fix(ir_lower): release the nullable-access hidden temp after its consuming chained read

src/ir_lower/context.rs

@@ -1118,7 +1118,7 @@ impl<'m, 'f> LoweringContext<'m, 'f> {
     }
 
     /// Returns whether the value is a read from a one-shot hidden expression temp.
-    fn value_is_owned_temp_load(&self, value: ValueId) -> bool {
+    pub(crate) fn value_is_owned_temp_load(&self, value: ValueId) -> bool {
         let Some(inst) = self.builder.value_defining_instruction(value) else {
             return false;
         };

src/ir_lower/expr/mod.rs

@@ -7268,14 +7268,32 @@ fn lower_array_access_from_value(
         _ => Op::RuntimeCall,
     };
     let result_type = array_access_result_type(ctx, array_value.value, op, expr);
-    ctx.emit_value(
+    let result = ctx.emit_value(
         op,
         vec![array_value.value, index_value.value],
         None,
         result_type,
         op.default_effects(),
         Some(expr.span),
-    )
+    );
+    // A receiver materialized through a one-shot hidden owned temp (e.g. the
+    // merge temp `lower_nullable_array_access` uses for a chained `?array`
+    // read) carries an owned reference that nothing else releases anymore:
+    // `take_owned_temp` already cleared the backing slot, so this read is the
+    // temp value's last consuming use. Drop that reference here, exactly once,
+    // on the loaded SSA value itself so both merge results are freed — the
+    // populated container from the non-null path and the boxed Mixed null from
+    // the null path (Release is a no-op on genuinely empty values). This is
+    // restricted to the boxed Mixed runtime read because
+    // `__rt_mixed_array_get` returns an owned, independent cell (string
+    // payloads are persisted and child heap pointers retained), so releasing
+    // the receiver cannot invalidate the result; typed reads (`ArrayGet`,
+    // `StrCharAt`, ...) can return payloads that still borrow from the
+    // receiver's storage and must keep it alive.
+    if op == Op::RuntimeCall && ctx.value_is_owned_temp_load(array_value.value) {
+        crate::ir_lower::ownership::release_if_owned(ctx, array_value, Some(expr.span));
+    }
+    result
 }
 
 /// Lowers nullable receiver indexing without evaluating the index on a null receiver.

tests/codegen/runtime_gc/regressions.rs

@@ -1230,3 +1230,72 @@ echo "done";
         "promoting an indexed array literal to hash storage must free the source array (issue #408)"
     );
 }
+
+/// Regression test for issue #525: a chained subscript read on a `?array`
+/// receiver materializes the intermediate container through the nullable-access
+/// hidden owned temp (`lower_nullable_array_access`), and the consuming read
+/// must release that temp's reference after its last use. Exercises both the
+/// non-null receiver (populated temp) and the null receiver (boxed-null temp)
+/// on every iteration and asserts the heap is clean at exit.
+#[test]
+fn test_regression_525_nullable_chained_read_releases_hidden_temp() {
+    let out = compile_and_run_with_heap_debug(
+        r#"<?php
+function probe(?array $r): int {
+    $x = $r[0][1];
+    if ($x !== null) {
+        return 1;
+    }
+    return 0;
+}
+$hits = 0;
+for ($k = 0; $k < 50; $k++) {
+    $a = [['a', 'b' . $k]];
+    $hits = $hits + probe($a);
+    $hits = $hits + probe(null);
+}
+echo $hits;
+"#,
+    );
+    assert!(out.success, "program failed: {}", out.stderr);
+    assert_eq!(out.stdout, "50");
+    assert!(
+        out.stderr.contains("HEAP DEBUG: leak summary: clean"),
+        "expected a clean heap, got: {}",
+        out.stderr
+    );
+}
+
+/// Regression test for issue #525 (multiple reads): each chained read on the
+/// same `?array` receiver creates its own nullable-access hidden temp, and every
+/// temp's reference must be released independently — using the receiver twice
+/// must not leak either intermediate container or double-release one of them.
+#[test]
+fn test_regression_525_nullable_receiver_read_twice_heap_clean() {
+    let out = compile_and_run_with_heap_debug(
+        r#"<?php
+function probe2(?array $r): int {
+    $a = $r[0][0];
+    $b = $r[0][1];
+    if ($a !== null && $b !== null) {
+        return 1;
+    }
+    return 0;
+}
+$hits = 0;
+for ($k = 0; $k < 50; $k++) {
+    $pair = [['a' . $k, 'b' . $k]];
+    $hits = $hits + probe2($pair);
+    $hits = $hits + probe2(null);
+}
+echo $hits;
+"#,
+    );
+    assert!(out.success, "program failed: {}", out.stderr);
+    assert_eq!(out.stdout, "50");
+    assert!(
+        out.stderr.contains("HEAP DEBUG: leak summary: clean"),
+        "expected a clean heap, got: {}",
+        out.stderr
+    );
+}