WastParser: tighten parsing of folded `if` (#2349)

This makes the `then` block mandatory per the spec, and parses
multiple foldedinstrs in the `if` predicate (exercised by the new
if.wast test).

4 files changed, 18 insertions, 55 deletions

diff --git a/src/wast-parser.cc b/src/wast-parser.cc
index 5d030668..ad4e2e65 100644
--- a/src/wast-parser.cc
+++ b/src/wast-parser.cc
@@ -3090,36 +3090,27 @@ Result WastParser::ParseExpr(ExprList* exprs) {
         CHECK_RESULT(ParseLabelOpt(&expr->true_.label));
         CHECK_RESULT(ParseBlockDeclaration(&expr->true_.decl));
 
-        if (PeekMatchExpr()) {
+        while (PeekMatchExpr()) {
           ExprList cond;
           CHECK_RESULT(ParseExpr(&cond));
           exprs->splice(exprs->end(), cond);
         }
 
-        if (MatchLpar(TokenType::Then)) {
-          CHECK_RESULT(ParseTerminatingInstrList(&expr->true_.exprs));
-          expr->true_.end_loc = GetLocation();
-          EXPECT(Rpar);
-
-          if (MatchLpar(TokenType::Else)) {
-            CHECK_RESULT(ParseTerminatingInstrList(&expr->false_));
-            EXPECT(Rpar);
-          } else if (PeekMatchExpr()) {
-            CHECK_RESULT(ParseExpr(&expr->false_));
-          }
-          expr->false_end_loc = GetLocation();
-        } else if (PeekMatchExpr()) {
-          CHECK_RESULT(ParseExpr(&expr->true_.exprs));
-          expr->true_.end_loc = GetLocation();
-          if (PeekMatchExpr()) {
-            CHECK_RESULT(ParseExpr(&expr->false_));
-            expr->false_end_loc = GetLocation();
-          }
-        } else {
-          ConsumeIfLpar();
+        EXPECT(Lpar);
+        if (!Match(TokenType::Then)) {
           return ErrorExpected({"then block"}, "(then ...)");
         }
 
+        CHECK_RESULT(ParseTerminatingInstrList(&expr->true_.exprs));
+        expr->true_.end_loc = GetLocation();
+        EXPECT(Rpar);
+
+        if (MatchLpar(TokenType::Else)) {
+          CHECK_RESULT(ParseTerminatingInstrList(&expr->false_));
+          EXPECT(Rpar);
+        }
+        expr->false_end_loc = GetLocation();
+
         exprs->push_back(std::move(expr));
         break;
       }
diff --git a/test/dump/br-loop-inner.txt b/test/dump/br-loop-inner.txt
index 2b38abf6..1ac9ae61 100644
--- a/test/dump/br-loop-inner.txt
+++ b/test/dump/br-loop-inner.txt
@@ -4,9 +4,9 @@
   (func
     (block $exit (loop $cont
       (if (i32.const 1)
-        (br $exit))
+        (then (br $exit)))
       (if (i32.const 2)
-        (br $cont))))))
+        (then (br $cont)))))))
 (;; STDERR ;;;
 0000000: 0061 736d                                 ; WASM_BINARY_MAGIC
 0000004: 0100 0000                                 ; WASM_BINARY_VERSION
diff --git a/test/parse/expr/bad-if-no-then.txt b/test/parse/expr/bad-if-no-then.txt
index 46525fe7..437e2ceb 100644
--- a/test/parse/expr/bad-if-no-then.txt
+++ b/test/parse/expr/bad-if-no-then.txt
@@ -2,7 +2,7 @@
 ;;; ERROR: 1
 (module (func (if (i32.const 0))))
 (;; STDERR ;;;
-out/test/parse/expr/bad-if-no-then.txt:3:32: error: unexpected token ")", expected then block (e.g. (then ...)).
+out/test/parse/expr/bad-if-no-then.txt:3:32: error: unexpected token ), expected (.
 (module (func (if (i32.const 0))))
                                ^
 ;;; STDERR ;;)
diff --git a/test/regress/regress-23.txt b/test/regress/regress-23.txt
index e74c6c2b..8bcf11fa 100644
--- a/test/regress/regress-23.txt
+++ b/test/regress/regress-23.txt
@@ -4,17 +4,6 @@
 ;; This regression test makes sure that the end_loc of `if` blocks is properly
 ;; set when using the folded format.
 
-;; if/else shorthand format, error in true branch.
-(func (result i32)
-  (if (result i32)
-    (i32.const 0)
-    (block
-      (unreachable)
-    )
-    (i32.const 0)
-  )
-)
-
 ;; if/else with `then`/`else` keywords, error in true branch.
 (func (result i32)
   (if (result i32)
@@ -30,17 +19,6 @@
   )
 )
 
-;; if/else shorthand format, error in false branch.
-(func (result i32)
-  (if (result i32)
-    (i32.const 0)
-    (i32.const 0)
-    (block
-      (unreachable)
-    )
-  )
-)
-
 ;; if/else with `then`/`else` keywords, error in false branch.
 (func (result i32)
   (if (result i32)
@@ -56,16 +34,10 @@
   )
 )
 (;; STDERR ;;;
-out/test/regress/regress-23.txt:13:5: error: type mismatch in `if true` branch, expected [i32] but got []
-    )
-    ^
-out/test/regress/regress-23.txt:25:7: error: type mismatch in `if true` branch, expected [i32] but got []
+out/test/regress/regress-23.txt:14:7: error: type mismatch in `if true` branch, expected [i32] but got []
       )
       ^
-out/test/regress/regress-23.txt:41:3: error: type mismatch in `if false` branch, expected [i32] but got []
-  )
-  ^
-out/test/regress/regress-23.txt:56:3: error: type mismatch in `if false` branch, expected [i32] but got []
+out/test/regress/regress-23.txt:34:3: error: type mismatch in `if false` branch, expected [i32] but got []
   )
   ^
 ;;; STDERR ;;)