feature#8288 [Process] Added support for stdout and stderr flush (Issue #7884) (imobilis)

This PR was squashed before being merged into the master branch (closes #8288).

Discussion
----------

[Process] Added support for stdout and stderr flush (Issue #7884)

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7884
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/2728

**To-do**
- [x] Submit changes to the documentation.
- [x] Fix a test broken on travis.
- [x] Fix mistakes on the documentation.
- [x] Removed flush + get methods.
- [x] Changed tests assert calls.

This PR introduces flushing methods for both stdout and stderr on Process class. The new methods are:
- flushOutput(): clears the output buffer.
- flushErrorOutput(): clears the error output buffer.

Tests for new methods are included on the PR.

Commits
-------

90daef7 [Process] Added support for stdout and stderr flush (Issue #7884)

src/Symfony/Component/Process/Process.php

@@ -396,6 +396,19 @@ class Process
         return $latest;
     }
 
+    /**
+     * Clears the process output.
+     *
+     * @return Process
+     */
+    public function flushOutput()
+    {
+        $this->stdout = '';
+        $this->incrementalOutputOffset = 0;
+
+        return $this;
+    }
+
     /**
      * Returns the current error output of the process (STDERR).
      *
@@ -429,6 +442,19 @@ class Process
         return $latest;
     }
 
+    /**
+     * Clears the process output.
+     *
+     * @return Process
+     */
+    public function flushErrorOutput()
+    {
+        $this->stderr = '';
+        $this->incrementalErrorOutputOffset = 0;
+
+        return $this;
+    }
+
     /**
      * Returns the exit code returned by the process.
      *

src/Symfony/Component/Process/Tests/AbstractProcessTest.php

@@ -169,6 +169,15 @@ abstract class AbstractProcessTest extends \PHPUnit_Framework_TestCase
         }
     }
 
+    public function testFlushErrorOutput()
+    {
+        $p = new Process(sprintf('php -r %s', escapeshellarg('$n = 0; while ($n < 3) { file_put_contents(\'php://stderr\', \'ERROR\'); $n++; }')));
+
+        $p->run();
+        $p->flushErrorOutput();
+        $this->assertEmpty($p->getErrorOutput());
+    }
+
     public function testGetOutput()
     {
         $p = new Process(sprintf('php -r %s', escapeshellarg('$n=0;while ($n<3) {echo \' foo \';$n++; usleep(500); }')));
@@ -188,6 +197,15 @@ abstract class AbstractProcessTest extends \PHPUnit_Framework_TestCase
         }
     }
 
+    public function testFlushOutput()
+    {
+        $p = new Process(sprintf('php -r %s', escapeshellarg('$n=0;while ($n<3) {echo \' foo \';$n++;}')));
+
+        $p->run();
+        $p->flushOutput();
+        $this->assertEmpty($p->getOutput());
+    }
+
     public function testExitCodeCommandFailed()
     {
         if (defined('PHP_WINDOWS_VERSION_BUILD')) {