fix(analyzer): correctly handle nullable generic templates

ref vimeo/psalm#10901

Signed-off-by: azjezz <[email protected]>

Author: azjezz

crates/analyzer/tests/cases/binary_throw_used.php

@@ -1,5 +1,8 @@
 <?php
 
+/**
+ * @throws RuntimeException
+ */
 function start(null|string $id): void
 {
     $id ?? throw new RuntimeException();

crates/analyzer/tests/cases/issue_583.php

@@ -8,8 +8,10 @@
  */
 function x($data): void
 {
-    $data['currency'] ?? throw new \InvalidArgumentException('Currency is required.'); // @mago-expect analysis: unused-statement
+    $data['currency'] ?? throw new \InvalidArgumentException('Currency is required.');
     accept_string($data['currency']);
 }
 
-function accept_string(string $_s): void {}
+function accept_string(string $_s): void
+{
+}

crates/analyzer/tests/cases/template_null_comparison.php

@@ -0,0 +1,60 @@
+<?php
+
+interface TestInterface
+{
+    public function test(): void;
+}
+
+/**
+ * @template T of TestInterface|null
+ */
+class Test
+{
+    /**
+     * @psalm-param T $value
+     */
+    public function __construct(
+        public TestInterface|null $value,
+    ) {}
+
+    public function getValue(): null|TestInterface
+    {
+        return $this->value;
+    }
+
+    public function getValue2(): TestInterface
+    {
+        if ($this->value === null) {
+            exit(1);
+        }
+
+        return $this->value;
+    }
+
+    public function getValue3(): TestInterface
+    {
+        return $this->value ?? exit(1);
+    }
+}
+
+/**
+ * @template T of string|null
+ */
+class ScalarTest
+{
+    /**
+     * @param T $value
+     */
+    public function __construct(
+        public string|null $value,
+    ) {}
+
+    public function getValue(): string
+    {
+        if ($this->value === null) {
+            return 'default';
+        }
+
+        return $this->value;
+    }
+}

crates/analyzer/tests/mod.rs

@@ -330,6 +330,7 @@ test_case!(type_assert);
 test_case!(string_callable_template_inference);
 test_case!(clear_narrowed_prop_after_call);
 test_case!(binary_throw_used);
+test_case!(template_null_comparison);
 
 // Github Issues
 test_case!(issue_659);

crates/codex/src/ttype/union.rs

@@ -796,6 +796,7 @@ impl TUnion {
     pub fn is_nullable(&self) -> bool {
         self.types.iter().any(|t| match t {
             TAtomic::Null => self.types.len() >= 2,
+            TAtomic::GenericParameter(param) => param.constraint.is_nullable(),
             _ => false,
         })
     }