Use warn(unused_crate_dependencies) in compiler crates.

The commit also removes fifteen unnecessary dependencies from
`Cargo.toml` files that this finds. And tweaks some conditional
dependencies.

There are three crates with false positives, relating to tests and
doc comments. For these three crates `allow(unused_crate_dependencies)`
is used along with an explanatory comment.

Author: nnethercote

Cargo.lock

@@ -3216,7 +3216,6 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_middle",
- "rustc_parse",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -3251,7 +3250,6 @@ version = "0.0.0"
 dependencies = [
  "itertools",
  "rustc_ast",
- "rustc_data_structures",
  "rustc_lexer",
  "rustc_span",
  "thin-vec",
@@ -3279,14 +3277,12 @@ 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_serialize",
  "rustc_session",
  "rustc_span",
  "thin-vec",
@@ -3413,15 +3409,13 @@ dependencies = [
  "rustc_abi",
  "rustc_arena",
  "rustc_ast",
- "rustc_ast_pretty",
  "rustc_attr_parsing",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_fluent_macro",
  "rustc_fs_util",
  "rustc_hashes",
  "rustc_hir",
- "rustc_hir_pretty",
  "rustc_incremental",
  "rustc_index",
  "rustc_macros",
@@ -3872,7 +3866,6 @@ dependencies = [
  "rustc_query_impl",
  "rustc_query_system",
  "rustc_resolve",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_symbol_mangling",
@@ -4037,13 +4030,11 @@ 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",
@@ -4250,7 +4241,6 @@ name = "rustc_query_impl"
 version = "0.0.0"
 dependencies = [
  "measureme",
- "rustc_attr_data_structures",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_hashes",
@@ -4324,7 +4314,6 @@ version = "0.0.0"
 dependencies = [
  "bitflags",
  "rustc_abi",
- "rustc_ast",
  "rustc_data_structures",
  "rustc_hir",
  "rustc_middle",
@@ -4379,7 +4368,6 @@ name = "rustc_smir"
 version = "0.0.0"
 dependencies = [
  "rustc_abi",
- "rustc_ast",
  "rustc_data_structures",
  "rustc_hir",
  "rustc_hir_pretty",
@@ -4421,7 +4409,6 @@ dependencies = [
  "punycode",
  "rustc-demangle",
  "rustc_abi",
- "rustc_ast",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_hashes",

compiler/rustc_abi/src/lib.rs

@@ -6,6 +6,7 @@
 #![cfg_attr(feature = "nightly", feature(rustdoc_internals))]
 #![cfg_attr(feature = "nightly", feature(step_trait))]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 /*! ABI handling for rustc

compiler/rustc_arena/src/lib.rs

@@ -24,6 +24,7 @@
 #![feature(rustc_attrs)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::alloc::Layout;

compiler/rustc_ast/src/lib.rs

@@ -20,6 +20,7 @@
 #![feature(rustdoc_internals)]
 #![feature(stmt_expr_attributes)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 pub mod util {

compiler/rustc_ast_ir/src/lib.rs

@@ -10,6 +10,7 @@
 #![cfg_attr(feature = "nightly", feature(never_type))]
 #![cfg_attr(feature = "nightly", feature(rustc_attrs))]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 #[cfg(feature = "nightly")]

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_lowering/src/lib.rs

@@ -39,6 +39,7 @@
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::sync::Arc;

compiler/rustc_ast_passes/src/lib.rs

@@ -11,6 +11,7 @@
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 pub mod ast_validation;

compiler/rustc_ast_pretty/Cargo.toml

@@ -7,7 +7,6 @@ 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" }
 thin-vec = "0.2.12"

compiler/rustc_ast_pretty/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(box_patterns)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 mod helpers;

compiler/rustc_attr_data_structures/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 mod attributes;

compiler/rustc_attr_parsing/Cargo.toml

@@ -9,14 +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_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 thin-vec = "0.2.12"

compiler/rustc_attr_parsing/src/lib.rs

@@ -81,6 +81,7 @@
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 #[macro_use]

compiler/rustc_baked_icu_data/src/lib.rs

@@ -26,6 +26,7 @@
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 // #![warn(unreachable_pub)] // don't use because this crate is mostly generated code
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 mod data {

compiler/rustc_borrowck/src/lib.rs

@@ -14,6 +14,7 @@
 #![feature(stmt_expr_attributes)]
 #![feature(try_blocks)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::borrow::Cow;

compiler/rustc_builtin_macros/src/lib.rs

@@ -19,6 +19,7 @@
 #![feature(string_from_utf8_lossy_owned)]
 #![feature(try_blocks)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 extern crate proc_macro;

compiler/rustc_codegen_cranelift/build_system/main.rs

@@ -1,6 +1,7 @@
 #![warn(rust_2018_idioms)]
 #![warn(unused_lifetimes)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 
 use std::path::PathBuf;
 use std::{env, process};

