add docs and error hints when a Call should be a CallImport (#1081)

* add docs and error hints when a Call should be a CallImport

* fix binaryen API docs in docs/

2 files changed, 9 insertions, 1 deletions

diff --git a/src/binaryen-c.h b/src/binaryen-c.h
index 90c7795f0..f37bcf085 100644
--- a/src/binaryen-c.h
+++ b/src/binaryen-c.h
@@ -281,6 +281,9 @@ BinaryenExpressionRef BinaryenSwitch(BinaryenModuleRef module, const char **name
 //                   type returned by the function being called, as that
 //                   function might not have been created yet, so we don't
 //                   know what it is.
+//                   Also note that WebAssembly does not differentiate
+//                   between Call and CallImport, but Binaryen does, so you
+//                   must use CallImport if calling an import, and vice versa.
 BinaryenExpressionRef BinaryenCall(BinaryenModuleRef module, const char *target, BinaryenExpressionRef* operands, BinaryenIndex numOperands, BinaryenType returnType);
 BinaryenExpressionRef BinaryenCallImport(BinaryenModuleRef module, const char *target, BinaryenExpressionRef* operands, BinaryenIndex numOperands, BinaryenType returnType);
 BinaryenExpressionRef BinaryenCallIndirect(BinaryenModuleRef module, BinaryenExpressionRef target, BinaryenExpressionRef* operands, BinaryenIndex numOperands, const char* type);
diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index 9421070e7..21bf68b62 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -168,7 +168,12 @@ void WasmValidator::visitSwitch(Switch *curr) {
 void WasmValidator::visitCall(Call *curr) {
   if (!validateGlobally) return;
   auto* target = getModule()->getFunctionOrNull(curr->target);
-  if (!shouldBeTrue(!!target, curr, "call target must exist")) return;
+  if (!shouldBeTrue(!!target, curr, "call target must exist")) {
+    if (getModule()->getImportOrNull(curr->target)) {
+      std::cerr << "(perhaps it should be a CallImport instead of Call?)\n";
+    }
+    return;
+  }
   if (!shouldBeTrue(curr->operands.size() == target->params.size(), curr, "call param number must match")) return;
   for (size_t i = 0; i < curr->operands.size(); i++) {
     if (!shouldBeEqualOrFirstIsUnreachable(curr->operands[i]->type, target->params[i], curr, "call param types must match")) {