Implemented includes shortening in backtrace.

src/Formatter/Backtrace_Formatter.php

@@ -13,12 +13,30 @@ class Backtrace_Formatter {
 		'wp-load.php',
 		'wp-config.php',
 		'admin.php',
+		'template-loader.php',
 		'locate_template',
 		'load_template',
 		'_wp_get_current_user',
 		'WP_Hook',
 	];
 
+	/** @var array $truncate_paths Paths to truncate from includes. */
+	protected $truncate_paths = [];
+
+	/**
+	 * Set up object properties.
+	 */
+	public function __construct() {
+
+		$this->truncate_paths = [
+			wp_normalize_path( ABSPATH ),
+			wp_normalize_path( WP_CONTENT_DIR ),
+			'wp-admin/',
+			'themes/',
+			'plugins/',
+		];
+	}
+
 	/**
 	 * @param array|string $backtrace Backtrace input as produced by WP.
 	 *
@@ -30,9 +48,10 @@ class Backtrace_Formatter {
 			$backtrace = explode( ', ', $backtrace );
 		}
 
-		// TODO shorten includes.
-
 		$backtrace = array_filter( $backtrace, [ $this, 'filter' ] );
+		$backtrace = array_map( [ $this, 'shorten_include' ], $backtrace );
+
+		// TODO compact redunant function sequences, such as transient into option calls.
 
 		return $backtrace;
 	}
@@ -52,4 +71,23 @@ class Backtrace_Formatter {
 
 		return true;
 	}
+
+	/**
+	 * @param string $item Backtrace item.
+	 *
+	 * @return string
+	 */
+	protected function shorten_include( $item ) {
+
+		if ( 0 === strpos( $item, 'include' ) || 0 === strpos( $item, 'require' ) ) {
+
+			$path = substr( $item, strpos( $item, '(\'' ) + 2, - 2 );
+			$path = wp_normalize_path( $path );
+			$path = ltrim( str_replace( $this->truncate_paths, '', $path ), '/' );
+
+			return $path;
+		}
+
+		return $item;
+	}
 }