exception-without-cause (#950)

* Add recipe for finding exceptions which are thrown from catch blocks that do not reference the caught exception

* Add recipe for finding exceptions which are thrown from catch blocks that do not reference the caught exception

* Update recipes.csv

Author: sambsnyd

recipe-writing-lessons.md

@@ -319,3 +319,37 @@ mark escape. Key learnings:
   the method type still declares the legacy type. With every reference re-typed, `maybeRemoveImport`
   removes the import with no downstream cleanup needed. `ReplaceSynchronizedType` is the shared base that
   implements this for `Hashtable`/`Vector`/`StringBuffer`.
+
+## Data flow / taint tracking (rewrite-analysis)
+
+### `Dataflow.findSinks` cannot track sources inside `catch` blocks
+`org.openrewrite.analysis.dataflow.Dataflow#findSinks` gates its results on control-flow
+*reachability*: it computes the control-flow graph of the enclosing method and prunes any
+flow whose nodes are not reachable on the normal control-flow path. A `catch` block is only
+entered via an exceptional edge, which the control-flow graph does not model, so every
+expression inside a `catch` is considered unreachable and the flow is pruned to empty —
+`findSinks` returns `Option.none()` even though `DataFlowNode.of(...)` and `spec.isSource(...)`
+both succeed.
+
+To taint-track a source that lives inside a `catch` block (e.g. connecting a caught exception
+to a newly thrown one), drive the flow engine directly and skip the reachability filter:
+```java
+DataFlowNode.of(cursor).forEach(node -> {
+    FlowGraph graph = ForwardFlow.findAllFlows(node, spec, FlowGraph.Factory.defaultFactory());
+    // BFS/DFS over graph.getEdges(); collect each node.getCursor().getValue() that is an Expression
+});
+```
+This yields the full forward taint graph (every expression the source flows into) without the
+control-flow reachability gate. See `FindNewExceptionWithoutCause`.
+
+### Matching a reference to a specific local/caught variable
+`JavaType.Variable.equals` is structural (compares `name` + `owner`), so a reference's
+`J.Identifier#getFieldType()` reliably equals the declaration's `NamedVariable#getVariableType()`.
+Fall back to simple-name comparison only when type attribution is missing.
+
+### `@Nullable` on a nested type is a type-use annotation
+Write `JavaType.@Nullable Variable`, not `@Nullable JavaType.Variable`. The latter annotates the
+scoping construct `JavaType` and fails to compile ("scoping construct cannot be annotated with
+type-use annotation"), which crashes the whole Lombok annotation-processing round and produces a
+misleading cascade of "does not override abstract method getDescription()" errors across every
+Lombok-annotated recipe.

