Allow plain `try` with no `catch` or `delegate` (#1676)

Matches recent changes in the exception handling spec that allowed
this case to reduce special cases in the syntax:

  https://github.com/WebAssembly/exception-handling/pull/157

11 files changed, 87 insertions, 67 deletions

diff --git a/src/binary-reader-ir.cc b/src/binary-reader-ir.cc
index 19fec5c9..06f4fa00 100644
--- a/src/binary-reader-ir.cc
+++ b/src/binary-reader-ir.cc
@@ -1010,7 +1010,7 @@ Result BinaryReaderIR::AppendCatch(Catch&& catch_) {
     return Result::Error;
   }
 
-  if (try_->kind == TryKind::Invalid) {
+  if (try_->kind == TryKind::Plain) {
     try_->kind = TryKind::Catch;
   } else if (try_->kind != TryKind::Catch) {
     PrintError("catch not allowed in try-delegate");
@@ -1041,7 +1041,7 @@ Result BinaryReaderIR::OnDelegateExpr(Index depth) {
 
   auto* try_ = cast<TryExpr>(label->context);
 
-  if (try_->kind == TryKind::Invalid) {
+  if (try_->kind == TryKind::Plain) {
     try_->kind = TryKind::Delegate;
   } else if (try_->kind != TryKind::Delegate) {
     PrintError("delegate not allowed in try-catch");
diff --git a/src/binary-writer.cc b/src/binary-writer.cc
index 5638bd4e..a1760023 100644
--- a/src/binary-writer.cc
+++ b/src/binary-writer.cc
@@ -1012,8 +1012,8 @@ void BinaryWriter::WriteExpr(const Func* func, const Expr* expr) {
                          GetLabelVarDepth(&try_expr->delegate_target),
                          "delegate depth");
           break;
-        case TryKind::Invalid:
-          // Should not occur.
+        case TryKind::Plain:
+          WriteOpcode(stream_, Opcode::End);
           break;
       }
       break;
diff --git a/src/expr-visitor.cc b/src/expr-visitor.cc
index fa572285..369c63bb 100644
--- a/src/expr-visitor.cc
+++ b/src/expr-visitor.cc
@@ -110,8 +110,8 @@ Result ExprVisitor::VisitExpr(Expr* root_expr) {
             case TryKind::Delegate:
               CHECK_RESULT(delegate_->OnDelegateExpr(try_expr));
               break;
-            case TryKind::Invalid:
-              // Should not happen.
+            case TryKind::Plain:
+              CHECK_RESULT(delegate_->EndTryExpr(try_expr));
               break;
           }
         }
diff --git a/src/ir.h b/src/ir.h
index d68cd141..4e49a09e 100644
--- a/src/ir.h
+++ b/src/ir.h
@@ -378,7 +378,7 @@ struct Catch {
 typedef std::vector<Catch> CatchVector;
 
 enum class TryKind {
-  Invalid,
+  Plain,
   Catch,
   Delegate
 };
@@ -603,7 +603,7 @@ class IfExpr : public ExprMixin<ExprType::If> {
 class TryExpr : public ExprMixin<ExprType::Try> {
  public:
   explicit TryExpr(const Location& loc = Location())
-      : ExprMixin<ExprType::Try>(loc), kind(TryKind::Invalid) {}
+      : ExprMixin<ExprType::Try>(loc), kind(TryKind::Plain) {}
 
