matchOne(file, pattern, partial = false) {
        const options = this.options;
        // UNC paths like //?/X:/... can match X:/... and vice versa
        // Drive letters in absolute drive or unc paths are always compared
        // case-insensitively.
        if (this.isWindows) {
            const fileDrive = typeof file[0] === 'string' && /^[a-z]:$/i.test(file[0]);
            const fileUNC = !fileDrive &&
                file[0] === '' &&
                file[1] === '' &&
                file[2] === '?' &&
                /^[a-z]:$/i.test(file[3]);
            const patternDrive = typeof pattern[0] === 'string' && /^[a-z]:$/i.test(pattern[0]);
            const patternUNC = !patternDrive &&
                pattern[0] === '' &&
                pattern[1] === '' &&
                pattern[2] === '?' &&
                typeof pattern[3] === 'string' &&
                /^[a-z]:$/i.test(pattern[3]);
            const fdi = fileUNC ? 3 : fileDrive ? 0 : undefined;
            const pdi = patternUNC ? 3 : patternDrive ? 0 : undefined;
            if (typeof fdi === 'number' && typeof pdi === 'number') {
                const [fd, pd] = [file[fdi], pattern[pdi]];
                if (fd.toLowerCase() === pd.toLowerCase()) {
                    pattern[pdi] = fd;
                    if (pdi > fdi) {
                        pattern = pattern.slice(pdi);
                    }
                    else if (fdi > pdi) {
                        file = file.slice(fdi);
                    }
                }
            }
        }
        // resolve and reduce . and .. portions in the file as well.
        // dont' need to do the second phase, because it's only one string[]
        const { optimizationLevel = 1 } = this.options;
        if (optimizationLevel >= 2) {
            file = this.levelTwoFileOptimize(file);
        }
        this.debug('matchOne', this, { file, pattern });
        this.debug('matchOne', file.length, pattern.length);
        for (var fi = 0, pi = 0, fl = file.length, pl = pattern.length; fi < fl && pi < pl; fi++, pi++) {
            this.debug('matchOne loop');
            var p = pattern[pi];
            var f = file[fi];
            this.debug(pattern, p, f);
            // should be impossible.
            // some invalid regexp stuff in the set.
            /* c8 ignore start */
            if (p === false) {
                return false;
            }
            /* c8 ignore stop */
            if (p === GLOBSTAR) {
                this.debug('GLOBSTAR', [pattern, p, f]);
                // "**"
                // a/**/b/**/c would match the following:
                // a/b/x/y/z/c
                // a/x/y/z/b/c
                // a/b/x/b/x/c
                // a/b/c
                // To do this, take the rest of the pattern after
                // the **, and see if it would match the file remainder.
                // If so, return success.
                // If not, the ** "swallows" a segment, and try again.
                // This is recursively awful.
                //
                // a/**/b/**/c matching a/b/x/y/z/c
                // - a matches a
                // - doublestar
                //   - matchOne(b/x/y/z/c, b/**/c)
                //     - b matches b
                //     - doublestar
                //       - matchOne(x/y/z/c, c) -> no
                //       - matchOne(y/z/c, c) -> no
                //       - matchOne(z/c, c) -> no
                //       - matchOne(c, c) yes, hit
                var fr = fi;
                var pr = pi + 1;
                if (pr === pl) {
                    this.debug('** at the end');
                    // a ** at the end will just swallow the rest.
                    // We have found a match.
                    // however, it will not swallow /.x, unless
                    // options.dot is set.
                    // . and .. are *never* matched by **, for explosively
                    // exponential reasons.
                    for (; fi < fl; fi++) {
                        if (file[fi] === '.' ||
                            file[fi] === '..' ||
                            (!options.dot && file[fi].charAt(0) === '.'))
                            return false;
                    }
                    return true;
                }
                // ok, let's see if we can swallow whatever we can.
                while (fr < fl) {
                    var swallowee = file[fr];
                    this.debug('\nglobstar while', file, fr, pattern, pr, swallowee);
                    // XXX remove this slice.  Just pass the start index.
                    if (this.matchOne(file.slice(fr), pattern.slice(pr), partial)) {
                        this.debug('globstar found match!', fr, fl, swallowee);
                        // found a match.
                        return true;
                    }
                    else {
                        // can't swallow "." or ".." ever.
                        // can only swallow ".foo" when explicitly asked.
                        if (swallowee === '.' ||
                            swallowee === '..' ||
                            (!options.dot && swallowee.charAt(0) === '.')) {
                            this.debug('dot detected!', file, fr, pattern, pr);
                            break;
                        }
                        // ** swallows a segment, and continue.
