def map(self, path: str, exists:Callable[[str], bool] = source_exists) -> str:
        """Map `path` through the aliases.

        `path` is checked against all of the patterns.  The first pattern to
        match is used to replace the root of the path with the result root.
        Only one pattern is ever used.  If no patterns match, `path` is
        returned unchanged.

        The separator style in the result is made to match that of the result
        in the alias.

        `exists` is a function to determine if the resulting path actually
        exists.

        Returns the mapped path.  If a mapping has happened, this is a
        canonical path.  If no mapping has happened, it is the original value
        of `path` unchanged.

        """
        if not self.pprinted:
            self.pprint()
            self.pprinted = True

        for original_pattern, regex, result in self.aliases:
            if m := regex.match(path):
                new = path.replace(m[0], result)
                new = new.replace(sep(path), sep(result))
                if not self.relative:
                    new = canonical_filename(new)
                dot_start = result.startswith(("./", ".\\")) and len(result) > 2
                if new.startswith(("./", ".\\")) and not dot_start:
                    new = new[2:]
                if not exists(new):
                    self.debugfn(
                        f"Rule {original_pattern!r} changed {path!r} to {new!r} " +
                        "which doesn't exist, continuing",
                    )
                    continue
                self.debugfn(
                    f"Matched path {path!r} to rule {original_pattern!r} -> {result!r}, " +
                    f"producing {new!r}",
                )
                return new

        # If we get here, no pattern matched.

        if self.relative:
            path = relative_filename(path)

        if self.relative and not isabs_anywhere(path):
            # Auto-generate a pattern to implicitly match relative files
            parts = re.split(r"[/\\]", path)
            if len(parts) > 1:
                dir1 = parts[0]
                pattern = f"*/{dir1}"
                regex_pat = fr"^(.*[\\/])?{re.escape(dir1)}[\\/]"
                result = f"{dir1}{os.sep}"
                # Only add a new pattern if we don't already have this pattern.
                if not any(p == pattern for p, _, _ in self.aliases):
                    self.debugfn(
                        f"Generating rule: {pattern!r} -> {result!r} using regex {regex_pat!r}",
                    )
                    self.aliases.append((pattern, re.compile(regex_pat), result))
                    return self.map(path, exists=exists)

        self.debugfn(f"No rules match, path {path!r} is unchanged")
        return path
Map `path` through the aliases.

        `path` is checked against all of the patterns.  The first pattern to
        match is used to replace the root of the path with the result root.
        Only one pattern is ever used.  If no patterns match, `path` is
        returned unchanged.

        The separator style in the result is made to match that of the result
        in the alias.

        `exists` is a function to determine if the resulting path actually
        exists.

        Returns the mapped path.  If a mapping has happened, this is a
        canonical path.  If no mapping has happened, it is the original value
        of `path` unchanged.

        
coverage/files.py