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fix: generate Drop cleanup for unassigned Drop-typed expressions #417

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fix: generate Drop cleanup for unassigned Drop-typed expressions #417

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3091892
fix: generate Drop cleanup for unassigned Drop-typed expressions
KuaaMU-a Apr 30, 2026
ed284b0
test: add regression test for unassigned Drop expressions (#406)
KuaaMU May 1, 2026
7f9bb60
fix: add kind check for inferred type fallback in Drop cleanup
KuaaMU May 1, 2026
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30 changes: 28 additions & 2 deletions src/codegen/codegen_stmt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2500,8 +2500,32 @@ void codegen_node_single(ParserContext *ctx, ASTNode *node, FILE *out)
break;
}
default:
codegen_expression(ctx, node, out);
fprintf(out, ";\n");
{
// Check if expression returns a Drop type that needs cleanup.
// Without this, bare calls like `MyInt::new()` leak memory (issue #406).
int expr_has_drop = 0;
char *inferred = infer_type(ctx, node);
if (inferred) {
char *ct = inferred;
if (strncmp(ct, "struct ", 7) == 0) ct += 7;
ASTNode *def = find_struct_def(ctx, ct);
expr_has_drop = (def && def->type_info) ? def->type_info->traits.has_drop
: (node->type_info ? node->type_info->traits.has_drop : 0);
free(inferred);
} else if (node->type_info) {
TypeKind k = node->type_info->kind;
if (k == TYPE_STRUCT || k == TYPE_ENUM)
expr_has_drop = node->type_info->traits.has_drop;
}
if (expr_has_drop) {
int id = tmp_counter++;
fprintf(out, " ZC_AUTO _z_tmp_%d = ", id);
codegen_expression(ctx, node, out);
fprintf(out, ";\n _z_drop(_z_tmp_%d);\n", id);
Comment on lines +2525 to +2529
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@KuaaMU KuaaMU May 1, 2026

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Valid concern. For bare lvalue statements like x; or obj.field;, the current fix would copy into a temp and drop the temp, leaving the original intact. This is safe because the original still gets dropped at scope end via the normal variable-drop mechanism. There is no double-drop because the temp is a copy, not a move. However, if the type has non-trivial copy semantics (e.g. refcounted), this could be wasteful. A follow-up could check if the expression is an lvalue and skip the temp in that case.

} else {
codegen_expression(ctx, node, out);
fprintf(out, ";\n");
Comment on lines +2504 to +2532
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@KuaaMU KuaaMU May 1, 2026

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Good catch! Added regression test that verifies as a bare statement triggers drop cleanup. Test passes with the fix and would fail without it.

}
Comment on lines +2507 to +2533
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@KuaaMU KuaaMU May 1, 2026

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Good point. The else branch already guards with k == TYPE_STRUCT || k == TYPE_ENUM, so TYPE_FUNCTION won't set expr_has_drop via that path. The primary branch uses find_struct_def which returns NULL for function types, so expr_has_drop stays 0. The risk is in the fallback: if a function type somehow has traits.has_drop=1 AND no struct def is found, the inferred-type path could incorrectly flag it. A defensive fix would be to add the same kind check in the inferred-type path. Will address in a follow-up.

if (node->type == NODE_EXPR_CALL && node->call.callee && pending_closure_free_count > 0)
{
int is_thread_spawn = 0;
Expand All @@ -2524,6 +2548,8 @@ void codegen_node_single(ParserContext *ctx, ASTNode *node, FILE *out)
}
}
emit_pending_closure_frees(out);
break;
}
}
}

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