'as boolean' coercion on null/absent property evaluates to null in assertion blocks (Groovy 5)

[sbglasius]

Describe the bug

In Spock then: or expect: blocks, using the as boolean operator on a null value or missing map entry—even when explicitly parenthesized—fails to coerce the value to false.

In standard Groovy 5, (null as boolean) == false evaluates to true. However, inside a Spock assertion block in spock-2.4-groovy-5.0, the AST rewriter bypasses the boolean coercion step, leaving the expression as null == false and causing the condition to fail.

To Reproduce

Run the following Specification with spock-core:2.4-groovy-5.0 and groovy:5.0.x:

import spock.lang.Specification

class AsBooleanGroovy5BugSpec extends Specification {

    def "as boolean cast should coerce null map entry to false in assertion block"() {
        given:
        def result = [error: true]

        expect:
        (result.success as boolean) == false
    }
}

Expected behavior

(result.success as boolean) should evaluate to false via Groovy Truth coercion, making false == false pass.

Actual behavior

The test fails with a ConditionNotSatisfiedError. Spock evaluates the left operand as null instead of false:

Condition not satisfied:

(result.success as boolean) == false
 |      |                   |
 |      null                false
 [error:true]

``

Java version

• Spock Version: 2.4-groovy-5.0
• Groovy Version: 5.0.x
• JDK Version: 17+

Buildtool version

------------------------------------------------------------
Gradle 9.6.0
------------------------------------------------------------

Build time:    2026-06-18 23:19:03 UTC
Revision:      3f750f03d77e42327c5f9fcb9992110088330a32

Kotlin:        2.3.21
Groovy:        4.0.32
Ant:           Apache Ant(TM) version 1.10.17 compiled on April 6 2026
Launcher JVM:  25.0.4 (BellSoft 25.0.4+9-LTS)
Daemon JVM:    /home/x/.sdkman/candidates/java/25.0.4-librca (no Daemon JVM specified, using current Java home)
OS:            Linux 6.17.0-1032-oem amd64

What operating system are you using

Linux

Dependencies

org.spockframework:spock-core:2.4-groovy-5.0
+--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT
|    \--- org.apache.grails:grails-bom:8.0.0-SNAPSHOT
|         +--- testCompileClasspath (requested org.apache.grails:grails-bom:8.0.0-M5)
|         +--- edu.berkeley.calnet.grails.plugins:registry-settings:3.0.0-SNAPSHOT
|         |    \--- testCompileClasspath
|         +--- edu.berkeley.calnet.grails.plugins:calnet-ui:3.0.0-SNAPSHOT (requested org.apache.grails:grails-bom:8.0.0-M5)
|         |    \--- testCompileClasspath
|         +--- edu.berkeley.calnet.grails.plugins:ucb-spring-security-cas-ldap:5.0.0-SNAPSHOT
|         |    \--- testCompileClasspath
|         +--- edu.berkeley.calnet.grails.plugins:registry-rest-client:3.0.0-SNAPSHOT (requested org.apache.grails:grails-bom:8.0.0-M5)
|         |    \--- testCompileClasspath
|         \--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
+--- org.apache.grails:grails-bom:8.0.0-SNAPSHOT (*)
+--- org.apache.grails:grails-testing-support-views-gson:8.0.0-SNAPSHOT
|    +--- testCompileClasspath (requested org.apache.grails:grails-testing-support-views-gson)
|    \--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
+--- org.apache.grails.testing:grails-test-core:8.0.0-SNAPSHOT
|    +--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
|    \--- org.apache.grails.testing:grails-testing-support-core:8.0.0-SNAPSHOT
|         +--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
|         \--- org.apache.grails:grails-testing-support-web:8.0.0-SNAPSHOT
|              +--- testCompileClasspath (requested org.apache.grails:grails-testing-support-web)
|              \--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
\--- org.spockframework:spock-bom:2.4-groovy-5.0
     +--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
     +--- org.apache.grails:grails-bom:8.0.0-SNAPSHOT (*)
     \--- org.spockframework:spock-core:2.4-groovy-5.0 (*)

org.spockframework:spock-core -> 2.4-groovy-5.0
\--- testCompileClasspath

Additional context

Work-around

Because as boolean is stripped/ignored by the condition rewriter under Groovy 5, use explicit null checking or defaulting instead:

• Elvis Operator: (result.success ?: false) == false
• Map Defaulting: result.get('success', false) == false
• Groovy Truth Assertion: !result.success

[Vampire]

Seems to be working fine: https://groovyconsole.dev/?g=groovy_5_0&codez=eNpVjz1uAkEMhfs5xRMVNNulQdoCmhwgZZRi8Ho3o5jxyp5BoIi7Z2ARKK-z9H4-p-OsVuCz0k8nMU_dx8yUxkSxJM0hkER37HyvKhzzu6meLm_7Ot184HPhPDj-hfAbApoGHrGKjsMSBUVvS99aZQApGzFyFcExzuBc7IKiGKM4I2W0WbZ73UEa3Gq9ab14aEonztvneVsy9ioFPT7ZTG2LYpW_wtPD58ZYXpn1Eui8EnF78QW6Qd8vHHfzNVz_ABLPXyY

[Vampire]

Also tested in a Gradle 9.6.0 build with Java 17 toolchain, works like expected.

[sbglasius]

I will try and make a full-fledged example, since this happens in customers Grails app.

There could be something else wrong, but I have seen this happen.

[sbglasius]

I cannot reproduce it as a stand alone app (https://github.com/sbglasius/spock-bug-asboolean), but I can reproduce it in a Grails app (https://github.com/sbglasius/spock-bug-grailsasboolean)

I do not understand the difference?

[Vampire]

The difference is indy vs. not-indy.
If I enable indy in your grails-reproducer, the test becomes green.
But the question is, whether this is a Spock bug or a Groovy bug.
Should indy vs. non-indy really behave differently?

[Vampire]

If this is a Spock issue, we should probably extend the tests so that they run twice, once with indy and once without indy.
The tests from the PR fail with indy switched off and also 2 existing Tests in spock-specs fail with indy turned off.