feat: add support for converting is_null ternaries to null coalescing operator

rules-tests/Php70/Rector/Ternary/TernaryToNullCoalescingRector/Fixture/is_null_function.php.inc

@@ -0,0 +1,33 @@
+<?php
+
+namespace Rector\Tests\Php70\Rector\Ternary\TernaryToNullCoalescingRector\Fixture;
+
+function ternaryWithIsNull()
+{
+    $x = is_null($value) ? 10 : $value;
+
+    $y = is_null($a) ? $b : $a;
+
+    $z = !is_null($value) ? $value : 10;
+
+    $w = !is_null($c) ? $c : $d;
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\Php70\Rector\Ternary\TernaryToNullCoalescingRector\Fixture;
+
+function ternaryWithIsNull()
+{
+    $x = $value ?? 10;
+
+    $y = $a ?? $b;
+
+    $z = $value ?? 10;
+
+    $w = $c ?? $d;
+}
+
+?>

rules/Php70/Rector/Ternary/TernaryToNullCoalescingRector.php

@@ -9,6 +9,8 @@
 use PhpParser\Node\Expr\BinaryOp\Coalesce;
 use PhpParser\Node\Expr\BinaryOp\Identical;
 use PhpParser\Node\Expr\BinaryOp\NotIdentical;
+use PhpParser\Node\Expr\BooleanNot;
+use PhpParser\Node\Expr\FuncCall;
 use PhpParser\Node\Expr\Isset_;
 use PhpParser\Node\Expr\Ternary;
 use Rector\NodeTypeResolver\Node\AttributeKey;
@@ -37,6 +39,7 @@ public function getRuleDefinition(): RuleDefinition
             [
                 new CodeSample('$value === null ? 10 : $value;', '$value ?? 10;'),
                 new CodeSample('isset($value) ? $value : 10;', '$value ?? 10;'),
+                new CodeSample('is_null($value) ? 10 : $value;', '$value ?? 10;'),
             ]
         );
     }
@@ -58,6 +61,17 @@ public function refactor(Node $node): ?Node
             return $this->processTernaryWithIsset($node, $node->cond);
         }
 
+        if ($node->cond instanceof FuncCall && $this->isName($node->cond, 'is_null')) {
+            return $this->processTernaryWithIsNull($node, $node->cond, false);
+        }
+
+        if (
+            $node->cond instanceof BooleanNot && $node->cond->expr instanceof FuncCall
+            && $this->isName($node->cond->expr, 'is_null')
+        ) {
+            return $this->processTernaryWithIsNull($node, $node->cond->expr, true);
+        }
+
         if ($node->cond instanceof Identical) {
             $checkedNode = $node->else;
             $fallbackNode = $node->if;
@@ -95,6 +109,42 @@ public function provideMinPhpVersion(): int
         return PhpVersionFeature::NULL_COALESCE;
     }
 
+    private function processTernaryWithIsNull(Ternary $ternary, FuncCall $isNullFuncCall, bool $isNegated): ?Coalesce
+    {
+        if (count($isNullFuncCall->args) !== 1) {
+            return null;
+        }
+
+        $firstArg = $isNullFuncCall->args[0];
+        if (! $firstArg instanceof Node\Arg) {
+            return null;
+        }
+
+        $checkedExpr = $firstArg->value;
+
+        if ($isNegated) {
+            if (! $ternary->if instanceof Expr) {
+                return null;
+            }
+
+            if (! $this->nodeComparator->areNodesEqual($ternary->if, $checkedExpr)) {
+                return null;
+            }
+
+            return new Coalesce($ternary->if, $ternary->else);
+        }
+
+        if (! $this->nodeComparator->areNodesEqual($ternary->else, $checkedExpr)) {
+            return null;
+        }
+
+        if (! $ternary->if instanceof Expr) {
+            return null;
+        }
+
+        return new Coalesce($ternary->else, $ternary->if);
+    }
+
     private function processTernaryWithIsset(Ternary $ternary, Isset_ $isset): ?Coalesce
     {
         if (! $ternary->if instanceof Expr) {