Fix with tuple only processing first binding in build_with_dispose

.release-notes/5077.md

@@ -0,0 +1,5 @@
+## Fix `with` tuple: process every binding in dispose generation
+
+The compiler walked only the first element of a tuple pattern in `with` when building dispose calls and checking for invalid `_` bindings. Later elements were skipped, so some programs compiled incorrectly (missing dispose for later bindings, or no error for `_` in a later position).
+
+Tuple patterns now walk every element. Programs using multi-binding `with` get correct cleanup and diagnostics.

src/libponyc/pass/sugar.c

@@ -592,7 +592,8 @@ static bool build_with_dispose(pass_opt_t* opt, ast_t* dispose_clause, ast_t* id
   {
     pony_assert(ast_id(p) == TK_SEQ);
     ast_t* let = ast_child(p);
-    return build_with_dispose(opt, dispose_clause, let);
+    if(!build_with_dispose(opt, dispose_clause, let))
+      return false;
   }
 
   return true;

test/libponyc/with.cc

@@ -31,3 +31,40 @@ TEST_F(WithTest, NoEarlyReturnFromWith)
   TEST_ERRORS_1(src,
     "use return only to exit early from a with block, not at the end");
 }
+
+TEST_F(WithTest, DontcareInTupleSecondBindingIsRejected)
+{
+  // Regression: without the tuple-loop fix in build_with_dispose (sugar.c),
+  // this compiles with 0 errors (wrong). With the fix, exactly one error.
+  // build_with_dispose must recurse through every tuple element; a prior bug
+  // returned after the first binding only, so `_` in a later position was not
+  // diagnosed.
+  const char* src =
+    "class D\n"
+    "  new create() => None\n"
+    "  fun dispose() => None\n"
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    with (a, _) = (D.create(), D.create()) do\n"
+    "      None\n"
+    "    end";
+
+  TEST_ERRORS_1(src, "_ isn't allowed for a variable in a with block");
+}
+
+TEST_F(WithTest, TwoElementTupleWithCompiles)
+{
+  // Happy path: both bindings get dispose calls; tuple loop must process every
+  // element (regression for early-return bug that only handled the first).
+  const char* src =
+    "class D\n"
+    "  new create() => None\n"
+    "  fun dispose() => None\n"
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    with (a, b) = (D.create(), D.create()) do\n"
+    "      None\n"
+    "    end";
+
+  TEST_COMPILE(src);
+}