Function extname

src/platform/vscode-path/path.ts:852–913

(path: string)

    },

    extname(path: string): string {
        validateString(path, 'path');
        let start = 0;
        let startDot = -1;
        let startPart = 0;
        let end = -1;
        let matchedSlash = true;
        // Track the state of characters (if any) we see before our first dot and
        // after any path separator we find
        let preDotState = 0;

        // Check for a drive letter prefix so as not to mistake the following
        // path separator as an extra separator at the end of the path that can be
        // disregarded

        if (path.length >= 2 && path.charCodeAt(1) === CHAR_COLON && isWindowsDeviceRoot(path.charCodeAt(0))) {
            start = startPart = 2;
        }

        for (let i = path.length - 1; i >= start; --i) {
            const code = path.charCodeAt(i);
            if (isPathSeparator(code)) {
                // If we reached a path separator that was not part of a set of path
                // separators at the end of the string, stop now
                if (!matchedSlash) {
                    startPart = i + 1;
                    break;
                }
                continue;
            }
            if (end === -1) {
                // We saw the first non-path separator, mark this as the end of our
                // extension
                matchedSlash = false;
                end = i + 1;
            }
            if (code === CHAR_DOT) {
                // If this is our first dot, mark it as the start of our extension
                if (startDot === -1) {
                    startDot = i;
                } else if (preDotState !== 1) {
                    preDotState = 1;
                }
            } else if (startDot !== -1) {
                // We saw a non-dot and non-path separator before our dot, so we should
                // have a good chance at having a non-empty extension
                preDotState = -1;
            }
        }

        if (
            startDot === -1 ||
            end === -1 ||
            // We saw a non-dot character immediately before the dot
            preDotState === 0 ||
            // The (right-most) trimmed path component is exactly '..'
            (preDotState === 1 && startDot === end - 1 && startDot === startPart + 1)
        ) {