Don't assume that method bodies produce the correct tuple type already

It's possible that the method body returns a subtype of the return type.
For example, a return value with type `((U32, U32) | (U32, None))` is
legal for a method with return type `(U32, (U32 | None))`, but it
requires a cast.

Fixes #2609, #2808

.release-notes/3723.md

@@ -0,0 +1,3 @@
+## Fix tuple related compiler segfaults
+
+Andreas Stührk indentified and fixed the source of two different open issues with tuple handling that caused the pony compiler to crash.

src/libponyc/codegen/genfun.c

@@ -468,17 +468,7 @@ static bool genfun_fun(compile_t* c, reach_type_t* t, reach_method_t* m)
       LLVMTypeRef f_type = LLVMGetElementType(LLVMTypeOf(c_m->func));
       LLVMTypeRef r_type = LLVMGetReturnType(f_type);
 
-      // If the result type is known to be a tuple, do the correct assignment
-      // cast even if the body type is not a tuple.
       ast_t* body_type = deferred_reify(m->fun, ast_type(body), c->opt);
-
-      if((ast_id(result) == TK_TUPLETYPE) && (ast_id(body_type) != TK_TUPLETYPE))
-      {
-        ast_free_unattached(body_type);
-        body_type = r_result;
-        r_result = NULL;
-      }
-
       LLVMValueRef ret = gen_assign_cast(c, r_type, value, body_type);
 
       ast_free_unattached(body_type);

test/libponyc/codegen.cc

@@ -989,3 +989,21 @@ TEST_F(CodegenTest, IfBlockEndingWithDontCareAssign)
   int exit_code = 0;
   ASSERT_TRUE(run_program(&exit_code));
 }
+
+TEST_F(CodegenTest, UnionValueForTupleReturnType)
+{
+  const char* src =
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    try _create_tuple()._2 as Bool end\n"
+
+    "  fun _create_tuple(): (U32, (Bool | None)) =>\n"
+    "    let x: ((U32, Bool) | (U32, None)) = (1, true)\n"
+    "    x\n";
+
+  TEST_COMPILE(src);
+
+  int exit_code = 0;
+  ASSERT_TRUE(run_program(&exit_code));
+  ASSERT_EQ(exit_code, 0);
+}