// Written in the D programming language.

/** This module is used to manipulate _path strings.

    All functions, with the exception of $(LREF expandTilde) (and in some
    cases $(LREF absolutePath) and $(LREF relativePath)), are pure
    string manipulation functions; they don't depend on any state outside
    the program, nor do they perform any actual file system actions.
    This has the consequence that the module does not make any distinction
    between a _path that points to a directory and a _path that points to a
    file, and it does not know whether or not the object pointed to by the
    _path actually exists in the file system.
    To differentiate between these cases, use $(XREF file,isDir) and
    $(XREF file,exists).

    Note that on Windows, both the backslash ($(D `\`)) and the slash ($(D `/`))
    are in principle valid directory separators.  This module treats them
    both on equal footing, but in cases where a $(I new) separator is
    added, a backslash will be used.  Furthermore, the $(LREF buildNormalizedPath)
    function will replace all slashes with backslashes on that platform.

    In general, the functions in this module assume that the input paths
    are well-formed.  (That is, they should not contain invalid characters,
    they should follow the file system's _path format, etc.)  The result
    of calling a function on an ill-formed _path is undefined.  When there
    is a chance that a _path or a file name is invalid (for instance, when it
    has been input by the user), it may sometimes be desirable to use the
    $(LREF isValidFilename) and $(LREF isValidPath) functions to check
    this.

    Most functions do not perform any memory allocations, and if a string is
    returned, it is usually a slice of an input string.  If a function
    allocates, this is explicitly mentioned in the documentation.

    Authors:
        Lars Tandle Kyllingstad,
        $(WEB digitalmars.com, Walter Bright),
        Grzegorz Adam Hankiewicz,
        Thomas Kühne,
        $(WEB erdani.org, Andrei Alexandrescu)
    Copyright:
        Copyright (c) 2000–2011, the authors. All rights reserved.
    License:
        $(WEB boost.org/LICENSE_1_0.txt, Boost License 1.0)
    Source:
        $(PHOBOSSRC std/_path.d)
    Macros:
        WIKI = Phobos/StdPath
*/
module std.path;


import std.algorithm;
import std.array;
import std.conv;
import std.file: getcwd;
import std.range;
import std.string;
import std.traits;

version(Posix)
{
    import core.exception;
    import core.stdc.errno;
    import core.sys.posix.pwd;
    import core.sys.posix.stdlib;
    private import core.exception : onOutOfMemoryError;
}




/** String used to separate directory names in a path.  Under
    POSIX this is a slash, under Windows a backslash.
*/
version(Posix)          enum string dirSeparator = "/";
else version(Windows)   enum string dirSeparator = "\\";
else static assert (0, "unsupported platform");




/** Path separator string.  A colon under POSIX, a semicolon
    under Windows.
*/
version(Posix)          enum string pathSeparator = ":";
else version(Windows)   enum string pathSeparator = ";";
else static assert (0, "unsupported platform");




/** Determines whether the given character is a directory separator.

    On Windows, this includes both $(D `\`) and $(D `/`).
    On POSIX, it's just $(D `/`).
*/
bool isDirSeparator(dchar c)  @safe pure nothrow
{
    if (c == '/') return true;
    version(Windows) if (c == '\\') return true;
    return false;
}


/*  Determines whether the given character is a drive separator.

    On Windows, this is true if c is the ':' character that separates
    the drive letter from the rest of the path.  On POSIX, this always
    returns false.
*/
private bool isDriveSeparator(dchar c)  @safe pure nothrow
{
    version(Windows) return c == ':';
    else return false;
}


/*  Combines the isDirSeparator and isDriveSeparator tests. */
version(Windows) private bool isSeparator(dchar c)  @safe pure nothrow
{
    return isDirSeparator(c) || isDriveSeparator(c);
}
version(Posix) private alias isDirSeparator isSeparator;


/*  Helper function that determines the position of the last
    drive/directory separator in a string.  Returns -1 if none
    is found.
*/
private ptrdiff_t lastSeparator(C)(in C[] path)  @safe pure nothrow
    if (isSomeChar!C)
{
    auto i = (cast(ptrdiff_t) path.length) - 1;
    while (i >= 0 && !isSeparator(path[i])) --i;
    return i;
}


version (Windows)
{
    private bool isUNC(C)(in C[] path) @safe pure nothrow  if (isSomeChar!C)
    {
        return path.length >= 3 && isDirSeparator(path[0]) && isDirSeparator(path[1])
            && !isDirSeparator(path[2]);
    }

    private ptrdiff_t uncRootLength(C)(in C[] path) @safe pure nothrow  if (isSomeChar!C)
        in { assert (isUNC(path)); }
        body
    {
        ptrdiff_t i = 3;
        while (i < path.length && !isDirSeparator(path[i])) ++i;
        if (i < path.length)
        {
            auto j = i;
            do { ++j; } while (j < path.length && isDirSeparator(path[j]));
            if (j < path.length)
            {
                do { ++j; } while (j < path.length && !isDirSeparator(path[j]));
                i = j;
            }
        }
        return i;
    }

    private bool hasDrive(C)(in C[] path)  @safe pure nothrow  if (isSomeChar!C)
    {
        return path.length >= 2 && isDriveSeparator(path[1]);
    }

    private bool isDriveRoot(C)(in C[] path)  @safe pure nothrow  if (isSomeChar!C)
    {
        return path.length >= 3 && isDriveSeparator(path[1])
            && isDirSeparator(path[2]);
    }
}


/*  Helper functions that strip leading/trailing slashes and backslashes
    from a path.
*/
private inout(C)[] ltrimDirSeparators(C)(inout(C)[] path)  @safe pure nothrow
    if (isSomeChar!C)
{
    int i = 0;
    while (i < path.length && isDirSeparator(path[i])) ++i;
    return path[i .. $];
}

private inout(C)[] rtrimDirSeparators(C)(inout(C)[] path)  @safe pure nothrow
    if (isSomeChar!C)
{
    auto i = (cast(ptrdiff_t) path.length) - 1;
    while (i >= 0 && isDirSeparator(path[i])) --i;
    return path[0 .. i+1];
}

private inout(C)[] trimDirSeparators(C)(inout(C)[] path)  @safe pure nothrow
    if (isSomeChar!C)
{
    return ltrimDirSeparators(rtrimDirSeparators(path));
}




/** This $(D enum) is used as a template argument to functions which
    compare file names, and determines whether the comparison is
    case sensitive or not.
*/
enum CaseSensitive : bool
{
    /// File names are case insensitive
    no = false,

    /// File names are case sensitive
    yes = true,

    /** The default (or most common) setting for the current platform.
        That is, $(D no) on Windows and Mac OS X, and $(D yes) on all
        POSIX systems except OS X (Linux, *BSD, etc.).
    */
    osDefault = osDefaultCaseSensitivity
}
version (Windows)    private enum osDefaultCaseSensitivity = false;
else version (OSX)   private enum osDefaultCaseSensitivity = false;
else version (Posix) private enum osDefaultCaseSensitivity = true;
else static assert (0);




/** Returns the name of a file, without any leading directory
    and with an optional suffix chopped off.

