Config: only determine screen width if/when needed

Follow up on 3761 for which tests were added in 3820.

I'm not sure about *nix, but on Windows, the call to `shell_exec('stty ...')` is slow.

As things were, the call to `shell_exec('stty ...')` would be:
* Made when the initial default value for `reportWidth` is being set in `restoreDefaults()`.
* Potentially made a second time if the users `CodeSniffer.conf` file contained a `report_width => 'auto'` entry.
* Potentially made a third time if any of the rulesets used for the run contained a `<config name="report-width" value="auto"/>` entry.
* Potentially made a fourth time if `--report-width=auto` would be passed from the command-line.

This is inefficient for the following reasons:
1. The output from `shell_exec('stty ...')` does not change between calls (well, providing the user doesn't resize their terminal in the microseconds between calls)
2. We don't actually need to _know_ the value `'auto'` translates to, until the `reportWidth` will be _used_.

Taking the above into account, making the same call up to four times is not desirable.

This commit moves the translation from `'auto'` to an actual terminal width from the `__set()` method to the `__get()` method and overwrites the `reportWidth` value from `'auto'` with the actual terminal width value, if available, and with the default value if the terminal width could not be determined.
This means that subsequent calls to `__get()` for the `reportWidth` will automatically use the previously determined value instead of trying to determine value again.

This removes the inefficiency and should make PHPCS runs a little bit faster (at the very least on Windows).

The only time multiple calls to `shell_exec('stty...')` could now need to be made, would be if the `reportWidth` would be changed (back to `'auto'`) between the first retrieval and a subsequent retrieval of the `reportWidth` value. As things are, this will never happen in a normal PHPCS run, though could possibly happen in a test situation.

Author: jrfnl

CHANGELOG.md

@@ -68,6 +68,7 @@ The file documents changes to the PHP_CodeSniffer project.
     - Thanks to Dan Wallis (@fredden) for the patch
 - Squiz.PHP.InnerFunctions sniff no longer reports on OO methods for OO structures declared within a function or closure
     - Thanks to @Daimona for the patch
+- Runtime performance improvement for PHPCS CLI users. The improvement should be most noticeable for users on Windows.
 
 ### Removed
 - Removed support for installing via PEAR

src/Config.php

@@ -207,6 +207,22 @@ public function __get($name)
             throw new RuntimeException("ERROR: unable to get value of property \"$name\"");
         }
 
+        // Figure out what the terminal width needs to be for "auto".
+        if ($name === 'reportWidth' && $this->settings[$name] === 'auto') {
+            if (function_exists('shell_exec') === true) {
+                $dimensions = shell_exec('stty size 2>&1');
+                if (is_string($dimensions) === true && preg_match('|\d+ (\d+)|', $dimensions, $matches) === 1) {
+                    $this->settings[$name] = (int) $matches[1];
+                }
+            }
+
+            if ($this->settings[$name] === 'auto') {
+                // If shell_exec wasn't available or didn't yield a usable value, set to the default.
+                // This will prevent subsequent retrievals of the reportWidth from making another call to stty.
+                $this->settings[$name] = self::DEFAULT_REPORT_WIDTH;
+            }
+        }
+
         return $this->settings[$name];
 
     }//end __get()
@@ -229,13 +245,9 @@ public function __set($name, $value)
 
         switch ($name) {
         case 'reportWidth' :
-            // Support auto terminal width.
-            if ($value === 'auto' && function_exists('shell_exec') === true) {
-                $dimensions = shell_exec('stty size 2>&1');
-                if (is_string($dimensions) === true && preg_match('|\d+ (\d+)|', $dimensions, $matches) === 1) {
-                    $value = (int) $matches[1];
-                    break;
-                }
+            if (is_string($value) === true && $value === 'auto') {
+                // Nothing to do. Leave at 'auto'.
+                break;
             }
 
             if (is_int($value) === true) {
@@ -246,6 +258,7 @@ public function __set($name, $value)
                 $value = self::DEFAULT_REPORT_WIDTH;
             }
             break;
+
         case 'standards' :
             $cleaned = [];