Require `then` and `else` with `if` (#6201)

We previously supported (and primarily used) a non-standard text format for
conditionals in which the condition, if-true expression, and if-false expression
were all simply s-expression children of the `if` expression. The standard text
format, however, requires the use of `then` and `else` forms to introduce the
if-true and if-false arms of the conditional. Update the legacy text parser to
require the standard format and update all tests to match. Update the printer to
print the standard format as well.

The .wast and .wat test inputs were mechanically updated with this script:
https://gist.github.com/tlively/85ae7f01f92f772241ec994c840ccbb1

7 files changed, 118 insertions, 74 deletions

diff --git a/test/spec/exception-handling-old.wast b/test/spec/exception-handling-old.wast
index 48fbe8389..75bfe70e8 100644
--- a/test/spec/exception-handling-old.wast
+++ b/test/spec/exception-handling-old.wast
@@ -605,8 +605,12 @@
           (throw $e-i32
             (if (result i32)
               (i32.const 0)
-              (pop i32) ;; pop is within an if true body
-              (i32.const 3)
+              (then
+                (pop i32) ;; pop is within an if true body
+              )
+              (else
+                (i32.const 3)
+              )
             )
           )
         )
diff --git a/test/spec/old_br_if.wast b/test/spec/old_br_if.wast
index 44aeffbe7..9ed24f153 100644
--- a/test/spec/old_br_if.wast
+++ b/test/spec/old_br_if.wast
@@ -37,10 +37,10 @@
   )
 
   (func (export "as-if-then") (param i32 i32)
-    (block (if (local.get 0) (br_if 1 (local.get 1)) (call $dummy)))
+    (block (if (local.get 0) (then (br_if 1 (local.get 1)) )(else (call $dummy))))
   )
   (func (export "as-if-else") (param i32 i32)
-    (block (if (local.get 0) (call $dummy) (br_if 1 (local.get 1))))
+    (block (if (local.get 0) (then (call $dummy) )(else (br_if 1 (local.get 1)))))
   )
 
   (func (export "nested-block-value") (param i32) (result i32)
diff --git a/test/spec/old_call.wast b/test/spec/old_call.wast
index 00bd97397..ed2cd286b 100644
--- a/test/spec/old_call.wast
+++ b/test/spec/old_call.wast
@@ -46,41 +46,61 @@
 
   (func $fac (export "fac") (param i64) (result i64)
     (if i64 (i64.eqz (local.get 0))
-      (i64.const 1)
-      (i64.mul (local.get 0) (call $fac (i64.sub (local.get 0) (i64.const 1))))
+      (then
+        (i64.const 1)
+      )
+      (else
+        (i64.mul (local.get 0) (call $fac (i64.sub (local.get 0) (i64.const 1))))
+      )
     )
   )
 
   (func $fac-acc (export "fac-acc") (param i64 i64) (result i64)
     (if i64 (i64.eqz (local.get 0))
-      (local.get 1)
-      (call $fac-acc
-        (i64.sub (local.get 0) (i64.const 1))
-        (i64.mul (local.get 0) (local.get 1))
+      (then
+        (local.get 1)
+      )
+      (else
+        (call $fac-acc
+          (i64.sub (local.get 0) (i64.const 1))
+          (i64.mul (local.get 0) (local.get 1))
+        )
       )
     )
   )
 
   (func $fib (export "fib") (param i64) (result i64)
     (if i64 (i64.le_u (local.get 0) (i64.const 1))
-      (i64.const 1)
-      (i64.add
-        (call $fib (i64.sub (local.get 0) (i64.const 2)))
-        (call $fib (i64.sub (local.get 0) (i64.const 1)))
+      (then
+        (i64.const 1)
+      )
+      (else
+        (i64.add
+          (call $fib (i64.sub (local.get 0) (i64.const 2)))
+          (call $fib (i64.sub (local.get 0) (i64.const 1)))
+        )
       )
     )
   )
 