    If $(D suffix) is specified, it will be compared to $(D path)
    using $(D filenameCmp!cs),
    where $(D cs) is an optional template parameter determining whether
    the comparison is case sensitive or not.  See the
    $(LREF filenameCmp) documentation for details.

    Examples:
    ---
    assert (baseName("dir/file.ext")         == "file.ext");
    assert (baseName("dir/file.ext", ".ext") == "file");
    assert (baseName("dir/file.ext", ".xyz") == "file.ext");
    assert (baseName("dir/filename", "name") == "file");
    assert (baseName("dir/subdir/")          == "subdir");

    version (Windows)
    {
        assert (baseName(`d:file.ext`)      == "file.ext");
        assert (baseName(`d:\dir\file.ext`) == "file.ext");
    }
    ---

    Note:
    This function $(I only) strips away the specified suffix, which
    doesn't necessarily have to represent an extension.  If you want
    to remove the extension from a path, regardless of what the extension
    is, use $(LREF stripExtension).
    If you want the filename without leading directories and without
    an extension, combine the functions like this:
    ---
    assert (baseName(stripExtension("dir/file.ext")) == "file");
    ---

    Standards:
    This function complies with
    $(LINK2 http://pubs.opengroup.org/onlinepubs/9699919799/utilities/basename.html,
    the POSIX requirements for the 'basename' shell utility)
    (with suitable adaptations for Windows paths).
*/
inout(C)[] baseName(C)(inout(C)[] path)
    @trusted pure //TODO: nothrow (BUG 5700)
    if (isSomeChar!C)
{
    auto p1 = stripDrive(path);
    if (p1.empty)
    {
        version (Windows) if (isUNC(path))
        {
            return cast(typeof(return)) dirSeparator.dup;
        }
        return null;
    }

    auto p2 = rtrimDirSeparators(p1);
    if (p2.empty) return p1[0 .. 1];

    return p2[lastSeparator(p2)+1 .. $];
}

/// ditto
inout(C)[] baseName(CaseSensitive cs = CaseSensitive.osDefault, C, C1)
    (inout(C)[] path, in C1[] suffix)
    @safe pure //TODO: nothrow (because of filenameCmp())
    if (isSomeChar!C && isSomeChar!C1)
{
    auto p = baseName(path);
    if (p.length > suffix.length
        && filenameCmp!cs(p[$-suffix.length .. $], suffix) == 0)
    {
        return p[0 .. $-suffix.length];
    }
    else return p;
}


unittest
{
    assert (baseName("").empty);
    assert (baseName("file.ext"w) == "file.ext");
    assert (baseName("file.ext"d, ".ext") == "file");
    assert (baseName("file", "file"w.dup) == "file");
    assert (baseName("dir/file.ext"d.dup) == "file.ext");
    assert (baseName("dir/file.ext", ".ext"d) == "file");
    assert (baseName("dir/file"w, "file"d) == "file");
    assert (baseName("dir///subdir////") == "subdir");
    assert (baseName("dir/subdir.ext/", ".ext") == "subdir");
    assert (baseName("dir/subdir/".dup, "subdir") == "subdir");
    assert (baseName("/"w.dup) == "/");
    assert (baseName("//"d.dup) == "/");
    assert (baseName("///") == "/");

    assert (baseName!(CaseSensitive.yes)("file.ext", ".EXT") == "file.ext");
    assert (baseName!(CaseSensitive.no)("file.ext", ".EXT") == "file");

    version (Windows)
    {
        assert (baseName(`dir\file.ext`) == `file.ext`);
        assert (baseName(`dir\file.ext`, `.ext`) == `file`);
        assert (baseName(`dir\file`, `file`) == `file`);
        assert (baseName(`d:file.ext`) == `file.ext`);
        assert (baseName(`d:file.ext`, `.ext`) == `file`);
        assert (baseName(`d:file`, `file`) == `file`);
        assert (baseName(`dir\\subdir\\\`) == `subdir`);
        assert (baseName(`dir\subdir.ext\`, `.ext`) == `subdir`);
        assert (baseName(`dir\subdir\`, `subdir`) == `subdir`);
        assert (baseName(`\`) == `\`);
        assert (baseName(`\\`) == `\`);
        assert (baseName(`\\\`) == `\`);
        assert (baseName(`d:\`) == `\`);
        assert (baseName(`d:`).empty);
        assert (baseName(`\\server\share\file`) == `file`);
        assert (baseName(`\\server\share\`) == `\`);
        assert (baseName(`\\server\share`) == `\`);
    }

    assert (baseName(stripExtension("dir/file.ext")) == "file");

    static assert (baseName("dir/file.ext") == "file.ext");
    static assert (baseName("dir/file.ext", ".ext") == "file");
}




/** Returns the directory part of a path.  On Windows, this
    includes the drive letter if present.

    This function performs a memory allocation if and only if $(D path)
    is mutable and does not have a directory (in which case a new mutable
    string is needed to hold the returned current-directory symbol,
    $(D ".")).

    Examples:
    ---
    assert (dirName("file")        == ".");
    assert (dirName("dir/file")    == "dir");
    assert (dirName("/file")       == "/");
    assert (dirName("dir/subdir/") == "dir");

    version (Windows)
    {
        assert (dirName("d:file")      == "d:");
        assert (dirName(`d:\dir\file`) == `d:\dir`);
        assert (dirName(`d:\file`)     == `d:\`);
        assert (dirName(`dir\subdir\`) == `dir`);
    }
    ---

    Standards:
    This function complies with
    $(LINK2 http://pubs.opengroup.org/onlinepubs/9699919799/utilities/dirname.html,
    the POSIX requirements for the 'dirname' shell utility)
    (with suitable adaptations for Windows paths).
*/
C[] dirName(C)(C[] path)
    //TODO: @safe (BUG 6169) pure nothrow (because of to())
    if (isSomeChar!C)
{
    if (path.empty) return to!(typeof(return))(".");

    auto p = rtrimDirSeparators(path);
    if (p.empty) return path[0 .. 1];

    version (Windows)
    {
        if (isUNC(p) && uncRootLength(p) == p.length)
            return p;
        if (p.length == 2 && isDriveSeparator(p[1]) && path.length > 2)
            return path[0 .. 3];
    }

    auto i = lastSeparator(p);
    if (i == -1) return to!(typeof(return))(".");
    if (i == 0) return p[0 .. 1];

    version (Windows)
    {
        // If the directory part is either d: or d:\, don't
        // chop off the last symbol.
        if (isDriveSeparator(p[i]) || isDriveSeparator(p[i-1]))
            return p[0 .. i+1];
    }

