[Parser] Support standalone import definitions

src/parser/contexts.h

@@ -1249,6 +1249,11 @@ struct ParseDefsCtx : TypeParserCtx<ParseDefsCtx> {
     return Ok{};
   }
 
+  Result<>
+  addMemory(Name, const std::vector<Name>&, ImportNames*, TableTypeT, Index) {
+    return Ok{};
+  }
+
   Result<> addGlobal(Name,
                      const std::vector<Name>&,
                      ImportNames*,
@@ -1259,7 +1264,7 @@ struct ParseDefsCtx : TypeParserCtx<ParseDefsCtx> {
   Result<> addImplicitElems(Type type, std::vector<Expression*>&& elems);
 
   Result<> addDeclareElem(Name, std::vector<Expression*>&&, Index) {
-    // TODO: Validate that referenced functions appear in a declaratve element
+    // TODO: Validate that referenced functions appear in a declarative element
     // segment.
     return Ok{};
   }
@@ -1273,6 +1278,11 @@ struct ParseDefsCtx : TypeParserCtx<ParseDefsCtx> {
   Result<>
   addData(Name, Name* mem, std::optional<ExprT> offset, DataStringT, Index pos);
 
+  Result<>
+  addTag(Name, const std::vector<Name>, ImportNames*, TypeUseT, Index) {
+    return Ok{};
+  }
+
   Result<> addExport(Index, Name value, Name name, ExternalKind kind) {
     wasm.addExport(builder.makeExport(name, value, kind));
     return Ok{};

src/parser/parsers.h

@@ -191,6 +191,7 @@ template<typename Ctx> Result<> strtype(Ctx&);
 template<typename Ctx> MaybeResult<typename Ctx::ModuleNameT> subtype(Ctx&);
 template<typename Ctx> MaybeResult<> deftype(Ctx&);
 template<typename Ctx> MaybeResult<typename Ctx::LocalsT> locals(Ctx&);
+template<typename Ctx> MaybeResult<> import_(Ctx&);
 template<typename Ctx> MaybeResult<> func(Ctx&);
 template<typename Ctx> MaybeResult<> table(Ctx&);
 template<typename Ctx> MaybeResult<> memory(Ctx&);
@@ -2168,6 +2169,71 @@ template<typename Ctx> MaybeResult<typename Ctx::LocalsT> locals(Ctx& ctx) {
   return {};
 }
 
+// import ::= '(' 'import' mod:name nm:name importdesc ')'
+// importdesc ::= '(' 'func' id? typeuse ')'
+//              | '(' 'table' id? tabletype ')'
+//              | '(' 'memory' id? memtype ')'
+//              | '(' 'global' id? globaltype ')'
+//              | '(' 'tag' id? typeuse ')'
+template<typename Ctx> MaybeResult<> import_(Ctx& ctx) {
+  auto pos = ctx.in.getPos();
+
+  if (!ctx.in.takeSExprStart("import"sv)) {
+    return {};
+  }
+
+  auto mod = ctx.in.takeName();
+  if (!mod) {
+    return ctx.in.err("expected import module name");
+  }
+
+  auto nm = ctx.in.takeName();
+  if (!nm) {
+    return ctx.in.err("expected import name");
+  }
+  ImportNames names{*mod, *nm};
+
+  if (ctx.in.takeSExprStart("func"sv)) {
+    auto name = ctx.in.takeID();
+    auto type = typeuse(ctx);
+    CHECK_ERR(type);
+    CHECK_ERR(
+      ctx.addFunc(name ? *name : Name{}, {}, &names, *type, std::nullopt, pos));
+  } else if (ctx.in.takeSExprStart("table"sv)) {
+    auto name = ctx.in.takeID();
+    auto type = tabletype(ctx);
+    CHECK_ERR(type);
+    CHECK_ERR(ctx.addTable(name ? *name : Name{}, {}, &names, *type, pos));
+  } else if (ctx.in.takeSExprStart("memory"sv)) {
+    auto name = ctx.in.takeID();
+    auto type = memtype(ctx);
+    CHECK_ERR(type);
+    CHECK_ERR(ctx.addMemory(name ? *name : Name{}, {}, &names, *type, pos));
+  } else if (ctx.in.takeSExprStart("global"sv)) {
+    auto name = ctx.in.takeID();
+    auto type = globaltype(ctx);
+    CHECK_ERR(type);
+    CHECK_ERR(ctx.addGlobal(
+      name ? *name : Name{}, {}, &names, *type, std::nullopt, pos));
+  } else if (ctx.in.takeSExprStart("tag"sv)) {
+    auto name = ctx.in.takeID();
+    auto type = typeuse(ctx);
+    CHECK_ERR(type);
+    CHECK_ERR(ctx.addTag(name ? *name : Name{}, {}, &names, *type, pos));
+  } else {
+    return ctx.in.err("expected import description");
+  }
+
+  if (!ctx.in.takeRParen()) {
+    return ctx.in.err("expected end of import description");
+  }
+  if (!ctx.in.takeRParen()) {
+    return ctx.in.err("expected end of import");
+  }
+
+  return Ok{};
+}
+
 // func ::= '(' 'func' id? ('(' 'export' name ')')*
 //              x,I:typeuse t*:vec(local) (in:instr)* ')'
 //        | '(' 'func' id? ('(' 'export' name ')')*
@@ -2651,6 +2717,10 @@ template<typename Ctx> MaybeResult<> modulefield(Ctx& ctx) {
     CHECK_ERR(res);
     return Ok{};
   }
+  if (auto res = import_(ctx)) {
+    CHECK_ERR(res);
+    return Ok{};
+  }
   if (auto res = func(ctx)) {
     CHECK_ERR(res);
     return Ok{};

src/parser/wat-parser.cpp

@@ -80,9 +80,13 @@ Result<> parseDefs(Ctx& ctx,
   for (auto& def : defs) {
     ctx.index = def.index;
     WithPosition with(ctx, def.pos);
-    auto parsed = parser(ctx);
-    CHECK_ERR(parsed);
-    assert(parsed);
+    if (auto parsed = parser(ctx)) {
+      CHECK_ERR(parsed);
+    } else {
+      auto im = import_(ctx);
+      assert(im);
+      CHECK_ERR(im);
+    }
   }
   return Ok{};
 }
@@ -174,9 +178,13 @@ Result<> parseModule(Module& wasm, std::string_view input) {
       ctx.index = i;
       CHECK_ERR(ctx.visitFunctionStart(wasm.functions[i].get()));
       WithPosition with(ctx, decls.funcDefs[i].pos);
-      auto parsed = func(ctx);
-      CHECK_ERR(parsed);
-      assert(parsed);
+      if (auto parsed = func(ctx)) {
+        CHECK_ERR(parsed);
+      } else {
+        auto im = import_(ctx);
+        assert(im);
+        CHECK_ERR(im);
+      }
     }
 
     // Parse exports.