   (func $even (export "even") (param i64) (result i32)
     (if i32 (i64.eqz (local.get 0))
-      (i32.const 44)
-      (call $odd (i64.sub (local.get 0) (i64.const 1)))
+      (then
+        (i32.const 44)
+      )
+      (else
+        (call $odd (i64.sub (local.get 0) (i64.const 1)))
+      )
     )
   )
   (func $odd (export "odd") (param i64) (result i32)
     (if i32 (i64.eqz (local.get 0))
-      (i32.const 99)
-      (call $even (i64.sub (local.get 0) (i64.const 1)))
+      (then
+        (i32.const 99)
+      )
+      (else
+        (call $even (i64.sub (local.get 0) (i64.const 1)))
+      )
     )
   )
 
diff --git a/test/spec/old_call_indirect.wast b/test/spec/old_call_indirect.wast
index 41f4316f6..00ecd0863 100644
--- a/test/spec/old_call_indirect.wast
+++ b/test/spec/old_call_indirect.wast
@@ -103,12 +103,16 @@
 
   (func $fac (export "fac") (type $over-i64)
     (if i64 (i64.eqz (local.get 0))
-      (i64.const 1)
-      (i64.mul
-        (local.get 0)
-        (call_indirect (type $over-i64)
-          (i64.sub (local.get 0) (i64.const 1))
-          (i32.const 12)
+      (then
+        (i64.const 1)
+      )
+      (else
+        (i64.mul
+          (local.get 0)
+          (call_indirect (type $over-i64)
+            (i64.sub (local.get 0) (i64.const 1))
+            (i32.const 12)
+          )
         )
       )
     )
@@ -116,15 +120,19 @@
 
   (func $fib (export "fib") (type $over-i64)
     (if i64 (i64.le_u (local.get 0) (i64.const 1))
-      (i64.const 1)
-      (i64.add
-        (call_indirect (type $over-i64)
-          (i64.sub (local.get 0) (i64.const 2))
-          (i32.const 13)
-        )
-        (call_indirect (type $over-i64)
-          (i64.sub (local.get 0) (i64.const 1))
-          (i32.const 13)
+      (then
+        (i64.const 1)
+      )
+      (else
+        (i64.add
+          (call_indirect (type $over-i64)
+            (i64.sub (local.get 0) (i64.const 2))
+            (i32.const 13)
+          )
+          (call_indirect (type $over-i64)
+            (i64.sub (local.get 0) (i64.const 1))
+            (i32.const 13)
+          )
         )
       )
     )
@@ -132,19 +140,27 @@
 
   (func $even (export "even") (param i32) (result i32)
     (if i32 (i32.eqz (local.get 0))
-      (i32.const 44)
-      (call_indirect (type $over-i32)
-        (i32.sub (local.get 0) (i32.const 1))
-        (i32.const 15)
+      (then
+        (i32.const 44)
+      )
+      (else
+        (call_indirect (type $over-i32)
+          (i32.sub (local.get 0) (i32.const 1))
+          (i32.const 15)
+        )
       )
     )
   )
   (func $odd (export "odd") (param i32) (result i32)
     (if i32 (i32.eqz (local.get 0))
-      (i32.const 99)
-      (call_indirect (type $over-i32)
-        (i32.sub (local.get 0) (i32.const 1))
-        (i32.const 14)
+      (then
+        (i32.const 99)
+      )
+      (else
+        (call_indirect (type $over-i32)
+          (i32.sub (local.get 0) (i32.const 1))
+          (i32.const 14)
+        )
       )
     )
   )
diff --git a/test/spec/old_float_exprs.wast b/test/spec/old_float_exprs.wast
index 854e21a62..c6e900f03 100644
--- a/test/spec/old_float_exprs.wast
+++ b/test/spec/old_float_exprs.wast
@@ -897,15 +897,15 @@
 ;; Test that x<y?x:y, etc. using if and else aren't folded to min, etc.
 
