Undefined index during merge

src/CodeCoverage.php

@@ -380,39 +380,23 @@ public function merge(self $that): void
                 continue;
             }
 
-            if ((\count($lines) > 0) && (\count($this->data[$file]) > 0) && (\count($lines) != \count($this->data[$file]))) {
-                if (\count($lines) > \count($ours = $this->data[$file])) {
-                    // More lines in the one being added in
-                    $lines = \array_filter(
-                        $lines,
-                        function ($value, $key) use ($ours) {
-                            return \array_key_exists($key, $ours);
-                        },
-                        \ARRAY_FILTER_USE_BOTH
-                    );
-                } else {
-                    // More lines in the one we currently have
-                    $this->data[$file] = \array_filter(
-                        $this->data[$file],
-                        function ($value, $key) use ($lines) {
-                            return \array_key_exists($key, $lines);
-                        },
-                        \ARRAY_FILTER_USE_BOTH
-                    );
-                }
-            }
+            // we should compare the lines if any of two contains data
+            $compareLineNumbers = \array_unique(
+                \array_merge(
+                    \array_keys($this->data[$file]),
+                    \array_keys($that->data[$file])
+                )
+            );
+
+            foreach ($compareLineNumbers as $line) {
+                $thatPriority = $this->getLinePriority($that->data[$file], $line);
+                $thisPriority = $this->getLinePriority($this->data[$file], $line);
 
-            foreach ($lines as $line => $data) {
-                if ($data === null || $this->data[$file][$line] === null) {
-                    // if the line is marked as "dead code" in either, mark it as dead code in the merged result
-                    $this->data[$file][$line] = null;
-                } elseif (!isset($this->data[$file][$line])) {
-                    // if no data has been set in the current data, overwrite all
-                    $this->data[$file][$line] = $data;
-                } else {
-                    // otherwise merge data from both coverage files
+                if ($thatPriority > $thisPriority) {
+                    $this->data[$file][$line] = $that->data[$file][$line];
+                } elseif ($thatPriority === $thisPriority && \is_array($this->data[$file][$line])) {
                     $this->data[$file][$line] = \array_unique(
-                        \array_merge($this->data[$file][$line], $data)
+                        \array_merge($this->data[$file][$line], $that->data[$file][$line])
                     );
                 }
             }
@@ -422,6 +406,33 @@ function ($value, $key) use ($lines) {
         $this->report = null;
     }
 
+    /**
+     * Determine the priority for a line
+     *
+     * 1 = the line is not set
+     * 2 = the line has not been tested
+     * 3 = the line is dead code
+     * 4 = the line has been tested
+     *
+     * During a merge, a higher number is better.
+     *
+     * @param array $data
+     * @param int $line
+     * @return int
+     */
+    protected function getLinePriority($data, $line)
+    {
+        if (!\array_key_exists($line, $data)) {
+            return 1;
+        } elseif (\is_array($data[$line]) && \count($data[$line]) === 0) {
+            return 2;
+        } elseif ($data[$line] === null) {
+            return 3;
+        }
+
+        return 4;
+    }
+
     public function setCacheTokens(bool $flag): void
     {
         $this->cacheTokens = $flag;

tests/TestCase.php

@@ -238,33 +238,39 @@ protected function getExpectedDataArrayForBankAccount()
                     0 => 'BankAccountTest::testBalanceIsInitiallyZero',
                     1 => 'BankAccountTest::testDepositWithdrawMoney'
                 ],
+                9  => null,
                 13 => [],
+                14 => [],
+                15 => [],
                 16 => [],
+                18 => [],
                 22 => [
                     0 => 'BankAccountTest::testBalanceCannotBecomeNegative2',
                     1 => 'BankAccountTest::testDepositWithdrawMoney'
                 ],
                 24 => [
                     0 => 'BankAccountTest::testDepositWithdrawMoney',
                 ],
+                25 => null,
                 29 => [
                     0 => 'BankAccountTest::testBalanceCannotBecomeNegative',
                     1 => 'BankAccountTest::testDepositWithdrawMoney'
                 ],
                 31 => [
                     0 => 'BankAccountTest::testDepositWithdrawMoney'
                 ],
+                32 => null
             ]
         ];
     }
 
-    protected function getExpectedDataArrayForBankAccount2()
+    protected function getExpectedDataArrayForBankAccountInReverseOrder()
     {
         return [
             TEST_FILES_PATH . 'BankAccount.php' => [
                 8 => [
-                    0 => 'BankAccountTest::testBalanceIsInitiallyZero',
-                    1 => 'BankAccountTest::testDepositWithdrawMoney'
+                    0 => 'BankAccountTest::testDepositWithdrawMoney',
+                    1 => 'BankAccountTest::testBalanceIsInitiallyZero'
                 ],
                 9  => null,
                 13 => [],
@@ -281,8 +287,8 @@ protected function getExpectedDataArrayForBankAccount2()
                 ],
                 25 => null,
                 29 => [
-                    0 => 'BankAccountTest::testBalanceCannotBecomeNegative',
-                    1 => 'BankAccountTest::testDepositWithdrawMoney'
+                    0 => 'BankAccountTest::testDepositWithdrawMoney',
+                    1 => 'BankAccountTest::testBalanceCannotBecomeNegative'
                 ],
                 31 => [
                     0 => 'BankAccountTest::testDepositWithdrawMoney'

tests/tests/CodeCoverageTest.php

@@ -10,6 +10,9 @@
 
 namespace SebastianBergmann\CodeCoverage;
 
+require __DIR__ . '/../_files/BankAccount.php';
+require __DIR__ . '/../_files/BankAccountTest.php';
+
 use SebastianBergmann\CodeCoverage\Driver\Driver;
 use SebastianBergmann\CodeCoverage\Driver\PHPDBG;
 use SebastianBergmann\CodeCoverage\Driver\Xdebug;
@@ -215,7 +218,7 @@ public function testCollect()
         $coverage = $this->getCoverageForBankAccount();
 
         $this->assertEquals(
-            $this->getExpectedDataArrayForBankAccount2(),
+            $this->getExpectedDataArrayForBankAccount(),
             $coverage->getData()
         );
 
@@ -241,6 +244,17 @@ public function testMerge()
         );
     }
 
+    public function testMergeReverseOrder()
+    {
+        $coverage = $this->getCoverageForBankAccountForLastTwoTests();
+        $coverage->merge($this->getCoverageForBankAccountForFirstTwoTests());
+
+        $this->assertEquals(
+            $this->getExpectedDataArrayForBankAccountInReverseOrder(),
+            $coverage->getData()
+        );
+    }
+
     public function testMerge2()
     {
         $coverage = new CodeCoverage(
@@ -251,7 +265,7 @@ public function testMerge2()
         $coverage->merge($this->getCoverageForBankAccount());
 
         $this->assertEquals(
-            $this->getExpectedDataArrayForBankAccount2(),
+            $this->getExpectedDataArrayForBankAccount(),
             $coverage->getData()
         );
     }