Ensure formatters only format, not modify results

When I changed the library to not overwrite existing names [1], I wasn't
happy with how `FirstResultStringFormatter` was changing the results,
because the results should be completely ready by the time they arrive
in the formatters.

This commit changes that behaviour, ensuring the results are complete
with all necessary information by the time they reach the formatters.

Along with those changes, I refactored some stringifiers and simplified
the `InterpolationRenderer`; we were not overwriting the "name"
parameter anyway, as it was just an unnecessary overhead.

[1] 8332d28acc

tests/unit/Message/Stringifier/SubjectStringifierTest.php

@@ -0,0 +1,146 @@
+<?php
+
+/*
+ * Copyright (c) Alexandre Gomes Gaigalas <alganet@gmail.com>
+ * SPDX-License-Identifier: MIT
+ */
+
+declare(strict_types=1);
+
+namespace Respect\Validation\Message\Stringifier;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Test;
+use Respect\Validation\Message\Placeholder\Subject;
+use Respect\Validation\Name;
+use Respect\Validation\Path;
+use Respect\Validation\Test\Message\TestingStringifier;
+use Respect\Validation\Test\TestCase;
+use stdClass;
+
+use function sprintf;
+
+#[CoversClass(SubjectStringifier::class)]
+final class SubjectStringifierTest extends TestCase
+{
+    #[Test]
+    #[DataProvider('providerForNonSubjectValues')]
+    public function itShouldNotStringifyWhenValueIsNotAnInstanceOfSubject(mixed $value): void
+    {
+        $stringifier = new SubjectStringifier(new TestingStringifier());
+
+        self::assertNull($stringifier->stringify($value, 0));
+    }
+
+    #[Test]
+    public function itShouldStringifyInputWhenPathAndNameAreNull(): void
+    {
+        $input = ['test' => 'value'];
+        $subject = new Subject($input);
+
+        $testingStringifier = new TestingStringifier();
+        $stringifier = new SubjectStringifier($testingStringifier);
+
+        $expected = $testingStringifier->stringify($input, 0);
+        $actual = $stringifier->stringify($subject, 0);
+
+        self::assertSame($expected, $actual);
+    }
+
+    #[Test]
+    public function itShouldStringifyPathWhenNameIsNull(): void
+    {
+        $path = new Path('field1');
+        $subject = new Subject('input', $path);
+
+        $testingStringifier = new TestingStringifier();
+        $stringifier = new SubjectStringifier($testingStringifier);
+
+        $expected = $testingStringifier->stringify($path, 0);
+        $actual = $stringifier->stringify($subject, 0);
+
+        self::assertSame($expected, $actual);
+    }
+
+    #[Test]
+    public function itShouldStringifyNameWhenPathIsNull(): void
+    {
+        $name = new Name('field_name');
+        $subject = new Subject('input', null, $name);
+
+        $testingStringifier = new TestingStringifier();
+        $stringifier = new SubjectStringifier($testingStringifier);
+
+        $expected = $testingStringifier->stringify($name, 0);
+        $actual = $stringifier->stringify($subject, 0);
+
+        self::assertSame($expected, $actual);
+    }
+
+    #[Test]
+    public function itShouldStringifyNameWhenNameHasPrecedence(): void
+    {
+        $path = new Path('field1');
+        $name = new Name('field_name');
+        $subject = new Subject('input', $path, $name, true);
+
+        $testingStringifier = new TestingStringifier();
+        $stringifier = new SubjectStringifier($testingStringifier);
+
+        $expected = $testingStringifier->stringify($name, 0);
+        $actual = $stringifier->stringify($subject, 0);
+
+        self::assertSame($expected, $actual);
+    }
+
+    #[Test]
+    public function itShouldStringifyWithPathAndNameWhenNameHasNoPrecedence(): void
+    {
+        $path = new Path('field1');
+        $name = new Name('field_name');
+        $subject = new Subject('input', $path, $name, false);
+
+        $testingStringifier = new TestingStringifier();
+        $stringifier = new SubjectStringifier($testingStringifier);
+
+        $pathString = $testingStringifier->stringify($path, 0);
+        $nameString = $testingStringifier->stringify($name, 0);
+        $expected = sprintf('%s (<- %s)', $pathString, $nameString);
+        $actual = $stringifier->stringify($subject, 0);
+
+        self::assertSame($expected, $actual);
+    }
+
+    #[Test]
+    public function itShouldStringifyWithNestedPathWhenNameHasNoPrecedence(): void
+    {
+        $path1 = new Path('field1');
+        $path2 = new Path('field2', $path1);
+        $name = new Name('field_name');
+        $subject = new Subject('input', $path2, $name, false);
+
+        $testingStringifier = new TestingStringifier();
+        $stringifier = new SubjectStringifier($testingStringifier);
+
+        $pathString = $testingStringifier->stringify($path2, 0);
+        $nameString = $testingStringifier->stringify($name, 0);
+        $expected = sprintf('%s (<- %s)', $pathString, $nameString);
+        $actual = $stringifier->stringify($subject, 0);
+
+        self::assertSame($expected, $actual);
+    }
+
+    /** @return array<string, array{mixed}> */
+    public static function providerForNonSubjectValues(): array
+    {
+        return [
+            'string' => ['test'],
+            'integer' => [123],
+            'boolean' => [true],
+            'array' => [['test']],
+            'object' => [new stdClass()],
+            'null' => [null],
+        ];
+    }
+}