feat(zend): resolve type-param vs type-name collisions via shadowing, error only at runtime use

azjezz · azjezz · commit 8d4cbe44d5bd · 2026-05-06T18:01:11.000+01:00
Signed-off-by: azjezz &lt;azjezz@protonmail.com&gt;
diff --git a/Zend/tests/generics/errors/type_param_in_catch.phpt b/Zend/tests/generics/errors/type_param_in_catch.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Errors: type parameter cannot be used at runtime in `catch`
+--FILE--
+<?php
+function f<T>(): void {
+    try { /* ... */ } catch (T $e) {}
+}
+?>
+--EXPECTF--
+Fatal error: Cannot use generic type parameter T as a class reference at runtime; bound-erased generic types have no runtime representation in %s on line %d
diff --git a/Zend/tests/generics/errors/type_param_in_class_const.phpt b/Zend/tests/generics/errors/type_param_in_class_const.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Errors: type parameter cannot be used at runtime in `T::class`
+--FILE--
+<?php
+function f<T>(): string {
+    return T::class;
+}
+?>
+--EXPECTF--
+Fatal error: Cannot use generic type parameter T as a class reference at runtime; bound-erased generic types have no runtime representation in %s on line %d
diff --git a/Zend/tests/generics/errors/type_param_in_instanceof.phpt b/Zend/tests/generics/errors/type_param_in_instanceof.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Errors: type parameter cannot be used at runtime in `instanceof`
+--FILE--
+<?php
+function f<T>($x): bool {
+    return $x instanceof T;
+}
+?>
+--EXPECTF--
+Fatal error: Cannot use generic type parameter T as a class reference at runtime; bound-erased generic types have no runtime representation in %s on line %d
diff --git a/Zend/tests/generics/errors/type_param_in_new_expression.phpt b/Zend/tests/generics/errors/type_param_in_new_expression.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Errors: type parameter cannot be used at runtime as a class in `new T()`
+--FILE--
+<?php
+function f<T>(): void {
+    $x = new T();
+}
+?>
+--EXPECTF--
+Fatal error: Cannot use generic type parameter T as a class reference at runtime; bound-erased generic types have no runtime representation in %s on line %d
diff --git a/Zend/tests/generics/errors/type_param_in_static_call.phpt b/Zend/tests/generics/errors/type_param_in_static_call.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Errors: type parameter cannot be used at runtime as a static-call target
+--FILE--
+<?php
+function f<T>(): void {
+    T::foo();
+}
+?>
+--EXPECTF--
+Fatal error: Cannot use generic type parameter T as a class reference at runtime; bound-erased generic types have no runtime representation in %s on line %d
diff --git a/Zend/tests/generics/scoping/expression_position_class.phpt b/Zend/tests/generics/scoping/expression_position_class.phpt
diff --git a/Zend/tests/generics/scoping/file_scope_class_does_not_shadow.phpt b/Zend/tests/generics/scoping/file_scope_class_does_not_shadow.phpt
@@ -0,0 +1,11 @@
+--TEST--
+Scoping: a file-scope class does NOT shadow a generic type parameter
+--FILE--
+<?php
+class T {}
+function f<T>(): void {
+    new T();
+}
+?>
+--EXPECTF--
+Fatal error: Cannot use generic type parameter T as a class reference at runtime; bound-erased generic types have no runtime representation in %s on line %d
diff --git a/Zend/tests/generics/scoping/fq_name_bypasses_type_param.phpt b/Zend/tests/generics/scoping/fq_name_bypasses_type_param.phpt
@@ -0,0 +1,15 @@
+--TEST--
+Scoping: a fully qualified name `\T` bypasses the type-parameter rule
+--FILE--
+<?php
+class T {
+    public int $v = 5;
+}
+function f<T>(): int {
+    $x = new \T();
+    return $x->v;
+}
+echo f(), "\n";
+?>
+--EXPECT--
+5
diff --git a/Zend/tests/generics/scoping/inner_class_does_not_capture_param.phpt b/Zend/tests/generics/scoping/inner_class_does_not_capture_param.phpt
diff --git a/Zend/tests/generics/scoping/inner_class_shadowing_is_case_insensitive.phpt b/Zend/tests/generics/scoping/inner_class_shadowing_is_case_insensitive.phpt
@@ -0,0 +1,15 @@
+--TEST--
+Scoping: inner-class shadowing of a type parameter is case-insensitive
+--FILE--
+<?php
+function f<T>(): void {
+    class t {
+        public int $v = 9;
+    }
+    $x = new T();
+    echo $x->v, "\n";
+}
+f();
+?>
+--EXPECT--
+9
diff --git a/Zend/tests/generics/scoping/inner_class_shadows_in_instanceof.phpt b/Zend/tests/generics/scoping/inner_class_shadows_in_instanceof.phpt
@@ -0,0 +1,14 @@
+--TEST--
+Scoping: inner class shadows the type parameter for `instanceof`
+--FILE--
+<?php
+function f<T>($x): bool {
+    class T {}
+    return $x instanceof T;
+}
+$called = false;
+$result = f(new stdClass);
+var_dump($result);
+?>
+--EXPECT--
+bool(false)
diff --git a/Zend/tests/generics/scoping/inner_class_shadows_type_param.phpt b/Zend/tests/generics/scoping/inner_class_shadows_type_param.phpt
@@ -0,0 +1,15 @@
+--TEST--
+Scoping: a class declared inside a generic body shadows the type parameter
+--FILE--
+<?php
+function f<T>(): void {
+    class T {
+        public int $v = 7;
+    }
+    $x = new T();
+    echo $x->v, "\n";
+}
+f();
+?>
+--EXPECT--
+7
diff --git a/Zend/tests/generics/scoping/instanceof_class_not_param.phpt b/Zend/tests/generics/scoping/instanceof_class_not_param.phpt
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
@@ -444,6 +444,7 @@ static void zend_generic_scope_push(zend_generic_parameter_list *params, uint8_t
 	entry->params = params;
 	entry->visible_count = params ? params->count : 0;
 	entry->self_compiling = NULL;
+	entry->shadowing_classes = NULL;
 	entry->origin = origin;
 	entry->outer = CG(generic_scope);
 	CG(generic_scope) = entry;
@@ -454,6 +455,11 @@ static void zend_generic_scope_pop(void) /* {{{ */
 {
 	zend_generic_scope_entry *top = CG(generic_scope);
 	ZEND_ASSERT(top != NULL);
+	if (top->shadowing_classes) {
+		zend_hash_destroy(top->shadowing_classes);
+		FREE_HASHTABLE(top->shadowing_classes);
+	}
+
 	CG(generic_scope) = top->outer;
 	efree(top);
 }
@@ -462,18 +468,28 @@ static void zend_generic_scope_pop(void) /* {{{ */
 static zend_generic_parameter *zend_generic_lookup_full(
 		const zend_string *name, uint8_t *origin_out, uint32_t *index_out) /* {{{ */
 {
+	zend_string *lc_name = zend_string_tolower(name);
 	for (zend_generic_scope_entry *e = CG(generic_scope); e; e = e->outer) {
+		if (e->shadowing_classes && zend_hash_exists(e->shadowing_classes, lc_name)) {
+			zend_string_release(lc_name);
+			return NULL;
+		}
+
 		zend_generic_parameter_list *params = e->params;
 		for (uint32_t i = 0; i < e->visible_count; i++) {
 			if (zend_string_equals(params->parameters[i].name, name)) {
 				if (origin_out) *origin_out = e->origin;
 				if (index_out) *index_out = i;
+				zend_string_release(lc_name);
 				return &params->parameters[i];
 			}
 		}
 	}
+
+	zend_string_release(lc_name);
 	return NULL;
 }
+/* }}} */
 
