Support $^ escape sequence for newlines.

[ildus]

Replace '$^' with the actual newlines.

Straight to use case:

rule one
    command = cmd /C file.bat
    rspfile = file.bat
    rspfile_content = echo "1" > $out $^echo "2"

build one.txt : one

This is required when the build system generates scripts, but trying to make one liners from every script is too bug prone. For example 'set ' in Windows cmd.exe requires delayed expansion when the variable (which is just set) was used in the same line. But writer of the building script could not know such details.

Another case is platforms where scripts can not be converted to oneliners in any way (I have a such use case for OpenVMS dcl).

'$^' currently gives an error (bad escape), so this change should not break the current usage of ninja in any way.

[AJIOB]

Why it named not a $n, similar to the $:?

[ildus]

Not so visible when surrounded with an another text, and ^ usually means the beginning like in regular expressions.

[jhasse]

Thanks! For this not to cause a lot of confusion in the future I think we should print a warning (or error?) if some uses it without ninja_minimum_version = 1.13 in the first line. Because then the error message for someone with older ninja will be more helpful. Not sure if that is easily doable with the current parser.

[digit-google]

Following the regression described in #2616, should these newlines be \r\n on Windows instead?

[ildus]

@digit-google That's a good question. I think it depends on the use case. For the scripts like in example cmd works just fine with both line endings, but I remember bash from cygwin could fail on windows endings. Although I could not reproduce it today, on my cygwin today it worked ok with '\r\n', maybe they fixed that.

[ildus]

Changed behavior on Windows for consistency, will add '\r\n' instead just '\n'.

[digit-google]

Thank you very much, apart from the latest two nits, this looks good to me. @jhasse , wdyt?

[ildus]

@digit-google Thanks for review!