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[Diagnostics] Tweak @propertyWrapper diags and add an educational note #30116

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Merged
merged 1 commit into from
Feb 29, 2020
Merged

[Diagnostics] Tweak @propertyWrapper diags and add an educational note #30116

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2 changes: 1 addition & 1 deletion include/swift/AST/DiagnosticsSema.def
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Original file line number Diff line number Diff line change
Expand Up @@ -4795,7 +4795,7 @@ ERROR(property_wrapper_wrong_initial_value_init, none,
"'wrappedValue' property type (%2) or an @autoclosure thereof",
(DeclName, Type, Type))
ERROR(property_wrapper_failable_init, none,
"%0 cannot be failable", (DeclName))
"property wrapper initializer %0 cannot be failable", (DeclName))
ERROR(property_wrapper_type_requirement_not_accessible,none,
"%select{private|fileprivate|internal|public|open}0 %1 %2 cannot have "
"more restrictive access than its enclosing property wrapper type %3 "
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9 changes: 9 additions & 0 deletions include/swift/AST/EducationalNotes.def
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Expand Up @@ -34,4 +34,13 @@ EDUCATIONAL_NOTES(invalid_dynamic_callable_type,
EDUCATIONAL_NOTES(missing_dynamic_callable_kwargs_method,
"dynamic-callable-requirements.md")

EDUCATIONAL_NOTES(property_wrapper_no_value_property,
"property-wrapper-requirements.md")
EDUCATIONAL_NOTES(property_wrapper_wrong_initial_value_init,
"property-wrapper-requirements.md")
EDUCATIONAL_NOTES(property_wrapper_failable_init,
"property-wrapper-requirements.md")
EDUCATIONAL_NOTES(property_wrapper_type_requirement_not_accessible,
"property-wrapper-requirements.md")

#undef EDUCATIONAL_NOTES
4 changes: 2 additions & 2 deletions test/decl/var/property_wrappers.swift
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Expand Up @@ -112,7 +112,7 @@ struct MultipleInitialValues<Value> {
struct InitialValueFailable<Value> {
var wrappedValue: Value

init?(wrappedValue initialValue: Value) { // expected-error{{'init(wrappedValue:)' cannot be failable}}
init?(wrappedValue initialValue: Value) { // expected-error{{property wrapper initializer 'init(wrappedValue:)' cannot be failable}}
return nil
}
}
Expand All @@ -121,7 +121,7 @@ struct InitialValueFailable<Value> {
struct InitialValueFailableIUO<Value> {
var wrappedValue: Value

init!(wrappedValue initialValue: Value) { // expected-error{{'init(wrappedValue:)' cannot be failable}}
init!(wrappedValue initialValue: Value) { // expected-error{{property wrapper initializer 'init(wrappedValue:)' cannot be failable}}
return nil
}
}
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7 changes: 7 additions & 0 deletions userdocs/diagnostics/property-wrapper-requirements.md
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@@ -0,0 +1,7 @@
Property Wrapper Implementation Requirements
---
If a type is marked with the `@propertyWrapper` attribute, it must meet certain requirements to be a valid property wrapper.

First, all property wrapper types must have a property named `wrappedValue`. This property cannot be static and must have the same access level as the property wrapper type. If the property wrapper provides a `projectedValue` property, it is subject to the same requirements.

Second, none of a property wrapper's initializers may be failable. Additionally, if a property wrapper initializer has a `wrappedValue` parameter, the type of that parameter must either be the same as the type of the `wrappedValue` property or an `@autoclosure` of that type.