Scott Murphy Heiberg created GROOVY-12741:
---------------------------------------------
Summary: groovy-contracts: a contract annotation on a trait or a
trait method with a body crashes the compiler or fails at run time
Key: GROOVY-12741
URL: https://issues.apache.org/jira/browse/GROOVY-12741
Project: Groovy
Issue Type: Bug
Components: groovy-contracts
Affects Versions: 6.0.0
Reporter: Scott Murphy Heiberg
h3. Problem
A {{@Requires}} on a trait method with a parameter crashes class generation:
{code:groovy}
import groovy.contracts.*
trait Bank {
BigDecimal balance = 0
@Requires({ amount > 0 })
void deposit(BigDecimal amount) { balance += amount }
}
class Account implements Bank {}
new Account().deposit(1); println 'ok'
{code}
{noformat}
General error during instruction selection: Index 1 out of bounds for length 1
java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1
at
org.codehaus.groovy.classgen.asm.InvocationWriter.loadArguments(InvocationWriter.java:379)
at
org.codehaus.groovy.classgen.asm.InvocationWriter.writeDirectMethodCall(InvocationWriter.java:292)
at
org.codehaus.groovy.classgen.asm.InvocationWriter.makeDirectCall(InvocationWriter.java:436)
at
org.codehaus.groovy.classgen.asm.InvocationWriter.makeCall(InvocationWriter.java:191)
at
org.codehaus.groovy.classgen.asm.InvocationWriter.writeInvokeMethod(InvocationWriter.java:622)
at
org.codehaus.groovy.classgen.AsmClassGenerator.visitMethodCallExpression(AsmClassGenerator.java:1244)
{noformat}
The same happens with {{@CompileStatic}} on the trait (in
{{StaticInvocationWriter.loadArguments}}). The other contract annotations do
not crash but do not work either:
* {{@Requires}} on a trait method without parameters, and {{@Ensures}} on any
trait method: the class compiles, then every call fails with
{{MissingPropertyException: No such property: $GCONTRACTS_ENABLED for class:
Bank$Trait$Helper}}.
* {{@Invariant}} on a trait: inherited by the implementing class like an
interface invariant, it fails at construction, while the trait's fields are
still being initialised (the condition sees {{balance}} as null).
A contract on an abstract trait method works (it applies to the implementing
class like an interface contract), and so does one on an interface method a
trait implements.
Reproduced on Groovy 6.0.0 and on master (df1fe66ed1).
h3. Cause
The contracts transform runs in SEMANTIC_ANALYSIS before the trait transform
and treats the trait as a class: it generates the condition class with the
trait method's parameters and marks the trait {{@Contracted}}. The trait
transform then moves each method with a body into the helper class as a static
method with a leading {{$self}} parameter, keeping the annotations, and copies
the class annotations to the helper. In INSTRUCTION_SELECTION the module weaves
the helper (it carries {{@Contracted}};
{{CandidateChecks.isContractsCandidate}} is not consulted), building the
{{doCall}} argument list from the helper method's parameters, one more than the
condition class accepts; without parameters the extra argument is dropped and
the woven {{$GCONTRACTS_ENABLED}} guard has no field to refer to in the helper.
h3. Fix
Supporting contracts on trait methods needs a design (where the check runs,
what {{this}} is, how a trait invariant interacts with trait field
initialisation, private and static trait methods). For now the module reports a
compile error instead of crashing:
{noformat}
[groovy-contracts] @Requires is not supported on a trait method with a body
(Bank.deposit); only an abstract trait method may carry a contract.
[groovy-contracts] @Invariant is not supported on a trait (Bank).
{noformat}
{{@ThrowsIf}} and {{@Decreases}} on a trait method with a body are reported the
same way (without the abstract-method hint, since on an abstract method they
stay informational). Their transforms run after the trait transform has moved
the method into the helper class and rewritten the body to reach trait state
through {{$self}}; the guard or measure woven there is not rewritten, so a
condition that refers to trait state fails at run time with a missing property
on the helper class, and only a condition that refers to parameters alone
happened to work (once the separate core crash in {{TraitComposer}} for
annotations with a closure member is fixed; that one is reported separately).
{noformat}
[groovy-contracts] @ThrowsIf is not supported on a trait method with a body
(Bank.withdraw).
[groovy-contracts] @Decreases is not supported on a trait method with a body
(Counting.sumUp).
{noformat}
A contract on an abstract trait method keeps working. Pull request to follow.
--
This message was sent by Atlassian Jira
(v10.3.26#10030026)
