Add integration test for recursive project.url variable reference (GH-11074)

[gnodet]

Description

This PR adds an integration test for GH-11074 that demonstrates the behavior difference between Maven 3 and Maven 4 when handling recursive variable references in project.url.

Changes

• New Integration Test: MavenITgh11074RecursiveProjectUrlTest.java
• Test Resources: Two test scenarios with supporting files

Test Scenarios

1. Direct Recursive Reference (Local Project Build)

• Location: gh-11074-recursive-project-url/
• Test: POM with <url>${project.url}</url>
• Expected: Both Maven 3 and 4 fail with "recursive variable reference: project.url"
• Purpose: Confirms both versions correctly reject building projects with recursive references

2. Dependency Recursive Reference (Pre-built Artifact Consumption)

• Location: gh-11074-recursive-project-url-dependency/
• Test: Consumer project depending on pre-built artifact with recursive project.url
• Expected:
  • Maven 4: Shows warning about invalid POM but continues build
  • Maven 3: May silently ignore the issue (no warning)
• Purpose: Demonstrates the key difference in dependency POM validation

Key Insight

The real difference between Maven 3 and 4 is not in building projects with recursive references (both fail), but in how they handle pre-built artifacts with recursive references when consumed as dependencies:

• Maven 4: Detects and warns about recursive references in dependency POMs
• Maven 3: May silently ignore these issues in dependency POMs

Verification

Both test scenarios have been manually verified:

# Direct recursive reference - Both Maven 3 and 4 fail
$ cd its/core-it-suite/src/test/resources/gh-11074-recursive-project-url
$ mvn validate
[ERROR] recursive variable reference: project.url

# Dependency recursive reference - Maven 4 warns, Maven 3 silent
$ cd its/core-it-suite/src/test/resources/gh-11074-recursive-project-url-dependency
$ mvn validate -s settings-template.xml
# Maven 4:
[WARNING] The POM for org.apache.maven.its.gh11074:bad-dependency:jar:1.0 is invalid
    - [ERROR] recursive variable reference: project.url
[INFO] BUILD SUCCESS

# Maven 3: (no warning about recursive reference)
[INFO] BUILD SUCCESS

Real-world Impact

This test reproduces the behavior observed with dependencies like com.slack.api:slack-api-client:jar:1.45.4 which contain recursive references in their POMs. These artifacts were published to repositories despite having recursive references, and Maven 4's improved validation now detects and warns about these issues during dependency resolution.

Related

• Fixes: Recursive variable reference in project.url causes different behavior between Maven 3 and 4 #11074
• Demonstrates Maven 4's improved dependency POM validation that detects recursive references

[slawekjaranowski]

@gnodet do you need a branch as PR is closed?