Update MultipleNullnessAnnotations to print the qualified names of the conflicting nullness annotations

PiperOrigin-RevId: 786842535

Author: cushon

check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessAnnotations.java

@@ -74,15 +74,20 @@ public static Optional<Nullness> fromAnnotationMirrors(
 
   public static boolean annotationsAreAmbiguous(
       Collection<? extends AnnotationMirror> annotations) {
-    return annotations.stream()
-            .map(a -> simpleName(a).toString())
-            .filter(ANNOTATION_RELEVANT_TO_NULLNESS)
-            .map(NULLABLE_ANNOTATION::test)
+    return annotationsRelevantToNullness(annotations).stream()
+            .map(a -> NULLABLE_ANNOTATION.test(simpleName(a).toString()))
             .distinct()
             .count()
         == 2;
   }
 
+  public static ImmutableList<AnnotationMirror> annotationsRelevantToNullness(
+      Collection<? extends AnnotationMirror> annotations) {
+    return annotations.stream()
+        .filter(a -> ANNOTATION_RELEVANT_TO_NULLNESS.test(simpleName(a).toString()))
+        .collect(toImmutableList());
+  }
+
   public static ImmutableList<AnnotationTree> annotationsRelevantToNullness(
       List<? extends AnnotationTree> annotations) {
     return annotations.stream()

core/src/main/java/com/google/errorprone/bugpatterns/nullness/MultipleNullnessAnnotations.java

@@ -17,9 +17,12 @@
 package com.google.errorprone.bugpatterns.nullness;
 
 import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.dataflow.nullnesspropagation.NullnessAnnotations.annotationsAreAmbiguous;
+import static com.google.errorprone.dataflow.nullnesspropagation.NullnessAnnotations.annotationsRelevantToNullness;
 import static com.google.errorprone.matchers.Description.NO_MATCH;
 import static com.google.errorprone.util.ASTHelpers.getSymbol;
 import static com.google.errorprone.util.ASTHelpers.getType;
+import static java.util.stream.Collectors.joining;
 
 import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.BugPattern;
@@ -28,7 +31,6 @@
 import com.google.errorprone.bugpatterns.BugChecker.AnnotatedTypeTreeMatcher;
 import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
 import com.google.errorprone.bugpatterns.BugChecker.VariableTreeMatcher;
-import com.google.errorprone.dataflow.nullnesspropagation.NullnessAnnotations;
 import com.google.errorprone.matchers.Description;
 import com.sun.source.tree.AnnotatedTypeTree;
 import com.sun.source.tree.MethodTree;
@@ -75,9 +77,14 @@ private Description match(Tree tree, Symbol symbol, Type type) {
   }
 
   private Description match(Tree tree, Collection<? extends AnnotationMirror> annotations) {
-    if (NullnessAnnotations.annotationsAreAmbiguous(annotations)) {
-      return describeMatch(tree);
+    if (!annotationsAreAmbiguous(annotations)) {
+      return NO_MATCH;
     }
-    return NO_MATCH;
+    return buildDescription(tree)
+        .setMessage(
+            annotationsRelevantToNullness(annotations).stream()
+                .map(a -> a.getAnnotationType().asElement().toString())
+                .collect(joining(", ", "This type use has conflicting nullness annotations: ", "")))
+        .build();
   }
 }