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` |
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