Use -Wunused_crate_dependencies for compiler crates.

It's very useful. There are some false positives involving integration
tests in `rustc_pattern_analysis` and `rustc_serialize`. There is also a
false positive involving `rustc_driver_impl`'s
`rustc_randomized_layouts` feature. And I removed a `rustc_span` mention
in a doc comment in `rustc_log` because it wasn't integral to the
comment but caused a dev-dependency.

Cargo.lock

@@ -3206,7 +3206,6 @@ dependencies = [
  "rustc_data_structures",
  "rustc_macros",
  "rustc_serialize",
- "rustc_span",
 ]
 
 [[package]]
@@ -3225,7 +3224,6 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_middle",
- "rustc_parse",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -3260,7 +3258,6 @@ version = "0.0.0"
 dependencies = [
  "itertools",
  "rustc_ast",
- "rustc_data_structures",
  "rustc_lexer",
  "rustc_span",
  "thin-vec",
@@ -3288,15 +3285,12 @@ dependencies = [
  "rustc_ast",
  "rustc_ast_pretty",
  "rustc_attr_data_structures",
- "rustc_data_structures",
  "rustc_errors",
  "rustc_feature",
  "rustc_fluent_macro",
  "rustc_hir",
  "rustc_lexer",
  "rustc_macros",
- "rustc_middle",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "thin-vec",
@@ -3423,7 +3417,6 @@ dependencies = [
  "rustc_abi",
  "rustc_arena",
  "rustc_ast",
- "rustc_ast_pretty",
  "rustc_attr_parsing",
  "rustc_data_structures",
  "rustc_errors",
@@ -3431,7 +3424,6 @@ dependencies = [
  "rustc_fs_util",
  "rustc_hashes",
  "rustc_hir",
- "rustc_hir_pretty",
  "rustc_incremental",
  "rustc_index",
  "rustc_macros",
@@ -3879,7 +3871,6 @@ dependencies = [
  "rustc_query_impl",
  "rustc_query_system",
  "rustc_resolve",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_symbol_mangling",
@@ -3954,7 +3945,6 @@ dependencies = [
 name = "rustc_log"
 version = "0.0.0"
 dependencies = [
- "rustc_span",
  "tracing",
  "tracing-core",
  "tracing-subscriber",
@@ -4043,13 +4033,11 @@ dependencies = [
 name = "rustc_mir_build"
 version = "0.0.0"
 dependencies = [
- "either",
  "itertools",
  "rustc_abi",
  "rustc_apfloat",
  "rustc_arena",
  "rustc_ast",
- "rustc_attr_parsing",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_fluent_macro",
@@ -4256,7 +4244,6 @@ version = "0.0.0"
 dependencies = [
  "measureme 12.0.1",
  "rustc_data_structures",
- "rustc_errors",
  "rustc_hashes",
  "rustc_hir",
  "rustc_index",
@@ -4265,7 +4252,6 @@ dependencies = [
  "rustc_serialize",
  "rustc_session",
  "rustc_span",
- "thin-vec",
  "tracing",
 ]
 
@@ -4290,7 +4276,6 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "smallvec",
- "thin-vec",
  "tracing",
 ]
 
@@ -4328,7 +4313,6 @@ version = "0.0.0"
 dependencies = [
  "bitflags",
  "rustc_abi",
- "rustc_ast",
  "rustc_data_structures",
  "rustc_hir",
  "rustc_middle",
@@ -4383,7 +4367,6 @@ name = "rustc_smir"
 version = "0.0.0"
 dependencies = [
  "rustc_abi",
- "rustc_ast",
  "rustc_data_structures",
  "rustc_hir",
  "rustc_hir_pretty",
@@ -4425,7 +4408,6 @@ dependencies = [
  "punycode",
  "rustc-demangle",
  "rustc_abi",
- "rustc_ast",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_hashes",
@@ -4520,7 +4502,6 @@ version = "0.0.0"
 dependencies = [
  "itertools",
  "rustc_abi",
- "rustc_attr_parsing",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_fluent_macro",

compiler/rustc_ast_ir/Cargo.toml

@@ -8,7 +8,6 @@ edition = "2024"
 rustc_data_structures = { path = "../rustc_data_structures", optional = true }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }
-rustc_span = { path = "../rustc_span", optional = true }
 # tidy-alphabetical-end
 
