[
https://issues.apache.org/jira/browse/GROOVY-12477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18131572#comment-18131572
]
ASF GitHub Bot commented on GROOVY-12477:
-----------------------------------------
paulk-asert merged PR #3006:
URL: https://github.com/apache/groovy/pull/3006
> @Modifies with an empty or no list isn't working correctly
> ----------------------------------------------------------
>
> Key: GROOVY-12477
> URL: https://issues.apache.org/jira/browse/GROOVY-12477
> Project: Groovy
> Issue Type: Bug
> Components: groovy-contracts, groovy-typecheckers
> Affects Versions: 6.0.0
> Reporter: Paul King
> Assignee: Paul King
> Priority: Minor
>
> h3. Problem
> There is no working way to declare that a method modifies nothing with
> {{@Modifies}}. The forms a user would reach for are either rejected or
> silently treated as if the method had no {{@Modifies}} at all.
> With {{@TypeChecked(extensions = 'groovy.typecheckers.ModifiesChecker')}} on
> a method whose body is {{balance -= n}}:
> ||Form||Result||
> |{{@Modifies(\{ this.other })}}|Error: {{'balance' is not declared in
> @Modifies}} (correct)|
> |{{@Modifies(\{ [] })}}|*Compiles; nothing is checked*|
> |{{@Modifies(\{})}}|Error: {{@Modifies closure must contain a field
> reference, parameter reference, or list of references}}|
> |{{@Modifies}}|*Compiles; nothing is checked*|
> {code:groovy}
> import groovy.contracts.Modifies
> import groovy.transform.TypeChecked
> @TypeChecked(extensions = 'groovy.typecheckers.ModifiesChecker')
> class Account {
> int balance
> @Modifies({ [] })
> void withdraw(int n) { balance -= n } // expected: error, actual:
> compiles
> }
> {code}
> h3. Cause
> * {{ModifiesASTTransformation}} stores the
> {{groovy.contracts.modifiesFields}} metadata only when the set is non-empty.
> An empty list therefore leaves no metadata. {{ModifiesChecker}} reads missing
> metadata as "no {{@Modifies}}, nothing to check".
> {{ModifiesEnsuresValidationTransformation}} returns early on an empty set
> too, so {{old.x}} in an {{@Ensures}} is not validated either.
> * An empty closure body is rejected because exactly one statement is required.
> * {{Modifies.value()}} has no default, so a bare {{@Modifies}} should be a
> missing-member error. The transform replaces {{value}} with {{Object.class}}
> unconditionally, which hides the missing member.
> The intent that "nothing" be expressible is already in the docs and the
> checker. The type checkers guide says {{@Pure}}, {{@SideEffectFree}} and
> {{@Contract(pure = true)}} each imply {{@Modifies({})}}, and
> {{ModifiesChecker}} substitutes an empty frame for them. A user cannot write
> that form themselves.
> h3. Proposed fix
> * {{@Modifies({})}} and {{@Modifies(\{ [] })}} both declare an empty frame:
> the method modifies no fields or parameters. The metadata is always stored,
> even when empty, so an empty frame is distinguishable from no annotation.
> * A bare {{@Modifies}} is a compile error. A frame condition is a claim the
> checker enforces, so "modifies nothing" should be explicit rather than
> inferred from a marker that could equally be read as "modifies something
> unspecified".
> * With an empty frame, {{@Ensures}} may not reference {{old.<field>}},
> consistent with the existing rule that {{old}} may only reference fields
> declared in {{@Modifies}}.
> * The contracts user guide states the empty-frame form.
> Both modules are {{@Incubating}}, so the tightening is low cost. The only
> existing code that changes behaviour is code using {{@Modifies(\{ [] })}} or
> a bare {{@Modifies}} and relying on it being unchecked.
--
This message was sent by Atlassian Jira
(v10.3.26#10030026)
