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, 26 insertions, 14 deletions

diff --git a/src/binary-writer.cc b/src/binary-writer.cc
index ab4d96ea..3f45863a 100644
--- a/src/binary-writer.cc
+++ b/src/binary-writer.cc
@@ -880,21 +880,33 @@ Result BinaryWriter::WriteModule() {
     BeginKnownSection(BinarySection::Type);
     WriteU32Leb128(stream_, module_->types.size(), "num types");
     for (size_t i = 0; i < module_->types.size(); ++i) {
-      const FuncType* func_type = cast<FuncType>(module_->types[i]);
-      const FuncSignature* sig = &func_type->sig;
-      WriteHeader("type", i);
-      WriteType(stream_, Type::Func);
-
-      Index num_params = sig->param_types.size();
-      Index num_results = sig->result_types.size();
-      WriteU32Leb128(stream_, num_params, "num params");
-      for (size_t j = 0; j < num_params; ++j) {
-        WriteType(stream_, sig->param_types[j]);
-      }
+      const TypeEntry* type = module_->types[i];
+      switch (type->kind()) {
+        case TypeEntryKind::Func: {
+          const FuncType* func_type = cast<FuncType>(type);
+          const FuncSignature* sig = &func_type->sig;
+          WriteHeader("type", i);  // TODO: switch to "func type"?
+          WriteType(stream_, Type::Func);
+
+          Index num_params = sig->param_types.size();
+          Index num_results = sig->result_types.size();
+          WriteU32Leb128(stream_, num_params, "num params");
+          for (size_t j = 0; j < num_params; ++j) {
+            WriteType(stream_, sig->param_types[j]);
+          }
 
-      WriteU32Leb128(stream_, num_results, "num results");
-      for (size_t j = 0; j < num_results; ++j) {
-        WriteType(stream_, sig->result_types[j]);
+          WriteU32Leb128(stream_, num_results, "num results");
+          for (size_t j = 0; j < num_results; ++j) {
+            WriteType(stream_, sig->result_types[j]);
+          }
+          break;
+        }
+
+        case TypeEntryKind::Struct:
+          WriteHeader("struct type", i);
+          WriteType(stream_, Type::Struct);
+          // TODO
+          break;
       }
     }
     EndSection();