While it is theoretically useful to know that `{ while(true) {} }`
returns Nothing, CFG node deadness is not precise enough to do that: if
the entire lambda is dead, it's no longer possible to find out whether
the loop is terminating. Besides, `while (true)` and `if (true)` are
pretty much the only constructs like that anyway.
Note that this commit does not affect resolution for lambdas that end in
a Nothing-returning expression, e.g. `throw`.
Test framework assumes that there won't be any files with same names
in one test. But there were cases when test declared test file
with same name as one of files with helpers (e.g. `functions.kt`)
Quick quiz:
Q: In a CFG, what does `a -> b -> c -> d` mean?
A: `a`, then `b`, then `c`, then `d`.
Q: In a CFG, what does `a -> b -> d; a -> c -> d` mean?
A: `a`, then `b` or `c`, then `d`.
Q: So how do you encode "a, then (b, then c) or (c, then b), then d`?
A: You can't.
Problem is, you need to, because that's what `a; run2({ b }, { c }); d`
does when `run2` has a contract that it calls both its lambda arguments
in-place: `shuffle(listOf(block1, block2)).forEach { it() }` is a
perfectly valid implementation for it, as little sense as that makes.
So that's what union nodes solve. When a node implements
`UnionNodeMarker`, its inputs are interpreted as "all visited in some
order" instead of the normal "one of the inputs is visited".
Currently this is used for data flow. It *should* also be used for
control flow, but it isn't. But it should be. But that's not so easy.
BTW, `try` exit is NOT a union node; although lambdas in one branch can
be completed according to types' of lambdas in another, data does not
flow between the branches anyway (since we don't know how much of the
`try` executed before jumping into `catch`, and `catch`es are mutually
exclusive) so a `try` expression is more like `when` than a function
call with called-in-place-exactly-once arguments. The fact that
`exitTryExpression` used `processUnionOfArguments` in a weird way
should've hinted at that, but now we know for certain.
If a certain type statement is true on loop entry and all continue
paths, then it is also true on exit if the condition did not reassign
the variable.
^KT-7676 tag fixed-in-k2
It's also not a backwards jump in do-while, unless it's in the loop's
condition, which is a stupid "feature" IMO. As you can probably tell
from the comments added in this commit.
This makes the `returns() implies` checker slightly cleaner, and also
fixes the case that I've missed where in RHS of `x ?:` type of `x` was
not set to `Nothing?`.
This also fixes some returnsNotNull contracts because the old code added
an implication that `== true` => `!= null` then promptly removed any
statement that this could've affected if the argument was a synthetic
variable.
^KT-26612 tag fixed-in-k2
If the right-hand side is evaluated at all, then in its flow those
statements were already approved. Re-approving them erases the effect of
reassignments.
^KT-28369 tag fixed-in-k2
In theory, forking persistent flows should be cheap because of object
reuse, so the proposal here is to start from scratch and prove
redundancy of forks on a case-by-case basis. Something something better
safe than sorry.
^KT-28333 tag fixed-in-k2
^KT-28489 tag fixed-in-k2
* wrong method was called from FirDataFlowAnalyzer.exitFunctionCall;
* map from function to affected properties should be keyed by symbol,
not FirFunction, as the latter may change;
* arguments of `return` and assignment statements should be visited,
as they may contain lambdas.
If we want to analyse some function's call, we need to know about its
contracts, otherwise resolving the following code would be broken.
Computing return type of function is a prerequisite to using it in any
sensible way, so it's the best place to resolve it to CONTRACTS
KT-50733
Marco Pennekamp