Fix GroovyParserVisitor crash on multi-variable field declarations (#7467)

* Fix `GroovyParserVisitor` crash on multi-variable field declarations

Groovy emits a separate `FieldNode` for each variable in a multi-variable
field declaration (e.g., `final String a, b`). The parser was treating each
one as a complete declaration and re-consuming the modifiers and type tokens,
desynchronizing the cursor and eventually throwing `StringIndexOutOfBoundsException`
when parsing later nodes.

Detect continuation fields in `visitVariableField` and emit a `MultiVariable`
marker with an empty type expression, mirroring the existing handling for
local multi-variable declarations like `def a = 1, b = 2`.

* Simplify multi-variable field handling by reusing `maybeMultiVariable`

* Keep `maybeMultiVariable` in `RewriteGroovyVisitor`

Call it through the existing `visitor` instance from `visitVariableField`
to avoid displacing the `sourceBefore` javadoc.

* Revert stray whitespace change in `ConstructorTest`

Author: timtebeek

rewrite-groovy/src/main/java/org/openrewrite/groovy/GroovyParserVisitor.java

@@ -586,9 +586,19 @@ private J.EnumValue visitEnumField(FieldNode field) {
         private void visitVariableField(FieldNode field) {
             RewriteGroovyVisitor visitor = new RewriteGroovyVisitor(field, this);
 
-            List<J.Annotation> annotations = visitAndGetAnnotations(field, this);
-            List<J.Modifier> modifiers = getModifiers();
-            TypeTree typeExpr = field.isDynamicTyped() ? null : visitTypeTree(field.getOriginType());
+            // Groovy emits a separate FieldNode per variable in a multi-variable declaration (e.g. `final String a, b`);
+            // continuation fields have no modifiers or type keyword in the source, so skip past just the comma.
+            Optional<MultiVariable> multiVariable = visitor.maybeMultiVariable();
+            List<J.Annotation> annotations = multiVariable.isPresent() ? emptyList() : visitAndGetAnnotations(field, this);
+            List<J.Modifier> modifiers = multiVariable.isPresent() ? emptyList() : getModifiers();
+            TypeTree typeExpr;
+            if (field.isDynamicTyped()) {
+                typeExpr = null;
+            } else if (multiVariable.isPresent()) {
+                typeExpr = new J.Identifier(randomId(), EMPTY, Markers.EMPTY, emptyList(), "", typeMapping.type(field.getOriginType()), null);
+            } else {
+                typeExpr = visitTypeTree(field.getOriginType());
+            }
 
             J.Identifier name = new J.Identifier(randomId(), sourceBefore(field.getName()), Markers.EMPTY,
                     emptyList(), field.getName(), typeMapping.type(field.getOriginType()), typeMapping.variableType(field));
@@ -612,7 +622,7 @@ private void visitVariableField(FieldNode field) {
             J.VariableDeclarations variableDeclarations = new J.VariableDeclarations(
                     randomId(),
                     EMPTY,
-                    Markers.EMPTY,
+                    multiVariable.<Markers>map(mv -> Markers.build(singleton(mv))).orElse(Markers.EMPTY),
                     annotations,
                     modifiers,
                     typeExpr,

rewrite-groovy/src/test/java/org/openrewrite/groovy/tree/VariableDeclarationsTest.java

@@ -125,6 +125,20 @@ void multipleTypeMultipleVariableDeclaration() {
         );
     }
 
+    @Issue("https://github.com/openrewrite/rewrite/issues/7463")
+    @Test
+    void multipleVariableFieldDeclaration() {
+        rewriteRun(
+          groovy(
+            """
+              class A {
+                  final String first, second
+              }
+              """
+          )
+        );
+    }
+
     @Test
     void genericVariableDeclaration() {
         rewriteRun(