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Require references from typealiases to be const (#516)

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This adds a language change that requires references from typealiases
to the enclosing module to be `const`.

This is required because typealiases are not late-bound.

Rationale is laid out in SPICE-0007.

Also:
* Update documentation to reflect new rules.
* Fix `Project.pkl`; mark method `const` to not break said rule.
This commit is contained in:
Daniel Chao
2024-06-10 09:01:05 -07:00
committed by GitHub
parent 9cc9816440
commit a4c0a271b4
5 changed files with 37 additions and 7 deletions
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17
docs/modules/language-reference/pages/index.adoc
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@@ -1147,9 +1147,13 @@ Therefore, the same rules that apply to `fixed` also apply to `const`:
* The const-ness of a property or method must be preserved when it is overridden by a child class.
[[class-and-annotation-const]]
*Class and Annotation Scoping*
*Class, Annotation, and Typealias Scoping*
Within a class or annotation body, any reference to a property or method of its enclosing module requires that the referenced member is `const`.
In these following scenarios, any reference to a property or method of its enclosing module requires that the referenced member is `const`:
* Class body
* Annotation body
* Typealiased constrained type
.invalid2.pkl
[source%parsed,{pkl}]
@@ -1162,15 +1166,18 @@ class Bird {
@Deprecated { message = "Replace with \(pigeonName)" } // <2>
oldPigeonName: String
typealias IsPigeonName = String(pigeonName) // <3>
----
<1> Error: cannot reference non-const property `pigeonName` from a class.
<2> Error: cannot reference non-const property `pigeonName` from an annotation.
<3> Error: cannot reference non-const property `pigeonname` from a typealias.
This rule exists because classes and annotations are not <<late-binding,late bound>>;
it is not possible to change the definition of a class or annotation by amending the module
This rule exists because classes, annotations, and typealiases are not <<late-binding,late bound>>;
it is not possible to change the definition of these members by amending the module
where it is defined.
Generally, there are two strategies for referencing a property from a class or annotation:
Generally, there are two strategies for referencing such properties:
*Add the `const` modifier to the referenced property*