fix(java): support Lombok builders on compact record constructors (#950)

@Builder on a compact record constructor (record R(...) { @Builder R {} }) failed in the
editor: ECJ has not filled in a compact constructor's implicit parameters when Lombok
runs, so the builder got no fields and builder() was undefined. A patch to Lombok's
Eclipse HandleBuilder takes the parameters from the record components in that case.

The bundled agent is now lombok-1.18.48-openidea.3, built from v1.18.48 with #4059,
#4089 and java/lombok/patches/builder-compact-constructor.patch through the documented
Ant build; only HandleBuilder differs from openidea.2. The new agent path gives JDT LS a
fresh workspace. java/lombok/tests/verify.py compiles and runs the regression cases with
javac and with ECJ plus the agent.

Co-authored-by: egasa21 <44431625+egasa21@users.noreply.github.com>

java/lombok/README.md

@@ -1,6 +1,6 @@
 # Lombok agent for JDT LS
 
-`lombok-1.18.48-openidea.2.jar` is the app-provided Java agent for JDT LS. It includes:
+`lombok-1.18.48-openidea.3.jar` is the app-provided Java agent for JDT LS. It includes:
 
 - [projectlombok/lombok#4059](https://github.com/projectlombok/lombok/pull/4059), which restores
   `lombok.config` lookup after Equinox removed `getModuleClassLoader(boolean)`.
@@ -10,6 +10,11 @@
   that call in the `@SneakyThrows` try block (ECJ then fails with "Internal Error compiling …
   BlockScope cannot be cast to MethodScope" and the whole workspace build fails) and put `@NonNull`
   checks before it; constructors Lombok generates lacked the statement.
+- [`patches/builder-compact-constructor.patch`](patches/builder-compact-constructor.patch), not yet
+  proposed upstream. `@Builder` on a compact record constructor (`record R(...) { @Builder R {} }`)
+  failed under ECJ ("The method builder() is undefined", missing builder setters), because ECJ has
+  not filled in a compact constructor's implicit parameters when Lombok runs. The builder now takes
+  its parameters from the record components in that case; javac was unaffected.
 
 The jar is embedded by `ide-tools`, so every platform receives the same bytes without a download.
 Both Java server startup and launch diagnostics obtain it through `managed_bundle`. Tool detection
@@ -19,7 +24,7 @@ The filename includes the patch version because JDT LS workspace keys include th
 changing agents must rebuild classes produced by the old agent. Old jars remain for running windows.
 
 Replace this temporary bundle with an official Maven Central release once that release includes
-#4059 and #4089. Restore the registry's Maven Central install method and remove the embedded jar. Keep the
+#4059, #4089 and the compact-constructor builder fix. Restore the registry's Maven Central install method and remove the embedded jar. Keep the
 workspace migration test when changing its path.
 
