Ignore differences in empty statements when parsing ajava files and s…

…ource files together

framework/src/main/java/org/checkerframework/framework/ajava/ExpectedTreesVisitor.java

@@ -4,6 +4,7 @@
 import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.ClassTree;
 import com.sun.source.tree.DoWhileLoopTree;
+import com.sun.source.tree.EmptyStatementTree;
 import com.sun.source.tree.ExpressionStatementTree;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.ForLoopTree;
@@ -399,4 +400,14 @@ public Void visitYield17(Tree tree, Void p) {
     // So skip yields.
     return null;
   }
+
+  @Override
+  public Void visitEmptyStatement(EmptyStatementTree tree, Void p) {
+    // JavaParser doesn't seem to include completely-empty classes.
+    // See https://github.com/typetools/checker-framework/issues/6570
+    // for a discussion of our motivation for excluding empty statements.
+    // Also, empty statements don't have semantics, so it's okay if there
+    // are arbitraily-many extra empty statements in one of the inputs.
+    return null;
+  }
 }

framework/src/main/java/org/checkerframework/framework/ajava/JointJavacJavaParserVisitor.java

@@ -647,8 +647,25 @@ public Void visitCompilationUnit(CompilationUnitTree javacTree, Node javaParserN
     CompilationUnit node = castNode(CompilationUnit.class, javaParserNode, javacTree);
     processCompilationUnit(javacTree, node);
     visitOptional(javacTree.getPackage(), node.getPackageDeclaration());
+
+    // This is the fix for https://github.com/typetools/checker-framework/issues/6570.
+    // If the input java file contains semicolons between classes, then
+    // the javac tree will contain "type declarations" for those semicolons
+    // (for some reason? a javac bug?) but an ajava file will not (JavaParser
+    // appears to strip them out? frankly, we're not sure why). This code works
+    // around the problem by filtering any "type declarations" that contain only
+    // a single semicolon from the javacTypeDecls list before passing the list
+    // to the rest of the visitor.
+    List<? extends Tree> javacTypeDecls = javacTree.getTypeDecls();
+    List<Tree> javacTypeDeclsWithoutSemicolons = new ArrayList<>();
+    for (Tree javacTypeDecl : javacTypeDecls) {
+      if (javacTypeDecl.getKind() != Tree.Kind.EMPTY_STATEMENT) {
+        javacTypeDeclsWithoutSemicolons.add(javacTypeDecl);
+      }
+    }
+
     visitLists(javacTree.getImports(), node.getImports());
-    visitLists(javacTree.getTypeDecls(), node.getTypes());
+    visitLists(javacTypeDeclsWithoutSemicolons, node.getTypes());
     return null;
   }
 

framework/tests/all-systems/EndsWithSemicolon.java

@@ -0,0 +1,6 @@
+// test case for https://github.com/typetools/checker-framework/issues/6570
+
+// A class is technically permitted to end with a semicolon (though it doesn't do
+// anything).
+public class EndsWithSemicolon {}
+;