From aad9ca84a28270228a8b3b9933e645ae39e1e39d Mon Sep 17 00:00:00 2001
From: Bonobo <github@in9.at>
Date: Wed, 2 Sep 2026 13:52:33 +0200
Subject: [PATCH] fix(dataflow): skip unreachable empty-try catches

---
 src/dataflow/cfg.ts                    | 26 ++++++++++++++++----------
 test/dataflow.test.ts                  |  9 +++++++++
 test/fixtures/dataflow-app/src/flow.ts |  8 ++++++++
 3 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/src/dataflow/cfg.ts b/src/dataflow/cfg.ts
index a8200d0..b567585 100644
--- a/src/dataflow/cfg.ts
+++ b/src/dataflow/cfg.ts
@@ -163,9 +163,13 @@ function collectStatementNodes(node: Node, out: Node[]): void {
       out.push(s);
       for (const clause of s.getClauses()) for (const cs of clause.getStatements()) collectStatementNodes(cs, out);
     } else if (Node.isTryStatement(s)) {
+      const beforeTry = out.length;
       collectStatementNodes(s.getTryBlock(), out);
+      const tryHasNodes = out.length > beforeTry;
       const cc = s.getCatchClause();
-      if (cc) {
+      // A catch after a structurally empty try is unreachable. Omitting that dead region keeps
+      // normal flow on the statement list and preserves the graph's all-nodes-reachable contract.
+      if (cc && tryHasNodes) {
         out.push(cc);
         collectStatementNodes(cc.getBlock(), out);
       }
@@ -377,15 +381,17 @@ class Lowerer {
     const exits: Dangling[] = [];
     let catchEntry: number | null = null;
     if (cc) {
-      const catchId = this.idOf.get(cc) as number; // binds the exception variable (a def, stage 3)
-      catchEntry = catchId;
-      const catchCtx: LowerCtx = { ...ctx, exceptionTarget: afterCatchTarget };
-      const catchBody = this.statements(cc.getBlock().getStatements(), catchCtx);
-      if (catchBody.entry !== null) {
-        this.addEdge(catchId, catchBody.entry, "fallthrough");
-        this.routeThroughFinally(catchBody.exits, finLowered, exits);
-      } else {
-        this.routeThroughFinally([{ from: catchId, kind: "fallthrough" }], finLowered, exits);
+      const catchId = this.idOf.get(cc);
+      if (catchId !== undefined) {
+        catchEntry = catchId; // binds the exception variable (a def, stage 3)
+        const catchCtx: LowerCtx = { ...ctx, exceptionTarget: afterCatchTarget };
+        const catchBody = this.statements(cc.getBlock().getStatements(), catchCtx);
+        if (catchBody.entry !== null) {
+          this.addEdge(catchId, catchBody.entry, "fallthrough");
+          this.routeThroughFinally(catchBody.exits, finLowered, exits);
+        } else {
+          this.routeThroughFinally([{ from: catchId, kind: "fallthrough" }], finLowered, exits);
+        }
       }
     }
 
diff --git a/test/dataflow.test.ts b/test/dataflow.test.ts
index 7e5a686..0a05e00 100644
--- a/test/dataflow.test.ts
+++ b/test/dataflow.test.ts
@@ -137,6 +137,15 @@ describe("CFG gate", () => {
     expect(e).toContainEqual({ source: 6, target: 8, kind: "exception" }); // finally → outward (EXIT)
   });
 
+  test("an empty try falls through instead of entering its unreachable catch", () => {
+    const cfg = cfgOf("src/flow.emptyTryCatch");
+    expect(cfg.nodes.map((node) => node.kind)).toEqual(["entry", "statement", "exit"]);
+    expect(cfg.edges).toEqual([
+      { source: 0, target: 1, kind: "fallthrough" },
+      { source: 1, target: 2, kind: "return" },
+    ]);
+  });
+
   test("throw with no handler edges to EXIT (parse)", () => {
     const cfg = cfgOf("src/flow.parse");
     const exit = cfg.nodes.length - 1;
diff --git a/test/fixtures/dataflow-app/src/flow.ts b/test/fixtures/dataflow-app/src/flow.ts
index b57b19b..a93c200 100644
--- a/test/fixtures/dataflow-app/src/flow.ts
+++ b/test/fixtures/dataflow-app/src/flow.ts
@@ -84,3 +84,11 @@ export function shadow(): number {
   }
   return x;
 }
+
+export function emptyTryCatch(): number {
+  try {
+  } catch {
+    return 1;
+  }
+  return 0;
+}