cmd: change the prompt in lua

[jankatins]

This keeps the PROMPT variable as is and changes the prompt to the cmder style
in the clink code.

This has two advantages:

• opening a cmd in a cmder session will now show the old prompt code instead of
  a ugly raw prompt without the replacements. This led to ugly output when a
  batch file echoed their content (e.g conda build recipe/).
• when a command rewrites the prompt (e.g. an activate in a virtualenv), these
  commands sometime simple overwrite the PROMPT so that the cmder enhancements
  were not anymore in place. Now we simply don't care and overwrite it with our
  stuff. This might mean that a user has to install a lua script so that e.g.
  conda environments are visible on the prompt.

Closes: #749

[jankatins]

Example old:

C:\Users\jschulz
λ cmd
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. Alle Rechte vorbehalten.

C:\Users\jschulz {git}{hg}
{lamb} exit

C:\Users\jschulz
λ

new:

c:\data\external\cmder (prompt-in-clink)
λ cmd
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. Alle Rechte vorbehalten.

c:\data\external\cmder>exit

c:\data\external\cmder (prompt-in-clink)
λ

[jankatins]

Just as a reference:

A filter which adds a conda environment string in the front of the lambda:

---
 -- Find out the basename of a file/directory (last element after \ or /
 -- @return {basename}
---
function basename(inputstr)
        sep = "\\/"
        local last = nil
        local t={} ; i=1
        for str in string.gmatch(inputstr, "([^"..sep.."]+)") do
                --t[i] = str
                --i = i + 1
                last = str
        end
        return last
end

---
 -- Find out current conda env
 -- @return {false|conda env name}
---
function get_conda_env()
    env_path = clink.get_env('CONDA_DEFAULT_ENV')
    if env_path then
        basen = basename(env_path)
        return basen
    end
    return false
end

---
 -- add conda env name 
---
function conda_prompt_filter()
    -- add in conda env name
    local conda_env = get_conda_env()
    if conda_env then
        clink.prompt.value = string.gsub(clink.prompt.value, "{lamb}", "["..conda_env.."] {lamb}")
    end
end

clink.prompt.register_filter(conda_prompt_filter, 20)

Looks like this:

c:\data\external\cmder (prompt-in-clink)
λ activate borked35
Deactivating environment "C:\portabel\miniconda"...
Activating environment "C:\portabel\miniconda\envs\borked35"...

c:\data\external\cmder (prompt-in-clink)
[borked35] λ

[jankatins]

Just for the record: I'm running my cmder with this PR since a few days and it works great: no more garbled output in conda build :-)

[nullpunkt]

I would like this a +1 hence my installation actually keeps displaying {git}{lamda} and the other placeholders even though i already installed 0.4.7 of clink.

[jankatins]

@nullpunkt I don't think this is the same "problem" :-( This only "fixes" the problem that a subshell gets a proper commandline, not the one which is started in cmder.

-> please discuss in a different issue

[jankatins]

rebased on top of current development

[MartiUK]

👍 LGTM

[Stanzilla]

Merged. Thank you for that! :)