[tycho-4.0.x] Improve the error message in case of a DependencyResolutionException

tycho-core/src/main/java/org/eclipse/tycho/core/maven/TychoProjectExecutionListener.java

@@ -110,7 +110,7 @@ public void beforeProjectLifecycleExecution(ProjectExecutionEvent event) throws
             try {
                 resolver.resolveProject(mavenSession, mavenProject);
             } catch (DependencyResolutionException e) {
-                ResolverException resolverException = findResolverException(e);
+                ResolverException resolverException = ResolverException.findResolverException(e);
                 if (resolverException == null) {
                     throw new LifecycleExecutionException(
                             "Cannot resolve dependencies of project " + mavenProject.getId(), null, mavenProject, e);
@@ -148,21 +148,6 @@ public void beforeProjectLifecycleExecution(ProjectExecutionEvent event) throws
         }
     }
 
-    private ResolverException findResolverException(Throwable t) {
-        if (t != null) {
-            if (t instanceof ResolverException re) {
-                return re;
-            }
-            for (Throwable sup : t.getSuppressed()) {
-                if (sup instanceof ResolverException re) {
-                    return re;
-                }
-            }
-            return findResolverException(t.getCause());
-        }
-        return null;
-    }
-
     private Set<MavenProject> checkBuildState(TychoProject tychoProject, MavenProject project) throws CoreException {
         ReactorProject reactorProject = DefaultReactorProject.adapt(project);
         DependencyArtifacts artifacts = tychoProject.getDependencyArtifacts(reactorProject);

tycho-core/src/main/java/org/eclipse/tycho/p2/resolver/ResolverException.java

@@ -67,4 +67,19 @@ public Stream<Explanation> explanations() {
         return explanation.stream();
     }
 
+    public static ResolverException findResolverException(Throwable t) {
+        if (t != null) {
+            if (t instanceof ResolverException re) {
+                return re;
+            }
+            for (Throwable sup : t.getSuppressed()) {
+                if (sup instanceof ResolverException re) {
+                    return re;
+                }
+            }
+            return findResolverException(t.getCause());
+        }
+        return null;
+    }
+
 }

tycho-core/src/main/java/org/eclipse/tycho/p2tools/RepositoryReferenceTool.java

@@ -17,6 +17,7 @@
 import java.io.IOException;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.apache.maven.execution.MavenSession;
 import org.apache.maven.plugin.MojoExecutionException;
@@ -27,6 +28,7 @@
 import org.eclipse.equinox.p2.metadata.IInstallableUnit;
 import org.eclipse.tycho.ArtifactDescriptor;
 import org.eclipse.tycho.DependencyArtifacts;
+import org.eclipse.tycho.DependencyResolutionException;
 import org.eclipse.tycho.ReactorProject;
 import org.eclipse.tycho.TargetPlatform;
 import org.eclipse.tycho.TychoConstants;
@@ -35,6 +37,7 @@
 import org.eclipse.tycho.core.TargetPlatformConfiguration;
 import org.eclipse.tycho.core.TychoProjectManager;
 import org.eclipse.tycho.p2.repository.RepositoryBlackboardKey;
+import org.eclipse.tycho.p2.resolver.ResolverException;
 import org.eclipse.tycho.p2.tools.RepositoryReferences;
 
 /**
@@ -144,6 +147,17 @@ private void addTargetPlatformRepository(RepositoryReferences sources, MavenSess
             sources.addMetadataRepository(repositoryLocation);
         } catch (IOException e) {
             throw new MojoExecutionException("I/O exception while writing the build target platform to disk", e);
+        } catch (DependencyResolutionException e) {
+            ResolverException resolverException = ResolverException.findResolverException(e);
+            if (resolverException == null) {
+                throw new MojoFailureException("Cannot resolve dependencies of project " + project.getId(), e);
+            } else {
+                throw new MojoFailureException("Cannot resolve dependencies of project "
+                        + project.getId() + System.lineSeparator() + " with context "
+                        + resolverException.getSelectionContext() + System.lineSeparator() + resolverException
+                                .explanations().map(exp -> "  " + exp.toString()).collect(Collectors.joining("\n")),
+                        resolverException);
+            }
         }
     }