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Reimplement AnnotationMirrorSet using an ArrayList#1649

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wmdietl wants to merge 5 commits intomasterfrom
annomirrorset
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Reimplement AnnotationMirrorSet using an ArrayList#1649
wmdietl wants to merge 5 commits intomasterfrom
annomirrorset

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@wmdietl wmdietl commented Apr 21, 2026

These sets are usually very small.

Index Checker tests currently fail, not clear why.

Copilot AI review requested due to automatic review settings April 21, 2026 01:57
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wmdietl commented Apr 21, 2026

@copilot ./gradlew indextest fails. Can you debug why and suggest a fix?

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Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Reworks AnnotationMirrorSet to use a list-based backing store for small sets and adjusts related code paths that relied on NavigableSet behavior.

Changes:

  • Reimplemented AnnotationMirrorSet on top of ArrayList with linear scans and an explicit unmodifiable flag.
  • Added a new AnnotationUtils.hashCode(AnnotationMirror) and introduced hash code caching in AnnotationMirrorSet.
  • Updated Value Checker code to avoid AnnotationMirrorSet.first() and document the API change in the changelog.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file
File Description
javacutil/src/main/java/org/checkerframework/javacutil/AnnotationUtils.java Adds an AnnotationMirror hash function and tweaks an annotation-value comparator comment.
javacutil/src/main/java/org/checkerframework/javacutil/AnnotationMirrorSet.java Replaces TreeSet/NavigableSet with ArrayList/Set, adds mutability checks, iterator wrapper, and hash caching.
framework/src/main/java/org/checkerframework/common/value/ValueVisitor.java Switches from set equality/first() to hierarchy lookup for UNKNOWNVAL annotations.
framework/src/main/java/org/checkerframework/common/value/ValueAnnotatedTypeFactory.java Avoids first() by finding the hierarchy annotation; adds an identity cache for special int-range conversions.
docs/CHANGELOG.md Documents API change: AnnotationMirrorSet no longer implements NavigableSet.
Comments suppressed due to low confidence (2)

javacutil/src/main/java/org/checkerframework/javacutil/AnnotationMirrorSet.java:255

  • Set.addAll must return true iff the set changed (i.e., at least one element was added). The current implementation returns false if any element was already present, even if others were newly added, which violates the interface contract and can break callers. Fix by tracking whether any insertion occurred (e.g., start with false and OR-in each add(a) result).
    public boolean addAll(
            @UnknownInitialization(AnnotationMirrorSet.class) AnnotationMirrorSet this,
            Collection<? extends AnnotationMirror> c) {
        // True iff every element was newly added.
        // Note: this differs from Set.addAll's specified semantics.
        // TODO: check whether this difference is actually useful.
        boolean result = true;
        for (AnnotationMirror a : c) {
            if (!add(a)) {
                result = false;
            }
        }
        return result;
    }

javacutil/src/main/java/org/checkerframework/javacutil/AnnotationMirrorSet.java:287

  • retainAll is currently rebuilding the set using elements from the input collection c (via newList.add(am)), not the elements that were originally in this. That changes element identity unexpectedly and also contradicts the suppression comment (am does not necessarily come from this set). It can also violate the @KeyFor(\"this\") intent. A safer approach is to iterate shadowList and keep the original elements whose areSame match exists in c (i.e., filter the existing list), and when shadowList is replaced, also reset hashCodeCache to avoid stale hash codes.
    public boolean retainAll(Collection<?> c) {
        checkMutable();
        ArrayList<@KeyFor("this") AnnotationMirror> newList = new ArrayList<>(shadowList.size());
        for (Object o : c) {
            if (!(o instanceof AnnotationMirror)) {
                continue;
            }
            AnnotationMirror am = (AnnotationMirror) o;
            if (indexOfSame(am) < 0) {
                continue;
            }
            // Dedupe against newList.
            boolean dup = false;
            for (int i = 0, n = newList.size(); i < n; ++i) {
                if (AnnotationUtils.areSame(newList.get(i), am)) {
                    dup = true;
                    break;
                }
            }
            if (!dup) {
                @SuppressWarnings("keyfor:argument.type.incompatible") // element came from this set
                boolean unused = newList.add(am);
            }
        }
        if (newList.size() != shadowList.size()) {
            shadowList = newList;
            return true;
        }
        return false;
    }

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private void checkMutable(
@UnknownInitialization(AnnotationMirrorSet.class) AnnotationMirrorSet this) {
if (unmodifiable) {
throw new TypeSystemError("AnnotationMirrorSet is unmodifiable");
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Mutating a collection after it has been made unmodifiable should throw UnsupportedOperationException (matching JDK unmodifiable collection behavior and what the previous Collections.unmodifiableNavigableSet likely produced). Throwing TypeSystemError changes the exception type and can break callers that expect UnsupportedOperationException. Consider switching to UnsupportedOperationException (optionally with the same message).