    // Remove any remaining trailing (back)slashes.
    return rtrimDirSeparators(p[0 .. i]);
}


unittest
{
    assert (dirName("") == ".");
    assert (dirName("file"w) == ".");
    assert (dirName("dir/"d) == ".");
    assert (dirName("dir///") == ".");
    assert (dirName("dir/file"w.dup) == "dir");
    assert (dirName("dir///file"d.dup) == "dir");
    assert (dirName("dir/subdir/") == "dir");
    assert (dirName("/dir/file"w) == "/dir");
    assert (dirName("/file"d) == "/");
    assert (dirName("/") == "/");
    assert (dirName("///") == "/");

    version (Windows)
    {
        assert (dirName(`dir\`) == `.`);
        assert (dirName(`dir\\\`) == `.`);
        assert (dirName(`dir\file`) == `dir`);
        assert (dirName(`dir\\\file`) == `dir`);
        assert (dirName(`dir\subdir\`) == `dir`);
        assert (dirName(`\dir\file`) == `\dir`);
        assert (dirName(`\file`) == `\`);
        assert (dirName(`\`) == `\`);
        assert (dirName(`\\\`) == `\`);
        assert (dirName(`d:`) == `d:`);
        assert (dirName(`d:file`) == `d:`);
        assert (dirName(`d:\`) == `d:\`);
        assert (dirName(`d:\file`) == `d:\`);
        assert (dirName(`d:\dir\file`) == `d:\dir`);
        assert (dirName(`\\server\share\dir\file`) == `\\server\share\dir`);
        assert (dirName(`\\server\share\file`) == `\\server\share`);
        assert (dirName(`\\server\share\`) == `\\server\share`);
        assert (dirName(`\\server\share`) == `\\server\share`);
    }

    static assert (dirName("dir/file") == "dir");
}




/** Returns the root directory of the specified path, or $(D null) if the
    path is not rooted.

    Examples:
    ---
    assert (rootName("foo") is null);
    assert (rootName("/foo") == "/");

    version (Windows)
    {
        assert (rootName(`\foo`) == `\`);
        assert (rootName(`c:\foo`) == `c:\`);
        assert (rootName(`\\server\share\foo`) == `\\server\share`);
    }
    ---
*/
inout(C)[] rootName(C)(inout(C)[] path)  @safe pure nothrow  if (isSomeChar!C)
{
    if (path.empty) return null;

    version (Posix)
    {
        if (isDirSeparator(path[0])) return path[0 .. 1];
    }
    else version (Windows)
    {
        if (isDirSeparator(path[0]))
        {
            if (isUNC(path)) return path[0 .. uncRootLength(path)];
            else return path[0 .. 1];
        }
        else if (path.length >= 3 && isDriveSeparator(path[1]) &&
            isDirSeparator(path[2]))
        {
            return path[0 .. 3];
        }
    }
    else static assert (0, "unsupported platform");

    assert (!isRooted(path));
    return null;
}


unittest
{
    assert (rootName("") is null);
    assert (rootName("foo") is null);
    assert (rootName("/") == "/");
    assert (rootName("/foo/bar") == "/");

    version (Windows)
    {
        assert (rootName("d:foo") is null);
        assert (rootName(`d:\foo`) == `d:\`);
        assert (rootName(`\\server\share\foo`) == `\\server\share`);
        assert (rootName(`\\server\share`) == `\\server\share`);
    }
}




/** Returns the drive of a path, or $(D null) if the drive
    is not specified.  In the case of UNC paths, the network share
    is returned.

    Always returns $(D null) on POSIX.

    Examples:
    ---
    version (Windows)
    {
        assert (driveName(`d:\file`) == "d:");
        assert (driveName(`\\server\share\file`) == `\\server\share`);
        assert (driveName(`dir\file`).empty);
    }
    ---
*/
inout(C)[] driveName(C)(inout(C)[] path)  @safe pure nothrow
    if (isSomeChar!C)
{
    version (Windows)
    {
        if (hasDrive(path))
            return path[0 .. 2];
        else if (isUNC(path))
            return path[0 .. uncRootLength(path)];
    }
    return null;
}


unittest
{
    version (Posix)  assert (driveName("c:/foo").empty);
    version (Windows)
    {
        assert (driveName(`dir\file`).empty);
        assert (driveName(`d:file`) == "d:");
        assert (driveName(`d:\file`) == "d:");
        assert (driveName("d:") == "d:");
        assert (driveName(`\\server\share\file`) == `\\server\share`);
        assert (driveName(`\\server\share\`) == `\\server\share`);
        assert (driveName(`\\server\share`) == `\\server\share`);

        static assert (driveName(`d:\file`) == "d:");
    }
}




/** Strips the drive from a Windows path.  On POSIX, the path is returned
    unaltered.

    Example:
    ---
    version (Windows)
    {
        assert (stripDrive(`d:\dir\file`) == `\dir\file`);
        assert (stripDrive(`\\server\share\dir\file`) == `\dir\file`);
    }
    ---
*/
inout(C)[] stripDrive(C)(inout(C)[] path)  @safe pure nothrow  if (isSomeChar!C)
{
    version(Windows)
    {
        if (hasDrive(path))      return path[2 .. $];
        else if (isUNC(path))    return path[uncRootLength(path) .. $];
    }
    return path;
}


unittest
{
    version(Windows)
    {
        assert (stripDrive(`d:\dir\file`) == `\dir\file`);
        assert (stripDrive(`\\server\share\dir\file`) == `\dir\file`);
        static assert (stripDrive(`d:\dir\file`) == `\dir\file`);
    }
    version(Posix)
    {
        assert (stripDrive(`d:\dir\file`) == `d:\dir\file`);
    }
}




/*  Helper function that returns the position of the filename/extension
    separator dot in path.  If not found, returns -1.
*/
private ptrdiff_t extSeparatorPos(C)(in C[] path)  @safe pure nothrow
    if (isSomeChar!C)
{
    auto i = (cast(ptrdiff_t) path.length) - 1;
    while (i >= 0 && !isSeparator(path[i]))
    {
        if (path[i] == '.' && i > 0 && !isSeparator(path[i-1])) return i;
        --i;
    }
    return -1;
}




/** Returns the _extension part of a file name, including the dot.

