[rustc] Tolerate spaces and blanks inside @response files

[fangism]

We have build tooling that generates rust command-line arguments inside response files, passed like rustc @args.rsp. In some cases, the tool emits response files with empty lines, or lines that contain only a single space.

Case (second line is a single space):

foo.rs

diagnostic:

error: multiple input filenames provided (first two filenames are `foo.rs` and ` `)

Case (second line is blank):

foo.rs

diagnostic:

error: multiple input filenames provided (first two filenames are `foo.rs` and ``)

Could the rustc compiler be updated to ignore space-only and blank lines in response files?

[Noratrieb]

Sounds reasonable to me, feel free to send in a PR. The PR would need an FCP from the compiler team because this is stable behavior. A compiler major change proposal is probably not needed because this is so small.

[fangism]

Case: leading and trailing spaces

 foo.rs
bar.rs 

(one space after bar.rs)

diagnostic:

error: multiple input filenames provided (first two filenames are ` foo.rs` and `bar.rs `)

[jsgf]

Rustc args files are intended to contain verbatim command line args, one per line. If you're generating spurious spaces or blank lines, you're not generating valid args files. So stripping out blank lines or "extra" whitespace is explicitly not a valid operation to perform on args files.

Can't you just update the generator to generate valid args files in the first place? What's the generator in this case?