 [features]
@@ -17,5 +16,4 @@ nightly = [
     "dep:rustc_serialize",
     "dep:rustc_data_structures",
     "dep:rustc_macros",
-    "dep:rustc_span",
 ]

compiler/rustc_ast_lowering/Cargo.toml

@@ -20,7 +20,6 @@ rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_parse = { path = "../rustc_parse" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_ast_pretty/Cargo.toml

@@ -7,8 +7,11 @@ edition = "2024"
 # tidy-alphabetical-start
 itertools = "0.12"
 rustc_ast = { path = "../rustc_ast" }
-rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_span = { path = "../rustc_span" }
+# tidy-alphabetical-end
+
+[dev-dependencies]
+# tidy-alphabetical-start
 thin-vec = "0.2.12"
 # tidy-alphabetical-end

compiler/rustc_attr_parsing/Cargo.toml

@@ -9,15 +9,12 @@ rustc_abi = { path = "../rustc_abi" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_attr_data_structures = { path = "../rustc_attr_data_structures" }
-rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_feature = { path = "../rustc_feature" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
-rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 thin-vec = "0.2.12"

compiler/rustc_codegen_ssa/Cargo.toml

@@ -19,7 +19,6 @@ regex = "1.4"
 rustc_abi = { path = "../rustc_abi" }
 rustc_arena = { path = "../rustc_arena" }
 rustc_ast = { path = "../rustc_ast" }
-rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_attr_parsing = { path = "../rustc_attr_parsing" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
@@ -27,7 +26,6 @@ rustc_fluent_macro = { path = "../rustc_fluent_macro" }
 rustc_fs_util = { path = "../rustc_fs_util" }
 rustc_hashes = { path = "../rustc_hashes" }
 rustc_hir = { path = "../rustc_hir" }
-rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_incremental = { path = "../rustc_incremental" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }

compiler/rustc_driver_impl/Cargo.toml

@@ -54,7 +54,7 @@ time = { version = "0.3.36", default-features = false, features = ["alloc", "for
 tracing = { version = "0.1.35" }
 # tidy-alphabetical-end
 
-[target.'cfg(unix)'.dependencies]
+[target.'cfg(all(unix, any(target_env = "gnu", target_os = "macos")))'.dependencies]
 # tidy-alphabetical-start
 libc = "0.2"
 # tidy-alphabetical-end

compiler/rustc_driver_impl/src/lib.rs

@@ -44,6 +44,10 @@ use rustc_errors::emitter::stderr_destination;
 use rustc_errors::registry::Registry;
 use rustc_errors::{ColorConfig, DiagCtxt, ErrCode, FatalError, PResult, markdown};
 use rustc_feature::find_gated_cfg;
+// This avoids a false positive with `-Wunused_crate_dependencies`.
+// `rust_index` isn't used in this crate's code, but it must be named in the
+// `Cargo.toml` for the `rustc_randomized_layouts` feature.
+use rustc_index as _;
 use rustc_interface::util::{self, get_codegen_backend};
 use rustc_interface::{Linker, create_and_enter_global_ctxt, interface, passes};
 use rustc_lint::unerased_lint_store;
@@ -89,6 +93,10 @@ pub mod pretty;
 #[macro_use]
 mod print;
 mod session_diagnostics;
+
+// Keep the OS parts of this `cfg` in sync with the `cfg` on the `libc`
+// dependency in `compiler/rustc_driver/Cargo.toml`, to keep
+// `-Wunused-crated-dependencies` satisfied.
 #[cfg(all(not(miri), unix, any(target_env = "gnu", target_os = "macos")))]
 mod signal_handler;
 