 (module
-  (func (export "f32.no_fold_lt_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.lt (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
-  (func (export "f32.no_fold_le_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.le (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
-  (func (export "f32.no_fold_gt_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.gt (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
-  (func (export "f32.no_fold_ge_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.ge (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
+  (func (export "f32.no_fold_lt_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.lt (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
+  (func (export "f32.no_fold_le_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.le (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
+  (func (export "f32.no_fold_gt_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.gt (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
+  (func (export "f32.no_fold_ge_if") (param $x f32) (param $y f32) (result f32) (if f32 (f32.ge (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
 
-  (func (export "f64.no_fold_lt_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.lt (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
-  (func (export "f64.no_fold_le_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.le (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
-  (func (export "f64.no_fold_gt_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.gt (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
-  (func (export "f64.no_fold_ge_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.ge (local.get $x) (local.get $y)) (local.get $x) (local.get $y)))
+  (func (export "f64.no_fold_lt_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.lt (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
+  (func (export "f64.no_fold_le_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.le (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
+  (func (export "f64.no_fold_gt_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.gt (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
+  (func (export "f64.no_fold_ge_if") (param $x f64) (param $y f64) (result f64) (if f64 (f64.ge (local.get $x) (local.get $y)) (then (local.get $x) )(else (local.get $y))))
 )
 
 (assert_return (invoke "f32.no_fold_lt_if" (f32.const 0.0) (f32.const nan)) (f32.const nan))
@@ -991,15 +991,15 @@
 ;; Test that x<0?-x:0, etc. using if aren't folded to abs
 
 (module
-  (func (export "f32.no_fold_lt_if_to_abs") (param $x f32) (result f32) (if f32 (f32.lt (local.get $x) (f32.const 0.0)) (f32.neg (local.get $x)) (local.get $x)))
-  (func (export "f32.no_fold_le_if_to_abs") (param $x f32) (result f32) (if f32 (f32.le (local.get $x) (f32.const -0.0)) (f32.neg (local.get $x)) (local.get $x)))
-  (func (export "f32.no_fold_gt_if_to_abs") (param $x f32) (result f32) (if f32 (f32.gt (local.get $x) (f32.const -0.0)) (local.get $x) (f32.neg (local.get $x))))
-  (func (export "f32.no_fold_ge_if_to_abs") (param $x f32) (result f32) (if f32 (f32.ge (local.get $x) (f32.const 0.0)) (local.get $x) (f32.neg (local.get $x))))
+  (func (export "f32.no_fold_lt_if_to_abs") (param $x f32) (result f32) (if f32 (f32.lt (local.get $x) (f32.const 0.0)) (then (f32.neg (local.get $x)) )(else (local.get $x))))
+  (func (export "f32.no_fold_le_if_to_abs") (param $x f32) (result f32) (if f32 (f32.le (local.get $x) (f32.const -0.0)) (then (f32.neg (local.get $x)) )(else (local.get $x))))
+  (func (export "f32.no_fold_gt_if_to_abs") (param $x f32) (result f32) (if f32 (f32.gt (local.get $x) (f32.const -0.0)) (then (local.get $x) )(else (f32.neg (local.get $x)))))
+  (func (export "f32.no_fold_ge_if_to_abs") (param $x f32) (result f32) (if f32 (f32.ge (local.get $x) (f32.const 0.0)) (then (local.get $x) )(else (f32.neg (local.get $x)))))
 
