[4.2] [Type checker] Improve diagnostics when an optional value is not unwrapped #17955
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
…apped.
When we determine that an optional value needs to be unwrapped to make
an expression type check, use notes to provide several different
Fix-It options (with descriptions) rather than always pushing users
toward '!'. Specifically, the errors + Fix-Its now looks like this:
error: value of optional type 'X?' must be unwrapped to a value of
type 'X'
f(x)
^
note: coalesce using '??' to provide a default when the optional
value contains 'nil'
f(x)
^
?? <#default value#>
note: force-unwrap using '!' to abort execution if the optional
value contains 'nil'
f(x)
^
!
Fixes rdar://problem/42081852.
(cherry picked from commit 945c09b)
…ional base.
Improve diagnostics when referencing a member of an optional base, where the
Optional type does not have the member but the wrapped type does. Specifically,
suggest both the chaining ‘?’ and the force-unwrapping ‘!’ Fix-Its via explanatory
notes, e.g.:
error: value of optional type '[Int]?' must be unwrapped to refer to member 'subscript' of wrapped base type '[Int]'
return foo.array[0]
^
note: chain the optional using '?' to access member 'subscript' only for non-'nil' base values
return foo.array[0]
^
?
note: force-unwrap using '!' to abort execution if the optional value contains 'nil'
return foo.array[0]
^
!
More of rdar://problem/42081852.
(cherry picked from commit 9ec3b00)
…mber access.
Introduce a new fix kind into the constraint solver to cover unwrapping the base
of a member access so we can refer to the a member of the unwrapped base.
Wire this fix kind to the just-added diagnostic that suggests either the
chaining ‘?’ or the force-unwrap ‘!’ via separate, descriptive Fix-Its.
Example:
error: value of optional type 'X?' must be unwrapped to refer to member 'f' of wrapped base type 'X'
let _: Int = x.f()
^
note: chain the optional using '?' to access member 'f' only for non-'nil' base values
let _: Int = x.f()
^
?
note: force-unwrap using '!' to abort execution if the optional value contains 'nil'
let _: Int = x.f()
^
!
Before this, we would sometimes get a Fix-It for just ‘?’ and sometimes get a Fix-It for the
coalescing ‘??’, neither of which is likely to be right.
More work on rdar://problem/42081852.
(cherry picked from commit e7eac0a)
…wraps more consistently. Replace the last (and most obscure) use of the poor “use ‘?’ or ‘!’” diagnostic with the new, more explanatory version that provides separate notes with Fix-Its for coalescing or force-unwrapping the value. Finishes rdar://problem/42081852. (cherry picked from commit 5db1901)
DougGregor
changed the title
|
@swift-ci please test |
|
@swift-ci please nominate |
|
Build failed |
|
@swift-ci please test macOS |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Explanation: The errors produced by the Swift compiler when a value of optional type is provided (but needs to be unwrapped) were poor, and led users to excessive force-unwraps (using '!') via a Fix-It. Improve the form of the diagnostics, taking the Fix-It off the primary diagnostic and instead providing two notes: one for either the coalescing operator (
?? <#default value#>) or chaining operator (?.), depending on context, and one for the force-unwrap (!), which makes it clear that the program will abort execution if the underlying value is nil.Scope: Affects ill-formed code that fails to properly unwrap optionals.
Risk: Effectively zero; this pull request is carefully factored to only improve on diagnostics, not touch the constraint solver core.
Testing: Compiler regression tests, including new tests.
Reviewer: @rudkx
SR / Radar: rdar://problem/42081852