feat(zend): enforce generic type-parameter variance at class declaration

Signed-off-by: azjezz <azjezz@protonmail.com>

Author: azjezz

Zend/tests/generics/declaration/variance/happy_path.phpt

@@ -0,0 +1,87 @@
+--TEST--
+Variance: full happy-path showing every legal combination
+--FILE--
+<?php
+class Animal {}
+class Dog extends Animal {}
+
+interface Producer<+T> { public function produce(): T; }
+interface Consumer<-T> { public function consume(T $x): void; }
+interface Inv<U> { public function rw(U $x): U; }
+
+class CoProducer<+T> {
+    public readonly T $tag;
+    public function __construct(T $tag) { $this->tag = $tag; }
+    public function get(): T {}
+    public function makeProducer(): Producer<T> {}
+    public function makeConsumerOfConsumers(): Consumer<Consumer<T>> {}
+}
+
+class ReadOnlyHooked<+T> {
+    private T $backing;
+    public function __construct(T $v) { $this->backing = $v; }
+    public T $val { get => $this->backing; }
+}
+
+class CoConsumer<-T> {
+    public function take(T $x): void {}
+    public function takeMany(T ...$xs): void {}
+    public function makeConsumer(): Consumer<T> {}
+    public function consumerOfProducers(Producer<T> $p): void {}
+}
+
+class Holder<T> {
+    public T $val;
+    public function __construct(T $v) { $this->val = $v; }
+    public function get(): T { return $this->val; }
+    public function set(T $v): void { $this->val = $v; }
+    public T $hooked {
+        get => $this->val;
+        set(T $v) { $this->val = $v; }
+    }
+}
+
+interface Source<+T> { public function fetch(): T; }
+class StringSource implements Source<string> {
+    public function fetch(): string { return "ok"; }
+}
+
+class CovariantChain<+T> implements Source<T> {
+    public function __construct(public readonly T $value) {}
+    public function fetch(): T { return $this->value; }
+}
+
+class MethodLevel<+T> {
+    public function map<U>(U $key): T {}
+}
+
+trait TraitProducer<+U> {
+    public function produceU(): U {}
+}
+class UsesProducerTrait {
+    use TraitProducer<int>;
+    public function produceU(): int { return 7; }
+}
+
+$h = new Holder::<int>(42);
+$h->set(7);
+echo $h->get(), "\n";
+
+$rh = new ReadOnlyHooked::<string>("hi");
+echo $rh->val, "\n";
+
+$cp = new CoProducer::<Dog>(new Dog());
+echo get_class($cp->tag), "\n";
+
+echo (new UsesProducerTrait)->produceU(), "\n";
+echo (new StringSource)->fetch(), "\n";
+
+echo "all variance combinations OK\n";
+?>
+--EXPECT--
+7
+hi
+Dog
+7
+ok
+all variance combinations OK

Zend/tests/generics/declaration/variance/violation_contravariant_in_get_hook.phpt

@@ -0,0 +1,15 @@
+--TEST--
+Variance: -T in a hooked property with set hook (invariant position) is rejected
+--FILE--
+<?php
+class A<-T> {
+    private T $backing;
+    public function __construct(T $v) { $this->backing = $v; }
+    public T $val {
+        get => $this->backing;
+        set(T $v) { $this->backing = $v; }
+    }
+}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared contravariant (-T) cannot appear in invariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_contravariant_in_readonly_property.phpt

@@ -0,0 +1,11 @@
+--TEST--
+Variance: -T in a readonly property (covariant position) is rejected
+--FILE--
+<?php
+class A<-T> {
+    public readonly T $val;
+    public function __construct(T $v) { $this->val = $v; }
+}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared contravariant (-T) cannot appear in covariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_contravariant_in_return.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Variance: -T in method return (covariant position) is rejected
+--FILE--
+<?php
+class A<-T> {
+    public function get(): T {}
+}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared contravariant (-T) cannot appear in covariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_contravariant_in_rw_property.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Variance: -T in a read/write typed property (invariant position) is rejected
+--FILE--
+<?php
+class A<-T> {
+    public T $val;
+}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared contravariant (-T) cannot appear in invariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_contravariant_through_covariant_arg_in_return.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Variance: -T composed through Producer<+U> in return (+ × + = +) is rejected
+--FILE--
+<?php
+interface Producer<+U> { public function produce(): U; }
+
+class A<-T> {
+    public function makeProducer(): Producer<T> {}
+}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared contravariant (-T) cannot appear in covariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_covariant_in_byref_get_hook.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Variance: +T in a hooked property with by-ref get (effectively invariant) is rejected
+--FILE--
+<?php
+class A<+T> {
+    private T $backing;
+    public function __construct(T $v) { $this->backing = $v; }
+    public T $val {
+        &get => $this->backing;
+    }
+}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared covariant (+T) cannot appear in invariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_covariant_in_default.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Variance: +T in a sibling type parameter's default (invariant position) is rejected
+--FILE--
+<?php
+interface Container<U> { public function get(): U; }
+
+class A<+T, U = Container<T>> {}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared covariant (+T) cannot appear in invariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_covariant_in_own_bound.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Variance: +T appearing in its own bound (invariant position) is rejected
+--FILE--
+<?php
+interface Box<U> { public function get(): U; }
+
+class A<+T : Box<T>> {}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared covariant (+T) cannot appear in invariant position in %s on line %d

Zend/tests/generics/declaration/variance/violation_covariant_in_param.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Variance: +T in method parameter (contravariant position) is rejected
+--FILE--
+<?php
+class A<+T> {
+    public function take(T $x): void {}
+}
+?>
+--EXPECTF--
+Fatal error: Type parameter T declared covariant (+T) cannot appear in contravariant position in %s on line %d