Escaping a string for substitute-command-keys

[Clément Pit-Claudel]

Hi emacs-devel,

I think I've seen a thread about this in the past, but I can't find it. What's 
the expected way to escape a string before its fed to substitute-command-keys, 
so that substitute-command-keys reconstructs the original string?

The reason for this question is that since 2015 Emacs has been calling 
substitute-command-keys on help-echo messages, which breaks flycheck and 
flymake (a simple way to reproduce the issue is to enable flymake in a Python 
buffer containing just xxx and to hover over the xxx with the mouse: Emacs 
shows a tooltip containing "Undefined name ’xxx’").

So, what's the right way to escape a string to be fed to 
substitute-command-keys?  Alternatively, is there be a way to disable the 
transformation for a particular help-echo string, rather than forcing an 
unnecessary rountrip?  Maybe we could add a text property, so that if a string 
is tagged with a 'text-quoting-style property that style is used instead of the 
default one?

Thanks!
Clément.