The front-end was treating both \r and \n as Enter and passing
that through to the terminal.
To verify behavior, pay attention to your termios configuration:
```
$ stty -icrnl
$ od -c
<CTRL-J><CTRL-D>
0000000 \n
0000001
$ od -c
<CTRL-M><CTRL-D><Enter>
0000000 \r \n
0000002
```
Closes https://github.com/wez/wezterm/issues/56
Similar to the windows IME support, the placement needs refinement, but
this is sufficient for pinyin input and insertion of emoji via the emoji
palette.
This isn't perfect, but is sufficient to allow using the IME to enter
eg: the heart emoji with cmd.exe.
We have some issues locating and rendering chinese characters that
make it difficult to prove/disprove that the IME is working 100%
because we just can't see the glyphs.
In addition, there appears to be something a bit wonky with conpty and
emoji. If we use eg: `wezterm ssh HOST` to log in to a remote system,
and use the IME to pick eg: the pig face emoji, this renders correctly.
In that scenario we don't use conpty at all.
The IME window is always placed in the top left corner of the window
at the moment, which isn't great, but is better than the system default
which is outside of the window. I need to introduce a way to set the
IME position in the window layer so that the front end gui can set it
to the current cursor position.
Forgetting to update the submodules is a commonly reported build
issue with an obscure error message:
```
CMake Error: The source directory "/home/USER/wezterm/target/debug/build/freetype-430fe24cb64c561c/out/zlib-src/zlib" does not appear to contain CMakeLists.txt.
```
this teaches the build.rs machinery to run the submodule update
if it looks like it is needed.
I thought that I'd broken something with the DEL processing in vim with
the new frontend but it turned out that the other frontend was emitting
BS always and that I'd actuall unbroken passing DEL through and that
other layers were translating DEL into an application cursor mode output
for DEL that emits a totally different sequence.
This diff preserves DEL and disables that other sequence.
Will follow up with some explicit configuration to control this
behavior, but in the short term, the default behavior should be much
closer to what people actually want and expect!
refs: https://github.com/wez/wezterm/issues/52
We handle this with a temporary buffer for the upload, which is
a little gross but avoids leaking that implementation aspect
out to the rest of the code.
This is still a bit rough because the terminal parser doesn't
understand the pixel sizes, so it relies on the hard coded
cell dimensions being accurate.
