Initial pass parsing/reading struct (#1352)

This parses just the format `(struct)` as a new type. I added a test for
this using `wat2wasm`, but that requires a rudimentary binary format.
The test runner automatically attempts to rountrip all wat2wasm tests,
so this required implementing the wat writing and binary reading too.

Here's a summary of the changes:

* binary-reader:h: Rename `BinaryReader::OnType` callbacks to `OnFuncType`
* binary-reader.h: Add `BinaryReader::OnStructType`
* binary-reader.cc: Use a switch after reading the type form to
    determine whether we're reading a function or struct.
* tokens.def: Add new `TokenType::Struct`
* lexer-keywords.txt: Add new `struct` keyword
* type.h: Add `Type::Struct` type form
* wast-parser.cc: Parse `(struct)` in text format
* wat-writer.cc: Write Func or Struct type forms

1 files changed, 5 insertions, 5 deletions

diff --git a/src/shared-validator.cc b/src/shared-validator.cc
index e72a2a0b..1d251e2e 100644
--- a/src/shared-validator.cc
+++ b/src/shared-validator.cc
@@ -44,11 +44,11 @@ void SharedValidator::OnTypecheckerError(const char* msg) {
   PrintError(*expr_loc_, "%s", msg);
 }
 
-Result SharedValidator::OnType(const Location& loc,
-                               Index param_count,
-                               const Type* param_types,
-                               Index result_count,
-                               const Type* result_types) {
+Result SharedValidator::OnFuncType(const Location& loc,
+                                   Index param_count,
+                                   const Type* param_types,
+                                   Index result_count,
+                                   const Type* result_types) {
   types_.push_back(FuncType{ToTypeVector(param_count, param_types),
                             ToTypeVector(result_count, result_types)});
   return Result::Ok;