Files/FileName: only throw the "missing basepath" warning once

No need to throw this for every single file. Throwing it once should be sufficient.

Includes moving the check for the missing basepath to earlier in the process flow.

Yoast/Sniffs/Files/FileNameSniff.php

@@ -104,6 +104,15 @@ final class FileNameSniff implements Sniff {
 	 */
 	private $validated_excluded_files = [];
 
+	/**
+	 * Track if the "missing basepath" warning has been thrown.
+	 *
+	 * This prevents this warning potentially being thrown for every single file in a PHPCS run.
+	 *
+	 * @var bool
+	 */
+	private $basepath_warning_thrown = false;
+
 	/**
 	 * Returns an array of tokens this test wants to listen for.
 	 *
@@ -177,6 +186,10 @@ public function process( File $phpcsFile, $stackPtr ) {
 		$error_code = 'NotHyphenatedLowercase';
 		$expected   = \strtolower( \preg_replace( '`[[:punct:]]`', '-', $file_name ) );
 
+		if ( ! isset( $phpcsFile->config->basepath ) ) {
+			$this->add_missing_basepath_warning( $phpcsFile );
+		}
+
 		if ( $this->is_file_excluded( $phpcsFile, $file ) === false ) {
 			$oo_structure = $phpcsFile->findNext( self::NAMED_OO_TOKENS, $stackPtr );
 			if ( $oo_structure !== false ) {
@@ -337,12 +350,6 @@ private function validate_oo_prefixes() {
 	private function validate_excluded_files( $phpcsFile ) {
 		// The basepath check needs to be done first as otherwise the previous/current comparison would be broken.
 		if ( ! isset( $phpcsFile->config->basepath ) ) {
-			$phpcsFile->addWarning(
-				'For the exclude property to work with relative file path files, the --basepath needs to be set.',
-				0,
-				'MissingBasePath'
-			);
-
 			// Only relevant for the tests: make sure previously set validated paths are cleared out.
 			$this->validated_excluded_files = [];
 
@@ -389,4 +396,25 @@ private function validate_excluded_files( $phpcsFile ) {
 			$this->validated_excluded_files = \array_flip( $this->validated_excluded_files );
 		}
 	}
+
+	/**
+	 * Throw a warning if the basepath is missing (and this warning hasn't been thrown before).
+	 *
+	 * @param File $phpcsFile The file being scanned.
+	 *
+	 * @return void
+	 */
+	private function add_missing_basepath_warning( File $phpcsFile ) {
+		if ( $this->basepath_warning_thrown === true ) {
+			return;
+		}
+
+		$phpcsFile->addWarning(
+			'For the exclude property to work with relative file path files, the --basepath needs to be set.',
+			0,
+			'MissingBasePath'
+		);
+
+		$this->basepath_warning_thrown = true;
+	}
 }