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Fix let? unwrap early return for option types #8091

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Fix let? unwrap early return for option types #8091

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@

- Reanalyze: make optional args analysis liveness-aware, preventing false positives when functions are only called from dead code. https://github.com/rescript-lang/rescript/pull/8082
- Fix: do not warn for "editor" field in `rescript.json`. https://github.com/rescript-lang/rescript/pull/8084
- Fix `let?` unwrap to use actual variable names from pattern instead of hardcoded "x"/"e". When using `let? Some(myVar) = ...`, the variable name `myVar` is now properly propagated in early returns. https://github.com/rescript-lang/rescript/issues/8085

#### :memo: Documentation

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25 changes: 17 additions & 8 deletions compiler/frontend/bs_builtin_ppx.ml
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Expand Up @@ -216,6 +216,15 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
}
in
let loc = {pvb_pat.ppat_loc with loc_ghost = true} in
(* Extract the variable name from the pattern (e.g., myVar from Some(myVar)) *)
let var_name =
match pvb_pat.ppat_desc with
| Ppat_construct (_, Some inner_pat) -> (
match Ast_pat.is_single_variable_pattern_conservative inner_pat with
| Some name when name <> "" -> name
| _ -> "x")
| _ -> "x"
in
let early_case =
match variant with
(* Result: continue on Ok(_), early-return on Error(e) *)
Expand All @@ -227,9 +236,9 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
(Ast_helper.Pat.construct ~loc
{txt = Lident "Error"; loc}
(Some (Ast_helper.Pat.any ~loc ())))
{txt = "e"; loc};
{txt = var_name; loc};
pc_guard = None;
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident "e"; loc};
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident var_name; loc};
}
(* Result: continue on Error(_), early-return on Ok(x) *)
| `Result_Error ->
Expand All @@ -239,9 +248,9 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
Ast_helper.Pat.alias
(Ast_helper.Pat.construct ~loc {txt = Lident "Ok"; loc}
(Some (Ast_helper.Pat.any ~loc ())))
{txt = "x"; loc};
{txt = var_name; loc};
pc_guard = None;
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident "x"; loc};
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident var_name; loc};
}
(* Option: continue on Some(_), early-return on None *)
| `Option_Some ->
Expand All @@ -250,9 +259,9 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
pc_lhs =
Ast_helper.Pat.alias
(Ast_helper.Pat.construct ~loc {txt = Lident "None"; loc} None)
{txt = "x"; loc};
{txt = var_name; loc};
pc_guard = None;
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident "x"; loc};
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident var_name; loc};
}
(* Option: continue on None, early-return on Some(x) *)
| `Option_None ->
Expand All @@ -262,9 +271,9 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
Ast_helper.Pat.alias
(Ast_helper.Pat.construct ~loc {txt = Lident "Some"; loc}
(Some (Ast_helper.Pat.any ~loc ())))
{txt = "x"; loc};
{txt = var_name; loc};
pc_guard = None;
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident "x"; loc};
pc_rhs = Ast_helper.Exp.ident ~loc {txt = Lident var_name; loc};
}
in
default_expr_mapper self
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