 /* Detects forward reference: a name that matches a parameter declared later in
  * the innermost scope's parameter list. Returns the index of the not-yet-visible
@@ -1552,10 +1568,20 @@ static zend_string *zend_resolve_class_name_ast(zend_ast *ast) /* {{{ */
 	if (ast->kind == ZEND_AST_GENERIC_NAMED_TYPE) {
 		ast = ast->child[0];
 	}
+
 	const zval *class_name = zend_ast_get_zval(ast);
 	if (Z_TYPE_P(class_name) != IS_STRING) {
 		zend_error_noreturn(E_COMPILE_ERROR, "Illegal class name");
 	}
+
+	if ((ast->attr & ZEND_NAME_NOT_FQ) == ZEND_NAME_NOT_FQ
+			&& zend_generic_lookup(Z_STR_P(class_name))) {
+		zend_error_noreturn(E_COMPILE_ERROR,
+			"Cannot use generic type parameter %s as a class reference at runtime; "
+			"bound-erased generic types have no runtime representation",
+			Z_STRVAL_P(class_name));
+	}
+
 	return zend_resolve_class_name(Z_STR_P(class_name), ast->attr);
 }
 /* }}} */
@@ -10037,6 +10063,20 @@ static void zend_compile_class_decl(znode *result, const zend_ast *ast, bool top
 		}
 
 		zend_register_seen_symbol(lcname, ZEND_SYMBOL_CLASS);
+
+		/* If a generic scope is active, this declaration shadows any generic
+		 * type parameter with the same (case-insensitive) name. Register the
+		 * unqualified lc_name in the innermost scope so subsequent lookups
+		 * resolve to the class instead of the type parameter. */
+		if (CG(generic_scope)) {
+			zend_string *unqualified_lc = zend_string_tolower(unqualified_name);
+			if (!CG(generic_scope)->shadowing_classes) {
+				ALLOC_HASHTABLE(CG(generic_scope)->shadowing_classes);
+				zend_hash_init(CG(generic_scope)->shadowing_classes, 4, NULL, NULL, 0);
+			}
+			zend_hash_add_empty_element(CG(generic_scope)->shadowing_classes, unqualified_lc);
+			zend_string_release(unqualified_lc);
+		}
 	} else {
 		/* Find an anon class name that is not in use yet. */
 		name = NULL;
diff --git a/Zend/zend_compile.h b/Zend/zend_compile.h
@@ -153,6 +153,7 @@ typedef struct _zend_generic_scope_entry {
 	zend_generic_parameter_list *params;
 	uint32_t visible_count; 						/* number of parameters in `params` already declared */
 	struct _zend_generic_parameter *self_compiling; /* param whose bound/default is being compiled, or NULL */
+	HashTable *shadowing_classes;                   /* lc_names of class-likes declared inside this scope; lazy-allocated */
 	uint8_t origin;  								/* 0 = class/interface/trait, 1 = function/method/closure/arrow-fn */
 	struct _zend_generic_scope_entry *outer;
 } zend_generic_scope_entry;