    If there is no _extension, $(D null) is returned.

    Examples:
    ---
    assert (extension("file").empty);
    assert (extension("file.ext")       == ".ext");
    assert (extension("file.ext1.ext2") == ".ext2");
    assert (extension("file.")          == ".");
    assert (extension(".file").empty);
    assert (extension(".file.ext")      == ".ext");
    ---
*/
inout(C)[] extension(C)(inout(C)[] path)  @safe pure nothrow  if (isSomeChar!C)
{
    auto i = extSeparatorPos(path);
    if (i == -1) return null;
    else return path[i .. $];
}


unittest
{
    assert (extension("file").empty);
    assert (extension("file.") == ".");
    assert (extension("file.ext"w) == ".ext");
    assert (extension("file.ext1.ext2"d) == ".ext2");
    assert (extension(".foo".dup).empty);
    assert (extension(".foo.ext"w.dup) == ".ext");

    assert (extension("dir/file"d.dup).empty);
    assert (extension("dir/file.") == ".");
    assert (extension("dir/file.ext") == ".ext");
    assert (extension("dir/file.ext1.ext2"w) == ".ext2");
    assert (extension("dir/.foo"d).empty);
    assert (extension("dir/.foo.ext".dup) == ".ext");

    version(Windows)
    {
        assert (extension(`dir\file`).empty);
        assert (extension(`dir\file.`) == ".");
        assert (extension(`dir\file.ext`) == `.ext`);
        assert (extension(`dir\file.ext1.ext2`) == `.ext2`);
        assert (extension(`dir\.foo`).empty);
        assert (extension(`dir\.foo.ext`) == `.ext`);

        assert (extension(`d:file`).empty);
        assert (extension(`d:file.`) == ".");
        assert (extension(`d:file.ext`) == `.ext`);
        assert (extension(`d:file.ext1.ext2`) == `.ext2`);
        assert (extension(`d:.foo`).empty);
        assert (extension(`d:.foo.ext`) == `.ext`);
    }

    static assert (extension("file").empty);
    static assert (extension("file.ext") == ".ext");
}




/** Returns the path with the extension stripped off.

    Examples:
    ---
    assert (stripExtension("file")           == "file");
    assert (stripExtension("file.ext")       == "file");
    assert (stripExtension("file.ext1.ext2") == "file.ext1");
    assert (stripExtension("file.")          == "file");
    assert (stripExtension(".file")          == ".file");
    assert (stripExtension(".file.ext")      == ".file");
    assert (stripExtension("dir/file.ext")   == "dir/file");
    ---
*/
inout(C)[] stripExtension(C)(inout(C)[] path)  @safe pure nothrow
    if (isSomeChar!C)
{
    auto i = extSeparatorPos(path);
    if (i == -1) return path;
    else return path[0 .. i];
}


unittest
{
    assert (stripExtension("file") == "file");
    assert (stripExtension("file.ext"w) == "file");
    assert (stripExtension("file.ext1.ext2"d) == "file.ext1");
    assert (stripExtension(".foo".dup) == ".foo");
    assert (stripExtension(".foo.ext"w.dup) == ".foo");

    assert (stripExtension("dir/file"d.dup) == "dir/file");
    assert (stripExtension("dir/file.ext") == "dir/file");
    assert (stripExtension("dir/file.ext1.ext2"w) == "dir/file.ext1");
    assert (stripExtension("dir/.foo"d) == "dir/.foo");
    assert (stripExtension("dir/.foo.ext".dup) == "dir/.foo");

    version(Windows)
    {
    assert (stripExtension("dir\\file") == "dir\\file");
    assert (stripExtension("dir\\file.ext") == "dir\\file");
    assert (stripExtension("dir\\file.ext1.ext2") == "dir\\file.ext1");
    assert (stripExtension("dir\\.foo") == "dir\\.foo");
    assert (stripExtension("dir\\.foo.ext") == "dir\\.foo");

    assert (stripExtension("d:file") == "d:file");
    assert (stripExtension("d:file.ext") == "d:file");
    assert (stripExtension("d:file.ext1.ext2") == "d:file.ext1");
    assert (stripExtension("d:.foo") == "d:.foo");
    assert (stripExtension("d:.foo.ext") == "d:.foo");
    }

    static assert (stripExtension("file") == "file");
    static assert (stripExtension("file.ext"w) == "file");
}




/** Returns a string containing the _path given by $(D path), but where
    the extension has been set to $(D ext).

    If the filename already has an extension, it is replaced.   If not, the
    extension is simply appended to the filename.  Including a leading dot
    in $(D ext) is optional.

    If the extension is empty, this function is equivalent to
    $(LREF stripExtension).

    This function normally allocates a new string (the possible exception
    being the case when path is immutable and doesn't already have an
    extension).

    Examples:
    ---
    assert (setExtension("file", "ext")      == "file.ext");
    assert (setExtension("file", ".ext")     == "file.ext");
    assert (setExtension("file.old", "")     == "file");
    assert (setExtension("file.old", "new")  == "file.new");
    assert (setExtension("file.old", ".new") == "file.new");
    ---
*/
immutable(Unqual!C1)[] setExtension(C1, C2)(in C1[] path, in C2[] ext)
    @trusted pure nothrow
    if (isSomeChar!C1 && !is(C1 == immutable) && is(Unqual!C1 == Unqual!C2))
{
    if (ext.length > 0 && ext[0] != '.')
        return cast(typeof(return))(stripExtension(path)~'.'~ext);
    else
        return cast(typeof(return))(stripExtension(path)~ext);
}

///ditto
immutable(C1)[] setExtension(C1, C2)(immutable(C1)[] path, const(C2)[] ext)
    @trusted pure nothrow
    if (isSomeChar!C1 && is(Unqual!C1 == Unqual!C2))
{
    if (ext.length == 0)
        return stripExtension(path);

    // Optimised for the case where path is immutable and has no extension
    if (ext.length > 0 && ext[0] == '.') ext = ext[1 .. $];
    auto i = extSeparatorPos(path);
    if (i == -1)
    {
        path ~= '.';
        path ~= ext;
        return path;
    }
    else if (i == path.length - 1)
    {
        path ~= ext;
        return path;
    }
    else
    {
        return cast(typeof(return))(path[0 .. i+1] ~ ext);
    }
}


unittest
{
    assert (setExtension("file", "ext") == "file.ext");
    assert (setExtension("file"w, ".ext"w) == "file.ext");
    assert (setExtension("file."d, "ext"d) == "file.ext");
    assert (setExtension("file.", ".ext") == "file.ext");
    assert (setExtension("file.old"w, "new"w) == "file.new");
    assert (setExtension("file.old"d, ".new"d) == "file.new");

    assert (setExtension("file"w.dup, "ext"w) == "file.ext");
    assert (setExtension("file"w.dup, ".ext"w) == "file.ext");
    assert (setExtension("file."w, "ext"w.dup) == "file.ext");
    assert (setExtension("file."w, ".ext"w.dup) == "file.ext");
    assert (setExtension("file.old"d.dup, "new"d) == "file.new");
    assert (setExtension("file.old"d.dup, ".new"d) == "file.new");

    static assert (setExtension("file", "ext") == "file.ext");
    static assert (setExtension("file.old", "new") == "file.new");

    static assert (setExtension("file"w.dup, "ext"w) == "file.ext");
    static assert (setExtension("file.old"d.dup, "new"d) == "file.new");

    // Issue 10601
    assert (setExtension("file", "") == "file");
    assert (setExtension("file.ext", "") == "file");
}



/** Returns the _path given by $(D path), with the extension given by
    $(D ext) appended if the path doesn't already have one.

