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fix(java): escape null/true/false discriminator values in generated identifiers #17430

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fix(java): escape null/true/false discriminator values in generated identifiers #17430

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fix(java): escape null/true/false discriminator values in generated i…
ChoMinGi Aug 15, 2026
6cb52ae
chore(java): add changelog entry and quote CsvSource literals
ChoMinGi Aug 15, 2026
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3 changes: 3 additions & 0 deletions generators/java/generator-utils/src/main/java/com/fern/java/utils/CasingConfiguration.java
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,7 @@ public final class CasingConfiguration {
"else",
"enum",
"extends",
"false",

@devin-ai-integration devin-ai-integration Bot Aug 15, 2026

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🟡 Java generator fix ships without a changelog/version entry

The Java generator bug fix changes shared casing logic (JAVA_RESERVED_KEYWORDS at generators/java/generator-utils/src/main/java/com/fern/java/utils/CasingConfiguration.java:62) without adding a corresponding release entry, so users get no released version containing the fix and no record of it.
Impact: The fix is not published or documented for users of the Java generator.

Repository rule requiring a versions.yml entry for generator changes

REVIEW.md states: "Generator changes (bug fixes or features) should include a versions.yml entry in the appropriate generator directory" and "The type field in changelog entries should match the PR type: fix for bug fixes". This PR only touches CasingConfiguration.java and its test; no entry was added to generators/java/sdk/versions.yml (or the other Java generator directories that consume generator-utils).

Prompt for agents 
REVIEW.md requires generator changes to include a versions.yml changelog entry in the appropriate generator directory with type matching the PR type. This PR fixes a Java generator crash caused by unescaped null/true/false discriminator values in CasingConfiguration, but no entry was added. Add a new version entry with a `fix` changelog summary to generators/java/sdk/versions.yml (and any other Java generator versions.yml files that ship generator-utils, e.g. spring/model, if applicable), following the formatting of existing entries.
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@ChoMinGi ChoMinGi Aug 15, 2026 •
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Fixed.
added a changelog entry at generators/java/sdk/changes/unreleased/fix-null-true-false-discriminator.yml per the REVIEW.md convention.

"final",
"finally",
"float",
Expand All @@ -73,6 +74,7 @@ public final class CasingConfiguration {
"long",
"native",
"new",
"null",
"package",
"private",
"protected",
Expand All @@ -88,6 +90,7 @@ public final class CasingConfiguration {
"throw",
"throws",
"transient",
"true",

@nitpickybot nitpickybot Bot Aug 15, 2026

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🔵 suggestion

Two independent reserved-word lists (KeyWordUtils and this one) drifting apart is exactly how this bug happened. Consider having one derive from the other, or at minimum add a test asserting JAVA_RESERVED_KEYWORDS is a superset of KeyWordUtils' set so the next divergence fails in CI instead of in a user's generate run.

@ChoMinGi ChoMinGi Aug 15, 2026 •
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Tried that — turns out _ doesn't work the same way.

KeyWordUtils does treat _ as reserved, but in CasingConfiguration it never gets that far. splitWords()'s regex doesn't match underscores at all, so computeName("_") collapses to an empty string before sanitizeName ever runs — I checked, and camelSafe comes back as "", not "_". So adding _ to JAVA_RESERVED_KEYWORDS would just be a no-op.

That looks like a bug in the word-splitting logic rather than the list drifting, so I'd rather leave it out of this PR. Happy to file it separately if that's useful.

"try",
"void",
"volatile",
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20 changes: 20 additions & 0 deletions ...ators/java/generator-utils/src/test/java/com/fern/java/utils/CasingConfigurationTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -957,4 +957,24 @@ private static CasingConfiguration buildConfig(boolean smartCasing, String langu
root.set("casingsConfig", casingsConfig);
return CasingConfiguration.fromIrJson(root);
}

// ===== keyword sanitization: Java literals =====

@Nested
class JavaLiteralKeywordTests {

@ParameterizedTest
@CsvSource({"'null',null_", "'true',true_", "'false',false_"})
void computeName_escapesJavaLiterals(String input, String expectedSafeName) {
CasingConfiguration config = buildConfig(true, "java", null);
CasingConfiguration.NameParts parts = config.computeName(input);
assertThat(parts.camelSafe).isEqualTo(expectedSafeName);
}

@Test
void computeName_ordinaryKeywordStillEscaped() {
CasingConfiguration config = buildConfig(true, "java", null);
assertThat(config.computeName("default").camelSafe).isEqualTo("default_");
}
}
}
11 changes: 11 additions & 0 deletions generators/java/sdk/changes/unreleased/fix-null-true-false-discriminator.yml
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@@ -0,0 +1,11 @@
# yaml-language-server: $schema=../../../../../fern-changes-yml.schema.json

- summary: |
Escape the Java literals `null`, `true`, and `false` when they're used as a
discriminated union's discriminator value. Previously the generated Java
identifier was left unescaped (e.g. a static factory method literally named
`null`), which JavaPoet rejected with `not a valid name: null`, aborting
generation. The identifier is now escaped to `null_`/`true_`/`false_`
(matching the existing convention for other reserved words like `static`),
while the serialized discriminator value is unchanged.
type: fix
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