Restrict sysroot crate imports to those defined in this repo.

It's common to import dependencies from the sysroot via `extern crate`
rather than use an explicit cargo dependency, when it's necessary to use
the same dependency version as used by rustc itself. However, this is
dangerous for crates.io crates, since rustc may not pull in the
dependency on some targets, or may pull in multiple versions. In both
cases, the `extern crate` fails to resolve.

To address this, re-export all such dependencies from the appropriate
`rustc_*` crates, and use this alias from crates which would otherwise
need to use `extern crate`.

Author: Diggsey

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -26,13 +26,12 @@ extern crate rustc_fs_util;
 extern crate rustc_hir;
 extern crate rustc_incremental;
 extern crate rustc_index;
+extern crate rustc_log;
 extern crate rustc_metadata;
 extern crate rustc_session;
 extern crate rustc_span;
 extern crate rustc_symbol_mangling;
 extern crate rustc_target;
-#[macro_use]
-extern crate tracing;
 
 // This prevents duplicating functions and statics that are already part of the host rustc process.
 #[allow(unused_extern_crates)]
@@ -46,6 +45,7 @@ use cranelift_codegen::isa::TargetIsa;
 use cranelift_codegen::settings::{self, Configurable};
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_codegen_ssa::{CodegenResults, TargetConfig};
+use rustc_log::tracing::info;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_session::Session;
 use rustc_session::config::OutputFilenames;

compiler/rustc_codegen_gcc/src/back/lto.rs

@@ -32,6 +32,7 @@ use rustc_codegen_ssa::{ModuleCodegen, ModuleKind, looks_like_rust_object_file};
 use rustc_data_structures::memmap::Mmap;
 use rustc_errors::{DiagCtxtHandle, FatalError};
 use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_log::tracing::info;
 use rustc_middle::bug;
 use rustc_middle::dep_graph::WorkProduct;
 use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel};

compiler/rustc_codegen_gcc/src/back/write.rs

@@ -6,6 +6,7 @@ use rustc_codegen_ssa::back::write::{BitcodeSection, CodegenContext, EmitObj, Mo
 use rustc_codegen_ssa::{CompiledModule, ModuleCodegen};
 use rustc_errors::DiagCtxtHandle;
 use rustc_fs_util::link_or_copy;
+use rustc_log::tracing::debug;
 use rustc_session::config::OutputType;
 use rustc_span::fatal_error::FatalError;
 use rustc_target::spec::SplitDebuginfo;

compiler/rustc_codegen_gcc/src/consts.rs

@@ -6,6 +6,7 @@ use rustc_codegen_ssa::traits::{
     BaseTypeCodegenMethods, ConstCodegenMethods, StaticCodegenMethods,
 };
 use rustc_hir::def::DefKind;
+use rustc_log::tracing::trace;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::interpret::{
     self, ConstAllocation, ErrorHandled, Scalar as InterpScalar, read_target_uint,

compiler/rustc_codegen_gcc/src/gcc_util.rs

@@ -1,8 +1,8 @@
 #[cfg(feature = "master")]
 use gccjit::Context;
 use rustc_codegen_ssa::target_features;
+use rustc_data_structures::smallvec::{SmallVec, smallvec};
 use rustc_session::Session;
-use smallvec::{SmallVec, smallvec};
 
 fn gcc_features_by_flags(sess: &Session, features: &mut Vec<String>) {
     target_features::retpoline_features_by_flags(sess, features);

compiler/rustc_codegen_gcc/src/lib.rs

@@ -26,12 +26,6 @@
 #![deny(clippy::pattern_type_mismatch)]
 #![allow(clippy::needless_lifetimes, clippy::uninlined_format_args)]
 
-// These crates are pulled from the sysroot because they are part of
-// rustc's public API, so we need to ensure version compatibility.
-extern crate smallvec;
-#[macro_use]
-extern crate tracing;
-
 // The rustc crates we need
 extern crate rustc_abi;
 extern crate rustc_apfloat;
@@ -46,6 +40,7 @@ extern crate rustc_hir;
 extern crate rustc_index;
 #[cfg(feature = "master")]
 extern crate rustc_interface;
+extern crate rustc_log;
 extern crate rustc_macros;
 extern crate rustc_middle;
 extern crate rustc_session;

compiler/rustc_data_structures/src/lib.rs

@@ -43,6 +43,7 @@ use std::fmt;
 pub use atomic_ref::AtomicRef;
 pub use ena::{snapshot_vec, undo_log, unify};
 pub use rustc_index::static_assert_size;
+pub use {either, indexmap, smallvec, thin_vec};
 
 pub mod aligned;
 pub mod base_n;

compiler/rustc_log/src/lib.rs

@@ -44,6 +44,8 @@ use tracing_subscriber::fmt::FmtContext;
 use tracing_subscriber::fmt::format::{self, FormatEvent, FormatFields};
 use tracing_subscriber::layer::SubscriberExt;
 use tracing_subscriber::{Layer, Registry};
+// Re-export tracing
+pub use {tracing, tracing_subscriber};
 
 /// The values of all the environment variables that matter for configuring a logger.
 /// Errors are explicitly preserved so that we can share error handling.

compiler/rustc_resolve/src/rustdoc.rs

@@ -2,6 +2,8 @@ use std::mem;
 use std::ops::Range;
 
 use itertools::Itertools;
+/// Re-export the markdown parser used by rustdoc.
+pub use pulldown_cmark;
 use pulldown_cmark::{
     BrokenLink, BrokenLinkCallback, CowStr, Event, LinkType, Options, Parser, Tag,
 };

src/librustdoc/clean/auto_trait.rs

@@ -1,12 +1,12 @@
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet, IndexEntry};
+use rustc_data_structures::thin_vec::ThinVec;
 use rustc_hir as hir;
 use rustc_infer::infer::region_constraints::{Constraint, RegionConstraintData};
 use rustc_middle::bug;
 use rustc_middle::ty::{self, Region, Ty, fold_regions};
 use rustc_span::def_id::DefId;
 use rustc_span::symbol::{Symbol, kw};
 use rustc_trait_selection::traits::auto_trait::{self, RegionTarget};
-use thin_vec::ThinVec;
 use tracing::{debug, instrument};
 
 use crate::clean::{