lang/sdk/issues/52189. Fixes #52183. Fixes #52241. Bug: https://github.com/dart-lang/sdk/issues/52183, https://github.com/dart-lang/sdk/issues/52241. Change-Id: I2449ce34c54325603bc2730d1660a7cfc7d79aec Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/298840 Reviewed-by: Johnni Winther <johnniwinther@google.com> Commit-Queue: Paul Berry <paulberry@google.com>
FE/analyzer shared code
This package contains logic that is shared between the front_end and analyzer packages. It is intended solely to facilitate development of the Dart SDK, and is not intended for use by end users. In particular, this package has no public API, so no guarantee is made of compatibility between one version of the package and the next.
End users should consider using the analyzer package to analyze Dart source code.