Merge the Lam IR into Lambda

AGENTS.md

@@ -47,8 +47,6 @@ The Makefile’s targets build on each other in this order:
 
 - **Don't use unit `()` with mandatory labeled arguments** - When a function has a mandatory labeled argument (like `~config`), don't add a trailing `()` parameter. The labeled argument already prevents accidental partial application. Only use `()` when all parameters are optional and you need to force evaluation. Example: `let forceDelayedItems ~config = ...` not `let forceDelayedItems ~config () = ...`
 
-- **Be careful with similar constructor names across different IRs** - Note that `Lam` (Lambda IR) and `Lambda` (typed lambda) have variants with similar constructor names like `Ltrywith`, but they represent different things in different compilation phases.
-
 - **Avoid warning suppressions** - Never use `[@@warning "..."]` to silence warnings. Instead, fix the underlying issue properly
 - **Skip trailing `; _` in record patterns** - The warning it targets is disabled in this codebase, so prefer `{field = x}` over `{field = x; _}`.
 
@@ -116,8 +114,8 @@ Read the area guide before changing a compiler subsystem:
   printing, and JSX transformation
 - [`compiler/ml/README.md`](compiler/ml/README.md) for the type checker and
   typed tree
-- [`compiler/core/README.md`](compiler/core/README.md) for Lambda, Lam, and
-  JavaScript generation
+- [`compiler/core/README.md`](compiler/core/README.md) for Lambda
+  optimization and JavaScript generation
 - [`analysis/README.md`](analysis/README.md) for editor analysis
 - [`rewatch/README.md`](rewatch/README.md) for the build system
 - [`tools/README.md`](tools/README.md) for `rescript-tools`

CHANGELOG.md

@@ -32,6 +32,9 @@
 
 #### :bug: Bug fix
 
+- Fix a recursive module with an empty signature discarding its right-hand side. Lambda-to-Lam conversion rewrote `Pupdate_mod` to unit when the module's shape had no fields, dropping the primitive's arguments - one of which is the right-hand side - so `module rec M: {} = { let () = Console.log("effect") }` emitted nothing for `M`. The elision now happens where the bindings are produced, with the right-hand side still in hand. https://github.com/rescript-lang/rescript/pull/8608
+- Fix `Int.Ref.increment` and `Int.Ref.decrement` evaluating their argument twice: `Int.Ref.increment(mkRef())` emitted `mkRef().contents = mkRef().contents + 1 | 0`. The `%incr` and `%decr` builtins lowered to an assignment that repeated the argument expression; they now bind the reference before the read-modify-write. Inlining decisions around an increment are taken on the code it stands for rather than on a single primitive node. https://github.com/rescript-lang/rescript/pull/8608
+- Fix a compiler crash on a polymorphic variant whose numeric name exceeds the `int32` range. `#99999999999("a")` and the same name in a pattern failed with `Failure("Int32.of_string")` and no location, because the range check ran in the frontend AST pass and matched only payload-free expressions. It now runs in `Typecore`, next to the integer literal decoding whose overflow error it mirrors, and covers both label positions. A bare `type t = [#99999999999]` still compiles, since nothing decodes a row field name. https://github.com/rescript-lang/rescript/pull/8608
 - Object typing errors now describe fields directly: assigning to a field without `@set` reports that the field is not settable and suggests the annotation, and missing-property errors name the field instead of a phantom `"x#="` member. https://github.com/rescript-lang/rescript/pull/8597
 - Fix signature inclusion rejecting equivalent object externals after type-alias expansion. https://github.com/rescript-lang/rescript/pull/8581
 - Fix externals whose result type is an alias of `unit` so they use the same unit-return behavior as externals declared to return `unit`. https://github.com/rescript-lang/rescript/pull/8581
@@ -60,6 +63,7 @@
 
 #### :house: Internal
 
+- Merge the duplicate Lam intermediate representation into Lambda, removing the conversion layer and obsolete supporting infrastructure. Lambda is now a single private, normalized representation, with generated JavaScript remaining semantically unchanged. https://github.com/rescript-lang/rescript/pull/8608
 - Rework the object-type representation end to end: object rows are plain field chains carrying a per-field mutability state (no phantom setter members), object literals are typed directly and property access and assignment are first-class AST and Lambda nodes shared between the Lambda and JS pipelines, and dead class-system remnants (the field-presence lattice, the class-abbreviation memo on object types, method-send typing) are removed. https://github.com/rescript-lang/rescript/pull/8597
 - Upgrade the development toolchain and primary CI builds to OCaml 5.5 while retaining OCaml 5.0 as the minimum supported version. https://github.com/rescript-lang/rescript/pull/8589
 - Upgrade the vendored Flow parser from 0.267.0 to 0.320.0, the final release of the OCaml implementation. https://github.com/rescript-lang/rescript/pull/8588