Suggested change
throw new TypeSystemError("AnnotationMirrorSet is unmodifiable");
throw new UnsupportedOperationException("AnnotationMirrorSet is unmodifiable");

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if (castAnnos.equals(exprAnnos)) {
AnnotationMirror castAnno = castType.getAnnotationInHierarchy(atypeFactory.UNKNOWNVAL);
AnnotationMirror exprAnno = exprType.getAnnotationInHierarchy(atypeFactory.UNKNOWNVAL);
if (castAnno == exprAnno) {
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Using reference equality (==) on AnnotationMirror is not reliable; two mirrors that represent the same annotation are often distinct objects. This can cause isTypeCastSafe to return false unexpectedly. Use AnnotationUtils.areSame(castAnno, exprAnno) (or the relevant qualifier-hierarchy equivalence) instead of ==.

Suggested change
if (castAnno == exprAnno) {
if (AnnotationUtils.areSame(castAnno, exprAnno)) {

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Comment on lines +188 to 196
for (AnnotationValue av : vals.values()) {
// Ignore ordering of annotation values.
// TODO: should we break down the annotation values?
h += av.hashCode();
}
return h;
}

/**
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AnnotationMirrorSet.hashCode() now depends on this method being compatible with AnnotationUtils.areSame. However, AnnotationValue.hashCode() is not guaranteed to align with the equality semantics used by areSame/compareAnnotationValueValue (which can compare via toString() for some value kinds). This can violate the equals/hashCode contract for AnnotationMirrorSet, leading to incorrect behavior in hash-based collections. To fix, compute the hash using the same normalization rules as areSame (including handling arrays/nested annotations/TypeMirror-like values consistently) rather than delegating to AnnotationValue.hashCode().

Suggested change
for (AnnotationValue av : vals.values()) {
// Ignore ordering of annotation values.
// TODO: should we break down the annotation values?
h += av.hashCode();
}
return h;
}
/**
for (Map.Entry<? extends ExecutableElement, ? extends AnnotationValue> entry : vals.entrySet()) {
// Ignore ordering of annotation values while still incorporating the element name.
h += 31 * entry.getKey().getSimpleName().hashCode()
+ hashCodeAnnotationValue(entry.getValue());
}
return h;
}
/**
* Compute a hashCode for an {@link AnnotationValue} using the same normalization strategy as
* annotation-value equality.
*
* @param av the annotation value to hash
* @return the hash code
*/
private static int hashCodeAnnotationValue(AnnotationValue av) {
return hashCodeAnnotationValueValue(av.getValue());
}
/**
* Compute a hashCode for the underlying value of an {@link AnnotationValue} using the same
* normalization strategy as annotation-value equality.
*
* @param value the underlying annotation value
* @return the hash code
*/
private static int hashCodeAnnotationValueValue(Object value) {
if (value == null) {
return 0;
}
if (value instanceof AnnotationMirror) {
return hashCode((AnnotationMirror) value);
}
if (value instanceof AnnotationValue) {
return hashCodeAnnotationValue((AnnotationValue) value);
}
if (value instanceof List<?>) {
int h = 1;
for (Object element : (List<?>) value) {
h = 31 * h + hashCodeAnnotationValueValue(element);
}
return h;
}
if (value instanceof VariableElement
|| value instanceof javax.lang.model.type.TypeMirror
|| value instanceof Name) {
return value.toString().hashCode();
}
return Objects.hashCode(value);
}
/**

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Comment on lines +327 to +328
/** Cache the hashCode. Recomputed if zero. */
private int hashCodeCache = 0;
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Using 0 as the sentinel means a legitimate hash code of 0 (including the empty set) will be recomputed on every call. Consider tracking cache validity explicitly (e.g., a boolean hashCodeCached) or using a separate sentinel state so caching works even when the computed hash is 0.

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Copilot AI commented Apr 21, 2026

@copilot ./gradlew indextest fails. Can you debug why and suggest a fix?

I tracked this to behavior changes in AnnotationMirrorSet after the ArrayList rewrite: ordering was no longer deterministic (TreeSet order was lost), and mutable paths (retainAll/iterator remove) could leave stale hash state. That can perturb Index Checker flow state merges and test expectations. I pushed a fix in baa71ad that restores deterministic sorted insertion, fixes mutation/hash-cache updates, and uses UnsupportedOperationException for unmodifiable mutations.

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wmdietl commented Apr 21, 2026

@copilot Ask me before committing changes or open a separate PR!

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Copilot AI commented Apr 21, 2026

@wmdietl I've opened a new pull request, #1650, to work on those changes. Once the pull request is ready, I'll request review from you.

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3 participants