Show extends/implements checks with -Ashowchecks

checker/tests/command-line/Makefile

@@ -1,14 +1,18 @@
 # All targets
-.PHONY: all clean skipped issue618
+.PHONY: all clean skipped issue618 issue1015
 
 # Tests that are currently passing
-all: issue618
+all: issue618 issue1015
 
 # Tests that are currently not passing
 skipped:
 
 issue618:
 	make -C issue618
 
+issue1015:
+	make -C issue1015
+
 clean:
 	make -C issue618 clean
+	make -C issue1015 clean

checker/tests/command-line/issue1015/Issue1015.java

@@ -0,0 +1,8 @@
+import org.checkerframework.checker.tainting.qual.Tainted;
+import org.checkerframework.checker.tainting.qual.Untainted;
+
+@Untainted class Issue1015 extends Super1015 implements Interface1015 {}
+
+@Untainted class Super1015 {}
+
+@Tainted interface Interface1015 {}

checker/tests/command-line/issue1015/Makefile

@@ -0,0 +1,9 @@
+.PHONY: all clean
+
+all:
+	$(JAVAC) -processor tainting -Ashowchecks Issue1015.java > out.txt 2>&1
+	diff -u expected.txt out.txt
+
+clean:
+	rm -f out.txt
+	rm -f *.class

checker/tests/command-line/issue1015/expected.txt

@@ -0,0 +1,12 @@
+TaintingVisitor about to test whether the class declaration annotation is a subtype of the extends clause annotation (at Issue1015.java:4:36): extends tree = IDENTIFIER Super1015
+     actual: @org.checkerframework.checker.tainting.qual.Untainted Issue1015
+   expected: @org.checkerframework.checker.tainting.qual.Untainted Super1015
+ success: class declaration annotation is subtype of extends clause annotation  (at Issue1015.java:4:36): extends tree = IDENTIFIER Super1015
+     actual: @org.checkerframework.checker.tainting.qual.Untainted Issue1015
+   expected: @org.checkerframework.checker.tainting.qual.Untainted Super1015
+TaintingVisitor about to test whether the class declaration annotation is a subtype of the implements clause annotation (at Issue1015.java:4:57): implements tree = IDENTIFIER Interface1015
+     actual: @org.checkerframework.checker.tainting.qual.Untainted Issue1015
+   expected: @org.checkerframework.checker.tainting.qual.Tainted Interface1015
+ success: class declaration annotation is subtype of implements clause annotation  (at Issue1015.java:4:57): implements tree = IDENTIFIER Interface1015
+     actual: @org.checkerframework.checker.tainting.qual.Untainted Issue1015
+   expected: @org.checkerframework.checker.tainting.qual.Tainted Interface1015

docs/CHANGELOG.md

@@ -231,7 +231,7 @@ median of four warm-daemon reps per side).
 
 **Closed issues:**
 
-eisop#433, eisop#792, eisop#863, eisop#1801.
+eisop#433, eisop#792, eisop#863, eisop#1015, eisop#1801.
 
 
 Version 3.49.5-eisop1 (April 26, 2026)

framework/src/main/java/org/checkerframework/common/basetype/BaseTypeVisitor.java

@@ -978,7 +978,11 @@ protected void checkExtendsOrImplements(
         TypeMirror boundTM = boundType.getUnderlyingType();
         for (AnnotationMirror classAnno : classBounds) {
             AnnotationMirror boundAnno = boundType.getAnnotationInHierarchy(classAnno);
-            if (!qualHierarchy.isSubtypeShallow(classAnno, classType, boundAnno, boundTM)) {
+            checkExtendsOrImplementsStartDiagnostic(
+                    boundClause, classAnno, classType, boundAnno, boundTM, isExtends);
+            boolean success =
+                    qualHierarchy.isSubtypeShallow(classAnno, classType, boundAnno, boundTM);
+            if (!success) {
                 checker.reportError(
                         boundClause,
                         (isExtends
@@ -987,6 +991,85 @@ protected void checkExtendsOrImplements(
                         classAnno,
                         boundAnno);
             }
+            checkExtendsOrImplementsEndDiagnostic(
+                    success, boundClause, classAnno, classType, boundAnno, boundTM, isExtends);
+        }
+    }
+
+    /**
+     * Prints a diagnostic about entering {@link #checkExtendsOrImplements}, if the showchecks
+     * option was set.
+     *
+     * @param boundClause an extends or implements clause
+     * @param classAnno the annotation on the class declaration
+     * @param classType the type being declared
+     * @param boundAnno the annotation on the extends or implements clause
+     * @param boundTM the type of the extends or implements clause
+     * @param isExtends true for an extends clause, false for an implements clause
+     */
+    protected final void checkExtendsOrImplementsStartDiagnostic(
+            Tree boundClause,
+            AnnotationMirror classAnno,
+            TypeMirror classType,
+            AnnotationMirror boundAnno,
+            TypeMirror boundTM,
+            boolean isExtends) {
+        if (showchecks) {
+            String clause = isExtends ? "extends" : "implements";
+            System.out.printf(
+                    "%s %s (at %s): %s tree = %s %s%n     actual: %s %s%n   expected: %s %s%n",
+                    this.getClass().getSimpleName(),
+                    "about to test whether the class declaration annotation is a subtype of the "
+                            + clause
+                            + " clause annotation",
+                    fileAndLineNumber(boundClause),
+                    clause,
+                    boundClause.getKind(),
+                    boundClause,
+                    classAnno,
+                    classType,
+                    boundAnno,
+                    boundTM);
+        }
+    }
+
+    /**
+     * Prints a diagnostic about exiting {@link #checkExtendsOrImplements}, if the showchecks option
+     * was set.
+     *
+     * @param success whether the check succeeded or failed
+     * @param boundClause an extends or implements clause
+     * @param classAnno the annotation on the class declaration
+     * @param classType the type being declared
+     * @param boundAnno the annotation on the extends or implements clause
+     * @param boundTM the type of the extends or implements clause
+     * @param isExtends true for an extends clause, false for an implements clause
+     */
+    protected final void checkExtendsOrImplementsEndDiagnostic(
+            boolean success,
+            Tree boundClause,
+            AnnotationMirror classAnno,
+            TypeMirror classType,
+            AnnotationMirror boundAnno,
+            TypeMirror boundTM,
+            boolean isExtends) {
+        if (showchecks) {
+            String clause = isExtends ? "extends" : "implements";
+            System.out.printf(
+                    " %s  (at %s): %s tree = %s %s%n     actual: %s %s%n   expected: %s %s%n",
+                    (success
+                                    ? "success: class declaration annotation is subtype of "
+                                    : "FAILURE: class declaration annotation is not subtype of ")
+                            + clause
+                            + " clause annotation",
+                    fileAndLineNumber(boundClause),
+                    clause,
+                    boundClause.getKind(),
+                    boundClause,
+                    classAnno,
+                    classType,
+                    boundAnno,
+                    boundTM);
         }
     }