    Including the dot in the extension is optional.

    This function always allocates a new string, except in the case when
    path is immutable and already has an extension.

    Examples:
    ---
    assert (defaultExtension("file", "ext")      == "file.ext");
    assert (defaultExtension("file", ".ext")     == "file.ext");
    assert (defaultExtension("file.", "ext")     == "file.");
    assert (defaultExtension("file.old", "new")  == "file.old");
    assert (defaultExtension("file.old", ".new") == "file.old");
    ---
*/
immutable(Unqual!C1)[] defaultExtension(C1, C2)(in C1[] path, in C2[] ext)
    @trusted pure // TODO: nothrow (because of to())
    if (isSomeChar!C1 && is(Unqual!C1 == Unqual!C2))
{
    auto i = extSeparatorPos(path);
    if (i == -1)
    {
        if (ext.length > 0 && ext[0] == '.')
            return cast(typeof(return))(path~ext);
        else
            return cast(typeof(return))(path~'.'~ext);
    }
    else return to!(typeof(return))(path);
}


unittest
{
    assert (defaultExtension("file", "ext") == "file.ext");
    assert (defaultExtension("file", ".ext") == "file.ext");
    assert (defaultExtension("file.", "ext")     == "file.");
    assert (defaultExtension("file.old", "new") == "file.old");
    assert (defaultExtension("file.old", ".new") == "file.old");

    assert (defaultExtension("file"w.dup, "ext"w) == "file.ext");
    assert (defaultExtension("file.old"d.dup, "new"d) == "file.old");

    static assert (defaultExtension("file", "ext") == "file.ext");
    static assert (defaultExtension("file.old", "new") == "file.old");

    static assert (defaultExtension("file"w.dup, "ext"w) == "file.ext");
    static assert (defaultExtension("file.old"d.dup, "new"d) == "file.old");
}


/** Combines one or more path segments.

    This function takes a set of path segments, given as an input
    range of string elements or as a set of string arguments,
    and concatenates them with each other.  Directory separators
    are inserted between segments if necessary.  If any of the
    path segments are absolute (as defined by $(LREF isAbsolute)), the
    preceding segments will be dropped.

    On Windows, if one of the path segments are rooted, but not absolute
    (e.g. $(D `\foo`)), all preceding path segments down to the previous
    root will be dropped.  (See below for an example.)

    This function always allocates memory to hold the resulting path.
    The variadic overload is guaranteed to only perform a single
    allocation, as is the range version if $(D paths) is a forward
    range.
*/
immutable(ElementEncodingType!(ElementType!Range))[]
    buildPath(Range)(Range segments)
        if (isInputRange!Range && isSomeString!(ElementType!Range))
{
    if (segments.empty) return null;

    // If this is a forward range, we can pre-calculate a maximum length.
    static if (isForwardRange!Range)
    {
        auto segments2 = segments.save;
        size_t precalc = 0;
        foreach (segment; segments2) precalc += segment.length + 1;
    }
    // Otherwise, just venture a guess and resize later if necessary.
    else size_t precalc = 255;

    auto buf = new Unqual!(ElementEncodingType!(ElementType!Range))[](precalc);
    size_t pos = 0;
    foreach (segment; segments)
    {
        if (segment.empty) continue;
        static if (!isForwardRange!Range)
        {
            immutable neededLength = pos + segment.length + 1;
            if (buf.length < neededLength)
                buf.length = reserve(buf, neededLength + buf.length/2);
        }
        if (pos > 0)
        {
            if (isRooted(segment))
            {
                version (Posix)
                {
                    pos = 0;
                }
                else version (Windows)
                {
                    if (isAbsolute(segment))
                        pos = 0;
                    else
                    {
                        pos = rootName(buf[0 .. pos]).length;
                        if (pos > 0 && isDirSeparator(buf[pos-1])) --pos;
                    }
                }
            }
            else if (!isDirSeparator(buf[pos-1]))
                buf[pos++] = dirSeparator[0];
        }
        buf[pos .. pos + segment.length] = segment[];
        pos += segment.length;
    }
    static U trustedCast(U, V)(V v) @trusted pure nothrow { return cast(U) v; }
    return trustedCast!(typeof(return))(buf[0 .. pos]);
}

/// ditto
immutable(C)[] buildPath(C)(const(C[])[] paths...)
    @safe pure nothrow
    if (isSomeChar!C)
{
    return buildPath!(typeof(paths))(paths);
}

///
unittest
{
    version (Posix)
    {
        assert (buildPath("foo", "bar", "baz") == "foo/bar/baz");
        assert (buildPath("/foo/", "bar/baz")  == "/foo/bar/baz");
        assert (buildPath("/foo", "/bar")      == "/bar");
    }

    version (Windows)
    {
        assert (buildPath("foo", "bar", "baz") == `foo\bar\baz`);
        assert (buildPath(`c:\foo`, `bar\baz`) == `c:\foo\bar\baz`);
        assert (buildPath("foo", `d:\bar`)     == `d:\bar`);
        assert (buildPath("foo", `\bar`)       == `\bar`);
        assert (buildPath(`c:\foo`, `\bar`)    == `c:\bar`);
    }
}

unittest // non-documented
{
    // ir() wraps an array in a plain (i.e. non-forward) input range, so that
    // we can test both code paths
    InputRange!(C[]) ir(C)(C[][] p...) { return inputRangeObject(p); }
    version (Posix)
    {
        assert (buildPath("foo") == "foo");
        assert (buildPath("/foo/") == "/foo/");
        assert (buildPath("foo", "bar") == "foo/bar");
        assert (buildPath("foo", "bar", "baz") == "foo/bar/baz");
        assert (buildPath("foo/".dup, "bar") == "foo/bar");
        assert (buildPath("foo///", "bar".dup) == "foo///bar");
        assert (buildPath("/foo"w, "bar"w) == "/foo/bar");
        assert (buildPath("foo"w.dup, "/bar"w) == "/bar");
        assert (buildPath("foo"w, "bar/"w.dup) == "foo/bar/");
        assert (buildPath("/"d, "foo"d) == "/foo");
        assert (buildPath(""d.dup, "foo"d) == "foo");
        assert (buildPath("foo"d, ""d.dup) == "foo");
        assert (buildPath("foo", "bar".dup, "baz") == "foo/bar/baz");
        assert (buildPath("foo"w, "/bar"w, "baz"w.dup) == "/bar/baz");

        static assert (buildPath("foo", "bar", "baz") == "foo/bar/baz");
        static assert (buildPath("foo", "/bar", "baz") == "/bar/baz");

