[EH] Allow catch/delegate-less trys (#3924)

This removes the restriction that `try` should have at least one
`catch`/`catch_all`/`delegate`. See WebAssembly/exception-handling#157.

3 files changed, 7 insertions, 11 deletions

diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 84834352b..db253fa6e 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -6080,10 +6080,12 @@ void WasmBinaryBuilder::visitTryOrTryInBlock(Expression*& out) {
   // blocks instead.
   curr->type = getType();
   curr->body = getBlockOrSingleton(curr->type);
-  if (lastSeparator != BinaryConsts::Catch &&
-      lastSeparator != BinaryConsts::CatchAll &&
-      lastSeparator != BinaryConsts::Delegate) {
-    throwError("No catch instruction within a try scope");
+
+  // try without catch or delegate
+  if (lastSeparator == BinaryConsts::End) {
+    curr->finalize();
+    out = curr;
+    return;
   }
 
   Builder builder(wasm);
@@ -6200,7 +6202,7 @@ void WasmBinaryBuilder::visitTryOrTryInBlock(Expression*& out) {
   //     (catch $e
   //       (block   ;; Now this can be deleted when writing binary
   //         ...
-  //         (br $label0)
+  //         (br $label)
   //       )
   //     )
   //   )
diff --git a/src/wasm/wasm-s-parser.cpp b/src/wasm/wasm-s-parser.cpp
index 9c2d028a4..8c0fb9b2d 100644
--- a/src/wasm/wasm-s-parser.cpp
+++ b/src/wasm/wasm-s-parser.cpp
@@ -2470,9 +2470,6 @@ Expression* SExpressionWasmBuilder::makeTry(Element& s) {
     throw ParseException(
       "there should be at most one catch_all block at the end", s.line, s.col);
   }
-  if (ret->catchBodies.empty() && !ret->isDelegate()) {
-    throw ParseException("no catch bodies or delegate", s.line, s.col);
-  }
 
   ret->finalize(type);
 
diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index 6035a38a9..15b17bf26 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -2078,9 +2078,6 @@ void FunctionValidator::visitTry(Try* curr) {
   shouldBeFalse(curr->isCatch() && curr->isDelegate(),
                 curr,
                 "try cannot have both catch and delegate at the same time");
-  shouldBeTrue(curr->isCatch() || curr->isDelegate(),
-               curr,
-               "try should have either catches or a delegate");
 
   if (curr->isDelegate()) {
     noteDelegate(curr->delegateTarget, curr);