-  (func (export "f64.no_fold_lt_if_to_abs") (param $x f64) (result f64) (if f64 (f64.lt (local.get $x) (f64.const 0.0)) (f64.neg (local.get $x)) (local.get $x)))
-  (func (export "f64.no_fold_le_if_to_abs") (param $x f64) (result f64) (if f64 (f64.le (local.get $x) (f64.const -0.0)) (f64.neg (local.get $x)) (local.get $x)))
-  (func (export "f64.no_fold_gt_if_to_abs") (param $x f64) (result f64) (if f64 (f64.gt (local.get $x) (f64.const -0.0)) (local.get $x) (f64.neg (local.get $x))))
-  (func (export "f64.no_fold_ge_if_to_abs") (param $x f64) (result f64) (if f64 (f64.ge (local.get $x) (f64.const 0.0)) (local.get $x) (f64.neg (local.get $x))))
+  (func (export "f64.no_fold_lt_if_to_abs") (param $x f64) (result f64) (if f64 (f64.lt (local.get $x) (f64.const 0.0)) (then (f64.neg (local.get $x)) )(else (local.get $x))))
+  (func (export "f64.no_fold_le_if_to_abs") (param $x f64) (result f64) (if f64 (f64.le (local.get $x) (f64.const -0.0)) (then (f64.neg (local.get $x)) )(else (local.get $x))))
+  (func (export "f64.no_fold_gt_if_to_abs") (param $x f64) (result f64) (if f64 (f64.gt (local.get $x) (f64.const -0.0)) (then (local.get $x) )(else (f64.neg (local.get $x)))))
+  (func (export "f64.no_fold_ge_if_to_abs") (param $x f64) (result f64) (if f64 (f64.ge (local.get $x) (f64.const 0.0)) (then (local.get $x) )(else (f64.neg (local.get $x)))))
 )
 
 (assert_return (invoke "f32.no_fold_lt_if_to_abs" (f32.const nan:0x200000)) (f32.const nan:0x200000))
diff --git a/test/spec/old_unreachable.wast b/test/spec/old_unreachable.wast
index ee61f794f..a1d7934c1 100644
--- a/test/spec/old_unreachable.wast
+++ b/test/spec/old_unreachable.wast
@@ -81,13 +81,13 @@
   )
 
   (func (export "as-if-cond") (result i32)
-    (if i32 (unreachable) (i32.const 0) (i32.const 1))
+    (if i32 (unreachable) (then (i32.const 0) )(else (i32.const 1)))
   )
   (func (export "as-if-then") (param i32 i32) (result i32)
-    (if i32 (local.get 0) (unreachable) (local.get 1))
+    (if i32 (local.get 0) (then (unreachable) )(else (local.get 1)))
   )
   (func (export "as-if-else") (param i32 i32) (result i32)
-    (if i32 (local.get 0) (local.get 1) (unreachable))
+    (if i32 (local.get 0) (then (local.get 1) )(else (unreachable)))
   )
 
   (func (export "as-select-first") (param i32 i32) (result i32)
diff --git a/test/spec/stack.wast b/test/spec/stack.wast
index d0c46955d..a8c79b698 100644
--- a/test/spec/stack.wast
+++ b/test/spec/stack.wast
@@ -34,15 +34,17 @@
         (i64.eq)
         (if
           (then (br $done))
-          (else
-            (local.get $i)
-            (local.get $res)
-            (i64.mul)
-            (local.set $res)
-            (local.get $i)
-            (i64.const 1)
-            (i64.sub)
-            (local.set $i)
+          (then
+            (else
+              (local.get $i)
+              (local.get $res)
+              (i64.mul)
+              (local.set $res)
+              (local.get $i)
+              (i64.const 1)
+              (i64.sub)
+              (local.set $i)
+            )
           )
         )
         (br $loop)
@@ -91,11 +93,13 @@
         (i64.eq (local.get $i) (i64.const 0))
         (if
           (then (br $done))
-          (else
-            (i64.mul (local.get $i) (local.get $res))
-            (local.set $res)
-            (i64.sub (local.get $i) (i64.const 1))
-            (local.set $i)
+          (then
+            (else
+              (i64.mul (local.get $i) (local.get $res))
+              (local.set $res)
+              (i64.sub (local.get $i) (i64.const 1))
+              (local.set $i)
+            )
           )
         )
         (br $loop)