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`. Also use workspace dependencies for such
crates so that only one version can exist within the sysroot (since
otherwise it is meaningless to try to match the rustc version).

Author: Diggsey

Cargo.toml

@@ -60,6 +60,17 @@ exclude = [
   "obj",
 ]
 
+[workspace.dependencies]
+# These dependencies are either explicitly part of rustc's public interface, or
+# are "singleton" crates that we want to only appear once in the dependency graph.
+either = "1.5"
+smallvec = { version = "1.8.1", features = ["const_generics", "union", "may_dangle"] }
+indexmap = "2.4"
+tracing = "0.1.28"
+tracing-subscriber = { version = "0.3.3", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"] }
+pulldown-cmark = { version = "0.11", features = ["html"], default-features = false }
+thin-vec = "0.2.12"
+
 [profile.release.package.rustc_thread_pool]
 # The rustc fork of Rayon has deadlock detection code which intermittently
 # causes overflows in the CI (see https://github.com/rust-lang/rust/issues/90227)

compiler/rustc_abi/Cargo.toml

@@ -14,7 +14,7 @@ rustc_index = { path = "../rustc_index", default-features = false }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }
 rustc_span = { path = "../rustc_span", optional = true }
-tracing = "0.1"
+tracing = { workspace = true }
 # tidy-alphabetical-end
 
 [features]

compiler/rustc_arena/Cargo.toml

@@ -5,5 +5,5 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
-smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
+smallvec = { workspace = true }
 # tidy-alphabetical-end

compiler/rustc_ast/Cargo.toml

@@ -14,7 +14,7 @@ rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
-smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
-thin-vec = "0.2.12"
-tracing = "0.1"
+smallvec = { workspace = true }
+thin-vec = { workspace = true }
+tracing = { workspace = true }
 # tidy-alphabetical-end

compiler/rustc_ast_lowering/Cargo.toml

@@ -24,7 +24,7 @@ rustc_middle = { path = "../rustc_middle" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
-smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
-thin-vec = "0.2.12"
-tracing = "0.1"
+smallvec = { workspace = true }
+thin-vec = { workspace = true }
+tracing = { workspace = true }
 # tidy-alphabetical-end

compiler/rustc_ast_passes/Cargo.toml

@@ -19,5 +19,5 @@ rustc_parse = { path = "../rustc_parse" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
-thin-vec = "0.2.12"
+thin-vec = { workspace = true }
 # tidy-alphabetical-end

compiler/rustc_ast_pretty/Cargo.toml

@@ -13,5 +13,5 @@ rustc_span = { path = "../rustc_span" }
 
 [dev-dependencies]
 # tidy-alphabetical-start
-thin-vec = "0.2.12"
+thin-vec = { workspace = true }
 # tidy-alphabetical-end

compiler/rustc_attr_data_structures/Cargo.toml

@@ -12,5 +12,5 @@ rustc_data_structures = {path = "../rustc_data_structures"}
 rustc_macros = {path = "../rustc_macros"}
 rustc_serialize = {path = "../rustc_serialize"}
 rustc_span = {path = "../rustc_span"}
-thin-vec = "0.2.12"
+thin-vec = { workspace = true }
 # tidy-alphabetical-end

compiler/rustc_attr_parsing/Cargo.toml

@@ -17,5 +17,5 @@ rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
-thin-vec = "0.2.12"
+thin-vec = { workspace = true }
 # tidy-alphabetical-end

compiler/rustc_borrowck/Cargo.toml

@@ -5,7 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
-either = "1.5.0"
+either = { workspace = true }
 itertools = "0.12"
 polonius-engine = "0.13.0"
 rustc_abi = { path = "../rustc_abi" }
@@ -24,6 +24,6 @@ rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_traits = { path = "../rustc_traits" }
-smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
-tracing = "0.1"
+smallvec = { workspace = true }
+tracing = { workspace = true }
 # tidy-alphabetical-end