feat(parser): support PHP's (object) cast

[Guikingone]

Closes #836.

What was wrong

(object) was rejected during parsing, so the issue's reproduction failed before the cast was ever considered:

$ target/debug/elephc --check repro.php
error[3:19]: Expected ']'

Approach

The conversion is an elephc-PHP prelude, not a runtime helper. PHP's rules are a key walk plus dynamic property writes, both of which already exist as ordinary elephc-PHP, so every supported target gets the cast with no per-target assembly — the same reason var_export is a prelude.

PHP's semantics, reproduced exactly:

• an array becomes a stdClass whose property names are the array's keys rendered as strings, so (object) ['x', 'y'] has the properties 0 and 1;
• null becomes an empty stdClass;
• every other non-object value becomes a stdClass carrying it under the literal scalar property;
• an object is returned unchanged — (object) $o === $o holds and no copy is made.

Two helpers keep the cast's static type precise. __elephc_cast_object is declared : stdClass and is what lower_cast calls when the source cannot be an object, so (object) ['a' => 1] types as stdClass and property reads stay on the nominal path; only a mixed/union source needs the : mixed __elephc_cast_object_dynamic, whose identity arm can return any class. An object source is lowered to the value itself, with no call at all.

The source is lowered once into a synthetic local and the helper call then names that local — the rewrite ref_place_args already uses — so the ordinary user-call path owns argument lowering, the return type, and owned-temporary release, and a source with a side effect cannot run twice.

The cast has no call syntax, so the reachability walk records both helpers when it sees an object cast; without that the prelude was pruned and the lowered call resolved to nothing. Detection of the cast itself rides on opcache_prelude::detect's single exhaustive walk (SymbolKind::ObjectCast) so no second traversal can drift out of step with the AST, and the prelude stays pay-for-use.

Verification

Output was diffed against reference PHP 8.5 for a fixture covering every arm (array literal, array variable, integer keys, each scalar type, null, object identity, instanceof/get_class, and the (array) round trip). It matches byte for byte, including object handle numbering.

• 13 new end-to-end codegen tests in tests/codegen/casts_and_constants/object_cast.rs
• 1 new parser test asserting the Cast { target: Object } node
• 3 new prelude unit tests (pay-for-use detection, detection inside a function body, the : stdClass signature)
• cargo test --lib (1679), --test parser_tests (397), --test error_tests (1518), --test codegen_tests casts_and_constants (117) and dead_strip (9) all pass; cargo build is warning-free

Out of scope

Two pre-existing gaps were confirmed on main and are untouched by this change:

• var_dump() of a stdClass carrying dynamic properties prints (0) { }. This reproduces with a plain new stdClass(); $o->x = 1; and no cast at all, so it is a separate var_dump bug rather than a cast one.
• The eval() bridge parses only scalar casts — (array) already fails there with Parse error: eval() fragment is invalid, and (object) does the same. Adding one without the other would be asymmetric; both belong in a single follow-up.

[greptile-apps]

Greptile Summary

This PR adds PHP-compatible (object) casts throughout the compiler pipeline.

• Parses (object) as a case-insensitive cast while preserving object as an ordinary identifier token.
• Infers and lowers object casts using pay-for-use prelude helpers, including casts introduced through compile-time autoloading.
• Implements array-key projection, scalar wrapping, null conversion, and object identity semantics.
• Adds documentation, a runnable example, end-to-end behavior tests, malformed-syntax tests, and heap-debug ownership coverage.
• All previous review findings are resolved in the current code.

Confidence Score: 5/5

The PR appears safe to merge; no outstanding correctness, security, ownership, or repository-rule issue remains.

The post-review changes fully address the prior autoload-helper failure, and the previously requested lexer, parser, error, example, and ownership coverage is present. All previous threads are resolved, and no new changes exist beyond the reviewed head.

Important Files Changed

Filename	Overview
src/parser/expr/calls.rs	Recognizes the case-insensitive object cast spelling through the existing cast parser.
src/object_cast_prelude.rs	Defines and conditionally injects the static and dynamic PHP helpers implementing object-cast semantics.
src/ir_lower/expr/ternary_cast.rs	Preserves object identity and lowers non-object sources once through the appropriate helper.
src/pipeline.rs	Injects object-cast helpers after autoload expansion so casts in loaded classes are covered.
src/optimize/reachability/usage/expressions.rs	Keeps the synthetically called cast helpers reachable during prelude pruning.
tests/codegen/casts_and_constants/object_cast.rs	Covers PHP conversion semantics, identity, evaluation count, helper reachability, and autoloaded casts.
tests/codegen/runtime_gc/object_cast.rs	Exercises ownership and cleanup for arrays, strings, mixed values, objects, loops, and dropped results.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    A[PHP object cast] --> B[Parser: CastType::Object]
    B --> C[Type inference]
    C --> D{Source statically object?}
    D -- Yes --> E[Return source unchanged]
    D -- No --> F{Mixed or union?}
    F -- Yes --> G[Dynamic cast helper]
    F -- No --> H[Static cast helper]
    G --> I[Object identity or conversion]
    H --> J[stdClass conversion]
    I --> K[EIR and native codegen]
    J --> K

Loading

_{Reviews (3): Last reviewed commit: "fix(object-cast): inject past autoload, ..." | Re-trigger Greptile}

[nahime0]

lgtm