compiler/bsc/rescript_compiler_main.ml

@@ -408,10 +408,10 @@ let command_line_flags : (string * Bsc_args.spec * string) array =
       "*internal* Disable cross module inlining(experimental)" );
     ( "-debug-ir",
       set Js_config.debug_ir,
-      "*internal* Dump compiler IR and enable Lam invariant checks" );
+      "*internal* Dump compiler IR and enable Lambda invariant checks" );
     ( "-check-lam",
       set Js_config.check_lam,
-      "*internal* Check Lam invariants after optimization passes" );
+      "*internal* Check Lambda invariants after optimization passes" );
     ( "-bs-no-check-div-by-zero",
       clear Js_config.check_div_by_zero,
       "*internal* unsafe mode, don't check div by zero and mod by zero" );

compiler/common/js_config.mli

@@ -53,7 +53,7 @@ val debug_ir : bool ref
 (** dump intermediate representations and related diagnostics *)
 
 val check_lam : bool ref
-(** check Lam invariants after optimization passes *)
+(** check Lambda invariants after optimization passes *)
 
 val no_builtin_ppx : bool ref
 (** options for builtin ppx *)

compiler/core/README.md

@@ -1,8 +1,8 @@
-# Lambda, Lam, and JavaScript generation
+# Lambda optimization and JavaScript generation
 
 This directory contains the compiler backend after typedtree translation. It
-owns ReScript's Lam representation, Lam optimization passes, JavaScript IR,
-and JavaScript output.
+owns the Lambda optimization passes, the JavaScript IR, and JavaScript output.
+Lambda itself is defined in [`../ml/lambda.mli`](../ml/lambda.mli).
 
 ## Pipeline and code map
 
@@ -11,16 +11,16 @@ Typedtree translation in `compiler/ml/translcore.ml` and
 `compiler/ml/lambda.mli`.
 
 [`lam_convert.ml`](lam_convert.ml)
-: Converts `Lambda.lambda` to the ReScript-specific [`Lam.t`](lam.mli),
-  normalizes aliases, and collects potential module dependencies.
+: Collects the modules a compilation unit depends on, read off the Lambda
+  term.
 
 `lam_pass_*.ml` and the other `lam_*.ml` modules
-: Analyze and transform Lam. [`lam_compile_main.ml`](lam_compile_main.ml)
+: Analyze and transform Lambda. [`lam_compile_main.ml`](lam_compile_main.ml)
   coordinates the backend pass sequence; read it before inserting or
   reordering a pass.
 
 [`lam_compile.ml`](lam_compile.ml)
-: Lowers Lam to JavaScript IR. Primitive-specific and FFI lowering is split
+: Lowers Lambda to JavaScript IR. Primitive-specific and FFI lowering is split
   into `lam_compile_primitive.ml`, `lam_compile_external_call.ml`, and related
   modules.
 
@@ -34,12 +34,14 @@ Typedtree translation in `compiler/ml/translcore.ml` and
 
 ## Changing a representation
 
-`Lambda` and `Lam` have similarly named constructors but are distinct IRs.
-When adding or changing one, search every producer, traversal, optimizer,
-printer, serializer, and consumer of that specific type. Do not assume a match
-on the other representation covers it.
+`Lambda.t` is private: every term is built through the constructors in
+[`../ml/lambda.mli`](../ml/lambda.mli), six of which normalize as they build.
+A constructor may replace a node with an equivalent one, but may not move code
+between branches - that is what a pass is for. When adding or changing a
+constructor, search every producer, traversal, optimizer, printer, serializer,
+and consumer.
 
-Check persistence boundaries as part of the change. `Lam.t` can be stored in
+Check persistence boundaries as part of the change. `Lambda.t` can be stored in
 `.cmj` data through `js_cmj_format`; a constructor or payload change therefore
 changes cached compiler data even when generated JavaScript is unchanged.
 