        // The following are mostly duplicates of the above, except that the
        // range version does not accept mixed constness.
        assert (buildPath(ir("foo")) == "foo");
        assert (buildPath(ir("/foo/")) == "/foo/");
        assert (buildPath(ir("foo", "bar")) == "foo/bar");
        assert (buildPath(ir("foo", "bar", "baz")) == "foo/bar/baz");
        assert (buildPath(ir("foo/".dup, "bar".dup)) == "foo/bar");
        assert (buildPath(ir("foo///".dup, "bar".dup)) == "foo///bar");
        assert (buildPath(ir("/foo"w, "bar"w)) == "/foo/bar");
        assert (buildPath(ir("foo"w.dup, "/bar"w.dup)) == "/bar");
        assert (buildPath(ir("foo"w.dup, "bar/"w.dup)) == "foo/bar/");
        assert (buildPath(ir("/"d, "foo"d)) == "/foo");
        assert (buildPath(ir(""d.dup, "foo"d.dup)) == "foo");
        assert (buildPath(ir("foo"d, ""d)) == "foo");
        assert (buildPath(ir("foo", "bar", "baz")) == "foo/bar/baz");
        assert (buildPath(ir("foo"w.dup, "/bar"w.dup, "baz"w.dup)) == "/bar/baz");
    }
    version (Windows)
    {
        assert (buildPath("foo") == "foo");
        assert (buildPath(`\foo/`) == `\foo/`);
        assert (buildPath("foo", "bar", "baz") == `foo\bar\baz`);
        assert (buildPath("foo", `\bar`) == `\bar`);
        assert (buildPath(`c:\foo`, "bar") == `c:\foo\bar`);
        assert (buildPath("foo"w, `d:\bar`w.dup) ==  `d:\bar`);
        assert (buildPath(`c:\foo\bar`, `\baz`) == `c:\baz`);
        assert (buildPath(`\\foo\bar\baz`d, `foo`d, `\bar`d) == `\\foo\bar\bar`d);

        static assert (buildPath("foo", "bar", "baz") == `foo\bar\baz`);
        static assert (buildPath("foo", `c:\bar`, "baz") == `c:\bar\baz`);

        assert (buildPath(ir("foo")) == "foo");
        assert (buildPath(ir(`\foo/`)) == `\foo/`);
        assert (buildPath(ir("foo", "bar", "baz")) == `foo\bar\baz`);
        assert (buildPath(ir("foo", `\bar`)) == `\bar`);
        assert (buildPath(ir(`c:\foo`, "bar")) == `c:\foo\bar`);
        assert (buildPath(ir("foo"w.dup, `d:\bar`w.dup)) ==  `d:\bar`);
        assert (buildPath(ir(`c:\foo\bar`, `\baz`)) == `c:\baz`);
        assert (buildPath(ir(`\\foo\bar\baz`d, `foo`d, `\bar`d)) == `\\foo\bar\bar`d);
    }

    // Test that allocation works as it should.
    auto manyShort = "aaa".repeat(1000).array();
    auto manyShortCombined = join(manyShort, dirSeparator);
    assert (buildPath(manyShort) == manyShortCombined);
    assert (buildPath(ir(manyShort)) == manyShortCombined);

    auto fewLong = 'b'.repeat(500).array().repeat(10).array();
    auto fewLongCombined = join(fewLong, dirSeparator);
    assert (buildPath(fewLong) == fewLongCombined);
    assert (buildPath(ir(fewLong)) == fewLongCombined);
}

unittest
{
    // Test for issue 7397
    string[] ary = ["a", "b"];
    version (Posix)
    {
        assert (buildPath(ary) == "a/b");
    }
    else version (Windows)
    {
        assert (buildPath(ary) == `a\b`);
    }
}


/** Performs the same task as $(LREF buildPath),
    while at the same time resolving current/parent directory
    symbols ($(D ".") and $(D "..")) and removing superfluous
    directory separators.
    On Windows, slashes are replaced with backslashes.

    Note that this function does not resolve symbolic links.

    This function always allocates memory to hold the resulting path.

    Examples:
    ---
    version (Posix)
    {
        assert (buildNormalizedPath("/foo/./bar/..//baz/") == "/foo/baz");
        assert (buildNormalizedPath("../foo/.") == "../foo");
        assert (buildNormalizedPath("/foo", "bar/baz/") == "/foo/bar/baz");
        assert (buildNormalizedPath("/foo", "/bar/..", "baz") == "/baz");
        assert (buildNormalizedPath("foo/./bar", "../../", "../baz") == "../baz");
        assert (buildNormalizedPath("/foo/./bar", "../../baz") == "/baz");
    }

    version (Windows)
    {
        assert (buildNormalizedPath(`c:\foo\.\bar/..\\baz\`) == `c:\foo\baz`);
        assert (buildNormalizedPath(`..\foo\.`) == `..\foo`);
        assert (buildNormalizedPath(`c:\foo`, `bar\baz\`) == `c:\foo\bar\baz`);
        assert (buildNormalizedPath(`c:\foo`, `bar/..`) == `c:\foo`);
        assert (buildNormalizedPath(`\\server\share\foo`, `..\bar`) == `\\server\share\bar`);
    }
    ---
*/
immutable(C)[] buildNormalizedPath(C)(const(C[])[] paths...)
    @trusted pure nothrow
    if (isSomeChar!C)
{
    import std.c.stdlib;
    auto paths2 = new const(C)[][](paths.length);
        //(cast(const(C)[]*)alloca((const(C)[]).sizeof * paths.length))[0 .. paths.length];