   TryKind kind;
   Block block;
diff --git a/src/wast-parser.cc b/src/wast-parser.cc
index 22dd5322..9fb09c5a 100644
--- a/src/wast-parser.cc
+++ b/src/wast-parser.cc
@@ -2597,8 +2597,6 @@ Result WastParser::ParseBlockInstr(std::unique_ptr<Expr>* out_expr) {
         CHECK_RESULT(ParseVar(&var));
         expr->delegate_target = var;
         expr->kind = TryKind::Delegate;
-      } else {
-        return ErrorExpected({"catch", "catch_all", "delegate"});
       }
       CHECK_RESULT(ErrorIfLpar({"a valid try clause"}));
       expr->block.end_loc = GetLocation();
@@ -2767,26 +2765,28 @@ Result WastParser::ParseExpr(ExprList* exprs) {
         EXPECT(Do);
         CHECK_RESULT(ParseInstrList(&expr->block.exprs));
         EXPECT(Rpar);
-        EXPECT(Lpar);
-        TokenType type = Peek();
-        switch (type) {
-          case TokenType::Catch:
-          case TokenType::CatchAll:
-            CHECK_RESULT(ParseCatchExprList(&expr->catches));
-            expr->kind = TryKind::Catch;
-            break;
-          case TokenType::Delegate: {
-            Consume();
-            Var var;
-            CHECK_RESULT(ParseVar(&var));
-            expr->delegate_target = var;
-            expr->kind = TryKind::Delegate;
-            EXPECT(Rpar);
-            break;
+        if (PeekMatch(TokenType::Lpar)) {
+          Consume();
+          TokenType type = Peek();
+          switch (type) {
+            case TokenType::Catch:
+            case TokenType::CatchAll:
+              CHECK_RESULT(ParseCatchExprList(&expr->catches));
+              expr->kind = TryKind::Catch;
+              break;
+            case TokenType::Delegate: {
+              Consume();
+              Var var;
+              CHECK_RESULT(ParseVar(&var));
+              expr->delegate_target = var;
+              expr->kind = TryKind::Delegate;
+              EXPECT(Rpar);
+              break;
+            }
+            default:
+              ErrorExpected({"catch", "catch_all", "delegate"});
+              break;
           }
-          default:
-            ErrorExpected({"catch", "catch_all", "delegate"});
-            break;
         }
         CHECK_RESULT(ErrorIfLpar({"a valid try clause"}));
         expr->block.end_loc = GetLocation();
diff --git a/src/wat-writer.cc b/src/wat-writer.cc
index 74964888..07e48799 100644
--- a/src/wat-writer.cc
+++ b/src/wat-writer.cc
@@ -1171,8 +1171,8 @@ void WatWriter::FlushExprTree(const ExprTree& expr_tree) {
           WriteVar(try_expr->delegate_target, NextChar::None);
           WritePuts(")", NextChar::Newline);
           break;
-        case TryKind::Invalid:
-          // Should not occur.
+        case TryKind::Plain:
+          // Nothing to do.
           break;
       }
       WriteCloseNewline();
diff --git a/test/dump/try.txt b/test/dump/try.txt
index 672dc2a9..33ec7c3d 100644
--- a/test/dump/try.txt
+++ b/test/dump/try.txt
@@ -3,6 +3,9 @@
 (module
   (tag $e (param i32))
   (func
+    try
+      nop
+    end
     try $try1 (result i32)
       nop
       i32.const 7
@@ -55,22 +58,26 @@
 0000021: 00                                        ; func body size (guess)
 0000022: 00                                        ; local decl count
 0000023: 06                                        ; try
-0000024: 7f                                        ; i32
+0000024: 40                                        ; void
 0000025: 01                                        ; nop
-0000026: 41                                        ; i32.const
-0000027: 07                                        ; i32 literal
-0000028: 07                                        ; catch
-0000029: 00                                        ; catch tag
-000002a: 1a                                        ; drop
-000002b: 41                                        ; i32.const
-000002c: 08                                        ; i32 literal
-000002d: 0b                                        ; end
+0000026: 0b                                        ; end
+0000027: 06                                        ; try
+0000028: 7f                                        ; i32
+0000029: 01                                        ; nop
+000002a: 41                                        ; i32.const
+000002b: 07                                        ; i32 literal
+000002c: 07                                        ; catch
+000002d: 00                                        ; catch tag
 000002e: 1a                                        ; drop
-000002f: 0b                                        ; end
-0000021: 0e                                        ; FIXUP func body size
-000001f: 10                                        ; FIXUP section size
-; move data: [1e, 30) -> [1b, 2d)
-; truncate to 45 (0x2d)
+000002f: 41                                        ; i32.const
+0000030: 08                                        ; i32 literal
+0000031: 0b                                        ; end
+0000032: 1a                                        ; drop
+0000033: 0b                                        ; end
+0000021: 12                                        ; FIXUP func body size
+000001f: 14                                        ; FIXUP section size
+; move data: [1e, 34) -> [1b, 31)
+; truncate to 49 (0x31)
 ;;; STDERR ;;)
 (;; STDOUT ;;;
 
