minify-maven-plugin fails on CI: A required class was missing while executing minify: org/codehaus/plexus/util/DirectoryScanner

[php-coder]

Yesterday, execution of the integration tests on GitHub Actions have started to fail:

Error:  Failed to execute goal com.samaxes.maven:minify-maven-plugin:1.7.6:minify (minify-resources) on project mystamps: Execution minify-resources of goal com.samaxes.maven:minify-maven-plugin:1.7.6:minify failed: A required class was missing while executing com.samaxes.maven:minify-maven-plugin:1.7.6:minify: org/codehaus/plexus/util/DirectoryScanner
Error:  -----------------------------------------------------
Error:  realm =    plugin>com.samaxes.maven:minify-maven-plugin:1.7.6
Error:  strategy = org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy
Error:  urls[0] = file:/home/runner/.m2/repository/com/samaxes/maven/minify-maven-plugin/1.7.6/minify-maven-plugin-1.7.6.jar
Error:  urls[1] = file:/home/runner/.m2/repository/com/yahoo/platform/yui/yuicompressor/2.4.8/yuicompressor-2.4.8.jar
Error:  urls[2] = file:/home/runner/.m2/repository/rhino/js/1.7R2/js-1.7R2.jar
Error:  urls[3] = file:/home/runner/.m2/repository/com/google/javascript/closure-compiler/v20161024/closure-compiler-v20161024.jar
Error:  urls[4] = file:/home/runner/.m2/repository/com/google/javascript/closure-compiler-externs/v20161024/closure-compiler-externs-v20161024.jar
Error:  urls[5] = file:/home/runner/.m2/repository/args4j/args4j/2.33/args4j-2.33.jar
Error:  urls[6] = file:/home/runner/.m2/repository/com/google/guava/guava/19.0/guava-19.0.jar
Error:  urls[7] = file:/home/runner/.m2/repository/com/google/protobuf/protobuf-java/3.0.2/protobuf-java-3.0.2.jar
Error:  urls[8] = file:/home/runner/.m2/repository/com/google/code/findbugs/jsr305/3.0.1/jsr305-3.0.1.jar
Error:  urls[9] = file:/home/runner/.m2/repository/com/google/jsinterop/jsinterop-annotations/1.0.0/jsinterop-annotations-1.0.0.jar
Error:  urls[10] = file:/home/runner/.m2/repository/com/google/code/gson/gson/2.8.0/gson-2.8.0.jar
Error:  Number of foreign imports: 1
Error:  import: Entry[import  from realm ClassRealm[maven.api, parent: null]]
Error:  
Error:  -----------------------------------------------------: org.codehaus.plexus.util.DirectoryScanner

Log: https://github.com/php-coder/mystamps/actions/runs/12975771490/job/36187232332

But tests worked 10 days ago: https://github.com/php-coder/mystamps/actions/runs/12830200842/job/35777833839

Also, they work on my machine (macos).

[php-coder]

Here what have changed:

 Runner Image
   Image: ubuntu-20.04
-  Version: 20250105.1.0
-  Included Software: https://github.com/actions/runner-images/blob/ubuntu20/20250105.1/images/ubuntu/Ubuntu2004-Readme.md
-  Image Release: https://github.com/actions/runner-images/releases/tag/ubuntu20%2F20250105.1
+  Version: 20250120.2.0
+  Included Software: https://github.com/actions/runner-images/blob/ubuntu20/20250120.2/images/ubuntu/Ubuntu2004-Readme.md
+  Image Release: https://github.com/actions/runner-images/releases/tag/ubuntu20%2F20250120.2
 Runner Image Provisioner
   2.0.414.1

[php-coder]

It caused by Maven update (3.8.8 => 3.9.9) (see actions/runner-images#11093). Here is also an explanation why this update triggered an error: https://stackoverflow.com/questions/75652635/a-required-class-was-missing-while-executing-maven-plugin-with-github-action

[php-coder]

In order to fix the build, we can:

1. update Maven to the same version (Update Maven to 3.9.10 #1542), reproduce the issue locally and apply a workaround
2. just apply a workaround and check whether it works on CI
3. consider replacing the plugin by one of it's alternatives/forks
4. pin Maven version, by using mvnw on CI (Use mvnw in build scripts #1064)

The last approach didn't really solve the issue but give us more time. Also it will make our builds more stable in future.

[php-coder]

See also: samaxes/minify-maven-plugin#176