Another example, testing rule priorities a bit

cranelift/isle/isle_examples/test2.isle

@@ -0,0 +1,19 @@
+(type u32 (primitive u32))
+(type A (enum
+  (A1 (x B) (y B))))
+(type B (enum
+  (B1 (x u32))))
+
+(decl A2B (A) B)
+
+(rule 1
+  (A2B (A.A1 _ (B.B1 x)))
+  (B.B1 x))
+
+(rule 1
+  (A2B (A.A1 (B.B1 x) _))
+  (B.B1 x))
+
+(rule -1
+  (A2B (A.A1 _ _))
+  (B.B1 42))

cranelift/isle/src/codegen.rs

@@ -712,7 +712,11 @@ impl<'a> Codegen<'a> {
 
             let mut body_ctx: BodyContext = Default::default();
             body_ctx.expected_return_vals = 1;
-            self.generate_body(code, /* depth = */ 0, trie, "    ", &mut body_ctx)?;
+            let returned =
+                self.generate_body(code, /* depth = */ 0, trie, "    ", &mut body_ctx)?;
+            if !returned {
+                writeln!(code, "    return None;")?;
+            }
 
             writeln!(code, "}}")?;
         }
@@ -768,7 +772,11 @@ impl<'a> Codegen<'a> {
             let mut body_ctx: BodyContext = Default::default();
             body_ctx.expected_return_vals = ret_tuple_tys.len();
             body_ctx.tuple_return = true;
-            self.generate_body(code, /* depth = */ 0, trie, "    ", &mut body_ctx)?;
+            let returned =
+                self.generate_body(code, /* depth = */ 0, trie, "    ", &mut body_ctx)?;
+            if !returned {
+                writeln!(code, "    return None;")?;
+            }
             writeln!(code, "}}")?;
         }
 
@@ -1092,9 +1100,6 @@ impl<'a> Codegen<'a> {
             }
         }
 
-        if !returned {
-            writeln!(code, "{}return None;", indent)?;
-        }
         Ok(returned)
     }
 }