[MPMD-399] Incorrect warning: The project X does not seem to be compiled. PMD results might be inaccurate.

Update also FAQ about aggregate and type resolution-

Co-authored-by: Andreas Dangel <adangel@apache.org>

This closes #154

Author: michael-o

src/main/java/org/apache/maven/plugins/pmd/AbstractPmdReport.java

@@ -140,7 +140,7 @@ public abstract class AbstractPmdReport extends AbstractMavenReport {
     private File[] excludeRoots;
 
     /**
-     * Run PMD on the tests.
+     * Run PMD on the tests as well.
      *
      * @since 2.2
      */
@@ -152,7 +152,8 @@ public abstract class AbstractPmdReport extends AbstractMavenReport {
      *
      * @since 2.2
      * @deprecated since 3.15.0 Use the goals <code>pmd:aggregate-pmd</code> and <code>pmd:aggregate-cpd</code>
-     * instead.
+     * instead. See <a href="https://maven.apache.org/plugins/maven-pmd-plugin/faq.html#typeresolution_aggregate">FAQ:
+     * Why do I get sometimes false positive and/or false negative violations?</a> for an explanation.
      */
     @Parameter(property = "aggregate", defaultValue = "false")
     @Deprecated

src/main/java/org/apache/maven/plugins/pmd/PmdReport.java

@@ -513,23 +513,11 @@ private String determineAuxClasspath() throws MavenReportException {
                                 resolvedArtifact.getArtifact().getFile().toString());
                     }
 
-                    List<String> projectClasspath = includeTests
-                            ? localProject.getTestClasspathElements()
-                            : localProject.getCompileClasspathElements();
-
-                    // Add the project's target folder first
-                    classpath.addAll(projectClasspath);
-                    if (!localProject.isExecutionRoot()) {
-                        for (String path : projectClasspath) {
-                            File pathFile = new File(path);
-                            String[] children = pathFile.list();
-
-                            if (!pathFile.exists() || (children != null && children.length == 0)) {
-                                getLog().warn("The project " + localProject.getArtifactId()
-                                        + " does not seem to be compiled. PMD results might be inaccurate.");
-                            }
-                        }
-                    }
+                    // Add the project's classes first
+                    classpath.addAll(
+                            includeTests
+                                    ? localProject.getTestClasspathElements()
+                                    : localProject.getCompileClasspathElements());
                 }
 
                 // Add the dependencies as last entries

src/site/fml/faq.fml

@@ -101,25 +101,24 @@ under the License.
     </faq>
     <faq id="typeresolution aggregate">
       <question>
-        What does the warning "The project xyz does not seem to be compiled. PMD results might be inaccurate." mean?
+        Why do I get sometimes false positive and/or false negative violations?
       </question>
       <answer>
         <p>
           In order to improve PMD's results, type resolution should be used. It is enabled by default
           (property <a href="pmd-mojo.html#typeResolution">typeResolution</a>) and helps to avoid false positive
-          findings by matching the exact types of method parameters or variables.
+          or false negative findings by matching the exact types of method parameters or variables.
         </p>
         <p>
-          However, this requires that the project is built first, so that not only the project's dependencies
+          However, this requires that the project is built first so that not only the project's dependencies
           can be used for type resolution, but also the project's classes as well.
         </p>
         <p>
           When using the property <a href="pmd-mojo.html#aggregate">aggregate</a>, this is problematic: With
           aggregate=true, PMD is executed at the root of a multi-module project <em>before the individual
           modules are built</em>. Then the types of the individual projects are not available, which might lead to
-          false positive findings e.g. for the rule "UnusedPrivateMethod".
-          If this might be the case, then the warning "The project xyz does not seem
-          to be compiled. PMD results might be inaccurate" is issued.
+          false positive findings e.g. for the rule "UnusedPrivateMethod". That's why this property has
+          been deprecated.
         </p>
         <p>
           In order to use type resolution and aggregate together, maven needs to be execute in two passes:
@@ -135,4 +134,4 @@ under the License.
       </answer>
     </faq>
   </part>
-</faqs>
+</faqs>