Implement getter generation for map setter keys

src/imp/gen_map_get.rs

@@ -15,14 +15,22 @@ impl Definition {
 impl Stmt {
   fn gen_map_get(&mut self, id: &mut usize) {
     match self {
-      Stmt::Assign { pat: _, val, nxt } => {
+      Stmt::Assign { pat, val, nxt } => {
+        let key_substitutions =
+          if let AssignPattern::MapSet(_, key) = pat { key.substitute_map_gets(id) } else { Vec::new() };
+
         if let Some(nxt) = nxt {
           nxt.gen_map_get(id);
         }
+
         let substitutions = val.substitute_map_gets(id);
         if !substitutions.is_empty() {
           *self = gen_get(self, substitutions);
         }
+
+        if !key_substitutions.is_empty() {
+          *self = gen_get(self, key_substitutions);
+        }
       }
       Stmt::Ask { pat: _, val, nxt } => {
         nxt.gen_map_get(id);

src/imp/mod.rs

@@ -46,9 +46,10 @@ pub struct MatchArm {
   pub rgt: Stmt,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Default)]
 pub enum AssignPattern {
   // "*"
+  #[default]
   Eraser,
   // [a-zA-Z_]+
   Var(Name),

tests/golden_tests/run_file/nested_map_set.bend

@@ -0,0 +1,5 @@
+def main():
+  map = { 0: 1, 1: 10, 2: 0, 3: 1, 4: 3 }
+  map[map[0]] = 99
+  map[map[2]] = 1
+  return map[map[map[4]]] + map[map[2]]

tests/snapshots/run_file__nested_map_set.bend.snap

@@ -0,0 +1,9 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/run_file/nested_map_set.bend
+---
+NumScott:
+100
+
+Scott:
+100