Add export tests and catch duplicate exports in checker

ml-proto/src/check.ml

@@ -271,9 +271,14 @@ let check_table c tab =
     List.iter (fun xI -> check_func_type (func c xI) s xI.at) xs;
     {c with tables = c.tables @ [s]}
 
-let check_export c ex =
-  let {name = _; func = x} = ex.it in
-  ignore (func c x)
+module NameSet = Set.Make(String)
+
+let check_export c set ex =
+  let {name; func = x} = ex.it in
+  ignore (func c x);
+  require (not (NameSet.mem name set)) ex.at
+    "duplicate export name";
+  NameSet.add name set
 
 let check_segment size prev_end seg =
   let seg_end = seg.it.Memory.addr + String.length seg.it.Memory.data in
@@ -295,4 +300,4 @@ let check_module m =
                  globals = List.map it globals} in
   let c' = List.fold_left check_table c tables in
   List.iter (check_func c') funcs;
-  List.iter (check_export c') exports
+  ignore (List.fold_left (check_export c') NameSet.empty exports)

ml-proto/test/exports.wasm

@@ -0,0 +1,22 @@
+(module (func (const.i32 1)) (export "a" 0))
+(module (func (const.i32 1)) (export "a" 0) (export "b" 0))
+(module (func (const.i32 1)) (func (const.i32 2)) (export "a" 0) (export "b" 1))
+(invalid
+  (module (func (const.i32 1)) (export "a" 1))
+  "unknown function 1")
+(invalid
+  (module (func (const.i32 1)) (func (const.i32 2)) (export "a" 0) (export "a" 1))
+  "duplicate export name")
+(invalid
+  (module (func (const.i32 1)) (export "a" 0) (export "a" 0))
+  "duplicate export name")
+
+(module
+  (func $f (param $n i32) (result i32)
+    (return (add.i32 (getlocal $n) (const.i32 1)))
+  )
+
+  (export "e" $f)
+)
+
+(asserteq (invoke "e" (const.i32 42)) (const.i32 43))