Leonard Brünings created GROOVY-12144:
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Summary: {{AstNodeToScriptAdapter}} decompiler drops or corrupts
several constructs when rendering AST back to source
Key: GROOVY-12144
URL: https://issues.apache.org/jira/browse/GROOVY-12144
Project: Groovy
Issue Type: Bug
Components: groovy-console
Reporter: Leonard Brünings
h2. Description
{{groovy.console.ui.AstNodeToScriptAdapter}} (class
{{{}AstNodeToScriptVisitor{}}}) turns a compiled AST back into Groovy source;
it backs the Groovy Console's AST browser and is usable from the command line.
Several node kinds are rendered incorrectly, producing source that does not
round-trip - it either fails to re-parse, or re-parses to a *different* program
(changed type or changed semantics).
Eight distinct rendering defects are present on {{{}master{}}}. They are
independent and each has a one-line cause in a single visitor method.
|| # ||Construct||Input||Rendered now (wrong)||Should render||
|1|Nested generic type arguments|{{Map<String, List<Integer>>}}|{{Map<String,
List>}}|{{Map<String, List<Integer>>}}|
|2|Range boundary exclusions|{{1..<5}} / {{1<..5}} / {{1<..<5}}|{{(1..5)}} (all
three)|{{(1..<5)}} / {{(1<..5)}} / {{(1<..<5)}}|
|3|Elvis operator|{{c ?: d}}|{{c ? c : d}} (evaluates {{c}} twice)|{{c ?: d}}|
|4|Attribute (direct field) access|{{obj.@f}} / {{obj*.@f}} /
{{obj?.@f}}|{{obj.f}} / {{obj*.f}} / {{obj?.f}} (silently becomes property
access)|{{obj.@f}} / {{obj*.@f}} / {{obj?.@f}}|
|5|Explicit zero-arg closure|{{{ -> foo() }}}|{{{ foo() }}} (re-parses with an
implicit {{{}it{}}})|{{{ -> foo() }}}|
|6|Safe index access|{{{{list?[0]}}}}|{{list[0]}}|{{list?[0]}}|
|7|Numeric literal type suffixes|{{42L}} / {{2.5f}} / {{3.5d}} / {{10G}}|{{42}}
/ {{2.5}} / {{3.5}} / {{10}} (re-parses as
{{{}Integer{}}}/{{{}BigDecimal{}}})|{{42L}} / {{2.5F}} / {{3.5D}} / {{10G}}|
|8|Explicit method-call type
arguments|{{Collections.<String>emptyList()}}|{{Collections.emptyList()}}|{{Collections.<String>emptyList()}}|
Defects 3, 5, 6 and 7 change the *meaning* of the recovered source, not just
its appearance.
h3. Root cause (per defect)
* *1* - {{visitGenerics}} prints {{it.name}} only and never recurses into a
concrete type argument's own generics.
* *2* - {{visitRangeExpression}} prints {{'..'}} unconditionally, ignoring
{{RangeExpression.isExclusiveLeft()}} / {{{}isExclusiveRight(){}}}.
* *3* - {{visitShortTernaryExpression}} delegates to
{{{}visitTernaryExpression{}}}, duplicating the condition.
* *4* - {{visitAttributeExpression}} delegates to
{{{}visitPropertyExpression{}}}, which always prints {{{}'.'{}}}.
* *5* - {{visitClosureExpression}} treats {{parameters == null}} (explicit
{{{}{ -> }{}}}) the same as {{parameters == Parameter.EMPTY_ARRAY}} (implicit
{{{}it{}}}); only the latter should omit the arrow.
* *6* - {{visitBinaryExpression}} detects the {{LEFT_SQUARE_BRACKET}} access
but prints a hardcoded {{{}'['{}}}, ignoring {{{}isSafe(){}}}.
* *7* - {{visitConstantExpression}} prints {{value.toString()}} with no type
suffix.
* *8* - {{visitMethodCallExpression}} ignores
{{{}MethodCallExpression.getGenericsTypes(){}}}.
h2. Steps to reproduce
{code:groovy}
import groovy.console.ui.AstNodeToScriptAdapter
import org.codehaus.groovy.control.CompilePhase
def src = 'def x = Collections.<String>emptyList(); def y = 1..<5; def z =
a?.@f'
println new AstNodeToScriptAdapter().compileToScript(src,
CompilePhase.SEMANTIC_ANALYSIS.phaseNumber)
// observe: Collections.emptyList(), (1..5), a.f -- all three wrong
{code}
h2. Suggested fix
One localized change per visitor method (all in
{{{}subprojects/groovy-console/src/main/groovy/groovy/console/ui/AstNodeToScriptAdapter.groovy{}}}),
plus one regression test per defect in {{{}AstNodeToScriptAdapterTest{}}}.
*Note for reviewers:* fix 4 makes {{AttributeExpression}} render faithfully as
{{{}.@{}}}. This changes the rendered output of AST-transform-generated code
that builds attribute nodes - e.g. {{@Log}} generates {{Level.@FINE}} for its
{{isLoggable}} guard. That output is now a faithful representation of the
actual AST node (previously mis-shown as property access {{{}Level.FINE{}}});
{{{}testLogAnnotation{}}}'s expectation is updated accordingly.
h2. Notes
* These fidelity bugs were originally found and fixed downstream in Spock's
transpiler (a fork of this class); this ticket upstreams them.
* Both projects are Apache-2.0 and the Spock file derives from this one, so
the contribution is clean.
* Depends on the test class actually running - see the companion ticket on the
JUnit 5 migration having left {{AstNodeToScriptAdapterTest}} unexecuted (commit
{{{}a1897e0811{}}}).
{panel:title=Provenance}
Assisted-by: Claude Code (Opus 4.8). Contributor is responsible for
correctness, licensing, and style.
{panel}
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