feat(turbopack): Consider cycles while spliting modules (vercel/turborepo#4595)

### Description

This is optimization for modules with cyclic dependencies between AST
nodes.

 - Fixes WEB-706.

### Testing Instructions

Look at `output.mdx` using GitHub diff view, and you can see it rendered
by selecting `Open file` from the context menu.

---------

Co-authored-by: Alex Kirszenberg <alex.kirszenberg@vercel.com>

Author: kdy1

crates/turbopack-ecmascript/src/tree_shake/graph.rs

@@ -370,9 +370,6 @@ impl DepGraph {
             global_done: &mut FxHashSet<u32>,
             group_done: &mut FxHashSet<u32>,
         ) -> bool {
-            // TODO(WEB-706): Consider cycles
-            //
-
             let mut changed = false;
 
             // Check deps of `start`.
@@ -416,6 +413,24 @@ impl DepGraph {
             }
         }
 
+        // Cycles should form a separate group
+        for id in self.g.graph_ix.iter() {
+            let ix = self.g.get_node(id);
+
+            if let Some(cycle) = cycles.iter().find(|v| v.contains(&ix)) {
+                if cycle.iter().all(|v| !global_done.contains(v)) {
+                    let ids = cycle
+                        .iter()
+                        .map(|&ix| self.g.graph_ix[ix as usize].clone())
+                        .collect::<Vec<_>>();
+
+                    global_done.extend(cycle.iter().copied());
+
+                    groups.push((ids, Default::default()));
+                }
+            }
+        }
+
         // Expand **starting** nodes
         for (ix, id) in self.g.graph_ix.iter().enumerate() {
             // If a node is reachable from two or more nodes, it should be in a

crates/turbopack-ecmascript/tests/tree-shaker/analyzer/3/config.json

@@ -0,0 +1,6 @@
+{
+    "exports":[
+        ["c1_3"],
+        ["c1_3", "c2_2"]
+    ]
+}

crates/turbopack-ecmascript/tests/tree-shaker/analyzer/3/input.js

@@ -0,0 +1,38 @@
+
+
+function d1() { }
+
+
+function d2() { }
+
+function d3() { }
+
+
+
+
+export function c1_1() {
+  return c1_2()
+}
+
+function c1_2() {
+  return c1_3(d1)
+}
+export function c1_3() {
+  return c1_1(d2)
+}
+
+
+function c2_1() {
+  return c2_2(d3)
+}
+
+export function c2_2() {
+  return c2_3()
+}
+function c2_3() {
+  return c2_1()
+}
+
+
+c1_3()
+c2_2()