[interpreter] Build wast.js with Js_of_ocaml (#1507)

.github/workflows/main.yml

@@ -21,6 +21,17 @@ jobs:
       - run: opam install --yes ocamlbuild.0.14.0
       - run: cd interpreter && opam exec make all
 
+  ref-interpreter-js-library:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup OCaml
+        uses: ocaml/setup-ocaml@v2
+        with:
+          ocaml-compiler: 4.12.x
+      - run: opam install --yes ocamlbuild.0.14.0 ocamlfind.1.9.5 js_of_ocaml.4.0.0 js_of_ocaml-ppx.4.0.0
+      - run: cd interpreter && opam exec make wast.js
+
   build-js-api-spec:
     runs-on: ubuntu-latest
     steps:

interpreter/Makefile

@@ -2,7 +2,7 @@
 # package manager to build. However, Opam package management is available
 # optionally through the check/install/uninstall targets.
 #
-# The $(JSLIB) target requires node.js and BuckleScript.
+# The $(JSLIB).js target requires Js_of_ocaml (using ocamlfind).
 #
 # See README.me for instructions.
 
@@ -14,14 +14,15 @@ UNOPT = 	$(NAME).debug
 OPT =   	$(NAME)
 LIB =		$(NAME)
 ZIP =		$(NAME).zip
-JSLIB =		wast.js
+JSLIB =		wast
 WINMAKE =	winmake.bat
 
 DIRS =		util syntax binary text valid runtime exec script host main tests
 LIBS =		bigarray
 FLAGS = 	-lexflags -ml -cflags '-w +a-4-27-42-44-45-70 -warn-error +a-3'
 OCBA =		ocamlbuild $(FLAGS) $(DIRS:%=-I %)
 OCB =		$(OCBA) $(LIBS:%=-libs %)
+JSO =		js_of_ocaml -q --opt 3
 JS =		# set to JS shell command to run JS tests
 
 
@@ -35,7 +36,7 @@ opt:		$(OPT)
 unopt:		$(UNOPT)
 libopt:		_build/$(LIB).cmx _build/$(LIB).cmxa
 libunopt:	_build/$(LIB).cmo _build/$(LIB).cma
-jslib:		$(JSLIB)
+jslib:		$(JSLIB).js
 all:		unopt opt libunopt libopt test
 land:		$(WINMAKE) all
 zip: 		$(ZIP)
@@ -108,14 +109,15 @@ _build/$(LIB).cmxa: $(FILES) $(LIB).mllib _tags Makefile
 
 # Building JavaScript library
 
-.PHONY:		$(JSLIB)
-$(JSLIB):	$(UNOPT)
-		mkdir -p _build/jslib/src
-		cp meta/jslib/* _build/jslib
-		cp $(DIRS:%=_build/%/*.ml*) meta/jslib/*.ml _build/jslib/src
-		rm _build/jslib/src/*.ml[^i]
-		(cd _build/jslib; ./build.sh ../../$@)
+JSLIB_DIR =		meta/jslib
+JSLIB_FLAGS =	-I $(JSLIB_DIR) -use-ocamlfind -pkg js_of_ocaml -pkg js_of_ocaml-ppx
 
+.INTERMEDIATE:	$(JSLIB).byte
+$(JSLIB).byte:	$(JSLIB_DIR)/$(JSLIB).ml
+		$(OCBA) $(JSLIB_FLAGS) $@
+
+$(JSLIB).js: $(JSLIB).byte
+		$(JSO) $<
 
 # Building Windows build file
 
@@ -181,7 +183,7 @@ $(ZIP):		$(WINMAKE)
 		git archive --format=zip --prefix=$(NAME)/ -o $@ HEAD
 
 clean:
-		rm -rf _build/jslib $(LIB).mlpack _tags
+		rm -rf _build/jslib $(LIB).mlpack _tags $(JSLIB).js
 		$(OCB) -clean
 
 

interpreter/README.md

@@ -65,7 +65,10 @@ The Makefile also provides a target to compile (parts of) the interpreter into a
 ```
 make wast.js
 ```
-Building this target requires node.js and BuckleScript.
+Building this target requires `js_of_ocaml`, which can be installed with OPAM:
+```
+opam install js_of_ocaml js_of_ocaml-ppx
+```
 
 
 ## Synopsis
@@ -139,7 +142,7 @@ WebAssemblyText.encode(source)
 ```
 which turns a module in S-expression syntax into a WebAssembly binary, and
 ```
-WebAssemblyText.decode(binary, width = 80)
+WebAssemblyText.decode(binary, width)
 ```
 which pretty-prints a binary back into a canonicalised S-expression string.
 
@@ -151,7 +154,7 @@ let binary = WebAssemblyText.encode(source)
 (new WebAssembly.Instance(new WebAssembly.Module(binary))).exports.f(3, 4)
 // => 7
 
-WebAssemblyText.decode(binary)
+WebAssemblyText.decode(binary, 80)
 // =>
 // (module
 //   (type $0 (func (param i32 i32) (result i32)))
@@ -160,6 +163,20 @@ WebAssemblyText.decode(binary)
 // )
 ```
 
+Depending on how you load the library, the object may be accessed in different ways. For example, using `require` in node.js:
+
+```
+let wast = require("./wast.js");
+let binary = wast.WebAssemblyText.encode("(module)");
+```
+
+Or using `load` from a JavaScript shell:
+
+```
+load("./wast.js");
+let binary = WebAssemblyText.encode("(module)");
+```
+
 
 ## S-Expression Syntax
 

interpreter/dune

@@ -4,10 +4,9 @@
  (name wasm)
  ; The 'main' module shall not be part of the library, as it would start the
  ; Wasm REPL every time in all the dependencies.
- ; We also need to exclude the 'wasm' module as it overlaps with the library
- ; name.
+ ; We exclude the 'wast' module as it is only used for the JS build.
  ; 'smallint' is a separate test module.
- (modules :standard \ main wasm smallint))
+ (modules :standard \ main smallint wast))
 
 (executable
  (name main)

interpreter/meta/jslib/wast.ml

@@ -0,0 +1,26 @@
+(* Implements a wrapper library that allows the use of the reference
+ * interpreter's encode/decode functionality in JavaScript.
+ *)
+open Js_of_ocaml
+
+let _ =
+  Js.export "WebAssemblyText"
+    (object%js (_self)
+
+      method encode (s : Js.js_string Js.t) : (Typed_array.arrayBuffer Js.t) =
+        let def = Parse.string_to_module (Js.to_string s) in
+        let bs =
+          match def.Source.it with
+          | Script.Textual m -> (Encode.encode m)
+          | Script.Encoded (_, bs) -> bs
+          | Script.Quoted (_, _) -> failwith "Unsupported" in
+        let buf = new%js Typed_array.arrayBuffer (String.length bs) in
+        let u8arr = new%js Typed_array.uint8Array_fromBuffer buf in
+        String.iteri (fun i c -> Typed_array.set u8arr i (int_of_char c)) bs; buf
+
+      method decode (buf : Typed_array.arrayBuffer Js.t) width : (Js.js_string Js.t) =
+        let s = Typed_array.String.of_uint8Array (new%js Typed_array.uint8Array_fromBuffer buf) in
+        let m = Decode.decode "(decode)" s in
+        Js.string (Sexpr.to_string width (Arrange.module_ m))
+
+    end)