[ASTPrinter] Escape @_lifetime arguments when needed
Printing a LifetimeDescriptor would never wrap it in backticks (even if originally wrapped in backticks). This would result in the output not being able to be parsed
rdar://159992995
Infer @_lifetime(self: copy self) for mutating methods without requiring the
experimental Lifetimes feature to be disabled. Treatment of mutating 'self' is
now consistent with other 'inout' parameters.
Example:
extension MutableSpan {
mutating func mutatingMethod() {...}
}
Restructure the inference logic to allow the same function declaration to
independently annotate or infer different lifetime targets.
For example:
@_lifetime(borrow a)
/* DEFAULT: @_lifetime(b: copy b)
func f(a: A, b: inout B) -> NE
The fact that we prevented this was somewhat accidental and surprising.
This restructuring simplifies the code but also gives us much more control over
the inference logic.
Fixes: rdar://159288750 ("A function cannot have a ~Escapable 'inout' parameter
in addition to other ~Escapable parameters" is not actionable)
Non-escapable struct definitions often have inicidental integer fields that are
unrelated to lifetime. Without an explicit initializer, the compiler would infer
these fields to be borrowed by the implicit intializer.
struct CountedSpan: ~Escapable {
let span: Span<Int>
let i: Int
/* infer: @lifetime(copy span, borrow i) init(...) */
}
This was done because
- we always want to infer lifetimes of synthesized code if possible
- inferring a borrow dependence is always conservative
But this was the wrong decision because it inevitabely results in lifetime
diagnostic errors elsewhere in the code that can't be tracked down at the use
site:
let span = CountedSpan(span: span, i: 3) // ERROR: span depends on the lifetime of this value
Instead, force the author of the data type to specify whether the type actually
depends on trivial fields or not. Such as:
struct CountedSpan: ~Escapable {
let span: Span<Int>
let i: Int
@lifetime(copy span) init(...) { ... }
}
This fix enables stricter diagnostics, so we need it in 6.2.
Fixes rdar://152130977 ([nonescapable] confusing diagnostic message when a
synthesized initializer generates dependence on an Int parameter)
Users commonly try to write a lifetime dependency on an 'inout' parameters as:
@_lifetime(a: &a)
func f_inout_useless(a: inout MutableRawSpan) {}
This is useless. Guide them toward what they really wanted:
@_lifetime(a: copy a)
Fixes rdar://151618856 (@lifetime(..) gives inconsistent error messages)
Correctly diagnose this as:
"invalid use of inout dependence on the same inout parameter
@_lifetime(a: &a)
func f_inout_useless(a: inout MutableRawSpan) {}
Correctly diagnose this as:
"lifetime-dependent parameter must be 'inout'":
@_lifetime(a: borrow a)
func f_inout_useless(a: borrowing MutableRawSpan) {}
This comes up often when passing a MutableSpan as an 'inout' argument. The
vague diagnostic was causing developers to attempt incorrect @_lifetime
annotations. Be clear about why the annotation is needed and which annotation
should be used.
This avoids diagnostic errors on synthesized accessors, which are impossible for developers to understand.
Fixes rdar://153793344 (Lifetime-dependent value returned by generated accessor '_read')
This fixes a small oversight in the type checker's LifetimeDependence
inference. Allow inference on _read accessors even when 'self' is a trivial
type. This is needed because the compiler synthesizes a _read accessor even when
the user defines a getter (this is probably a mistake, but it's easire to just
fix inference at this point). There is no workaround because it defining both a
getter and '_read' is illegal!
extension UnsafeMutableRawBufferPointer {
var mutableBytes: MutableRawSpan {
@_lifetime(borrow self)
get {
unsafe MutableRawSpan(_unsafeBytes: self)
}
}
}
Fixes rdar://153346478 (Can't compile the
UnsafeMutableRawBufferPointer.mutableBytes property)
This adds a new lifetime inference rule, loosening the requirement for @lifetime
annotations even when the experimental LifetimeDependence mode is
enabled. Additionally, it enables this new inference rule even when the
experimental mode is disabled. All other inference rules continue to require the
experimental feature. The rule is:
If a function or method has a single inout non-Escapable parameter other than
'self' and has no other non-Escapable parameters including 'self', then infer a
single @lifetime(copy) dependency on the inout parameter from its own incoming
value.
This supports the common case in which the user of a non-Escapable type,
such as MutableSpan, wants to modify the span's contents without modifying
the span value itself. It should be possible to use MutableSpan this way
without requiring any knowledge of lifetime annotations. The tradeoff is
that it makes authoring non-Escapable types less safe. For example, a
MutableSpan method could update the underlying unsafe pointer and forget to
declare a dependence on the incoming pointer.
Disallowing other non-Escapable parameters rules out the easy mistake of
programmers attempting to trivially reassign the inout parameter. There's
is no way to rule out the possibility that they derive another
non-Escapable value from an Escapable parameteter. So users can still write
the following:
func reassign(s: inout MutableSpan<Int>, a: [Int]) {
s = a.mutableSpan
}
The 'reassign' declaration will type check, but it's implementation will
diagnose a lifetime error on 's'.
Fixes rdar://150557314 ([nonescapable] Declaration of inout MutableSpan
parameter requires LifetimeDependence experimental feature)
A setter on a non-Escapable type may have a dependency on both it's incoming
'self' and 'newValue'. If the 'newValue' dependency does not match the getter's
dependency, then lifetime diagnostics will not accept the generated '_modify'
accessor:
error: lifetime-dependent value returned by generated accessor '_modify'
To fix this, make sure that we don't (conservatively) infer a borrow
dependency on 'newValue'.
Fixes rdar://150444400
When type checking a .swiftinterface file, Assume that a mutating methods does
not depend on its parameters. This is unsafe but needed because some
MutableSpan APIs snuck into the standard library interface without specifying
dependencies.
Fixes rdar://148697444 error: a mutating method with a ~Escapable 'self' requires '@lifetime(self:
...)'
When a generic function has potentially Escapable outputs, those outputs
declare lifetime dependencies, which have no effect when substitution
leads to those types becoming `Escapable` in a concrete context.
This means that type substitution should canonically eliminate lifetime
dependencies targeting Escapable parameters or returns, and that
type checking should allow a function value with potentially-Escapable
lifetime dependencies to bind to a function type without those dependencies
when the target of the dependencies is Escapable.
Fixes rdar://147533059.
Preserve conditionallyAddressableParamIndices independent of any
addressableParamIndices. The conditional dependencies are subject to change
based on type substitution.