compiler/rustc_interface/Cargo.toml

@@ -7,7 +7,6 @@ edition = "2024"
 # tidy-alphabetical-start
 rustc-rayon = { version = "0.5.0" }
 rustc-rayon-core = { version = "0.5.0" }
-rustc_abi = { path = "../rustc_abi" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_lowering = { path = "../rustc_ast_lowering" }
 rustc_ast_passes = { path = "../rustc_ast_passes" }
@@ -41,7 +40,6 @@ rustc_privacy = { path = "../rustc_privacy" }
 rustc_query_impl = { path = "../rustc_query_impl" }
 rustc_query_system = { path = "../rustc_query_system" }
 rustc_resolve = { path = "../rustc_resolve" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_symbol_mangling = { path = "../rustc_symbol_mangling" }
@@ -52,6 +50,11 @@ rustc_ty_utils = { path = "../rustc_ty_utils" }
 tracing = "0.1"
 # tidy-alphabetical-end
 
+[dev-dependencies]
+# tidy-alphabetical-start
+rustc_abi = { path = "../rustc_abi" }
+# tidy-alphabetical-end
+
 [features]
 # tidy-alphabetical-start
 llvm = ['dep:rustc_codegen_llvm']

compiler/rustc_log/Cargo.toml

@@ -11,11 +11,6 @@ tracing-subscriber = { version = "0.3.3", default-features = false, features = [
 tracing-tree = "0.3.1"
 # tidy-alphabetical-end
 
-[dev-dependencies]
-# tidy-alphabetical-start
-rustc_span = { path = "../rustc_span" }
-# tidy-alphabetical-end
-
 [features]
 # tidy-alphabetical-start
 max_level_info = ['tracing/max_level_info']

compiler/rustc_log/src/lib.rs

@@ -9,17 +9,12 @@
 //! [dependencies]
 //! rustc_ast = { path = "../rust/compiler/rustc_ast" }
 //! rustc_log = { path = "../rust/compiler/rustc_log" }
-//! rustc_span = { path = "../rust/compiler/rustc_span" }
 //! ```
 //!
 //! ```
 //! fn main() {
 //!     rustc_log::init_logger(rustc_log::LoggerConfig::from_env("LOG")).unwrap();
-//!
+//!     /* ... */
-//!     let edition = rustc_span::edition::Edition::Edition2021;
-//!     rustc_span::create_session_globals_then(edition, None, || {
-//!         /* ... */
-//!     });
 //! }
 //! ```
 //!

compiler/rustc_metadata/Cargo.toml

@@ -6,7 +6,6 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
-libc = "0.2"
 libloading = "0.8.0"
 odht = { version = "0.3.1", features = ["nightly"] }
 rustc_abi = { path = "../rustc_abi" }
@@ -30,3 +29,8 @@ rustc_target = { path = "../rustc_target" }
 tempfile = "3.2"
 tracing = "0.1"
 # tidy-alphabetical-end
+
+[target.'cfg(target_os = "aix")'.dependencies]
+# tidy-alphabetical-start
+libc = "0.2"
+# tidy-alphabetical-end

compiler/rustc_mir_build/Cargo.toml

@@ -5,14 +5,12 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
-either = "1.5.0"
 itertools = "0.12"
 
 rustc_abi = { path = "../rustc_abi" }
 rustc_apfloat = "0.2.0"
 rustc_arena = { path = "../rustc_arena" }
 rustc_ast = { path = "../rustc_ast" }
-rustc_attr_parsing = { path = "../rustc_attr_parsing" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }

compiler/rustc_parse_format/Cargo.toml

@@ -5,6 +5,8 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
-rustc_index = { path = "../rustc_index", default-features = false }
 rustc_lexer = { path = "../rustc_lexer" }
 # tidy-alphabetical-end
+
+[target.'cfg(target_pointer_width = "64")'.dependencies]
+rustc_index = { path = "../rustc_index", default-features = false }

compiler/rustc_pattern_analysis/src/lib.rs

@@ -5,6 +5,7 @@
 // tidy-alphabetical-start
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
+#![allow(unused_crate_dependencies)]
 #![cfg_attr(feature = "rustc", feature(let_chains))]
 // tidy-alphabetical-end
 

compiler/rustc_pattern_analysis/tests/complexity.rs

@@ -1,5 +1,7 @@
 //! Test the pattern complexity limit.
 
