Document and clean up validation options (#730)

* document and clean up validation options

1 files changed, 31 insertions, 9 deletions

diff --git a/src/wasm-validator.h b/src/wasm-validator.h
index d741fafdc..36dc6ad04 100644
--- a/src/wasm-validator.h
+++ b/src/wasm-validator.h
@@ -17,6 +17,22 @@
 //
 // Simple WebAssembly module validator.
 //
+// There are some options regarding how to validate:
+//
+//  * validateWeb: The Web platform doesn't have i64 values, so it is illegal
+//                 to import or export such a value. When this option is set,
+//                 such imports/exports are validation errors.
+//
+//  * validateGlobally: Binaryen supports building modules in parallel, which
+//                      means you can add and optimize a function before the
+//                      module is complete, for example, you can add function A
+//                      with a call to function B before function B exists.
+//                      When validateGlobally is disabled, we don't look at
+//                      global correctness, and instead only check inside
+//                      each function (so in the example above we wouldn't care
+//                      about function B not existing yet, but we would care
+//                      if e.g. inside function A an i32.add receives an i64).
+//
 
 #ifndef wasm_wasm_validator_h
 #define wasm_wasm_validator_h
@@ -28,6 +44,8 @@ namespace wasm {
 
 struct WasmValidator : public PostWalker<WasmValidator, Visitor<WasmValidator>> {
   bool valid = true;
+
+  // what to validate, see comment up top
   bool validateWeb = false;
   bool validateGlobally = true;
 
@@ -342,23 +360,27 @@ public:
   }
 
   void visitImport(Import* curr) {
-    if (!validateWeb) return;
     if (!validateGlobally) return;
     if (curr->kind == Import::Function) {
-      shouldBeUnequal(curr->functionType->result, i64, curr->name, "Imported function must not have i64 return type");
-      for (WasmType param : curr->functionType->params) {
-        shouldBeUnequal(param, i64, curr->name, "Imported function must not have i64 parameters");
+      if (validateWeb) {
+        shouldBeUnequal(curr->functionType->result, i64, curr->name, "Imported function must not have i64 return type");
+        for (WasmType param : curr->functionType->params) {
+          shouldBeUnequal(param, i64, curr->name, "Imported function must not have i64 parameters");
+        }
       }
     }
   }
 
   void visitExport(Export* curr) {
-    if (!validateWeb) return;
     if (!validateGlobally) return;
-    Function* f = getModule()->getFunction(curr->value);
-    shouldBeUnequal(f->result, i64, f->name, "Exported function must not have i64 return type");
-    for (auto param : f->params) {
-      shouldBeUnequal(param, i64, f->name, "Exported function must not have i64 parameters");
+    if (curr->kind == Export::Function) {
+      if (validateWeb) {
+        Function* f = getModule()->getFunction(curr->value);
+        shouldBeUnequal(f->result, i64, f->name, "Exported function must not have i64 return type");
+        for (auto param : f->params) {
+          shouldBeUnequal(param, i64, f->name, "Exported function must not have i64 parameters");
+        }
+      }
     }
   }