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Name-based pattern matcher needed some hardening against
unapply methods with the right name but wrong types. Only
isEmpty methods which return Boolean are acceptable.
Catching it directly rather than indirectly also allowed
for better error messages.
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An extractor is no longer required to return Option[T], and
can instead return anything which directly contains methods
with these signatures:
def isEmpty: Boolean
def get: T
If the type of get contains methods with the names of
product selectors (_1, _2, etc.) then the type and arity
of the extraction is inferred from the type of get. If
it does not contain _1, then it is a single value
extractor analogous like Option[T].
This has significant benefits and opens new territory:
- an AnyVal based Option-like class can be used which
leverages null as None, and no allocations are necessary
- for primitive types the benefit is squared (see below)
- the performance difference between case classes and
extractors should now be largely eliminated
- this in turn allows us to recapture great swaths of
memory which are currently squandered (e.g. every
TypeRef has fields for pre and args, even though these
are more than half the time NoPrefix and Nil)
Here is a primitive example:
final class OptInt(val x: Int) extends AnyVal {
def get: Int = x
def isEmpty = x == Int.MinValue // or whatever is appropriate
}
// This boxes TWICE: Int => Integer => Some(Integer)
def unapply(x: Int): Option[Int]
// This boxes NONCE
def unapply(x: Int): OptInt
As a multi-value example, after I contribute some methods to TypeRef:
def isEmpty = false
def get = this
def _1 = pre
def _2 = sym
def _3 = args
Then it's extractor becomes
def unapply(x: TypeRef) = x
Which, it need hardly be said, involves no allocations.
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Filter out unapplies which can't be called (such as those with
a second non-implicit parameter list) and report the error in a
meaningful fashion.
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To facilitate debugging pattern matches, we store the values for
sub-patterns of extractor (synthetic or user-defined) patterns in local variables.
When performing an optimized build, and when possible, we don't do store but inline them directly.
For soundness, SI-5158, SI-6070, we must always store the values of mutable case class fields.
(Specifying -optimize is the only way to suppress emitting these local variables.
An unoptimized build will always generate them, which was deemed the right default during the meeting.)
(updated flags for t4425 to get consistent runs on optimized and non-optimized partest runs
by always passing -optimize)
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Also closes SI-5158 (debuggability), SI-6070 (soundness).
To improve both debuggability and soundness,
we now store the result of an extractor (user-defined and synthetic)
in local variables.
For the case class case, this also fixes the soundness bug SI-6070,
as this prevents post-match mutation of bound variables.
The core of the refactoring consisted of introducing the PreserveSubPatBinders
trait, which introduces local variables instead of substituting symbols
for the RHS of those variables (so this can be seen as reverting the premature optimization
of inline the case-class getters into the case body).
Since TreeMakerToCond fuses the substitutions performed in a match to find out
which symbolic values binders evaluate to, masquerade PreserveSubPatBinders's
binding of subPatBinders and subPatRefs as the corresponding substitution.
Consider `case class Foo(bar: Int)`, then `case y@Foo(x) => println(x)`
gives rise to `{val x = y.bar; println(x)}` (instead of `println(y.bar)`),
and `subPatternsAsSubstitution` pretends we still replace `x` by `y.bar`,
instead of storing it in a local variable so that the rest of the analysis need not be modified.
Misc notes:
- correct type for seq-subpattern
- more error resilience (ill-typed patterns sometimes slip past the typechecker -- reopened SI-4425)
TODO: come up with a more abstract framework for expressing bound symbols and their values
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some tests (unreachability, exhaustivity, @switch annotation checking) are still run under -Xoldpatmat,
but that will change before we go into RC mode (then the test/ partest of this commit will be reverted)
removed irrelevant dependency on patmat
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