[JENKINS-45927] Truncate verbose CauseOfBlockage messages in queue

core/src/main/java/jenkins/model/queue/CompositeCauseOfBlockage.java

@@ -29,6 +29,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.TreeMap;
+import java.util.stream.Collectors;
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.NoExternalUse;
 
@@ -47,9 +48,20 @@ public CompositeCauseOfBlockage(List<CauseOfBlockage> delegates) {
         }
     }
 
+    private static final int MAX_REASONS_TO_DISPLAY = 5;
+
     @Override
     public String getShortDescription() {
-        return String.join("; ", uniqueReasons.keySet());
+        int totalReasons = uniqueReasons.size();
+        if (totalReasons <= MAX_REASONS_TO_DISPLAY) {
+            return String.join("; ", uniqueReasons.keySet());
+        }
+        // Truncate long lists to avoid extremely verbose tooltips (JENKINS-45927)
+        String truncatedReasons = uniqueReasons.keySet().stream()
+                .limit(MAX_REASONS_TO_DISPLAY)
+                .collect(Collectors.joining("; "));
+        int remaining = totalReasons - MAX_REASONS_TO_DISPLAY;
+        return truncatedReasons + "; ... and " + remaining + " more";
     }
 
     @Override

core/src/test/java/jenkins/model/queue/CompositeCauseOfBlockageTest.java

@@ -0,0 +1,102 @@
+/*
+ * The MIT License
+ *
+ * Copyright 2025 Steve Armstrong
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package jenkins.model.queue;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import hudson.model.queue.CauseOfBlockage;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class CompositeCauseOfBlockageTest {
+
+    @Test
+    void getShortDescriptionWithFewReasons() {
+        List<CauseOfBlockage> reasons = new ArrayList<>();
+        reasons.add(createCause("Reason 1"));
+        reasons.add(createCause("Reason 2"));
+        reasons.add(createCause("Reason 3"));
+
+        CompositeCauseOfBlockage composite = new CompositeCauseOfBlockage(reasons);
+        String description = composite.getShortDescription();
+
+        assertEquals("Reason 1; Reason 2; Reason 3", description);
+    }
+
+    @Test
+    void getShortDescriptionWithExactlyMaxReasons() {
+        List<CauseOfBlockage> reasons = new ArrayList<>();
+        for (int i = 1; i <= 5; i++) {
+            reasons.add(createCause("Reason " + i));
+        }
+
+        CompositeCauseOfBlockage composite = new CompositeCauseOfBlockage(reasons);
+        String description = composite.getShortDescription();
+
+        assertEquals("Reason 1; Reason 2; Reason 3; Reason 4; Reason 5", description);
+    }
+
+    @Test
+    void getShortDescriptionTruncatesLongList() {
+        List<CauseOfBlockage> reasons = new ArrayList<>();
+        for (int i = 1; i <= 10; i++) {
+            // Use zero-padded numbers to ensure correct alphabetical sorting in TreeMap
+            reasons.add(createCause(String.format("Reason %02d", i)));
+        }
+
+        CompositeCauseOfBlockage composite = new CompositeCauseOfBlockage(reasons);
+        String description = composite.getShortDescription();
+
+        assertTrue(description.contains("... and 5 more"));
+        assertTrue(description.startsWith("Reason 01; Reason 02; Reason 03; Reason 04; Reason 05"));
+    }
+
+    @Test
+    void getShortDescriptionWithManyReasons() {
+        List<CauseOfBlockage> reasons = new ArrayList<>();
+        for (int i = 1; i <= 100; i++) {
+            // Use zero-padded numbers to ensure correct alphabetical sorting in TreeMap
+            reasons.add(createCause(String.format("Node %03d doesn't have label", i)));
+        }
+
+        CompositeCauseOfBlockage composite = new CompositeCauseOfBlockage(reasons);
+        String description = composite.getShortDescription();
+
+        assertTrue(description.contains("... and 95 more"));
+        // Should not be extremely long
+        assertTrue(description.length() < 500);
+    }
+
+    private CauseOfBlockage createCause(String message) {
+        return new CauseOfBlockage() {
+            @Override
+            public String getShortDescription() {
+                return message;
+            }
+        };
+    }
+}