src/main/java/org/openrewrite/staticanalysis/FindNewExceptionWithoutCause.java

@@ -0,0 +1,251 @@
+/*
+ * Copyright 2026 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.staticanalysis;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+import org.jspecify.annotations.Nullable;
+import org.openrewrite.Cursor;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Preconditions;
+import org.openrewrite.Recipe;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.analysis.dataflow.DataFlowNode;
+import org.openrewrite.analysis.dataflow.TaintFlowSpec;
+import org.openrewrite.analysis.dataflow.analysis.FlowGraph;
+import org.openrewrite.analysis.dataflow.analysis.ForwardFlow;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.tree.Expression;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JavaSourceFile;
+import org.openrewrite.java.tree.JavaType;
+import org.openrewrite.marker.SearchResult;
+import org.openrewrite.staticanalysis.groovy.GroovyFileChecker;
+import org.openrewrite.staticanalysis.java.JavaFileChecker;
+import org.openrewrite.staticanalysis.kotlin.KotlinFileChecker;
+import org.openrewrite.staticanalysis.table.ExceptionsWithoutCause;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+@Value
+@EqualsAndHashCode(callSuper = false)
+public class FindNewExceptionWithoutCause extends Recipe {
+
+    private static final String TAINTED_KEY = "caughtExceptionTaintedExpressions";
+    private static final String CAUGHT_KEY = "caughtExceptionVariable";
+
+    transient ExceptionsWithoutCause report = new ExceptionsWithoutCause(this);
+
+    @Override
+    public String getDisplayName() {
+        return "Find new exceptions thrown without the caught exception";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Finds `catch` blocks that throw a newly created exception without referencing the caught exception, " +
+               "which discards the original exception's stack trace and message. Data flow (taint) tracking is used " +
+               "to establish whether the caught exception—or any value derived from it—reaches the thrown exception, " +
+               "so indirect references through local variables and string concatenation are not falsely reported. " +
+               "This mirrors PMD's `PreserveStackTrace` rule.";
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        return Preconditions.check(Preconditions.or(
+                new JavaFileChecker<>(),
+                new GroovyFileChecker<>(),
+                new KotlinFileChecker<>()
+        ), new JavaIsoVisitor<ExecutionContext>() {
+
+            @Override
+            public J.Try.Catch visitCatch(J.Try.Catch aCatch, ExecutionContext ctx) {
+                J.VariableDeclarations.NamedVariable caughtVar = aCatch.getParameter().getTree().getVariables().get(0);
+                JavaType.Variable caughtType = caughtVar.getVariableType();
+                String caughtName = caughtVar.getSimpleName();
+
+                // Seed a taint analysis from every reference to the caught exception (and every value read off of it,
+                // e.g. `e.getMessage()`) and collect all expressions the caught exception flows into.
+                Set<Expression> tainted = new HashSet<>();
+                ExceptionTaintSpec spec = new ExceptionTaintSpec(caughtType, caughtName);
+                new JavaIsoVisitor<Set<Expression>>() {
+                    @Override
+                    public J.Identifier visitIdentifier(J.Identifier identifier, Set<Expression> set) {
+                        if (referencesCaught(identifier, caughtType, caughtName)) {
+                            seedFlow(getCursor(), spec, set);
+                        }
+                        return identifier;
+                    }
+
+                    @Override
+                    public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, Set<Expression> set) {
+                        if (rootReferencesCaught(method.getSelect(), caughtType, caughtName)) {
+                            seedFlow(getCursor(), spec, set);
+                        }
+                        return super.visitMethodInvocation(method, set);
+                    }
+                }.visit(aCatch.getBody(), tainted, getCursor());
+
+                getCursor().putMessage(TAINTED_KEY, tainted);
+                getCursor().putMessage(CAUGHT_KEY, caughtVar);
+                return super.visitCatch(aCatch, ctx);
+            }
+
+            @Override
+            public J.Throw visitThrow(J.Throw thrown, ExecutionContext ctx) {
+                J.Throw t = super.visitThrow(thrown, ctx);
+                if (!(t.getException() instanceof J.NewClass)) {
+                    return t;
+                }
+                J.NewClass newException = (J.NewClass) t.getException();
+
+                // Find the `catch` clause that directly governs this `throw`, bailing out if a `try` body, lambda,
+                // or other execution boundary sits between them.
+                Cursor governing = null;
+                for (Cursor c = getCursor().getParent(); c != null; c = c.getParent()) {
+                    Object v = c.getValue();
+                    if (v instanceof J.Try.Catch) {
+                        governing = c;
+                        break;
+                    }
+                    if (v instanceof J.Try || v instanceof J.Lambda || v instanceof J.MethodDeclaration ||
+                        v instanceof J.ClassDeclaration ||
+                        (v instanceof J.NewClass && ((J.NewClass) v).getBody() != null)) {
+                        break;
+                    }
+                }
+                if (governing == null) {
+                    return t;
+                }
+
+                J.VariableDeclarations.NamedVariable caughtVar = governing.getMessage(CAUGHT_KEY);
+                Set<Expression> tainted = governing.getMessage(TAINTED_KEY);
+                if (caughtVar == null || tainted == null) {
+                    return t;
+                }
+
+                JavaType.Variable caughtType = caughtVar.getVariableType();
+                String caughtName = caughtVar.getSimpleName();
+                if (referencesCaughtException(newException, caughtType, caughtName, tainted)) {
