Fix bug in Python backend

compiler/scalc/ast.ml

@@ -20,6 +20,8 @@ module L = Lcalc.Ast
 module TopLevelName = Uid.Make (Uid.MarkedString) ()
 module LocalName = Uid.Make (Uid.MarkedString) ()
 
+let dead_value = LocalName.fresh ("dead_value", Pos.no_pos)
+
 type expr =
   | EVar of LocalName.t
   | EFunc of TopLevelName.t

compiler/scalc/compile_from_lambda.ml

@@ -242,7 +242,18 @@ and translate_statements (ctxt : ctxt) (block_expr : 'm L.marked_expr) : A.block
     let s_e_try = translate_statements ctxt e_try in
     let s_e_catch = translate_statements ctxt e_catch in
     [A.STryExcept (s_e_try, except, s_e_catch), D.pos block_expr]
-  | L.ERaise except -> [A.SRaise except, D.pos block_expr]
+  | L.ERaise except ->
+    (* Before raising the exception, we still give a dummy definition to the
+       current variable so that tools like mypy don't complain. *)
+    (match ctxt.inside_definition_of with
+    | None -> []
+    | Some x ->
+      [
+        ( A.SLocalDef
+            ((x, D.pos block_expr), (Ast.EVar Ast.dead_value, D.pos block_expr)),
+          D.pos block_expr );
+      ])
+    @ [A.SRaise except, D.pos block_expr]
   | _ -> (
     let e_stmts, new_e = translate_expr ctxt block_expr in
     e_stmts

runtimes/python/catala/src/catala/runtime.py

@@ -614,6 +614,13 @@ def no_input() -> Callable[[Unit], Alpha]:
         raise EmptyError
     return closure
 
+
+# This value is used for the Python code generation to trump mypy and forcing
+# it to accept dead code. Indeed, when raising an exception during a variable
+# definition, mypy complains that the later dead code will not know what
+# this variable was. So we give this variable a dead value.
+dead_value: Any = 0
+
 # =======
 # Logging
 # =======

tests/test_scope/good/nothing.catala_en

@@ -0,0 +1,10 @@
+## Test
+
+```catala
+declaration scope Foo2:
+  output bar content integer
+```
+
+```catala-test {id="foo_2_scalc"}
+catala Scalc -s Foo2 -O -t
+```

tests/test_scope/good/output/nothing.catala_en.foo_2_scalc

@@ -0,0 +1,7 @@
+let Foo2 (Foo2_in : Foo2_in{}) =
+  decl temp_bar : any;
+  temp_bar = dead_value_1;
+  raise NoValueProvided;
+  decl bar : integer;
+  bar = temp_bar_4;
+  return Foo2_out {"bar_out": bar_3}

tests/test_scope/good/output/simple.catala_en.Lcalc

@@ -1,8 +1,7 @@
-let Foo_29 : Foo_in{} → Foo_out{"bar_out": integer} =
-  λ (Foo_in_30: Foo_in{}) →
-    let bar_31 : integer =
+let Foo =
+  λ (Foo_in_28: Foo_in{}) →
+    let bar_29 : integer =
       try
-        handle_default_0 [] (λ (__32: any) → true) (λ (__33: any) → 0)
+        handle_default_0 [] (λ (__30: any) → true) (λ (__31: any) → 0)
         with EmptyError -> raise NoValueProvided in
-    Foo_out {"bar_out": bar_31} in
-Foo_29
+    Foo_out {"bar_out": bar_29}

tests/test_scope/good/simple.catala_en

@@ -9,5 +9,5 @@ scope Foo:
 ```
 
 ```catala-test {id="Lcalc"}
-catala Lcalc
+catala Lcalc -s Foo
 ```