    // Check whether the resulting path will be absolute or rooted,
    // calculate its maximum length, and discard segments we won't use.
    typeof(paths[0][0])[] rootElement;
    int numPaths = 0;
    bool seenAbsolute;
    size_t segmentLengthSum = 0;
    foreach (i; 0 .. paths.length)
    {
        auto p = paths[i];
        if (p.empty) continue;
        else if (isRooted(p))
        {
            immutable thisIsAbsolute = isAbsolute(p);
            if (thisIsAbsolute || !seenAbsolute)
            {
                if (thisIsAbsolute) seenAbsolute = true;
                rootElement = rootName(p);
                paths2[0] = p[rootElement.length .. $];
                numPaths = 1;
                segmentLengthSum = paths2[0].length;
            }
            else
            {
                paths2[0] = p;
                numPaths = 1;
                segmentLengthSum = p.length;
            }
        }
        else
        {
            paths2[numPaths++] = p;
            segmentLengthSum += p.length;
        }
    }
    if (rootElement.length + segmentLengthSum == 0) return null;
    paths2 = paths2[0 .. numPaths];
    immutable rooted = !rootElement.empty;
    assert (rooted || !seenAbsolute); // absolute => rooted

    // Allocate memory for the resulting path, including room for
    // extra dir separators
    auto fullPath = new C[rootElement.length + segmentLengthSum + paths2.length];

    // Copy the root element into fullPath, and let relPart be
    // the remaining slice.
    typeof(fullPath) relPart;
    if (rooted)
    {
        // For Windows, we also need to perform normalization on
        // the root element.
        version (Posix)
        {
            fullPath[0 .. rootElement.length] = rootElement[];
        }
        else version (Windows)
        {
            foreach (i, c; rootElement)
            {
                if (isDirSeparator(c))
                {
                    static assert (dirSeparator.length == 1);
                    fullPath[i] = dirSeparator[0];
                }
                else fullPath[i] = c;
            }
        }
        else static assert (0);

        // If the root element doesn't end with a dir separator,
        // we add one.
        if (!isDirSeparator(rootElement[$-1]))
        {
            static assert (dirSeparator.length == 1);
            fullPath[rootElement.length] = dirSeparator[0];
            relPart = fullPath[rootElement.length + 1 .. $];
        }
        else
        {
            relPart = fullPath[rootElement.length .. $];
        }
    }
    else relPart = fullPath;

    // Now, we have ensured that all segments in path are relative to the
    // root we found earlier.
    bool hasParents = rooted;
    ptrdiff_t i;
    foreach (path; paths2)
    {
        path = trimDirSeparators(path);

        enum Prev { nonSpecial, dirSep, dot, doubleDot }
        Prev prev = Prev.dirSep;
        foreach (j; 0 .. path.length+1)
        {
            // Fake a dir separator between path segments
            immutable c = (j == path.length ? dirSeparator[0] : path[j]);

            if (isDirSeparator(c))
            {
                final switch (prev)
                {
                    case Prev.doubleDot:
                        if (hasParents)
                        {
                            while (i > 0 && !isDirSeparator(relPart[i-1])) --i;
                            if (i > 0) --i; // skip the dir separator
                            while (i > 0 && !isDirSeparator(relPart[i-1])) --i;
                            if (i == 0) hasParents = rooted;
                        }
                        else
                        {
                            relPart[i++] = '.';
                            relPart[i++] = '.';
                            static assert (dirSeparator.length == 1);
                            relPart[i++] = dirSeparator[0];
                        }
                        break;
                    case Prev.dot:
                        while (i > 0 && !isDirSeparator(relPart[i-1])) --i;
                        break;
                    case Prev.nonSpecial:
                        static assert (dirSeparator.length == 1);
                        relPart[i++] = dirSeparator[0];
                        hasParents = true;
                        break;
                    case Prev.dirSep:
                        break;
                }
                prev = Prev.dirSep;
            }
            else if (c == '.')
            {
                final switch (prev)
                {
                    case Prev.dirSep:
                        prev = Prev.dot;
                        break;
                    case Prev.dot:
                        prev = Prev.doubleDot;
                        break;
                    case Prev.doubleDot:
                        prev = Prev.nonSpecial;
                        relPart[i .. i+3] = "...";
                        i += 3;
                        break;
                    case Prev.nonSpecial:
                        relPart[i] = '.';
                        ++i;
                        break;
                }
            }
            else
            {
                final switch (prev)
                {
                    case Prev.doubleDot:
                        relPart[i] = '.';
                        ++i;
                        goto case;
                    case Prev.dot:
                        relPart[i] = '.';
                        ++i;
                        break;
                    case Prev.dirSep:       break;
                    case Prev.nonSpecial:   break;
                }
                relPart[i] = c;
                ++i;
                prev = Prev.nonSpecial;
            }
        }
    }

    // Return path, including root element and excluding the
    // final dir separator.
    immutable len = (relPart.ptr - fullPath.ptr) + (i > 0 ? i - 1 : 0);
    fullPath = fullPath[0 .. len];
    version (Windows)
    {
        // On Windows, if the path is on the form `\\server\share`,
        // with no further segments, normalization will have turned it
        // into `\\server\share\`.  If so, we need to remove the final
        // backslash.
        if (isUNC(fullPath) && uncRootLength(fullPath) == fullPath.length - 1)
            fullPath = fullPath[0 .. $-1];
    }
    return cast(typeof(return)) fullPath;
}

unittest
{
    assert (buildNormalizedPath("") is null);
    assert (buildNormalizedPath("foo") == "foo");

