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https://issues.apache.org/jira/browse/GROOVY-12559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18134686#comment-18134686
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ASF GitHub Bot commented on GROOVY-12559:
-----------------------------------------
paulk-asert merged PR #3087:
URL: https://github.com/apache/groovy/pull/3087
> Ternary of two ternaries of class literals is cast to the classes' common
> supertype under invokedynamic
> -------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12559
> URL: https://issues.apache.org/jira/browse/GROOVY-12559
> Project: Groovy
> Issue Type: Bug
> Components: Compiler
> Affects Versions: 5.1.3, 6.0.0
> Reporter: James Daugherty
> Priority: Major
>
> Since 5.0.0-alpha-4 (GROOVY-10936) the type of a ternary expression is the
> common supertype of its branches' types. A class literal's type is the class
> it names, not {{java.lang.Class}}, so a ternary that chooses between two
> ternaries of class literals
> {code:groovy}
> interface Marker {}
> class First implements Marker {}
> class Second implements Marker {}
> class Third implements Marker {}
> class Fourth implements Marker {}
> class Chooser {
> Class<?> choose(boolean a, boolean b, boolean c) {
> a ? (b ? First : Second) : (c ? Third : Fourth)
> }
> }
> assert new Chooser().choose(false, true, true) == Third
> {code}
> is typed as the classes' common supertype, {{Marker}}. The chosen {{Class}}
> object is then converted _from_ {{Marker}} wherever it is used: returned,
> passed as an argument, or assigned to a typed variable. With invokedynamic
> that conversion is a {{cast}} call site declared as {{(Marker)Class}}, and
> linking it casts the {{Class}} object to {{Marker}}:
> {noformat}
> java.lang.ClassCastException: Cannot cast java.lang.Class to Marker
> {noformat}
> Groovy 4, and Groovy 5 and 6 with classic call sites, return the chosen
> class. A single-level ternary of class literals, {{a ? First : Second}}, is
> unaffected, because the bytecode writer resolves a class literal operand to
> {{Class<First>}} itself; a ternary's own type is consulted only when it is an
> operand of another ternary. A Grails application moving from classic call
> sites to invokedynamic (the Grails 9 default) meets this in code that picks a
> class by conditions.
> *Reproducer:*
> https://github.com/jdaugherty/groovy-ternary-class-literal-reproducer
> ({{./run.sh 4.0.33 5.1.3 6.0.0}}): returning the chosen class and passing it
> as an argument both fail on 5.1.3 and 6.0.0 with indy, and pass on 4.0.33 and
> with classic call sites.
> *Cause:* {{TernaryExpression.getType()}} returns
> {{WideningCategories.lowestUpperBound()}} of its branches' {{getType()}}, and
> {{ClassExpression.getType()}} is the class the literal names.
> {{BinaryExpressionHelper.evaluateTernaryExpression()}} types each branch with
> {{StatementMetaTypeChooser.resolveType()}}, which answers {{Class<T>}} for a
> class expression but {{getType()}} for a nested ternary. So the inner
> ternaries are typed {{Marker}}, the outer ternary's common type is
> {{Marker}}, and the operand stack carries {{Marker}} for a value that is a
> {{Class}}. The conversion to {{Class}} is then written as {{invokedynamic
> cast:(LMarker;)Ljava/lang/Class;}}, whose method type makes the JVM cast the
> argument to {{Marker}} before the call site sees it. Classic call sites
> convert the value to {{Class}} directly and accept it.
> *Proposed fix:* in {{TernaryExpression.getType()}}, give a class literal
> operand the type {{Class<T>}}, as {{StatementMetaTypeChooser.resolveType()}}
> does, so a ternary of class literals is typed {{Class}} wherever it appears.
> A patch with a test follows as a pull request against master, with backports
> for the 6.0.x and 5.1.x lines.
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