James Fredley created GROOVY-12063:
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Summary: Anonymous inner class extending Map: enclosing-class
field references in the instance initializer compile to dynamic getProperty on
'this' and silently resolve to null - regression in 5.0.x
Key: GROOVY-12063
URL: https://issues.apache.org/jira/browse/GROOVY-12063
Project: Groovy
Issue Type: Bug
Components: class generator, Compiler
Affects Versions: 5.0.6, 5.0.5, 6.0.0-alpha-1, 5.0.7
Environment: JDK 21; reproduces with and without @CompileStatic, and
in both indy and classic codegen
Reporter: James Fredley
h2. Summary
In an anonymous inner class that extends {{java.util.Map}} (e.g. {{HashMap}}),
bareword references to the *enclosing class's fields* inside the AIC
instance-initializer block are no longer resolved to those fields. As of Groovy
5.0.x they compile to dynamic property reads on {{this}}
({{this.getProperty("FIELD")}}); because {{this}} is a {{Map}}, the MOP turns
that into a key lookup {{this.get("FIELD")}} on the still-empty map, so the
reference silently evaluates to {{null}}. This is a regression: 3.0.x and 4.0.x
resolve it correctly. The {{Map}} base class makes it fail *silently* - a
non-Map AIC would instead throw {{MissingPropertyException}}.
h2. Steps to reproduce
Single self-contained script:
{code:groovy}
class Holder {
static final String VALUE = 'expected'
static final Map<String, String> MAP = new HashMap<String, String>() {
{
put('literalKey', VALUE) // 'VALUE' is the enclosing class's
static field
}
}
}
println "Groovy ${GroovySystem.version} -> ${Holder.MAP}"
assert Holder.MAP.get('literalKey') == 'expected'
{code}
h2. Actual result (Groovy 5.0.5 / 5.0.6 / 5.0.7-SNAPSHOT / 6.0.0-alpha-1)
{noformat}
Groovy 5.0.7-SNAPSHOT -> [literalKey:null]
Assertion failed:
assert Holder.MAP.get('literalKey') == 'expected'
| | | |
| | null false
{noformat}
h2. Expected result (as on Groovy 3.0.24 / 4.0.32)
{noformat}
Groovy 4.0.32 -> [literalKey:expected]
(assertion passes)
{noformat}
h2. Affected versions
|| Groovy || Holder.MAP || Result ||
| 3.0.24 | {{[literalKey:expected]}} | correct |
| 4.0.32 | {{[literalKey:expected]}} | correct |
| 5.0.5 | {{[literalKey:null]}} | broken |
| 5.0.6 | {{[literalKey:null]}} | broken |
| 5.0.7-SNAPSHOT | {{[literalKey:null]}} | broken |
| 6.0.0-alpha-1 | {{[literalKey:null]}} | broken |
Notes: reproduces for a plain class, a {{@CompileStatic}} class, and a
{{@CompileStatic}} interface - so it is not specific to {{@CompileStatic}}. The
literal key survives (an {{LDC}} constant); only the bareword field reference
degrades to {{null}}. If both key and value are field references, the map
collapses to {{[null:null]}}.
h2. Bytecode evidence
{{Holder$1.<init>}} (the anonymous HashMap initializer), {{javap -c}}, Groovy
5.0.7-SNAPSHOT:
{noformat}
13: aload_0 // receiver = this (the HashMap)
14: ldc "literalKey" // key: literal ->
correct
16: aload_0
17: invokedynamic #0:getProperty:(LHolder$1;) // value:
this.getProperty("VALUE") -> BUG
22: invokedynamic #1:invoke:(...) // this.put(key, value), dynamic
28: return
{noformat}
The BootstrapMethods table confirms the call-site name is the source identifier
({{IndyInterface.bootstrap(..., "VALUE", 12)}}). The enclosing {{<clinit>}} is
correct - {{VALUE}} is assigned before {{new Holder$1()}} runs - so the defect
is purely the AIC initializer compiling the bareword as a dynamic read on
{{this}} instead of {{GETSTATIC}}. At runtime {{MetaClassImpl.getProperty}}
special-cases {{Map}} receivers as {{((Map) this).get(name)}}; the map is empty
during its own initializer, so the read returns {{null}}. The JDK is not
involved - the emitted bytecode is wrong.
h2. Root cause
* The bareword {{VALUE}} inside the AIC initializer is resolved as a dynamic
property read on {{this}} ({{invokedynamic getProperty}}) rather than a
{{GETSTATIC}} of the enclosing class's field.
* Because the AIC extends {{Map}}, Groovy's MOP turns that property read into a
map-key lookup {{this.get("VALUE")}}; the map is empty while its own
initializer runs, so it returns {{null}} instead of failing fast.
* Groovy 3.0.x / 4.0.x resolve the bareword to the enclosing-class field
correctly.
h2. Real-world impact
Apache Grails {{grails.gorm.validation.ConstrainedProperty}} builds its
default-messages map with exactly this idiom ({{new HashMap<String,String>() {
{ put(CODE, MESSAGE) } }}}); under Groovy 5 the map ends up effectively empty
({{[null:null]}}), so default validation messages fail to resolve
(apache/grails-core PR #15557).
h2. Workarounds
* Avoid the anonymous-Map-with-instance-initializer idiom; use {{Map.of(...)}},
a literal map, or a statically compiled static block.
* Or fully qualify the references: {{put('literalKey', Holder.VALUE)}}.
h2. Suggested fix
Resolve bareword identifiers inside an AIC instance-initializer against the
lexical scope (enclosing-class members) before falling back to a dynamic
property read on {{this}}, regardless of whether {{this}} is a {{Map}} - i.e.
restore 4.0.x name-resolution for AIC initializer blocks.
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