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https://issues.apache.org/jira/browse/GROOVY-12446?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Daniel Sun resolved GROOVY-12446.
---------------------------------
Fix Version/s: 7.0.0-alpha-1
Assignee: Daniel Sun
Resolution: Fixed
> STC: stop writing UnionTypeClassNode into inferred-return signatures
> --------------------------------------------------------------------
>
> Key: GROOVY-12446
> URL: https://issues.apache.org/jira/browse/GROOVY-12446
> Project: Groovy
> Issue Type: Improvement
> Reporter: Daniel Sun
> Assignee: Daniel Sun
> Priority: Major
> Fix For: 7.0.0-alpha-1
>
>
> h2. Context
> {{UnionTypeClassNode}} is a checker-only {{ClassNode}}. It represents a flow
> type such as {{x instanceof A}} or {{x instanceof B}}. Its Javadoc says it
> must not leak outside the type checker.
> {{SignatureCodecVersion1}} encodes an inferred return type as a Base64
> {{DataOutputStream}} payload for {{@TypeChecked.TypeCheckingInfo}}. The first
> UTF string in that payload is the simple name of the stored {{ClassNode}}
> subclass.
> GROOVY-12445 locked the unknown-version rule and left union payload layout as
> separate work. The compiler has not written {{@TypeCheckingInfo}}
> inferred-return annotations since GROOVY-6401. There is no production reader
> today. The codec still has to define what that payload may contain.
> h2. Problem
> {{doEncode}} wrote the tag {{UnionTypeClassNode}}, then the arm count, then
> each arm. {{doDecode}} rebuilt a {{UnionTypeClassNode}}. That round-trips a
> checker-only node through a class-file annotation.
> A union name is synthetic and is not a binary name. A later reader that
> treated the decoded node as a loadable type would see a name
> {{Class.forName}} cannot resolve.
> h2. Contract
> Version {{1}} stays version {{1}}. Newly encoded signatures never start with
> the {{UnionTypeClassNode}} tag.
> On encode, a union is replaced with a type that has a stable binary name,
> then that type is encoded:
> * the lowest upper bound of the arms, unwrapped until a real class or
> interface remains
> * {{Object}} if there is no such type: empty arms, a
> {{LowestUpperBoundClassNode}} whose superclass is {{Object}}, or a name that
> is empty or starts with '<'
> A {{LowestUpperBoundClassNode}} supplied directly still round-trips,
> including its interfaces. The primitive encoding tail (array flag, type
> descriptor, generics) is unchanged.
> On decode, a historical payload whose first tag is {{UnionTypeClassNode}} is
> still consumed. The arms are decoded, then widened by the same rule. An arm
> count of {{0}} or less decodes as {{Object}}.
> ||Input||Encode writes||Decode returns||
> |disjoint types, e.g. {{String}} and {{List}}|{{Object}}; first tag is not
> {{UnionTypeClassNode}}|{{Object}}|
> |{{RuntimeException}} and {{Exception}}|{{Exception}}|{{Exception}}|
> |two types that share one interface|that interface|that interface|
> |historical {{UnionTypeClassNode}} tag|(read path only)|same widening|
> |direct {{LowestUpperBoundClassNode}}|LUB tag, as today|same LUB node|
> Callers of {{SignatureCodecVersion1.decode}} that expected a union node now
> receive the shared supertype. Method descriptors are unchanged, so
> {{japicmp}} does not report this.
> h2. Touch points
> * {{org.codehaus.groovy.transform.stc.SignatureCodecVersion1}} — encode and
> historical decode
> *
> {{src/test/groovy/org/codehaus/groovy/transform/stc/SignatureCodecTest.groovy}}
> — stable-bound and historical-payload tests
> * {{COMPATIBILITY.md}} — behavioural-change note
> h2. Scope
> This issue covers union payload layout only. The unknown-version rule is
> GROOVY-12445. Rewiring {{addTypeCheckingInfoAnnotation}} onto
> {{startMethodInference}}, and a new compiler diagnostic, remain separate work.
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