[lldb-dev] Editline Rewrite : issues surround wide character handling on different platforms

[Vince Harron]

> codecvt> : the patch uses a c++ 11 class std::codecvt_utf8, this is a
facet implementation that will do utf8 to wchar convervsion.  It is part of
c++ 11 standard, but not yet supported in gcc.

Should we drop support for building with gcc on Linux?

> - take libedit source files (or subset) and add to the lldb project.  We
could either build a .so file, or just statically link the .cpp files.

Is it a problem to drop these "berkeley stype license" files into the
project?

> - rework the Editline rewrite, so it either uses standard 8 bit chars, or
wchar_t/utf8 depending on the platform.  This would be conditionally built
depending on the platform.

This would be my favorite option if possible.  wchar_t never really took
roots in Linux AFAIK.

> - introduce custom step for new linux lldb users, where they download
libedit source and build and install a wchar version

Not as good as options above but we can work with this.




On Tue, Oct 28, 2014 at 12:42 PM, Shawn Best <sbest at blueshiftinc.com> wrote:

> There is a significant Editline rewrite, adding a bunch of improvements.
> It has been well tested on OSx, but not yet upstreamed.  I have spent some
> time reviewing the proposed patch and working through issues to get it
> running on linux.  To see the patch and accompanying discussion, refer to:
> http://reviews.llvm.org/D5835    The main issues that came up are related
> to handling wide characters and differences between platforms.
>
> Internally, lldb uses std::string which is an array of 8 bit chars, that
> can either be 7 bit ascii, or utf8 encoded wide characters. Libedit uses
> either char, or wchar_t which is a 32 bit char on linux.
>
> <codecvt> : the patch uses a c++ 11 class std::codecvt_utf8, this is a
> facet implementation that will do utf8 to wchar convervsion.  It is part of
> c++ 11 standard, but not yet supported in gcc.  I can use #ifdef to
> temporarily write equivalent functionality in that case while we wait for
> gcc to catch up.
>
> libedit : libedit is a prerequisite that a new linux/lldb user installs (
> sudo apt-get install libedit-dev ).  A few years ago, libedit added
> versions of its functions that work on wchar_t. Unfortunately, this option
> is not built by default, and not present in the Ubuntu distribution.  To
> get around this, I see a few options:
>
> - take libedit source files (or subset) and add to the lldb project.  We
> could either build a .so file, or just statically link the .cpp files.
>
> - rework the Editline rewrite, so it either uses standard 8 bit chars, or
> wchar_t/utf8 depending on the platform.  This would be conditionally built
> depending on the platform.
>
> - modify Ubuntu, so 'sudo apt-get install dev-libedit' installs a version
> that has been built with wide character support enabled.
>
> - introduce custom step for new linux lldb users, where they download
> libedit source and build and install a wchar version
>
> The last 2 options don't seem that great.
>
> I expect there will be problems on Windows, which I think uses utf16
> coding.  The file EditLineWin.cpp, contains prototypes for most of the
> structures and functions needed, but they look stubbed out.
>
> Any thoughts?
>
> Shawn.
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-- 

Vince Harron | Technical Lead Manager | vharron at google.com | 858-442-0868
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