+                    return t;
+                }
+
+                JavaSourceFile sourceFile = getCursor().firstEnclosing(JavaSourceFile.class);
+                report.insertRow(ctx, new ExceptionsWithoutCause.Row(
+                        sourceFile == null ? "" : sourceFile.getSourcePath().toString(),
+                        String.valueOf(caughtType == null ? caughtVar.getType() : caughtType.getType()),
+                        String.valueOf(newException.getType())
+                ));
+                return t.withException(SearchResult.found(newException));
+            }
+
+            private void seedFlow(Cursor cursor, ExceptionTaintSpec spec, Set<Expression> tainted) {
+                // Dataflow#findSinks gates on control-flow reachability, but a `catch` block is only reached via
+                // an exceptional edge that the control-flow graph does not model, so its expressions are considered
+                // unreachable and pruned. Drive ForwardFlow directly to obtain the taint graph without that gate.
+                DataFlowNode.of(cursor).forEach(node -> {
+                    FlowGraph graph = ForwardFlow.findAllFlows(node, spec, FlowGraph.Factory.defaultFactory());
+                    Deque<FlowGraph> worklist = new ArrayDeque<>();
+                    worklist.add(graph);
+                    while (!worklist.isEmpty()) {
+                        FlowGraph current = worklist.poll();
+                        Object value = current.getNode().getCursor().getValue();
+                        if (value instanceof Expression) {
+                            tainted.add((Expression) value);
+                        }
+                        worklist.addAll(current.getEdges());
+                    }
+                });
+            }
+
+            private boolean referencesCaughtException(J newException, JavaType.@Nullable Variable caughtType,
+                                                      String caughtName, Set<Expression> tainted) {
+                AtomicBoolean referenced = new AtomicBoolean(false);
+                new JavaIsoVisitor<AtomicBoolean>() {
+                    @Override
+                    public Expression visitExpression(Expression expression, AtomicBoolean found) {
+                        if (found.get()) {
+                            return expression;
+                        }
+                        if (tainted.contains(expression) ||
+                            (expression instanceof J.Identifier &&
+                             referencesCaught((J.Identifier) expression, caughtType, caughtName))) {
+                            found.set(true);
+                            return expression;
+                        }
+                        return super.visitExpression(expression, found);
+                    }
+                }.visit(newException, referenced);
+                return referenced.get();
+            }
+        });
+    }
+
+    private static boolean referencesCaught(J.Identifier identifier, JavaType.@Nullable Variable caughtType,
+                                            String caughtName) {
+        JavaType.Variable fieldType = identifier.getFieldType();
+        if (caughtType != null && fieldType != null) {
+            return caughtType.equals(fieldType);
+        }
+        return caughtName.equals(identifier.getSimpleName());
+    }
+
+    private static boolean rootReferencesCaught(@Nullable Expression select, JavaType.@Nullable Variable caughtType,
+                                                String caughtName) {
+        Expression e = select;
+        while (e != null) {
+            if (e instanceof J.Identifier) {
+                return referencesCaught((J.Identifier) e, caughtType, caughtName);
+            }
+            if (e instanceof J.MethodInvocation) {
+                e = ((J.MethodInvocation) e).getSelect();
+            } else if (e instanceof J.FieldAccess) {
+                e = ((J.FieldAccess) e).getTarget();
+            } else {
+                return false;
+            }
+        }
+        return false;
+    }
+
+    @Value
+    @EqualsAndHashCode(callSuper = false)
+    private static class ExceptionTaintSpec extends TaintFlowSpec {
+        JavaType.@Nullable Variable caughtType;
+        String caughtName;
+
+        @Override
+        public boolean isSource(DataFlowNode srcNode) {
+            Object v = srcNode.getCursor().getValue();
+            if (v instanceof J.Identifier) {
+                return referencesCaught((J.Identifier) v, caughtType, caughtName);
+            }
+            if (v instanceof J.MethodInvocation) {
+                return rootReferencesCaught(((J.MethodInvocation) v).getSelect(), caughtType, caughtName);
+            }
+            return false;
+        }
+
+        @Override
+        public boolean isSink(DataFlowNode sinkNode) {
+            return true;
+        }
+    }
+}

src/main/java/org/openrewrite/staticanalysis/table/ExceptionsWithoutCause.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2026 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.staticanalysis.table;
+
+import com.fasterxml.jackson.annotation.JsonIgnoreType;
+import lombok.Value;
+import org.openrewrite.Column;
+import org.openrewrite.DataTable;
+import org.openrewrite.Recipe;
+
+@JsonIgnoreType
+public class ExceptionsWithoutCause extends DataTable<ExceptionsWithoutCause.Row> {
+
+    public ExceptionsWithoutCause(Recipe recipe) {
+        super(recipe,
+                "Exceptions thrown without the caught cause",
+                "New exceptions thrown from a `catch` block that do not reference the caught exception.");
+    }
+
+    @Value
+    public static class Row {
+        @Column(displayName = "Source path",
+                description = "The path to the source file containing the offending `throw`.")
+        String sourcePath;
+
+        @Column(displayName = "Caught exception type",
+                description = "The declared type of the exception caught by the enclosing `catch` clause.")
+        String caughtType;
+
+        @Column(displayName = "Thrown exception type",
+                description = "The type of the new exception thrown without referencing the caught exception.")
+        String thrownType;
+    }
+}