@@ -79,13 +86,16 @@ try.wasm:	file format wasm 0x1
 Code Disassembly:
 
 00001f func[0]:
- 000020: 06 7f                      | try i32
+ 000020: 06 40                      | try
  000022: 01                         |   nop
- 000023: 41 07                      |   i32.const 7
- 000025: 07 00                      | catch 0
- 000027: 1a                         |   drop
- 000028: 41 08                      |   i32.const 8
- 00002a: 0b                         | end
- 00002b: 1a                         | drop
- 00002c: 0b                         | end
+ 000023: 0b                         | end
+ 000024: 06 7f                      | try i32
+ 000026: 01                         |   nop
+ 000027: 41 07                      |   i32.const 7
+ 000029: 07 00                      | catch 0
+ 00002b: 1a                         |   drop
+ 00002c: 41 08                      |   i32.const 8
+ 00002e: 0b                         | end
+ 00002f: 1a                         | drop
+ 000030: 0b                         | end
 ;;; STDOUT ;;)
diff --git a/test/parse/expr/bad-try-clause.txt b/test/parse/expr/bad-try-clause.txt
new file mode 100644
index 00000000..f8575c8c
--- /dev/null
+++ b/test/parse/expr/bad-try-clause.txt
@@ -0,0 +1,10 @@
+;;; TOOL: wat2wasm
+;;; ARGS: --enable-exceptions
+;;; ERROR: 1
+(module
+  (func (try (do) (foo)))
+(;; STDERR ;;;
+out/test/parse/expr/bad-try-clause.txt:5:20: error: unexpected token "foo", expected catch, catch_all or delegate.
+  (func (try (do) (foo)))
+                   ^^^
+;;; STDERR ;;)
diff --git a/test/parse/expr/bad-try-no-catch.txt b/test/parse/expr/bad-try-no-catch.txt
deleted file mode 100644
index c85756fb..00000000
--- a/test/parse/expr/bad-try-no-catch.txt
+++ /dev/null
@@ -1,14 +0,0 @@
-;;; TOOL: wat2wasm
-;;; ARGS: --enable-exceptions
-;;; ERROR: 1
-(module
-  (func try nop end)
-  (func (try (do nop))))
-(;; STDERR ;;;
-out/test/parse/expr/bad-try-no-catch.txt:5:17: error: unexpected token "end", expected catch, catch_all or delegate.
-  (func try nop end)
-                ^^^
-out/test/parse/expr/bad-try-no-catch.txt:6:22: error: unexpected token ), expected (.
-  (func (try (do nop))))
-                     ^
-;;; STDERR ;;)
diff --git a/test/parse/expr/try.txt b/test/parse/expr/try.txt
index c10eebc2..51ed83b5 100644
--- a/test/parse/expr/try.txt
+++ b/test/parse/expr/try.txt
@@ -3,6 +3,12 @@
 (module
   (tag (param i32))
 
+  ;; no catch
+  (func
+    try
+      nop
+    end)
+
   ;; bare
   (func
     try
diff --git a/test/roundtrip/fold-try.txt b/test/roundtrip/fold-try.txt
index d33dbbe2..412e34ca 100644
--- a/test/roundtrip/fold-try.txt
+++ b/test/roundtrip/fold-try.txt
@@ -3,6 +3,10 @@
 (module
   (func (result i32)
     try (result i32)
+      i32.const 6
+    end
+    drop
+    try (result i32)
       nop
       i32.const 7
     catch_all
@@ -14,6 +18,10 @@
 (module
   (type (;0;) (func (result i32)))
   (func (;0;) (type 0) (result i32)
+    (drop
+      (try (result i32)  ;; label = @1
+        (do
+          (i32.const 6))))
     (try (result i32)  ;; label = @1
       (do
         (nop)