Format string behaviour inconsistent (escape characters)

[Kangie]

Describe the bug

I have recently been working on porting fvwm3 from autotools to Meson, however there is a requirement that the autotools build system stay in place for now.

As part of validating my output, I have diffed various configured files and noticed that configure_file replaces instances of \@ with @ in the output.

After a pointer from Eli (thanks!), the reason for this has been revealed:

Format strings in various parts of Meson use @ as the delimiter. The behavior is inconsistent, configure_file() recognizes \ as an escape character, but format strings in string.format() and custom_target command arguments do not.

• From the Muon docs

This is unintuitive, apparently un(der?)documented, and probably easily avoided.

To Reproduce

Tba when I'm at a computer

Expected behavior

Configure file should We should not be escaping individual characters. If anything, whole substitutions on a line could be escaped, but that requires matching on two @s

[Kangie]

Closing as as dupe.