fix(semantic/cfg): correct unreachability propagation in try-finally. (…

…#3667)

closes #3663


[oxlint-ecosystem-ci](https://github.com/rzvxa/oxlint-ecosystem-ci/actions/runs/9511509383/job/26217870705)

From this:

![Screenshot 2024-06-14
092916](https://github.com/oxc-project/oxc/assets/3788964/9e6a9a01-984a-4a19-8a73-abc3b71fb9c2)

To this:

![Screenshot 2024-06-14
092852](https://github.com/oxc-project/oxc/assets/3788964/46483bc2-a227-4416-b8da-07b11ab96990)

Since try-finally (without a catch) wouldn't join after finalization.

crates/oxc_linter/src/rules/eslint/no_unreachable.rs

@@ -50,25 +50,18 @@ impl Rule for NoUnreachable {
         // In our first path we first check if each block is definitely unreachable, If it is then
         // we set it as such, If we encounter an infinite loop we keep its end block since it can
         // prevent other reachable blocks from ever getting executed.
-        let _: Control<()> = depth_first_search(graph, Some(root.cfg_id()), |event| match event {
-            DfsEvent::Finish(node, _) => {
-                let bb = cfg.basic_block(node);
-                let unreachable = if bb.unreachable {
-                    true
-                } else {
-                    graph
-                        .edges_directed(node, Direction::Incoming)
-                        .any(|edge| matches!(edge.weight(), EdgeType::Join))
-                };
+        let _: Control<()> = depth_first_search(graph, Some(root.cfg_id()), |event| {
+            if let DfsEvent::Finish(node, _) = event {
+                let unreachable = cfg.basic_block(node).unreachable;
                 unreachables[node.index()] = unreachable;
 
-                if let Some(it) = cfg.is_infinite_loop_start(node, nodes) {
-                    infinite_loops.push(it);
+                if !unreachable {
+                    if let Some(it) = cfg.is_infinite_loop_start(node, nodes) {
+                        infinite_loops.push(it);
+                    }
                 }
-
-                Control::Continue
             }
-            _ => Control::Continue,
+            Control::Continue
         });
 
         // In the second path we go for each infinite loop end block and follow it marking all
@@ -255,6 +248,14 @@ fn test() {
             b();
         }
         ",
+        "
+        try {
+            a();
+        } finally {
+            b();
+        }
+        c();
+        ",
     ];
 
     let fail = vec![

crates/oxc_semantic/src/builder.rs

@@ -1248,7 +1248,11 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
                 self.cfg.add_edge(
                     finally_block_end_ix,
                     after_try_statement_block_ix,
-                    EdgeType::Join,
+                    if self.cfg.basic_block(after_try_block_graph_ix).unreachable {
+                        EdgeType::Unreachable
+                    } else {
+                        EdgeType::Join
+                    },
                 );
             }
         }

crates/oxc_semantic/src/control_flow/builder/mod.rs

@@ -91,7 +91,7 @@ impl<'a> ControlFlowGraphBuilder<'a> {
     pub fn add_edge(&mut self, a: BasicBlockId, b: BasicBlockId, weight: EdgeType) {
         if matches!(weight, EdgeType::NewFunction) {
             self.basic_block_mut(b).unreachable = false;
-        } else if self.basic_block(a).unreachable {
+        } else if matches!(weight, EdgeType::Unreachable) || self.basic_block(a).unreachable {
             if self.graph.edges_directed(b, Direction::Incoming).count() == 0 {
                 self.basic_block_mut(b).unreachable = true;
             }

crates/oxc_semantic/tests/integration/snapshots/integration__cfg__cfg_files@labelled_try_break.js-2.snap

@@ -31,7 +31,7 @@ digraph {
     7 -> 8 [ label = "Unreachable" , style = "dotted" ]
     9 -> 2 [ label = "Error(Implicit)" , style = "dotted" ]
     3 -> 5 [ label = "Normal" ]
-    8 -> 9 [ label = "Join" , style = "dotted" ]
+    8 -> 9 [ label = "Unreachable" , style = "dotted" ]
     10 -> 2 [ label = "Error(Implicit)" ]
     9 -> 10 [ label = "Normal" , style = "dotted" ]
     7 -> 10 [ label = "Jump" ]