                        this.debug('globstar swallow a segment, and continue');
                        fr++;
                    }
                }
                // no match was found.
                // However, in partial mode, we can't say this is necessarily over.
                /* c8 ignore start */
                if (partial) {
                    // ran out of file
                    this.debug('\n>>> no match, partial?', file, fr, pattern, pr);
                    if (fr === fl) {
                        return true;
                    }
                }
                /* c8 ignore stop */
                return false;
            }
            // something other than **
            // non-magic patterns just have to match exactly
            // patterns with magic have been turned into regexps.
            let hit;
            if (typeof p === 'string') {
                hit = f === p;
                this.debug('string match', p, f, hit);
            }
            else {
                hit = p.test(f);
                this.debug('pattern match', p, f, hit);
            }
            if (!hit)
                return false;
        }
        // Note: ending in / means that we'll get a final ""
        // at the end of the pattern.  This can only match a
        // corresponding "" at the end of the file.
        // If the file ends in /, then it can only match a
        // a pattern that ends in /, unless the pattern just
        // doesn't have any more for it. But, a/b/ should *not*
        // match "a/b/*", even though "" matches against the
        // [^/]*? pattern, except in partial mode, where it might
        // simply not be reached yet.
        // However, a/b/ should still satisfy a/*
        // now either we fell off the end of the pattern, or we're done.
        if (fi === fl && pi === pl) {
            // ran out of pattern and filename at the same time.
            // an exact hit!
            return true;
        }
        else if (fi === fl) {
            // ran out of file, but still had pattern left.
            // this is ok if we're doing the match as part of
            // a glob fs traversal.
            return partial;
        }
        else if (pi === pl) {
            // ran out of pattern, still have file left.
            // this is only acceptable if we're on the very last
            // empty segment of a file with a trailing slash.
            // a/* should match a/b/
            return fi === fl - 1 && file[fi] === '';
            /* c8 ignore start */
        }
        else {
            // should be unreachable.
            throw new Error('wtf?');
        }
        /* c8 ignore stop */
    }
/<rest>
    // ^-- not valid because ** doens't follow symlinks
    secondPhasePreProcess(globParts) {
        for (let i = 0; i < globParts.length - 1; i++) {
            for (let j = i + 1; j < globParts.length; j++) {
                const matched = this.partsMatch(globParts[i], globParts[j], !this.preserveMultipleSlashes);
                if (!matched)
                    continue;
                globParts[i] = matched;
                globParts[j] = [];
            }
        }
        return globParts.filter(gs => gs.length);
    }
    partsMatch(a, b, emptyGSMatch = false) {
        let ai = 0;
        let bi = 0;
        let result = [];
        let which = '';
        while (ai < a.length && bi < b.length) {
            if (a[ai] === b[bi]) {
                result.push(which === 'b' ? b[bi] : a[ai]);
                ai++;
                bi++;
            }
            else if (emptyGSMatch && a[ai] === '**' && b[bi] === a[ai + 1]) {
                result.push(a[ai]);
                ai++;
            }
            else if (emptyGSMatch && b[bi] === '**' && a[ai] === b[bi + 1]) {
                result.push(b[bi]);
                bi++;
            }
            else if (a[ai] === '*' &&
                b[bi] &&
                (this.options.dot || !b[bi].startsWith('.')) &&
                b[bi] !== '**') {
                if (which === 'b')
                    return false;
                which = 'a';
                result.push(a[ai]);
                ai++;
                bi++;
            }
            else if (b[bi] === '*' &&
                a[ai] &&
                (this.options.dot || !a[ai].startsWith('.')) &&
                a[ai] !== '**') {
                if (which === 'a')
                    return false;
                which = 'b';
                result.push(b[bi]);
                ai++;
                bi++;
            }
            else {
                return false;
            }
        }
        // if we fall out of the loop, it means they two are identical
        // as long as their lengths match
        return a.length === b.length && result;
    }
    parseNegate() {
        if (this.nonegate)
            return;
        const pattern = this.pattern;
        let negate = false;
        let negateOffset = 0;
        for (let i = 0; i < pattern.length && pattern.charAt(i) === '!'; i++) {
            negate = !negate;
            negateOffset++;
        }
        if (negateOffset)
            this.pattern = pattern.slice(negateOffset);
        this.negate = negate;
    }
    // set partial to true to test if, for example,
    // "/a/b" matches the start of "/