problems with `-C link-args` that have arguments with spaces

[japaric]

If you use something like this:

[ build]
rustflags = [
  "-C",
  "link-args=-Tlayout.ld -nostartfiles"
]

in your .cargo/config, the executable with fail to link because three arguments will be passed to rustc: -C, -link-args=-Tlayout.ld and -nostartfiles. This a problem with Xargo because it uses RUSTFLAGS to pass these (and --sysroot) as a string to Cargo and then Cargo parses RUSTFLAGS by splitting it at whitespaces.

There is no real solution for this other than to use -C link-arg (rust-lang/rust#36574) multiple times instead of -C link-args.

Once that PR lands in rust-lang/rust, let's have Cargo print a warning about this problem and also suggest using -C link-arg instead of -C link-args.

[sanmai-NL]

@japaric: Small reminder in response to your last paragraph: the PR has landed.

[flukejones]

A small note for anyone who stumbles across this via google.

If you need multiple args, the first arg must not have -s, while the rest do. For example:

-- -C link-arg='EXTRA_EXPORTED_RUNTIME_METHODS=["ccall","cwrap"]' -C link-arg='-s' -C link-arg='ASSERTIONS=1' -C link-arg='-s' -C link-arg='ALLOW_MEMORY_GROWTH=1'

[timboudreau]

As one of those people who stumbled across @flukejones comment, which was very helpful: I'm not sure what all of the -s's were supposed to do on Linux, but on Mac OS's ld they will not be accepted - but simply a sequence of -C link-arg=blah -C link-arg=blee. It gets somewhat clunky - e.g. -C link-arg=-macos_version_min -C link-arg=13.0 but works.