    version (Posix)
    {
        assert (buildNormalizedPath("/", "foo", "bar") == "/foo/bar");
        assert (buildNormalizedPath("foo", "bar", "baz") == "foo/bar/baz");
        assert (buildNormalizedPath("foo", "bar/baz") == "foo/bar/baz");
        assert (buildNormalizedPath("foo", "bar//baz///") == "foo/bar/baz");
        assert (buildNormalizedPath("/foo", "bar/baz") == "/foo/bar/baz");
        assert (buildNormalizedPath("/foo", "/bar/baz") == "/bar/baz");
        assert (buildNormalizedPath("/foo/..", "/bar/./baz") == "/bar/baz");
        assert (buildNormalizedPath("/foo/..", "bar/baz") == "/bar/baz");
        assert (buildNormalizedPath("/foo/../../", "bar/baz") == "/bar/baz");
        assert (buildNormalizedPath("/foo/bar", "../baz") == "/foo/baz");
        assert (buildNormalizedPath("/foo/bar", "../../baz") == "/baz");
        assert (buildNormalizedPath("/foo/bar", ".././/baz/..", "wee/") == "/foo/wee");
        assert (buildNormalizedPath("//foo/bar", "baz///wee") == "/foo/bar/baz/wee");
        static assert (buildNormalizedPath("/foo/..", "/bar/./baz") == "/bar/baz");
        // Examples in docs:
        assert (buildNormalizedPath("/foo", "bar/baz/") == "/foo/bar/baz");
        assert (buildNormalizedPath("/foo", "/bar/..", "baz") == "/baz");
        assert (buildNormalizedPath("foo/./bar", "../../", "../baz") == "../baz");
        assert (buildNormalizedPath("/foo/./bar", "../../baz") == "/baz");
    }
    else version (Windows)
    {
        assert (buildNormalizedPath(`\`, `foo`, `bar`) == `\foo\bar`);
        assert (buildNormalizedPath(`foo`, `bar`, `baz`) == `foo\bar\baz`);
        assert (buildNormalizedPath(`foo`, `bar\baz`) == `foo\bar\baz`);
        assert (buildNormalizedPath(`foo`, `bar\\baz\\\`) == `foo\bar\baz`);
        assert (buildNormalizedPath(`\foo`, `bar\baz`) == `\foo\bar\baz`);
        assert (buildNormalizedPath(`\foo`, `\bar\baz`) == `\bar\baz`);
        assert (buildNormalizedPath(`\foo\..`, `\bar\.\baz`) == `\bar\baz`);
        assert (buildNormalizedPath(`\foo\..`, `bar\baz`) == `\bar\baz`);
        assert (buildNormalizedPath(`\foo\..\..\`, `bar\baz`) == `\bar\baz`);
        assert (buildNormalizedPath(`\foo\bar`, `..\baz`) == `\foo\baz`);
        assert (buildNormalizedPath(`\foo\bar`, `../../baz`) == `\baz`);
        assert (buildNormalizedPath(`\foo\bar`, `..\.\/baz\..`, `wee\`) == `\foo\wee`);

        assert (buildNormalizedPath(`c:\`, `foo`, `bar`) == `c:\foo\bar`);
        assert (buildNormalizedPath(`c:foo`, `bar`, `baz`) == `c:foo\bar\baz`);
        assert (buildNormalizedPath(`c:foo`, `bar\baz`) == `c:foo\bar\baz`);
        assert (buildNormalizedPath(`c:foo`, `bar\\baz\\\`) == `c:foo\bar\baz`);
        assert (buildNormalizedPath(`c:\foo`, `bar\baz`) == `c:\foo\bar\baz`);
        assert (buildNormalizedPath(`c:\foo`, `\bar\baz`) == `c:\bar\baz`);
        assert (buildNormalizedPath(`c:\foo\..`, `\bar\.\baz`) == `c:\bar\baz`);
        assert (buildNormalizedPath(`c:\foo\..`, `bar\baz`) == `c:\bar\baz`);
        assert (buildNormalizedPath(`c:\foo\..\..\`, `bar\baz`) == `c:\bar\baz`);
        assert (buildNormalizedPath(`c:\foo\bar`, `..\baz`) == `c:\foo\baz`);
        assert (buildNormalizedPath(`c:\foo\bar`, `..\..\baz`) == `c:\baz`);
        assert (buildNormalizedPath(`c:\foo\bar`, `..\.\\baz\..`, `wee\`) == `c:\foo\wee`);

        assert (buildNormalizedPath(`\\server\share`, `foo`, `bar`) == `\\server\share\foo\bar`);
        assert (buildNormalizedPath(`\\server\share\`, `foo`, `bar`) == `\\server\share\foo\bar`);
        assert (buildNormalizedPath(`\\server\share\foo`, `bar\baz`) == `\\server\share\foo\bar\baz`);
        assert (buildNormalizedPath(`\\server\share\foo`, `\bar\baz`) == `\\server\share\bar\baz`);
        assert (buildNormalizedPath(`\\server\share\foo\..`, `\bar\.\baz`) == `\\server\share\bar\baz`);
        assert (buildNormalizedPath(`\\server\share\foo\..`, `bar\baz`) == `\\server\share\bar\baz`);
        assert (buildNormalizedPath(`\\server\share\foo\..\..\`, `bar\baz`) == `\\server\share\bar\baz`);
        assert (buildNormalizedPath(`\\server\share\foo\bar`, `..\baz`) == `\\server\share\foo\baz`);
        assert (buildNormalizedPath(`\\server\share\foo\bar`, `..\..\baz`) == `\\server\share\baz`);
        assert (buildNormalizedPath(`\\server\share\foo\bar`, `..\.\\baz\..`, `wee\`) == `\\server\share\foo\wee`);

        static assert (buildNormalizedPath(`\foo\..\..\`, `bar\baz`) == `\bar\baz`);

        // Examples in docs:
        assert (buildNormalizedPath(`c:\foo`, `bar\baz\`) == `c:\foo\bar\baz`);
        assert (buildNormalizedPath(`c:\foo`, `bar/..`) == `c:\foo`);
        assert (buildNormalizedPath(`\\server\share\foo`, `..\bar`) == `\\server\share\bar`);
    }
    else static assert (0);
}

unittest
{
    version (Posix)
    {
        // Trivial
        assert (buildNormalizedPath("").empty);
        assert (buildNormalizedPath("foo/bar") == "foo/bar");

        // Correct handling of leading slashes
        assert (buildNormalizedPath("/") == "/");
        assert (buildNormalizedPath("///") == "/");
        assert (buildNormalizedPath("////") == "/");
        assert (buildNormalizedPath("/foo/bar") == "/foo/bar");
        assert (buildNormalizedPath("//foo/bar") == "/foo/bar");
        assert (buildNormalizedPath("///foo/bar") == "/foo/bar");
        assert (buildNormalizedPath("////foo/bar") == "/foo/bar");

        // Correct handling of single-dot symbol (current directory)
        assert (buildNormalizedPath("/./foo") == "/foo");
        assert (buildNormalizedPath("/foo/./bar") == "/foo/bar");

        assert (buildNormalizedPath("./foo") == "foo");
        assert (buildNormalizedPath("././foo") == "foo");
        assert (buildNormalizedPath("foo/././bar") == "foo/bar");

        // Correct handling of double-dot symbol (previous directory)
        assert (buildNormalizedPath("/foo/../bar") == "/bar");
        assert (buildNormalizedPath("/foo/../../bar") == "/bar");
        assert (buildNormalizedPath("/../foo") == "/foo");
        assert (buildNormalizedPath("/../../foo") == "/foo");
        assert (buildNormalizedPath("/foo/..") == "/");
        assert (buildNormalizedPath("/foo/../..") == "/");

        assert (buildNormalizedPath("foo/../bar") == "bar");
        assert (buildNormalizedPath("foo/../../bar") == "../bar");
        assert (buildNormalizedPath("../foo") == "../foo");
        assert (buildNormalizedPa…