Add unreachable_pub to RUSTC_LINT_FLAGS for compiler/ crates.

And fix the new errors in the handful of crates that didn't have a
`#![warn(unreachable_pub)]`.

Author: nnethercote

Diff for: compiler/rustc_baked_icu_data/src/lib.rs

@@ -23,6 +23,7 @@
 // tidy-alphabetical-start
 #![allow(elided_lifetimes_in_paths)]
 #![allow(internal_features)]
+#![allow(unreachable_pub)] // because this crate is mostly generated code
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 // #![warn(unreachable_pub)] // don't use because this crate is mostly generated code

Diff for: compiler/rustc_data_structures/src/graph/tests.rs

@@ -3,15 +3,15 @@ use std::cmp::max;
 use super::*;
 use crate::fx::FxHashMap;
 
-pub struct TestGraph {
+pub(super) struct TestGraph {
     num_nodes: usize,
     start_node: usize,
     successors: FxHashMap<usize, Vec<usize>>,
     predecessors: FxHashMap<usize, Vec<usize>>,
 }
 
 impl TestGraph {
-    pub fn new(start_node: usize, edges: &[(usize, usize)]) -> Self {
+    pub(super) fn new(start_node: usize, edges: &[(usize, usize)]) -> Self {
         let mut graph = TestGraph {
             num_nodes: start_node + 1,
             start_node,

Diff for: compiler/rustc_data_structures/src/obligation_forest/mod.rs

@@ -313,7 +313,7 @@ pub struct Error<O, E> {
 
 mod helper {
     use super::*;
-    pub type ObligationTreeIdGenerator = impl Iterator<Item = ObligationTreeId>;
+    pub(super) type ObligationTreeIdGenerator = impl Iterator<Item = ObligationTreeId>;
     impl<O: ForestObligation> ObligationForest<O> {
         pub fn new() -> ObligationForest<O> {
             ObligationForest {

Diff for: compiler/rustc_data_structures/src/sync.rs

@@ -88,7 +88,7 @@ mod mode {
 
     // Whether thread safety might be enabled.
     #[inline]
-    pub fn might_be_dyn_thread_safe() -> bool {
+    pub(super) fn might_be_dyn_thread_safe() -> bool {
         DYN_THREAD_SAFE_MODE.load(Ordering::Relaxed) != DYN_NOT_THREAD_SAFE
     }
 

Diff for: compiler/rustc_data_structures/src/sync/parallel.rs

@@ -46,7 +46,7 @@ pub fn parallel_guard<R>(f: impl FnOnce(&ParallelGuard) -> R) -> R {
     ret
 }
 
-pub fn serial_join<A, B, RA, RB>(oper_a: A, oper_b: B) -> (RA, RB)
+fn serial_join<A, B, RA, RB>(oper_a: A, oper_b: B) -> (RA, RB)
 where
     A: FnOnce() -> RA,
     B: FnOnce() -> RB,

Diff for: compiler/rustc_data_structures/src/tagged_ptr/tests.rs

@@ -7,7 +7,7 @@ use crate::stable_hasher::{HashStable, StableHasher};
 
 /// A tag type used in [`TaggedRef`] tests.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum Tag2 {
+enum Tag2 {
     B00 = 0b00,
     B01 = 0b01,
     B10 = 0b10,

Diff for: compiler/rustc_index_macros/src/newtype.rs

@@ -305,7 +305,7 @@ impl Parse for Newtype {
     }
 }
 
-pub fn newtype(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+pub(crate) fn newtype(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input = parse_macro_input!(input as Newtype);
     input.0.into()
 }

Diff for: compiler/rustc_pattern_analysis/tests/common/mod.rs

@@ -5,7 +5,7 @@ use rustc_pattern_analysis::usefulness::{PlaceValidity, UsefulnessReport};
 use rustc_pattern_analysis::{MatchArm, PatCx, PrivateUninhabitedField};
 
 /// Sets up `tracing` for easier debugging. Tries to look like the `rustc` setup.
-pub fn init_tracing() {
+fn init_tracing() {
     use tracing_subscriber::Layer;
     use tracing_subscriber::layer::SubscriberExt;
     use tracing_subscriber::util::SubscriberInitExt;
@@ -24,7 +24,7 @@ pub fn init_tracing() {
 /// A simple set of types.
 #[allow(dead_code)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
-pub enum Ty {
+pub(super) enum Ty {
     /// Booleans
     Bool,
     /// 8-bit unsigned integers
@@ -41,7 +41,7 @@ pub enum Ty {
 
 /// The important logic.
 impl Ty {
-    pub fn sub_tys(&self, ctor: &Constructor<Cx>) -> Vec<Self> {
+    pub(super) fn sub_tys(&self, ctor: &Constructor<Cx>) -> Vec<Self> {
         use Constructor::*;
         match (ctor, *self) {
             (Struct, Ty::Tuple(tys)) => tys.iter().copied().collect(),
@@ -63,7 +63,7 @@ impl Ty {
         }
     }
 
-    pub fn ctor_set(&self) -> ConstructorSet<Cx> {
+    fn ctor_set(&self) -> ConstructorSet<Cx> {
         match *self {
             Ty::Bool => ConstructorSet::Bool,
             Ty::U8 => ConstructorSet::Integers {
@@ -104,7 +104,7 @@ impl Ty {
         }
     }
 
-    pub fn write_variant_name(
+    fn write_variant_name(
         &self,
         f: &mut std::fmt::Formatter<'_>,
         ctor: &Constructor<Cx>,
@@ -120,7 +120,7 @@ impl Ty {
 }
 
 /// Compute usefulness in our simple context (and set up tracing for easier debugging).
-pub fn compute_match_usefulness<'p>(
+pub(super) fn compute_match_usefulness<'p>(
     arms: &[MatchArm<'p, Cx>],
     ty: Ty,
     scrut_validity: PlaceValidity,
@@ -137,7 +137,7 @@ pub fn compute_match_usefulness<'p>(
 }
 
 #[derive(Debug)]
-pub struct Cx;
+pub(super) struct Cx;
 
 /// The context for pattern analysis. Forwards anything interesting to `Ty` methods.
 impl PatCx for Cx {

Diff for: src/bootstrap/src/core/builder/cargo.rs

@@ -1071,6 +1071,7 @@ impl Builder<'_> {
             // FIXME(edition_2024): Change this to `-Wrust_2024_idioms` when all
             // of the individual lints are satisfied.
             lint_flags.push("-Wkeyword_idents_2024");
+            lint_flags.push("-Wunreachable_pub");
             lint_flags.push("-Wunsafe_op_in_unsafe_fn");
         }