 ## Provenance and build
@@ -33,10 +38,12 @@ workspace migration test when changing its path.
   - PR #4089 (`Rawi01/lombok` `eclipse-constructor-call-statement`):
     - `7832faa49b35c839088866daf865384c82cd555f`
     - `3f3a80b857a969839ab1baba12767aec4965ac32`
-- Upstream version: `1.18.48`; `openidea.2` identifies this distribution of the patched agent
-  (`openidea.1` had #4059 only).
+- Then `git apply` [`patches/builder-compact-constructor.patch`](patches/builder-compact-constructor.patch)
+  (changes `src/core/lombok/eclipse/handlers/HandleBuilder.java` only).
+- Upstream version: `1.18.48`; `openidea.3` identifies this distribution of the patched agent
+  (`openidea.1` had #4059 only; `openidea.2` added #4089).
   Upstream's own `java -jar ... --version` still reports `1.18.48`.
-- SHA-256: `2978d8b2d55dac1bb4936ba44562bc4549931d4e71a7ebfeaebccd60bcdf7379`
+- SHA-256: `26069a8138680f5e1100c83cd064d6aa7314385a1afcef74269cdcc41beb0442`
 - License: [MIT, including bundled component notices](LICENSE), also retained inside the jar.
 - Build environment: macOS arm64, Temurin 25.0.5, Apache Ant 1.10.15, upstream Ivy setup
   (`openidea.1` was built with OpenJDK 23.0.1).
@@ -51,8 +58,9 @@ git fetch https://github.com/chagong/lombok.git fix-equinox-bundle-wiring
 git fetch https://github.com/Rawi01/lombok.git eclipse-constructor-call-statement
 git cherry-pick 2d535482a913de46c27d06c5b0b294918ede3f9c 3098f4dd78b5349c2f382e7310e64db810dd380b
 git cherry-pick 7832faa49b35c839088866daf865384c82cd555f 3f3a80b857a969839ab1baba12767aec4965ac32
+git apply /path/to/openidea/java/lombok/patches/builder-compact-constructor.patch
 ant dist
-cp dist/lombok.jar /path/to/openidea/java/lombok/lombok-1.18.48-openidea.2.jar
+cp dist/lombok.jar /path/to/openidea/java/lombok/lombok-1.18.48-openidea.3.jar
 ```
 
 The changelog context conflicts because the first commit adds a release-note line under the
@@ -62,13 +70,15 @@ skipped). The #4089 commits apply cleanly. The final source diff from v1.18.48 c
 `src/eclipseAgent/lombok/launch/PatchFixesHider.java`, `test/core/src/lombok/TestEclipse.java`,
 `test/core/src/lombok/launch/PatchFixesHiderTest.java` (#4059) and the Eclipse handlers
 `EclipseHandlerUtil`, `HandleConstructor`, `HandleFieldNameConstants`, `HandleNonNull`,
-`HandleSneakyThrows`, `HandleStandardException`, `HandleSuperBuilder`, `HandleUtilityClass` (#4089);
-no other Java source changes were made.
-In the build checkout, the two remote resolvers in
-`buildScripts/ivysettings.xml` were reordered to try Maven Central before Eclipse staging; the
-local resolver and all dependency coordinates were retained. The JVM was configured to use the
-local HTTP/HTTPS proxy for downloads. Ant's timestamps mean a rebuild need not be byte-identical;
-`SHA256SUMS` records the checked-in artifact and is verified by the Rust regression tests.
+`HandleSneakyThrows`, `HandleStandardException`, `HandleSuperBuilder`, `HandleUtilityClass` (#4089)
+and `HandleBuilder` (the compact-constructor patch); no other Java source changes were made.
+`openidea.3` was built with the unmodified upstream build scripts. (`openidea.2`'s build checkout
+reordered the two remote resolvers in `buildScripts/ivysettings.xml` to try Maven Central before
+Eclipse staging and used a local HTTP/HTTPS proxy for downloads.) Compared with `openidea.2`, the
+only changed class is `HandleBuilder`; other differences are build timestamps in the generated
+`META-INF/services` files and the nested `mavenEcjBootstrapAgent.jar`. Ant's timestamps mean a
+rebuild need not be byte-identical; `SHA256SUMS` records the checked-in artifact and is verified by
+the Rust regression tests.
 
 ## Validation
 
@@ -98,6 +108,17 @@ On macOS arm64 with JDT LS 1.63.0 / Equinox 3.25.0, server OpenJDK 25 and projec
   Failed with three internal errors and wrote no classes; `openidea.2` Succeeded with all classes.
 - `java/java-usages/tests/verify.py` and `read-write.py` passed with `openidea.2`.
 
+`openidea.3` (compact-constructor builders) on macOS arm64, JDT LS ECJ
+`compiler.batch_3.46.200.v20261008-1115`, Temurin 25:
+
+- [`tests/verify.py`](tests/verify.py) compiles and runs
+  [`tests/BuilderCompactConstructor.java`](tests/BuilderCompactConstructor.java) with javac and with
+  ECJ plus the agent: builders on compact constructors (with validation, `toBuilder`, `setterPrefix`,
