js: support WASM interoperability using `wasm_import`/`wasm_export` fn tags (#12212)

vlib/v/gen/js/fn.v

@@ -405,6 +405,17 @@ fn (mut g JsGen) is_used_by_main(node ast.FnDecl) bool {
 fn (mut g JsGen) gen_fn_decl(it ast.FnDecl) {
 	res := g.fn_gen_type(it)
 	if it.language == .js {
+		for attr in it.attrs {
+			match attr.name {
+				'wasm_import' {
+					mut x := g.wasm_export[attr.arg] or { []string{} }
+					x << it.name
+					g.wasm_import[attr.arg] = x
+				}
+				else {}
+			}
+		}
+
 		return
 	}
 	if g.inside_builtin {
@@ -535,12 +546,39 @@ fn (mut g JsGen) gen_method_decl(it ast.FnDecl, typ FnGenType) {
 		// g.write(')')
 	}
 	g.writeln('')
-
 	for attr in it.attrs {
 		match attr.name {
 			'export' {
 				g.writeln('globalThis.$attr.arg = ${g.js_name(it.name)};')
 			}
+			'wasm_export' {
+				mut x := g.wasm_export[attr.arg] or { []string{} }
+				g.write('function \$wasm${g.js_name(it.name)}(')
+				g.fn_args(args, it.is_variadic)
+				g.writeln(') {')
+				g.write('\treturn $name (')
+				for i, arg in args {
+					is_varg := i == args.len - 1 && it.is_variadic
+					arg_name := g.js_name(arg.name)
+					if is_varg {
+						g.write('...$arg_name')
+					} else {
+						g.gen_cast_tmp(arg_name, arg.typ)
+					}
+					if i != args.len - 1 {
+						g.write(',')
+					}
+				}
+				g.writeln(').valueOf();')
+				g.writeln('}')
+				x << it.name
+				g.wasm_export[attr.arg] = x
+			}
+			'wasm_import' {
+				mut x := g.wasm_export[attr.arg] or { []string{} }
+				x << name
+				g.wasm_import[attr.arg] = x
+			}
 			else {}
 		}
 	}

vlib/v/gen/js/js.v

@@ -84,6 +84,8 @@ mut:
 	defer_ifdef            string
 	out                    strings.Builder = strings.new_builder(128)
 	array_sort_fn          map[string]bool
+	wasm_export            map[string][]string
+	wasm_import            map[string][]string
 }
 
 fn (mut g JsGen) write_tests_definitions() {
@@ -211,14 +213,38 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 			}
 		}
 	}
-	g.write('js_main();')
+	if !g.pref.is_shared {
+		g.write('loadRoutine().then(_ => js_main());')
+	}
 	g.escape_namespace()
 	// resolve imports
-	deps_resolved := graph.resolve()
-	nodes := deps_resolved.nodes
+	// deps_resolved := graph.resolve()
+	// nodes := deps_resolved.nodes
 
 	mut out := g.definitions.str() + g.hashes()
-
+	out += '\nlet wasmExportObject;\n'
+	out += 'const loadRoutine = async () => {\n'
+	for mod, functions in g.wasm_import {
+		if g.pref.backend == .js_browser {
+			out += '\nawait fetch("$mod").then(respone => respone.arrayBuffer()).then(bytes => '
+			out += 'WebAssembly.instantiate(bytes,'
+			exports := g.wasm_export[mod]
+			out += '{ imports: { \n'
+			for i, exp in exports {
+				out += g.js_name(exp) + ':' + '\$wasm' + g.js_name(exp)
+				if i != exports.len - 1 {
+					out += ',\n'
+				}
+			}
+			out += '}})).then(obj => wasmExportObject = obj.instance.exports);\n'
+			for fun in functions {
+				out += 'globalThis.${g.js_name(fun)} = wasmExportObject.${g.js_name(fun)};\n'
+			}
+		} else {
+			verror('WebAssembly export is supported only for browser backend at the moment')
+		}
+	}
+	out += '}\n'
 	// equality check for js objects
 	// TODO: Fix msvc bug that's preventing $embed_file('fast_deep_equal.js')
 	// unsafe {
@@ -226,12 +252,12 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 	//	out += eq_fn.data().vstring()
 	//}
 	out += fast_deep_eq_fn
-
+	/*
 	if pref.is_shared {
 		// Export, through CommonJS, the module of the entry file if `-shared` was passed
 		export := nodes[nodes.len - 1].name
 		out += 'if (typeof module === "object" && module.exports) module.exports = $export;\n'
-	}
+	}*/
 	out += '\n'
 
 	out += g.out.str()
@@ -2982,6 +3008,40 @@ fn (mut g JsGen) gen_typeof_expr(it ast.TypeOf) {
 	}
 }
 
+fn (mut g JsGen) gen_cast_tmp(tmp string, typ_ ast.Type) {
+	// Skip cast if type is the same as the parrent caster
+	tsym := g.table.get_final_type_symbol(typ_)
+	if tsym.kind == .i64 || tsym.kind == .u64 {
+		g.write('new ')
+
+		g.write('$tsym.kind.str()')
+		g.write('(BigInt(')
+		g.write(tmp)
+		g.write('n))')
+		return
+	}
+	g.cast_stack << typ_
+	typ := g.typ(typ_)
+
+	if typ_.is_ptr() {
+		g.write('new \$ref(')
+	}
+
+	g.write('new ')
+	g.write('${typ}(')
+	g.write(tmp)
+	if typ == 'string' {
+		g.write('.toString()')
+	}
+
+	g.write(')')
+	if typ_.is_ptr() {
+		g.write(')')
+	}
+
+	g.cast_stack.delete_last()
+}
+
 fn (mut g JsGen) gen_type_cast_expr(it ast.CastExpr) {
 	is_literal := ((it.expr is ast.IntegerLiteral && it.typ in ast.integer_type_idxs)
 		|| (it.expr is ast.FloatLiteral && it.typ in ast.float_type_idxs))

vlib/v/parser/fn.v

@@ -195,6 +195,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			'direct_array_access' { is_direct_arr = true }
 			'keep_args_alive' { is_keep_alive = true }
 			'export' { is_exported = true }
+			'wasm_export' { is_exported = true }
 			'unsafe' { is_unsafe = true }
 			'trusted' { is_trusted = true }
 			'c2v_variadic' { is_c2v_variadic = true }

vlib/v/parser/parser.v

@@ -1502,7 +1502,7 @@ fn (mut p Parser) attributes() {
 	for p.tok.kind != .rsbr {
 		start_pos := p.tok.position()
 		attr := p.parse_attr()
-		if p.attrs.contains(attr.name) {
+		if p.attrs.contains(attr.name) && attr.name != 'wasm_export' {
 			p.error_with_pos('duplicate attribute `$attr.name`', start_pos.extend(p.prev_tok.position()))
 			return
 		}