[DeadCode] Add RemoveDeadIfBlocksRector

Removes ifs, elseifs, and elses with no body.
Combines them with others when appropriate.

```diff
class RemoveDeadIfBlock
{
    public function run($condition)
    {
-        if ($value) {
-        } elseif ($differentValue) {
-        if ($differentValue) {
-        } else {
-        }
-
        if ($differentValue) {
            echo 'different';
-        } elseif ($value) {
-        } else {
        }

-        if ($differentValue) {
-        } elseif ($value) {
+        if (!$differentValue && $value) {
            echo 'value';
        } else {
        }

        return $differentValue;
    }
}
```

We avoid merging `if`` into following conditions
when the `if` itself has a comment, because we
can't tell if the comment will still be correct for
the negated condition.

At first, I tried adding logic to
RemoveDeadIfForeachForRector to remove elseifs
and elses. That worked, but as I added code it
was clunky to have so much unrelated `if` logic
in `for` and `foreach` rector. So I moved it to
a brand new rector with a simpler implementation.
I borrowed significant code from
RemoveAlwaysTrueIfConditionRector as well.

This can serve as support for smarter rectors
like "RemoveAlwaysTrueIf" and my WIP
"RemoveAlwaysFalseIf". Properly modifying `if`s
requires a lot of extra logic that complicates
the implementation of those rectors. In the
future, they can do something simpler like
removing the body statements but leaving the if
structure in place. Then this rector can perform
the restructuring of the if.

Author: john-shaffer

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/fixture.php.inc

@@ -0,0 +1,52 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class RemoveDeadIfBlock
+{
+    public function run($condition)
+    {
+        if ($value) {
+        } elseif ($differentValue) {
+        } else {
+        }
+
+        if ($differentValue) {
+            echo 'different';
+        } elseif ($value) {
+        } else {
+        }
+
+        if ($differentValue) {
+        } elseif ($value) {
+            echo 'value';
+        } else {
+        }
+
+        return $differentValue;
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class RemoveDeadIfBlock
+{
+    public function run($condition)
+    {
+        if ($differentValue) {
+            echo 'different';
+        }
+
+        if (!$differentValue && $value) {
+            echo 'value';
+        }
+
+        return $differentValue;
+    }
+}
+
+?>

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/if_else_no_stmt.php.inc

@@ -0,0 +1,32 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfElseNoStmt
+{
+    public function run($condition)
+    {
+        if ($condition) {
+            echo "something";
+        } else {
+        }
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfElseNoStmt
+{
+    public function run($condition)
+    {
+        if ($condition) {
+            echo "something";
+        }
+    }
+}
+
+?>

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/if_elseif_no_stmt.php.inc

@@ -0,0 +1,36 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfElseNoStmt
+{
+    public function run($condition)
+    {
+        if ($condition) {
+            echo "something";
+        } elseif (!$condition) {
+        } elseif (true) {
+            echo "global";
+        }
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfElseNoStmt
+{
+    public function run($condition)
+    {
+        if ($condition) {
+            echo "something";
+        } elseif (true) {
+            echo "global";
+        }
+    }
+}
+
+?>

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/if_no_stmt_with_else.php.inc

@@ -0,0 +1,32 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfNoStmtWithElse
+{
+    public function run($condition)
+    {
+        if ($condition) {
+        } else {
+            echo "something";
+        }
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfNoStmtWithElse
+{
+    public function run($condition)
+    {
+        if (!$condition) {
+            echo "something";
+        }
+    }
+}
+
+?>

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/if_no_stmt_with_else_no_stmt.php.inc

@@ -0,0 +1,28 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfNoStmtWithElseNoStmt
+{
+    public function run($condition)
+    {
+        if ($condition) {
+        } else {
+        }
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class IfNoStmtWithElseNoStmt
+{
+    public function run($condition)
+    {
+    }
+}
+
+?>

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/side_effect_checks.php.inc

@@ -0,0 +1,33 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class SideEffectChecks
+{
+    public function run()
+    {
+        if (10) {
+        }
+
+        if (true) {
+        }
+
+        if (5 + 10) {
+        }
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class SideEffectChecks
+{
+    public function run()
+    {
+    }
+}
+
+?>

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/skip_if_comment.php.inc

@@ -0,0 +1,19 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class MergeComments
+{
+    public function run($b)
+    {
+        // toplevel
+        if ($b) {
+        } elseif (!$b) {
+            // first innner
+            f();
+            // second inner
+        }
+    }
+}
+
+?>

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/skip_used_in_next_stmt.php.inc

@@ -0,0 +1,19 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class SkipUsedInNextStmt
+{
+    public function run($resultLen, $result, $decimalSep)
+    {
+        for ($i = $resultLen - 1; $i >= 0 && $result[$i] === '0'; $i--) {
+            ;
+        }
+
+        if ($i >= 0 && $result[$i] === $decimalSep) {
+          $i--;
+        }
+
+        $result = substr($result, 0, $i + 1);
+    }
+}

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/Fixture/skip_used_in_next_stmt2.php.inc

@@ -0,0 +1,19 @@
+<?php
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector\Fixture;
+
+class SkipUsedInNextStmt2
+{
+    public function run($resultLen, $result, $decimalSep)
+    {
+        foreach ($result as $i => $value) {
+            ;
+        }
+
+        if ($i >= 0 && $result[$i] === $decimalSep) {
+          $i--;
+        }
+
+        $result = substr($result, 0, $i + 1);
+    }
+}

rules-tests/DeadCode/Rector/If_/RemoveDeadIfBlocksRector/RemoveDeadIfBlocksRectorTest.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\DeadCode\Rector\If_\RemoveDeadIfBlocksRector;
+
+use Iterator;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+
+final class RemoveDeadIfBlocksRectorTest extends AbstractRectorTestCase
+{
+    #[DataProvider('provideData')]
+    public function test(string $filePath): void
+    {
+        $this->doTestFile($filePath);
+    }
+
+    public static function provideData(): Iterator
+    {
+        return self::yieldFilesFromDirectory(__DIR__ . '/Fixture');
+    }
+
+    public function provideConfigFilePath(): string
+    {
+        return __DIR__ . '/config/configured_rule.php';
+    }
+}