+  generics, `@Singular`, `@NonNull`, empty records), a long-form canonical constructor, a
+  non-canonical record constructor, type-level record builders, and the #4089 constructor cases.
+  Both passed with `openidea.3`; with `openidea.2`, ECJ failed on every compact-constructor builder.
+- `java/java-usages/tests/verify.py` and `read-write.py` passed with `openidea.3`.
+
 Windows and Linux runtime validation has not been performed. Rust tests cover source selection
 for both supported architectures on all three OS variants, offline provisioning, corruption
 repair, concurrent windows, explicit user overrides, and JDT LS workspace migration.

java/lombok/SHA256SUMS

@@ -1 +1 @@
-2978d8b2d55dac1bb4936ba44562bc4549931d4e71a7ebfeaebccd60bcdf7379  lombok-1.18.48-openidea.2.jar
+26069a8138680f5e1100c83cd064d6aa7314385a1afcef74269cdcc41beb0442  lombok-1.18.48-openidea.3.jar

java/lombok/patches/builder-compact-constructor.patch

@@ -0,0 +1,21 @@
+diff --git a/src/core/lombok/eclipse/handlers/HandleBuilder.java b/src/core/lombok/eclipse/handlers/HandleBuilder.java
+index 64a3fa9..6ebaaaf 100755
+--- a/src/core/lombok/eclipse/handlers/HandleBuilder.java
++++ b/src/core/lombok/eclipse/handlers/HandleBuilder.java
+@@ -493,10 +493,13 @@ public class HandleBuilder extends EclipseAnnotationHandler<Builder> {
+ 		if (!checkBuilderClassNameAnnotationConflict("Builder", "lombok.Builder", job.builderClassName, ast, annotationNode)) return;
+ 		
+ 		if (fillParametersFrom != null) {
+-			for (EclipseNode param : fillParametersFrom.down()) {
+-				if (param.getKind() != Kind.ARGUMENT) continue;
++			// ECJ has not populated the implicit arguments of a compact record constructor yet.
++			boolean compactConstructor = parent.get() instanceof ConstructorDeclaration
++				&& isRecord(job.parentType) && (parent.get().bits & IsCanonicalConstructor) != 0;
++			for (EclipseNode param : (compactConstructor ? job.parentType : fillParametersFrom).down()) {
++				if (compactConstructor ? !isRecordField(param) : param.getKind() != Kind.ARGUMENT) continue;
+ 				BuilderFieldData bfd = new BuilderFieldData();
+-				Argument arg = (Argument) param.get();
++				AbstractVariableDeclaration arg = (AbstractVariableDeclaration) param.get();
+ 				
+ 				Annotation[] copyableAnnotations = findCopyableAnnotations(param);
+ 				

java/lombok/tests/BuilderCompactConstructor.java

@@ -0,0 +1,139 @@
+import java.math.BigDecimal;
+import java.util.List;
+import lombok.Builder;
+import lombok.NonNull;
+import lombok.Singular;
+import lombok.SneakyThrows;
+import lombok.RequiredArgsConstructor;
+
+public class BuilderCompactConstructor {
+    @Builder(toBuilder = true)
+    record Payment(String number, String phone, BigDecimal amount,
+                   BigDecimal serviceCharge, BigDecimal total, Status status) {
+        @Builder
+        Payment {
+            if (serviceCharge == null) serviceCharge = BigDecimal.ZERO;
+        }
+    }
+
+    enum Status { PENDING, SUCCESS, EXPIRED }
+
+    record ConstructorOnly(String name, int count) {
+        @Builder(toBuilder = true, setterPrefix = "with")
+        ConstructorOnly {
+            if (count < 0) throw new IllegalArgumentException("count");
+        }
+    }
+
+    @Builder(toBuilder = true)
+    record TypeOnly(int count) {
+        TypeOnly { count++; }
+    }
+
+    record Generic<T>(@NonNull T value, @Singular List<String> tags) {
+        static final String IGNORED = "not a component";
+
+        @Builder(toBuilder = true)
+        Generic {}
+    }
+
+    record Empty() {
+        @Builder
+        Empty {}
+    }
+
+    record Canonical(String name, int count) {
+        @Builder
+        Canonical(String name, int count) {
+            this.name = name.trim();
+            this.count = count;
+        }
+    }
+
+    record Explicit(String name, int count) {
+        @Builder
+        Explicit(String name) { this(name, 7); }
+    }
+
+    static class Ordinary {
+        final String name;
+
+        @Builder
+        @SneakyThrows
+        Ordinary(String name) { this.name = name; }
+    }
+
+    static class Parent {
+        Parent(String name) {}
+    }
+
+    static class ConstructorCalls extends Parent {
+        final String name;
+
+        @SneakyThrows
+        ConstructorCalls() {
+            this("default");
+            assert name.equals("default");
+        }
+
+        @SneakyThrows
+        ConstructorCalls(@NonNull String name) {
