Avoid repeated plan generation and unused diagnostics in layout fuzzers

tests/generated.rs

@@ -14,7 +14,7 @@
 #[path = "scenario/mod.rs"]
 mod scenario;
 
-use iris::random::{Edits, plan};
+use iris::random::{Edits, Plan, plan};
 use scenario::{ALL, Case, diverges, env, over_seeds};
 
 /// How deep the generator branches. The generator widens two to four ways per
@@ -32,8 +32,11 @@ fn depth() -> usize {
 const SEEDS: [u64; 10] = [1, 2, 3, 5, 8, 10, 13, 20, 86, 98];
 
 fn check(seed: u64, depth: usize, case: Case) {
-    let grown = plan(seed, depth, &Edits::default());
+    check_plan(&plan(seed, depth, &Edits::default()), seed, depth, case);
-    if let Some(how) = diverges(&grown, case, seed) {
+}
+
+fn check_plan(grown: &Plan, seed: u64, depth: usize, case: Case) {
+    if let Some(how) = diverges(grown, case, seed) {
         panic!(
             "seed {seed} at depth {depth} differs after {}: {how}\n\
              reduce it with SHRINK_SEED={seed} SHRINK_DEPTH={depth} \
@@ -119,8 +122,9 @@ fn a_long_run_of_seeds_agrees() {
         None => (1..=env("IRIS_GENERATED_SEEDS", 100_u64)).collect(),
     };
     over_seeds(seeds, |seed| {
+        let grown = plan(seed, depth, &Edits::default());
         for case in ALL {
-            check(seed, depth, case);
+            check_plan(&grown, seed, depth, case);
         }
     });
 }

tests/scenario/mod.rs

@@ -444,12 +444,6 @@ pub fn diverges(plan: &Plan, case: Case, seed: u64) -> Option<String> {
     cold.state.root = Some(root);
     cold.frame();
 
-    let places: HashMap<WidgetId, usize> = tree
-        .ids
-        .iter()
-        .enumerate()
-        .map(|(i, &id)| (id, i))
-        .collect();
     let mut drawn = 0;
     for (i, (&w, &c)) in tree.ids.iter().zip(&cold_tree.ids).enumerate() {
         let (got, want) = (warm.region(&w), cold.region(&c));
@@ -457,6 +451,12 @@ pub fn diverges(plan: &Plan, case: Case, seed: u64) -> Option<String> {
         if got == want {
             continue;
         }
+        let places: HashMap<WidgetId, usize> = tree
+            .ids
+            .iter()
+            .enumerate()
+            .map(|(i, &id)| (id, i))
+            .collect();
         // Where two trees disagree is rarely where the cause is, so the
         // ancestry comes with it, marking the widgets that own a region.
         let mut chain = Vec::new();