[wasm2js] Support exports of Globals (#4523)

Export an object with a `.value` property like the wasm JS API does
in browsers, and implement them with a getter and setter.

Fixes #4522

3 files changed, 55 insertions, 7 deletions

diff --git a/src/emscripten-optimizer/parser.cpp b/src/emscripten-optimizer/parser.cpp
index de749817f..016966299 100644
--- a/src/emscripten-optimizer/parser.cpp
+++ b/src/emscripten-optimizer/parser.cpp
@@ -107,6 +107,8 @@ IString ATOMICS("Atomics");
 IString COMPARE_EXCHANGE("compareExchange");
 IString LOAD("load");
 IString STORE("store");
+IString GETTER("get");
+IString SETTER("set");
 
 IStringSet
   keywords("var const function if else do while for break continue return "
diff --git a/src/emscripten-optimizer/parser.h b/src/emscripten-optimizer/parser.h
index 3e1623c19..c4d596058 100644
--- a/src/emscripten-optimizer/parser.h
+++ b/src/emscripten-optimizer/parser.h
@@ -124,6 +124,8 @@ extern IString ATOMICS;
 extern IString COMPARE_EXCHANGE;
 extern IString LOAD;
 extern IString STORE;
+extern IString GETTER;
+extern IString SETTER;
 
 extern IStringSet keywords;
 
@@ -207,8 +209,8 @@ template<class NodeRef, class Builder> class Parser {
   };
 
   struct Frag {
-  // MSVC does not allow unrestricted unions:
-  // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2544.pdf
+    // MSVC does not allow unrestricted unions:
+    // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2544.pdf
 #ifndef _MSC_VER
     union {
 #endif
diff --git a/src/emscripten-optimizer/simple_ast.h b/src/emscripten-optimizer/simple_ast.h
index 7644daac3..64db04d79 100644
--- a/src/emscripten-optimizer/simple_ast.h
+++ b/src/emscripten-optimizer/simple_ast.h
@@ -1463,12 +1463,24 @@ struct JSPrinter {
         newline();
       }
       bool needQuote = false;
+      const char* getterSetter = nullptr;
+      const char* setterParam = nullptr;
       const char* str;
       if (args[i][0]->isArray()) {
-        assert(args[i][0][0] == STRING);
-        // A quoted string.
-        needQuote = true;
-        str = args[i][0][1]->getCString();
+        if (args[i][0][0] == STRING) {
+          // A quoted string.
+          needQuote = true;
+          str = args[i][0][1]->getCString();
+        } else if (args[i][0][0] == GETTER) {
+          getterSetter = GETTER.c_str();
+          str = args[i][0][1]->getCString();
+        } else if (args[i][0][0] == SETTER) {
+          getterSetter = SETTER.c_str();
+          str = args[i][0][1]->getCString();
+          setterParam = args[i][0][2]->getCString();
+        } else {
+          abort();
+        }
       } else {
         // Just a raw string, no quotes.
         str = args[i][0]->getCString();
@@ -1481,6 +1493,10 @@ struct JSPrinter {
         }
         check++;
       }
+      if (getterSetter != nullptr) {
+        emit(getterSetter);
+        space();
+      }
       if (needQuote) {
         emit('"');
       }
@@ -1488,7 +1504,15 @@ struct JSPrinter {
       if (needQuote) {
         emit('"');
       }
-      emit(":");
+      if (getterSetter != nullptr) {
+        emit('(');
+        if (setterParam != nullptr) {
+          emit(setterParam);
+        }
+        emit(')');
+      } else {
+        emit(":");
+      }
       space();
       print(args[i][1]);
     }
@@ -1828,6 +1852,26 @@ public:
       &makeRawArray(2)->push_back(makeString(key)).push_back(value));
   }
 
+  static void appendToObjectAsGetter(Ref array, IString key, Ref value) {
+    assert(array[0] == OBJECT);
+    array[1]->push_back(&makeRawArray(2)
+                           ->push_back(&makeRawArray(2)
+                                          ->push_back(makeRawString(GETTER))
+                                          .push_back(makeRawString(key)))
+                           .push_back(value));
+  }
+
+  static void
+  appendToObjectAsSetter(Ref array, IString key, IString param, Ref value) {
+    assert(array[0] == OBJECT);
+    array[1]->push_back(&makeRawArray(2)
+                           ->push_back(&makeRawArray(3)
+                                          ->push_back(makeRawString(SETTER))
+                                          .push_back(makeRawString(key))
+                                          .push_back(makeRawString(param)))
+                           .push_back(value));
+  }
+
   static Ref makeSub(Ref obj, Ref index) {
     return &makeRawArray(2)
               ->push_back(makeRawString(SUB))