+            super(name);
+            this.name = name;
+        }
+    }
+
+    @RequiredArgsConstructor
+    static class GeneratedConstructor {
+        final int initialized = 7;
+        @NonNull final String name;
+    }
+
+    @Builder(builderMethodName = "methodBuilder", builderClassName = "MethodBuilder")
+    static String named(String name) { return name; }
+
+    public static void main(String[] args) {
+        var payment = Payment.builder().number("inquiry").phone("123")
+            .amount(BigDecimal.TEN).total(BigDecimal.TEN).status(Status.PENDING).build();
+        assert payment.number().equals("inquiry");
+        assert payment.phone().equals("123");
+        assert payment.amount().equals(BigDecimal.TEN);
+        assert payment.serviceCharge().equals(BigDecimal.ZERO);
+        assert payment.total().equals(BigDecimal.TEN);
+        assert payment.status() == Status.PENDING;
+        assert payment.toBuilder().phone("456").build().phone().equals("456");
+        assert Payment.builder().serviceCharge(BigDecimal.ONE).build().serviceCharge().equals(BigDecimal.ONE);
+
+        var constructor = ConstructorOnly.builder().withName("test").withCount(2).build();
+        assert constructor.toBuilder().withCount(3).build().count() == 3;
+        assert constructor.name().equals("test");
+        try {
+            ConstructorOnly.builder().withCount(-1).build();
+            throw new AssertionError("compact constructor validation was bypassed");
+        } catch (IllegalArgumentException expected) {}
+
+        assert TypeOnly.builder().count(2).build().count() == 3;
+        assert Empty.builder().build().equals(new Empty());
+        var generic = Generic.<String>builder().value("value").tag("one").build();
+        assert generic.value().equals("value");
+        assert generic.tags().equals(List.of("one"));
+        assert generic.toBuilder().tag("two").build().tags().equals(List.of("one", "two"));
+        try {
+            Generic.<String>builder().build();
+            throw new AssertionError("non-null check was bypassed");
+        } catch (NullPointerException expected) {}
+
+        assert Canonical.builder().name(" test ").count(2).build().equals(new Canonical("test", 2));
+        assert Explicit.builder().name("test").build().equals(new Explicit("test", 7));
+        assert Ordinary.builder().name("test").build().name.equals("test");
+        assert methodBuilder().name("test").build().equals("test");
+        assert new ConstructorCalls().name.equals("default");
+        assert new ConstructorCalls("explicit").name.equals("explicit");
+        assert new GeneratedConstructor("generated").initialized == 7;
+        assert new GeneratedConstructor("generated").name.equals("generated");
+        try {
+            new ConstructorCalls(null);
+            throw new AssertionError("constructor non-null check was bypassed");
+        } catch (NullPointerException expected) {}
+    }
+}

java/lombok/tests/verify.py

@@ -0,0 +1,33 @@
+"""Compile and run builder regressions with javac and the compiler shipped by JDT LS.
+
+Usage: python3 java/lombok/tests/verify.py /path/to/jdtls /path/to/lombok.jar
+Requires a JDK 21+ on PATH. All generated files stay in a temporary directory.
+"""
+
+import os
+import pathlib
+import subprocess
+import sys
+import tempfile
+
+
+def main():
+    home, lombok = (pathlib.Path(p).resolve() for p in sys.argv[1:3])
+    ecj, = (home / "plugins").glob("org.eclipse.jdt.core.compiler.batch_*.jar")
+    source = pathlib.Path(__file__).with_name("BuilderCompactConstructor.java")
+    with tempfile.TemporaryDirectory(prefix="openidea-lombok-builders-") as tmp:
+        for compiler in ("javac", "ecj"):
+            output = pathlib.Path(tmp) / compiler
+            output.mkdir()
+            if compiler == "javac":
+                command = ["javac", "--release", "21", "-processorpath", str(lombok)]
+            else:
+                command = ["java", f"-javaagent:{lombok}", "-jar", str(ecj), "-21"]
+            subprocess.run(command + ["-cp", str(lombok), "-d", str(output), str(source)], check=True)
+            subprocess.run(["java", "-ea", "-cp", os.pathsep.join((str(output), str(lombok))),
+                            "BuilderCompactConstructor"], check=True)
+            print(f"{compiler}: builder regression assertions passed", flush=True)
+
+
+if __name__ == "__main__":
+    main()