Move the original get_draw_order code into the tree_iter module.

src/nix_util/tree_iter/tests.rs

@@ -0,0 +1,55 @@
+use crate::nix_util::running_build::is_transparent_predicate;
+use crate::nix_util::running_build::print_dag;
+
+use super::ReverseTreeIter;
+use super::get_draw_order;
+use super::test_util::BuildInstruction;
+use super::test_util::build_activity_tree_from_instructions;
+use super::test_util::get_every_possible_addition;
+
+fn compare_single_tree(
+    instructions: &Vec<BuildInstruction>,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let activity_tree = build_activity_tree_from_instructions(instructions, true)?;
+    let original_draw_order = get_draw_order(&activity_tree);
+    let reverse_draw_order = ReverseTreeIter::new(
+        &activity_tree,
+        None,
+        |entry| entry.get_activity().is_active(),
+        is_transparent_predicate,
+        |_entry| true,
+    )
+    .get_draw_order();
+
+    if original_draw_order != reverse_draw_order {
+        println!("Draw order mismatch!");
+        println!("Instructions: {:?}", instructions);
+        println!("Original: {:?}", original_draw_order);
+        println!("Reverse: {:?}", reverse_draw_order);
+        print_dag(&activity_tree, original_draw_order);
+        print_dag(&activity_tree, reverse_draw_order);
+        return Err("mismatch".into());
+    }
+
+    Ok(())
+}
+
+#[test]
+#[ignore]
+fn reverse_tree_order_draw_order_iterative() -> Result<(), Box<dyn std::error::Error>> {
+    let mut prev_generation: Vec<Vec<BuildInstruction>> = Vec::new();
+    let mut current_generation: Vec<Vec<BuildInstruction>> = vec![vec![]];
+
+    // Iterate through every possible tree with N nodes.
+    for _ in 0..7 {
+        std::mem::swap(&mut prev_generation, &mut current_generation);
+        for old_state in prev_generation.drain(..) {
+            for new_state in get_every_possible_addition(&old_state) {
+                compare_single_tree(&new_state)?;
+                current_generation.push(new_state);
+            }
+        }
+    }
+
+    Ok(())
+}