[WIP] Initial support for compact imports proposal. NFC.

https://github.com/WebAssembly/compact-import-section

Author: sbc100

src/parser/parsers.h

@@ -384,6 +384,7 @@ template<typename Ctx> MaybeResult<> typedef_(Ctx&);
 template<typename Ctx> MaybeResult<> rectype(Ctx&);
 template<typename Ctx> MaybeResult<typename Ctx::LocalsT> locals(Ctx&);
 template<typename Ctx> MaybeResult<> import_(Ctx&);
+template<typename Ctx> MaybeResult<> importItem(Ctx&, Name module);
 template<typename Ctx> MaybeResult<> func(Ctx&);
 template<typename Ctx> MaybeResult<> table(Ctx&);
 template<typename Ctx> MaybeResult<> memory(Ctx&);
@@ -3308,7 +3309,12 @@ template<typename Ctx> MaybeResult<typename Ctx::LocalsT> locals(Ctx& ctx) {
   return {};
 }
 
+template<typename Ctx> MaybeResult<> importItem(Ctx& ctx, Name name) {
+  return Ok{};
+}
+
 // import ::= '(' 'import' mod:name nm:name importdesc ')'
+//            '(' 'import' mod:name compactimportdesc ')'
 // importdesc ::= '(' 'func' id? exacttypeuse ')'
 //              | '(' 'table' id? tabletype ')'
 //              | '(' 'memory' id? memtype ')'
@@ -3326,6 +3332,16 @@ template<typename Ctx> MaybeResult<> import_(Ctx& ctx) {
     return ctx.in.err("expected import module name");
   }
 
+  if (ctx.in.peekSExprStart("item"sv)) {
+    while (ctx.in.peekSExprStart("item"sv)) {
+      CHECK_ERR(importItem(ctx, *mod));
+    }
+    if (!ctx.in.takeRParen()) {
+      return ctx.in.err("expected end of import");
+    }
+    return Ok{};
+  }
+
   auto nm = ctx.in.takeName();
   if (!nm) {
     return ctx.in.err("expected import name");

src/wasm-binary.h

@@ -461,6 +461,7 @@ extern const char* BulkMemoryOptFeature;
 extern const char* CallIndirectOverlongFeature;
 extern const char* CustomDescriptorsFeature;
 extern const char* RelaxedAtomicsFeature;
+extern const char* CompactImportsFeature;
 
 enum Subsection {
   NameModule = 0,
@@ -1637,6 +1638,11 @@ class WasmBinaryReader {
                           Address defaultIfNoMax);
   void readImports();
 
+  void addImport(uint32_t kind, std::unique_ptr<Importable> importable);
+  std::unique_ptr<Importable>
+  readImportDetails(Name module, Name field, uint32_t kind);
+  std::unique_ptr<Importable> copyImportable(uint32_t kind, Importable& details);
+
   // The signatures of each function, including imported functions, given in the
   // import and function sections. Store HeapTypes instead of Signatures because
   // reconstructing the HeapTypes from the Signatures is expensive.

src/wasm-features.h

@@ -56,11 +56,12 @@ struct FeatureSet {
     CallIndirectOverlong = 1 << 20,
     CustomDescriptors = 1 << 21,
     RelaxedAtomics = 1 << 22,
+    CompactImports = 1 << 23,
     MVP = None,
     // Keep in sync with llvm default features:
     // https://github.com/llvm/llvm-project/blob/c7576cb89d6c95f03968076e902d3adfd1996577/clang/lib/Basic/Targets/WebAssembly.cpp#L150-L153
     Default = SignExt | MutableGlobals,
-    All = (1 << 23) - 1,
+    All = (1 << 24) - 1,
   };
 
   static std::string toString(Feature f) {
@@ -111,6 +112,8 @@ struct FeatureSet {
         return "custom-descriptors";
       case RelaxedAtomics:
         return "relaxed-atomics";
+      case CompactImports:
+        return "compact-imports";
       case MVP:
       case Default:
       case All:
@@ -172,6 +175,7 @@ struct FeatureSet {
     return (features & CustomDescriptors) != 0;
   }
   bool hasRelaxedAtomics() const { return (features & RelaxedAtomics) != 0; }
+  bool hasCompactImports() const { return (features & CompactImports) != 0; }
   bool hasAll() const { return (features & All) != 0; }
 
   void set(FeatureSet f, bool v = true) {