Merge pull request #2132 from DanielXMoore/claude/issue-2131-20260530-1726

Fix postfix if/unless followed by ; emitting invalid JS

Author: STRd6

source/parser.hera

@@ -6206,8 +6206,8 @@ MaybeNestedExpression ::unknown
 # (e.g. for `return` or `yield`)
 # This also doesn't allow initial __ (whereas MaybeNestedExpression does)
 MaybeParenNestedExpression
-  # Skip if there's a postfix if/etc.
-  &( _? PostfixStatement NoBlock ) -> ""
+  # Skip if there's a postfix if/etc., possibly followed by `;` (see #2131).
+  &( _? PostfixStatement ( NoBlock / ( _? Semicolon ) ) ) -> ""
   # Not nested case
   !EOS Expression -> $2
   # Avoid double wrapping nested array/object return value in parentheses.

source/parser/function.civet

@@ -1343,11 +1343,19 @@ function skipImplicitArguments(args: ASTNode[]): boolean
     if arg0!.type is "StatementExpression"
       arg0 = arg0.statement
 
-    return (and)
-      arg0!.type is "IterationExpression"
-      arg0!.subtype !== "DoStatement"
-      !arg0!.async
-      isEmptyBareBlock arg0.block
+    if arg0!.type is "IterationExpression"
+      return (and)
+        arg0!.subtype !== "DoStatement"
+        !arg0!.async
+        isEmptyBareBlock arg0.block
+
+    // Postfix `if`/`unless` followed by `;` (empty body) should be treated
+    // as a postfix modifier, not as an implicit-call argument with an empty
+    // consequent. See #2131.
+    if arg0!.type is "IfStatement"
+      return (and)
+        !arg0!.else
+        isEmptyBareBlock arg0.then
 
   return false
 

test/if.civet

@@ -636,6 +636,46 @@ describe "if", ->
     let x = 2
   """
 
+  testCase """
+    postfix if followed by semicolon (#2131)
+    ---
+    foo() if x;
+    ---
+    if (x) { foo() };
+  """
+
+  testCase """
+    postfix unless followed by semicolon (#2131)
+    ---
+    foo() unless x;
+    ---
+    if (!x) { foo() };
+  """
+
+  testCase """
+    return postfix unless followed by semicolon (#2131)
+    ---
+    return unless x;
+    ---
+    if (!x) { return };
+  """
+
+  testCase """
+    return postfix if followed by semicolon (#2131)
+    ---
+    return if x;
+    ---
+    if (x) { return };
+  """
+
+  testCase """
+    throw postfix unless followed by semicolon (#2131)
+    ---
+    throw err unless x;
+    ---
+    if (!x) { throw err };
+  """
+
   testCase """
     postfix if with indented condition
     ---