Function cargo::core::compiler::build_context::target_info::extra_args

fn extra_args(
    config: &Config,
    requested_kinds: &[CompileKind],
    host_triple: &str,
    target_cfg: Option<&[Cfg]>,
    kind: CompileKind,
    flags: Flags
) -> CargoResult<Vec<String>>

Acquire extra flags to pass to the compiler from various locations.

The locations are:

• the CARGO_ENCODED_RUSTFLAGS environment variable
• the RUSTFLAGS environment variable

then if none of those were found

• target.*.rustflags from the config (.cargo/config)
• target.cfg(..).rustflags from the config
• host.*.rustflags from the config if compiling a host artifact or without --target (requires -Zhost-config)

then if none of those were found

• build.rustflags from the config

The behavior differs slightly when cross-compiling (or, specifically, when --target is provided) for artifacts that are always built for the host (plugins, build scripts, …). For those artifacts, only host.*.rustflags is respected, and no other configuration sources, regardless of the value of target-applies-to-host. This is counterintuitive, but necessary to retain backwards compatibility with older versions of Cargo.