+#![allow(unused_crate_dependencies)]
+
 use common::*;
 use rustc_pattern_analysis::MatchArm;
 use rustc_pattern_analysis::pat::DeconstructedPat;

compiler/rustc_pattern_analysis/tests/exhaustiveness.rs

@@ -1,5 +1,7 @@
 //! Test exhaustiveness checking.
 
+#![allow(unused_crate_dependencies)]
+
 use common::*;
 use rustc_pattern_analysis::MatchArm;
 use rustc_pattern_analysis::pat::{DeconstructedPat, WitnessPat};

compiler/rustc_pattern_analysis/tests/intersection.rs

@@ -1,5 +1,7 @@
 //! Test the computation of arm intersections.
 
+#![allow(unused_crate_dependencies)]
+
 use common::*;
 use rustc_pattern_analysis::MatchArm;
 use rustc_pattern_analysis::pat::DeconstructedPat;

compiler/rustc_query_impl/Cargo.toml

@@ -7,7 +7,6 @@ edition = "2024"
 # tidy-alphabetical-start
 measureme = "12.0.1"
 rustc_data_structures = { path = "../rustc_data_structures" }
-rustc_errors = { path = "../rustc_errors" }
 rustc_hashes = { path = "../rustc_hashes" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
@@ -16,6 +15,5 @@ rustc_query_system = { path = "../rustc_query_system" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
-thin-vec = "0.2.12"
 tracing = "0.1"
 # tidy-alphabetical-end

compiler/rustc_query_system/Cargo.toml

@@ -22,6 +22,5 @@ rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
-thin-vec = "0.2.12"
 tracing = "0.1"
 # tidy-alphabetical-end

compiler/rustc_sanitizers/Cargo.toml

@@ -8,7 +8,6 @@ bitflags = "2.5.0"
 tracing = "0.1"
 twox-hash = "1.6.3"
 rustc_abi = { path = "../rustc_abi" }
-rustc_ast = { path = "../rustc_ast" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_middle = { path = "../rustc_middle" }

compiler/rustc_serialize/src/lib.rs

@@ -3,6 +3,8 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![allow(rustc::internal)]
+// FIXME
+#![allow(unused_crate_dependencies)]
 #![cfg_attr(test, feature(test))]
 #![doc(
     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",

compiler/rustc_serialize/tests/leb128.rs

@@ -1,3 +1,6 @@
+// FIXME
+#![allow(unused_crate_dependencies)]
+
 use rustc_serialize::Decoder;
 use rustc_serialize::leb128::*;
 use rustc_serialize::opaque::{MAGIC_END_BYTES, MemDecoder};

compiler/rustc_serialize/tests/opaque.rs

@@ -1,4 +1,6 @@
 #![allow(rustc::internal)]
+// FIXME
+#![allow(unused_crate_dependencies)]
 
 use std::fmt::Debug;
 use std::fs;

compiler/rustc_smir/Cargo.toml

@@ -6,7 +6,6 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 rustc_abi = { path = "../rustc_abi" }
-rustc_ast = { path = "../rustc_ast" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }

compiler/rustc_symbol_mangling/Cargo.toml

@@ -9,7 +9,6 @@ punycode = "0.4.0"
 rustc-demangle = "0.1.21"
 
 rustc_abi = { path = "../rustc_abi" }
-rustc_ast = { path = "../rustc_ast" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_hashes = { path = "../rustc_hashes" }

compiler/rustc_ty_utils/Cargo.toml

@@ -7,7 +7,6 @@ edition = "2024"
 # tidy-alphabetical-start
 itertools = "0.12"
 rustc_abi = { path = "../rustc_abi" }
-rustc_attr_parsing = { path = "../rustc_attr_parsing" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }

src/bootstrap/src/core/builder/cargo.rs

@@ -1073,6 +1073,7 @@ impl Builder<'_> {
             lint_flags.push("-Wkeyword_idents_2024");
             lint_flags.push("-Wunreachable_pub");
             lint_flags.push("-Wunsafe_op_in_unsafe_fn");
+            lint_flags.push("-Wunused_crate_dependencies");
         }
 
         // This does not use RUSTFLAGS for two reasons.