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Generate a zero-branch root for empty tries #140

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Merged
mcculls merged 1 commit into from
Oct 19, 2026
Merged

Generate a zero-branch root for empty tries #140

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3 changes: 3 additions & 0 deletions utils/src/main/java/datadog/instrument/utils/ClassNameTrie.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1058,6 +1058,9 @@ public static boolean generateJavaTrie(
int chunkSize = 0;
StringBuilder buf = new StringBuilder();
buf.append(" \"");
if (trie.isEmpty()) {
buf.append("\\000"); // encode an empty root node with zero branches
}
for (int i = 0; i < trie.trieLength; i++) {
char c = trie.trieData[i];
if (++chunkSize > 10_000) {
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22 changes: 22 additions & 0 deletions utils/src/test/java/datadog/instrument/utils/ClassNameTrieTest.java
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Expand Up @@ -166,6 +166,28 @@ void generateJavaSource(@TempDir File classesDir) throws Exception {
assertEquals(5, trieApply.invoke(null, "com.foobar.Five"));
}

@Test
void generateEmptyJavaSource(@TempDir File classesDir) throws Exception {
Files.createFile(new File(classesDir, "empty.trie").toPath());
ClassNameTrie.JavaGenerator.main(
new String[] {classesDir.toString(), classesDir.toString(), "empty.trie"});

assertEquals(
0,
getSystemJavaCompiler()
.run(null, null, null, new File(classesDir, "EmptyTrie.java").toString()));

try (URLClassLoader cl = URLClassLoader.newInstance(new URL[] {classesDir.toURI().toURL()})) {
Class<?> trieClass = cl.loadClass("EmptyTrie");
Method apply = trieClass.getMethod("apply", String.class);
Method applyFromIndex = trieClass.getMethod("apply", String.class, int.class);
for (String key : new String[] {"", "a", "com.example.Type"}) {
assertEquals(-1, apply.invoke(null, key));
assertEquals(-1, applyFromIndex.invoke(null, "prefix/" + key, 7));
}
}
}

@Test
@SuppressWarnings("UnnecessaryUnicodeEscape")
void manual() throws IOException {
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