8825942e86
Allow making `RUSTC_BOOTSTRAP` conditional on the crate name Motivation: This came up in the [Zulip stream](https://rust-lang.zulipchat.com/#narrow/stream/233931-t-compiler.2Fmajor-changes/topic/Require.20users.20to.20confirm.20they.20know.20RUSTC_.E2.80.A6.20compiler-team.23350/near/208403962) for https://github.com/rust-lang/compiler-team/issues/350. See also https://github.com/rust-lang/cargo/pull/6608#issuecomment-458546258; this implements https://github.com/rust-lang/cargo/issues/6627. The goal is for this to eventually allow prohibiting setting `RUSTC_BOOTSTRAP` in build.rs (https://github.com/rust-lang/cargo/issues/7088). ## User-facing changes - `RUSTC_BOOTSTRAP=1` still works; there is no current plan to remove this. - Things like `RUSTC_BOOTSTRAP=0` no longer activate nightly features. In practice this shouldn't be a big deal, since `RUSTC_BOOTSTRAP` is the opposite of stable and everyone uses `RUSTC_BOOTSTRAP=1` anyway. - `RUSTC_BOOTSTRAP=x` will enable nightly features only for crate `x`. - `RUSTC_BOOTSTRAP=x,y` will enable nightly features only for crates `x` and `y`. ## Implementation changes The main change is that `UnstableOptions::from_environment` now requires an (optional) crate name. If the crate name is unknown (`None`), then the new feature is not available and you still have to use `RUSTC_BOOTSTRAP=1`. In practice this means the feature is only available for `--crate-name`, not for `#![crate_name]`; I'm interested in supporting the second but I'm not sure how. Other major changes: - Added `Session::is_nightly_build()`, which uses the `crate_name` of the session - Added `nightly_options::match_is_nightly_build`, a convenience method for looking up `--crate-name` from CLI arguments. `Session::is_nightly_build()`should be preferred where possible, since it will take into account `#![crate_name]` (I think). - Added `unstable_features` to `rustdoc::RenderOptions` I'm not sure whether this counts as T-compiler or T-lang; _technically_ RUSTC_BOOTSTRAP is an implementation detail, but it's been used so much it seems like this counts as a language change too. r? `@joshtriplett` cc `@Mark-Simulacrum` `@hsivonen`
The driver crate is effectively the "main" function for the rust
compiler. It orchestrates the compilation process and "knits together"
the code from the other crates within rustc. This crate itself does
not contain any of the "main logic" of the compiler (though it does
have some code related to pretty printing or other minor compiler
options).
For more information about how the driver works, see the rustc dev guide.