rustdoc: Tracking issue for command-line option `--doctest-build-arg`

[GuillaumeGomez]

A command line option to pass program arguments to the underlying compiler building doctests.

Original issue motivating this feature: #67533.

Note

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Steps

• Implementation PR
• Stabilization PR

Unresolved Questions

• Should argument parsing be closer to what already exists for RUSTFLAGS (whitespace splitting and nothing else) or should it be closer to how shell parses input (take into account escaped characters and quote characters)? Or should we offer two options, one that works like RUSTFLAGS for human users and one that works like CARGO_ENCODED_RUSTLFAGS for tool usage? Update: #137096 (comment) changed the requirements and #139863 the design!
• From #139863: Even though we don't process the argument passed to --doctest-build-arg, we end up passing it via an argument file (rustc @argfile) which delimits arguments by line break (LF or CRLF, via) meaning ultimately the arguments still get split which is unfortunate. Is there are good way to resolve this (obvious but intrusive solution: smh signal to rustc not to split inside the argsfile)?

Implementation History

• Add --doctest-compilation-args option to add compilation flags to doctest compilation #128780
• rustdoc: Replace unstable flag --doctest-compilation-args with a simpler one: --doctest-build-arg #139863

[weihanglo]

Considering all linked issues (#67533, #66623, rust-lang/cargo#13697, rust-lang/miri#3869) are actually Cargo-related, I wonder how to integrate this flag to help Cargo users. Cargo doesn't parse RUSTFLAGS so it may not know if --cap-lints=warn is there and pass to --doctest-compilation-args accordingly.

Also, the feature seems to open a door way bigger than what #67533 was looking for. It accepts arbitrary rustc flags. Mind sharing why propagating -cap-lints isn't under consideration? Maybe there are other use cases for arbitrary flags I am missing. We all know that once we provide more stuff to users, we might have no chance to take it back 😓.

That said, I don't think this feature on its own is bad. Thank you for working on a fix!!