#4997 added more precise type inference for count() returning 0 or positive-int on known arrays (#4999)

* #4997 added more precise stub for `count()` returning `0` or `positive-int` on known types

* #4997 updated `count()` to support `\SimpleXmlElement` and `\ResourceBundle` counting, as well as handling hardcoded 2-element-arrays cases

This patch:

 * adds support for `count(\SimpleXmlElement)` (https://www.php.net/manual/en/simplexmlelement.count.php)
 * adds support for `count(\ResourceBundle)` (https://www.php.net/manual/en/resourcebundle.count.php)
 * removes usage of global constants from stub (not supported - see https://www.php.net/manual/en/function.count.php)
 * adds support for identifying fixed-element-count arrays, for example `count(callable&array)`, which is always `2`

* #4997 adapted `FunctionCallReturnTypeFetcher` to infer `TPositiveInt` for `count(TNonEmptyArray)` and `count(TNonEmptyList)`

* The `FunctionCallReturnTypeFetcher` is responsible for defining the precise type of a `\count(T)`
expression when given a `T`, so we baked the whole type resolution for `positive-int`, `0` and
`positive-int|0` directly in there.

While this complicates things, it is also true that it is not possible right now (for the stubs)
to provide the level of detail around `count()` that is required by the type inference system
for such a complex function with so many different semantics.

src/Psalm/Internal/Analyzer/Statements/Expression/Call/FunctionCallReturnTypeFetcher.php

@@ -300,7 +300,7 @@ class FunctionCallReturnTypeFetcher
                                     return new Type\Union([
                                         $atomic_types['array']->count !== null
                                             ? new Type\Atomic\TLiteralInt($atomic_types['array']->count)
-                                            : new Type\Atomic\TInt
+                                            : new Type\Atomic\TPositiveInt
                                     ]);
                                 }
 
@@ -308,7 +308,7 @@ class FunctionCallReturnTypeFetcher
                                     return new Type\Union([
                                         $atomic_types['array']->count !== null
                                             ? new Type\Atomic\TLiteralInt($atomic_types['array']->count)
-                                            : new Type\Atomic\TInt
+                                            : new Type\Atomic\TPositiveInt
                                     ]);
                                 }
 
@@ -319,6 +319,11 @@ class FunctionCallReturnTypeFetcher
                                         new Type\Atomic\TLiteralInt(count($atomic_types['array']->properties))
                                     ]);
                                 }
+
+                                return new Type\Union([
+                                    new Type\Atomic\TLiteralInt(0),
+                                    new Type\Atomic\TPositiveInt
+                                ]);
                             }
                         }
                     }

tests/FunctionCallTest.php

@@ -1054,6 +1054,83 @@ class FunctionCallTest extends TestCase
                         }
                     }'
             ],
+            'countNonEmptyArrayShouldBePositiveInt' => [
+                '<?php
+                    /**
+                     * @psalm-pure
+                     * @param non-empty-list $x
+                     * @return positive-int
+                     */
+                    function example($x) : int {
+                        return count($x);
+                    }',
+            ],
+            'countListShouldBeZeroOrPositive' => [
+                '<?php
+                    /**
+                     * @psalm-pure
+                     * @param list $x
+                     * @return positive-int|0
+                     */
+                    function example($x) : int {
+                        return count($x);
+                    }',
+            ],
+            'countArrayShouldBeZeroOrPositive' => [
+                '<?php
+                    /**
+                     * @psalm-pure
+                     * @param array $x
+                     * @return positive-int|0
+                     */
+                    function example($x) : int {
+                        return count($x);
+                    }',
+            ],
+            'countEmptyArrayShouldBeZero' => [
+                '<?php
+                    /**
+                     * @psalm-pure
+                     * @param array<empty, empty> $x
+                     * @return 0
+                     */
+                    function example($x) : int {
+                        return count($x);
+                    }',
+            ],
+            'countConstantSizeArrayShouldBeConstantInteger' => [
+                '<?php
+                    /**
+                     * @psalm-pure
+                     * @param array{int, int, string} $x
+                     * @return 3
+                     */
+                    function example($x) : int {
+                        return count($x);
+                    }',
+            ],
+            'countCallableArrayShouldBe2' => [
+                '<?php
+                    /**
+                     * @psalm-pure
+                     * @return 2
+                     */
+                    function example(callable $x) : int {
+                        assert(is_array($x));
+                        return count($x);
+                    }',
+            ],
+            'countOnPureObjectIsPure' => [
+                '<?php
+                    class PureCountable implements \Countable {
+                        /** @psalm-pure */
+                        public function count(): int { return 1; }
+                    }
+                    /** @psalm-pure */
+                    function example(PureCountable $x) : int {
+                        return count($x);
+                    }',
+            ],
             'refineWithTraitExists' => [
                 '<?php
                     function foo(string $s) : void {
@@ -1820,6 +1897,22 @@ class FunctionCallTest extends TestCase
                     }',
                 'error_message' => 'TypeDoesNotContainType',
             ],
+            'countOnObjectCannotBePositive' => [
+                '<?php
+                    /** @return positive-int|0 */
+                    function example(\Countable $x) : int {
+                        return count($x);
+                    }',
+                'error_message' => 'LessSpecificReturnStatement',
+            ],
+            'countOnUnknownObjectCannotBePure' => [
+                '<?php
+                    /** @psalm-pure */
+                    function example(\Countable $x) : int {
+                        return count($x);
+                    }',
+                'error_message' => 'ImpureFunctionCall',
+            ],
             'coerceCallMapArgsInStrictMode' => [
                 '<?php
                     declare(strict_types=1);