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -9,6 +9,7 @@
 // Note: please avoid adding other feature gates where possible
 #![warn(rust_2018_idioms)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 #![warn(unused_lifetimes)]
 // tidy-alphabetical-end
 

compiler/rustc_codegen_gcc/src/lib.rs

@@ -20,6 +20,7 @@
 #![allow(broken_intra_doc_links)]
 #![recursion_limit = "256"]
 #![warn(rust_2018_idioms)]
+#![warn(unused_crate_dependencies)]
 #![warn(unused_lifetimes)]
 #![deny(clippy::pattern_type_mismatch)]
 #![allow(clippy::needless_lifetimes)]

compiler/rustc_codegen_llvm/src/lib.rs

@@ -21,6 +21,7 @@
 #![feature(slice_as_array)]
 #![feature(try_blocks)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::any::Any;

compiler/rustc_codegen_ssa/Cargo.toml

@@ -19,15 +19,13 @@ 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" }
 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_codegen_ssa/src/lib.rs

@@ -15,6 +15,7 @@
 #![feature(trait_alias)]
 #![feature(try_blocks)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 //! This crate contains codegen code that is used by all codegen backends (LLVM and others).

compiler/rustc_const_eval/src/lib.rs

@@ -17,6 +17,7 @@
 #![feature(yeet_expr)]
 #![warn(unqualified_local_imports)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 pub mod check_consts;

compiler/rustc_data_structures/src/lib.rs

@@ -37,6 +37,7 @@
 #![feature(thread_id_value)]
 #![feature(type_alias_impl_trait)]
 #![feature(unwrap_infallible)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::fmt;

compiler/rustc_driver/src/lib.rs

@@ -5,6 +5,7 @@
 #![allow(internal_features)]
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 pub use rustc_driver_impl::*;

compiler/rustc_driver_impl/Cargo.toml

@@ -24,7 +24,6 @@ rustc_hir_analysis = { path = "../rustc_hir_analysis" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_hir_typeck = { path = "../rustc_hir_typeck" }
 rustc_incremental = { path = "../rustc_incremental" }
-rustc_index = { path = "../rustc_index" }
 rustc_infer = { path = "../rustc_infer" }
 rustc_interface = { path = "../rustc_interface" }
 rustc_lint = { path = "../rustc_lint" }
@@ -75,7 +74,6 @@ ctrlc = "3.4.4"
 llvm = ['rustc_interface/llvm']
 max_level_info = ['rustc_log/max_level_info']
 rustc_randomized_layouts = [
-    'rustc_index/rustc_randomized_layouts',
     'rustc_middle/rustc_randomized_layouts'
 ]
 # tidy-alphabetical-end

compiler/rustc_driver_impl/src/lib.rs

@@ -17,6 +17,7 @@
 #![feature(rustdoc_internals)]
 #![feature(try_blocks)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::cmp::max;

compiler/rustc_error_codes/src/lib.rs

@@ -7,6 +7,7 @@
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 // This higher-order macro defines the error codes that are in use. It is used

compiler/rustc_error_messages/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(rustdoc_internals)]
 #![feature(type_alias_impl_trait)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::borrow::Cow;

compiler/rustc_errors/src/lib.rs

@@ -25,6 +25,7 @@
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 extern crate self as rustc_errors;

compiler/rustc_expand/src/lib.rs

@@ -14,6 +14,7 @@
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 extern crate proc_macro as pm;

compiler/rustc_feature/src/lib.rs

@@ -16,6 +16,7 @@
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 mod accepted;

compiler/rustc_fluent_macro/src/lib.rs

@@ -8,6 +8,7 @@
 #![feature(rustdoc_internals)]
 #![feature(track_path)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use proc_macro::TokenStream;

compiler/rustc_fs_util/src/lib.rs

@@ -1,3 +1,7 @@
+// tidy-alphabetical-start
+#![warn(unused_crate_dependencies)]
+// tidy-alphabetical-end
+
 use std::ffi::CString;
 use std::path::{Path, PathBuf, absolute};
 use std::{fs, io};

compiler/rustc_graphviz/src/lib.rs

@@ -278,6 +278,7 @@
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
+#![warn(unused_crate_dependencies)]
 // tidy-alphabetical-end
 
 use std::borrow::Cow;