test: add struct deep copy integration test (#1466)

Author: SchoolyB

TESTING.md

@@ -52,7 +52,7 @@ Integration tests compile and run `.ez` programs end-to-end through the full com
 
 **Structure:**
 
-- `integration-tests/pass/core/` — 121 core language feature tests (arrays, control flow, structs, enums, maps, typeof, named returns, import variants, C interop, #strict when, or_return, raw strings, bigint arrays, pointer collections, non-standard map key ops, wide numeric map keys, [func] arrays, func var calls, enum map keys, map deep copy, wildcard types, [func] arrays of struct-namespaced refs, nested array deep copy, etc.)
+- `integration-tests/pass/core/` — 122 core language feature tests (arrays, control flow, structs, enums, maps, typeof, named returns, import variants, C interop, #strict when, or_return, raw strings, bigint arrays, pointer collections, non-standard map key ops, wide numeric map keys, [func] arrays, func var calls, enum map keys, map deep copy, wildcard types, [func] arrays of struct-namespaced refs, nested array deep copy, struct deep copy, etc.)
 - `integration-tests/pass/stdlib/` — 28 stdlib module tests
 - `integration-tests/pass/warnings/` — 22 warning detection tests
 - `integration-tests/pass/multi-file/` — 30 multi-file import tests (basic, alias, structs, enums, constants, private visibility, transitive, circular, collision, nested, struct functions)

integration-tests/pass/core/struct_deep_copy.ez

@@ -0,0 +1,90 @@
+/*
+ * struct_deep_copy.ez - copy() on structs and struct-containing shapes
+ * performs a deep copy of collection-typed fields.
+ *
+ * Regression for #1466 (commits 9b055bd + a366112):
+ *   - 9b055bd: TK_STRUCT branch in copy() deep-copies direct array/map
+ *     fields instead of falling through to a bitwise C struct copy.
+ *   - a366112: unified recursive deep-copy emitter covers transitive
+ *     struct nesting, arrays of structs with collection fields, and
+ *     maps whose values are structs with collection content.
+ *
+ * Three user-observable independence probes. A fourth gap — map[K:Struct]
+ * where Struct holds a collection — is correct internally (verified by
+ * reading the generated C during QA) but not observable from EZ user
+ * code today because map reads return struct copies, so mutations can't
+ * propagate back to the backing storage for an independence check
+ * without additional ref semantics.
+ */
+
+const Bag struct {
+    name string
+    items [int]
+}
+
+const Inner struct {
+    tag string
+    nums [int]
+}
+
+const Outer struct {
+    id int
+    inner Inner
+}
+
+do main() {
+    println("=== Struct Deep Copy Test ===")
+    mut passed int = 0
+    mut failed int = 0
+
+    // -- direct array field (fix in 9b055bd) --
+    mut bag Bag = Bag{name: "orig", items: {1, 2, 3}}
+    mut bag_copy Bag = copy(bag)
+    bag_copy.items[0] = 999
+    bag_copy.name = "copy"
+    if bag.name == "orig" && bag.items[0] == 1 &&
+       bag_copy.name == "copy" && bag_copy.items[0] == 999 {
+        println("  [PASS] direct array field in struct")
+        passed += 1
+    } otherwise {
+        println("  [FAIL] direct array field in struct")
+        failed += 1
+    }
+
+    // -- transitive struct-in-struct with inner collection (fix in a366112) --
+    mut o1 Outer = Outer{id: 1, inner: Inner{tag: "x", nums: {10, 20, 30}}}
+    mut o2 Outer = copy(o1)
+    o2.inner.nums[0] = 888
+    o2.inner.tag = "y"
+    if o1.inner.nums[0] == 10 && o1.inner.tag == "x" &&
+       o2.inner.nums[0] == 888 && o2.inner.tag == "y" {
+        println("  [PASS] transitive struct-in-struct-with-array")
+        passed += 1
+    } otherwise {
+        println("  [FAIL] transitive struct-in-struct-with-array")
+        failed += 1
+    }
+
+    // -- array of structs with a collection field (fix in a366112) --
+    mut bags [Bag] = {Bag{name: "a", items: {1, 2}}, Bag{name: "b", items: {3, 4}}}
+    mut bags_copy [Bag] = copy(bags)
+    bags_copy[0].items[0] = 777
+    bags_copy[0].name = "A"
+    if bags[0].items[0] == 1 && bags[0].name == "a" &&
+       bags_copy[0].items[0] == 777 && bags_copy[0].name == "A" {
+        println("  [PASS] array of structs with collection field")
+        passed += 1
+    } otherwise {
+        println("  [FAIL] array of structs with collection field")
+        failed += 1
+    }
+
+    println("")
+    println("Results: ${passed} passed, ${failed} failed")
+
+    if failed > 0 {
+        println("SOME TESTS FAILED")
+    } otherwise {
+        println("ALL TESTS PASSED")
+    }
+}