@@ -65,5 +67,5 @@ compiler flags below to compare intermediate forms for a small source file:
 ./cli/bsc.js -drawlambda example.res
 ```
 
-For Lam-specific debugging, use [`lam_print.ml`](lam_print.ml) at the relevant
+For backend debugging, use [`lam_print.ml`](lam_print.ml) at the relevant
 pass boundary and remove temporary output before committing.

compiler/core/ir_diagnostics.ml

@@ -29,14 +29,14 @@ let next_path diagnostics ~kind ~pass ~extension =
 
 let dump_lam diagnostics ~pass lam =
   let path = next_path diagnostics ~kind:"lam" ~pass ~extension:".lam" in
-  Ext_log.dwarn ~__POS__ "Dumping Lam pass %s to %s" pass path;
-  Lam_print.serialize path lam
+  Ext_log.dwarn ~__POS__ "Dumping pass %s to %s" pass path;
+  Printlambda.serialize path lam
 
 let dump_groups diagnostics groups =
   let path =
     next_path diagnostics ~kind:"lam" ~pass:"groups" ~extension:".lambda"
   in
-  Ext_log.dwarn ~__POS__ "Dumping Lam groups to %s" path;
+  Ext_log.dwarn ~__POS__ "Dumping groups to %s" path;
   Ext_fmt.with_file_as_pp path (fun fmt ->
       Format.pp_print_list ~pp_sep:Format.pp_print_newline Lam_group.pp_group
         fmt groups)

compiler/core/ir_diagnostics.mli

@@ -1,6 +1,6 @@
 type t
 
 val create : output_prefix:string -> t
-val dump_lam : t -> pass:string -> Lam.t -> unit
+val dump_lam : t -> pass:string -> Lambda.t -> unit
 val dump_groups : t -> Lam_group.t list -> unit
 val dump_js : t -> pass:string -> J.program -> unit

compiler/core/js_block_runtime.ml

@@ -24,10 +24,7 @@
 
 let option_id = Ident.create_persistent Primitive_modules.option
 
-let curry_id = Ident.create_persistent Primitive_modules.curry
-
 let check_additional_id (x : J.expression) : Ident.t option =
   match x.expression_desc with
   | Optional_block (_, false) -> Some option_id
-  | Call (_, _, {arity = NA}) -> Some curry_id
   | _ -> None

compiler/core/js_call_info.ml

@@ -22,8 +22,6 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
 
-type arity = Full | NA
-
 type call_info =
   | Call_ml (* called by plain ocaml expression *)
   | Call_builtin_runtime (* built-in externals *)
@@ -33,15 +31,12 @@ type call_info =
    {[ fun x y -> (f x y) === f ]} when [f] is an atom
 *)
 
-type t = {call_info: call_info; arity: arity; call_transformed_jsx: bool}
-
-let dummy = {arity = NA; call_info = Call_na; call_transformed_jsx = false}
+type t = {call_info: call_info; call_transformed_jsx: bool}
 
 let builtin_runtime_call =
-  {arity = Full; call_info = Call_builtin_runtime; call_transformed_jsx = false}
+  {call_info = Call_builtin_runtime; call_transformed_jsx = false}
 
-let ml_full_call =
-  {arity = Full; call_info = Call_ml; call_transformed_jsx = false}
+let ml_full_call = {call_info = Call_ml; call_transformed_jsx = false}
 
 let na_full_call transformed_jsx =
-  {arity = Full; call_info = Call_na; call_transformed_jsx = transformed_jsx}
+  {call_info = Call_na; call_transformed_jsx = transformed_jsx}

compiler/core/js_call_info.mli

@@ -24,8 +24,6 @@
 
 (** Type for collecting call site information, used in JS IR *)
 
-type arity = Full | NA
-
 type call_info =
   | Call_ml (* called by plain ocaml expression *)
   | Call_builtin_runtime (* built-in externals *)
@@ -35,9 +33,7 @@ type call_info =
    {[ fun x y -> f x y === f ]} when [f] is an atom
 *)
 
-type t = {call_info: call_info; arity: arity; call_transformed_jsx: bool}
-
-val dummy : t
+type t = {call_info: call_info; call_transformed_jsx: bool}
 
 val builtin_runtime_call : t
 

compiler/core/js_cmj_format.ml

@@ -29,7 +29,7 @@ type arity = Single of Lam_arity.t | Submodule of Lam_arity.t array
 (* TODO: add a magic number *)
 type cmj_value = {
   arity: arity;
-  persistent_closed_lambda: Lam.t option;
+  persistent_closed_lambda: Lambda.t option;
       (** Either constant or closed functor *)
 }
 
@@ -40,7 +40,7 @@ let single_na = Single Lam_arity.na
 type keyed_cmj_value = {
   name: string;
   arity: arity;
-  persistent_closed_lambda: Lam.t option;
+  persistent_closed_lambda: Lambda.t option;
 }
 
 type keyed_cmj_values = keyed_cmj_value array

compiler/core/js_cmj_format.mli

@@ -49,15 +49,16 @@ type arity = Single of Lam_arity.t | Submodule of Lam_arity.t array
 
 type cmj_value = {
   arity: arity;
-  persistent_closed_lambda: Lam.t option; (* Either constant or closed functor *)
+  persistent_closed_lambda: Lambda.t option;
+      (* Either constant or closed functor *)
 }
 
 type effect_ = string option
 
 type keyed_cmj_value = {
   name: string;
   arity: arity;
-  persistent_closed_lambda: Lam.t option;
+  persistent_closed_lambda: Lambda.t option;
 }
 
 type hoisted_export = {