I've begun prototyping what it might look like to integrate the
current shared type analysis functionality with the analyzer and CFE,
and I've discovered some API improvements that are needed:
- The shared logic now handles the possibility that switch cases that
share a body have been merged prior to type analysis (because the
CFE merges them during parsing), in addition to the pre-existing
functionality which assumed that switch case merging had to be done
in the shared logic.
- The shared logic now returns several pieces of information as the
result of a call to `analyzeSwitchStatement`: whether the switch
statement had a `default` clause, whether it was exhaustive, whether
the last case body terminates, and the type of the scrutinee. These
are all needed by the CFE.
- The shared logic now allows `TypeAnalyzer.errors` to be `null`,
indicating that no errors should be reported. This reflects how
errors are suppressed during top level inference in the CFE.
- If a switch case lacks a `when` clause, this is reported by calling
`handleNoWhen` rather than passing a boolean to `handleCaseHead`.
- The shared logic now reports the appropriate error when a case
constant doesn't properly match the scrutinee's static type.
- Information about case labels is now delivered to flow analysis via
`switchStatement_endAlternatives` rather than
`switchStatement_beginCase`. This made it possible to rewrite the
shared `analyzeSwitchStatement` method in a way that requires less
bookkeeping, because it no longer has to peek ahead to look for
labels associated with a given case body.
- `TypeAnalyzer.analyzeExpression` is now responsible for
understanding that "no context" and a context of `dynamic` should
both be coalesced to `?`. The analyzer does this (although it's not
100% why), and it's definitely "business logic" that eventually
belongs in the shared type analyzer.
- `TypeAnalyzer.analyzeSwitchExpression` and
`TypeAnalyzer.analyzeSwitchStatement` no longer receive a list of
ExpressionCaseInfo / StatementCaseInfo objects describing the cases;
instead they query for them using a callback. This reduces the
lifetime of the ExpressionCaseInfo / StatementCaseInfo objects. In
the future, when we have record support, we could replace these
objects with records, which would then be passed on the stack,
avoiding any allocations.
- A new hook, `handleSwitchScrutinee`, is called right after visiting
the "scrutinee" expression of a switch expression or switch
statement. This hook is needed by the analyzer to compute
exhaustiveness. In a future CL, I hope to move exhaustiveness
analysis into the shared code as well, which should make this hook
unnecessary.
- `TypeAnalyzer.analyzeSwitchStatement` now reports an error if a
switch case completes normally and pattern support is not enabled.
- The test class `_MiniAstTypeAnalyzer` no longer overrides
`analyzeExpression` to provide a default context type; instead,
every call to `analyzeExpression` that didn't previously provide a
context now provides a context of `?`. Note that not all of these
are correct, but they are close enough for the unit tests we have
today. I plan to fix them in future CLs as I replace this logic
with shared logic.
- The hook `handleVariablePattern` is now always provided with a
static type. Previously, it was only provided with a static type if
this was the first time the variable was bound in the pattern.
Change-Id: I70e3c5468312a9329fcf4ad2e13749a32d2418e7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/257487
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Paul Berry
466494f5be