diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index fae8b5647fc..3303e4ee752 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -204,7 +204,7 @@ pub trait LintDiagnostic<'a, G: EmissionGuarantee> {
 }
 
 #[derive(Clone, Debug, Encodable, Decodable)]
-pub struct DiagLocation {
+pub(crate) struct DiagLocation {
     file: Cow<'static, str>,
     line: u32,
     col: u32,
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 9ce5d77ef6c..2bc29dabd18 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -2387,7 +2387,7 @@ enum DisplaySuggestion {
 impl FileWithAnnotatedLines {
     /// Preprocess all the annotations so that they are grouped by file and by line number
     /// This helps us quickly iterate over the whole message (including secondary file spans)
-    pub fn collect_annotations(
+    pub(crate) fn collect_annotations(
         emitter: &dyn Emitter,
         args: &FluentArgs<'_>,
         msp: &MultiSpan,
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index fd203c38318..99ee8fb17d7 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -25,6 +25,7 @@
 #![feature(trait_alias)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 extern crate self as rustc_errors;
@@ -1701,7 +1702,7 @@ impl DiagCtxtInner {
     }
 
     /// Translate `message` eagerly with `args` to `SubdiagMessage::Eager`.
-    pub fn eagerly_translate<'a>(
+    fn eagerly_translate<'a>(
         &self,
         message: DiagMessage,
         args: impl Iterator<Item = DiagArg<'a>>,
@@ -1710,7 +1711,7 @@ impl DiagCtxtInner {
     }
 
     /// Translate `message` eagerly with `args` to `String`.
-    pub fn eagerly_translate_to_string<'a>(
+    fn eagerly_translate_to_string<'a>(
         &self,
         message: DiagMessage,
         args: impl Iterator<Item = DiagArg<'a>>,
diff --git a/compiler/rustc_errors/src/lock.rs b/compiler/rustc_errors/src/lock.rs
index 915542c9092..7557969f374 100644
--- a/compiler/rustc_errors/src/lock.rs
+++ b/compiler/rustc_errors/src/lock.rs
@@ -12,7 +12,7 @@
 use std::any::Any;
 
 #[cfg(windows)]
-pub fn acquire_global_lock(name: &str) -> Box<dyn Any> {
+pub(crate) fn acquire_global_lock(name: &str) -> Box<dyn Any> {
     use std::ffi::CString;
     use std::io;
 
@@ -80,6 +80,6 @@ pub fn acquire_global_lock(name: &str) -> Box<dyn Any> {
 }
 
 #[cfg(not(windows))]
-pub fn acquire_global_lock(_name: &str) -> Box<dyn Any> {
+pub(crate) fn acquire_global_lock(_name: &str) -> Box<dyn Any> {
     Box::new(())
 }
diff --git a/compiler/rustc_errors/src/markdown/parse.rs b/compiler/rustc_errors/src/markdown/parse.rs
index 46f8959b6f2..b1db44dd215 100644
--- a/compiler/rustc_errors/src/markdown/parse.rs
+++ b/compiler/rustc_errors/src/markdown/parse.rs
@@ -74,7 +74,7 @@ enum ParseOpt {
 }
 
 /// Parse a buffer
-pub fn entrypoint(txt: &str) -> MdStream<'_> {
+pub(crate) fn entrypoint(txt: &str) -> MdStream<'_> {
     let ctx = Context { top_block: true, prev: Prev::Newline };
     normalize(parse_recursive(txt.trim().as_bytes(), ctx), &mut Vec::new())
 }
diff --git a/compiler/rustc_errors/src/markdown/term.rs b/compiler/rustc_errors/src/markdown/term.rs
index 06c1333d93d..579e00b8b85 100644
--- a/compiler/rustc_errors/src/markdown/term.rs
+++ b/compiler/rustc_errors/src/markdown/term.rs
@@ -15,7 +15,7 @@ thread_local! {
 }
 
 /// Print to terminal output to a buffer
-pub fn entrypoint(stream: &MdStream<'_>, buf: &mut Buffer) -> io::Result<()> {
+pub(crate) fn entrypoint(stream: &MdStream<'_>, buf: &mut Buffer) -> io::Result<()> {
     #[cfg(not(test))]
     if let Some((w, _)) = termize::dimensions() {
         WIDTH.with(|c| c.set(std::cmp::min(w, DEFAULT_COLUMN_WIDTH)));
@@ -47,7 +47,7 @@ fn write_stream(
     Ok(())
 }
 
-pub fn write_tt(tt: &MdTree<'_>, buf: &mut Buffer, indent: usize) -> io::Result<()> {
+fn write_tt(tt: &MdTree<'_>, buf: &mut Buffer, indent: usize) -> io::Result<()> {
     match tt {
         MdTree::CodeBlock { txt, lang: _ } => {
             buf.set_color(ColorSpec::new().set_dimmed(true))?;
diff --git a/compiler/rustc_errors/src/snippet.rs b/compiler/rustc_errors/src/snippet.rs
index 50abf8a49c2..8485d7087cf 100644
--- a/compiler/rustc_errors/src/snippet.rs
+++ b/compiler/rustc_errors/src/snippet.rs
@@ -5,13 +5,13 @@ use rustc_macros::{Decodable, Encodable};
 use crate::{Level, Loc};
 
 #[derive(Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
-pub struct Line {
+pub(crate) struct Line {
     pub line_index: usize,
     pub annotations: Vec<Annotation>,
 }
 
 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Default)]
-pub struct AnnotationColumn {
+pub(crate) struct AnnotationColumn {
     /// the (0-indexed) column for *display* purposes, counted in characters, not utf-8 bytes
     pub display: usize,
     /// the (0-indexed) column in the file, counted in characters, not utf-8 bytes.
@@ -31,13 +31,13 @@ pub struct AnnotationColumn {
 }
 
 impl AnnotationColumn {
-    pub fn from_loc(loc: &Loc) -> AnnotationColumn {
+    pub(crate) fn from_loc(loc: &Loc) -> AnnotationColumn {
         AnnotationColumn { display: loc.col_display, file: loc.col.0 }
     }
 }
 
 #[derive(Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
-pub struct MultilineAnnotation {
+pub(crate) struct MultilineAnnotation {
     pub depth: usize,
     pub line_start: usize,
     pub line_end: usize,
@@ -49,19 +49,19 @@ pub struct MultilineAnnotation {
 }
 
 impl MultilineAnnotation {
-    pub fn increase_depth(&mut self) {
+    pub(crate) fn increase_depth(&mut self) {
         self.depth += 1;
     }
 
     /// Compare two `MultilineAnnotation`s considering only the `Span` they cover.
-    pub fn same_span(&self, other: &MultilineAnnotation) -> bool {
+    pub(crate) fn same_span(&self, other: &MultilineAnnotation) -> bool {
         self.line_start == other.line_start
             && self.line_end == other.line_end
             && self.start_col == other.start_col
             && self.end_col == other.end_col
     }
 
-    pub fn as_start(&self) -> Annotation {
+    pub(crate) fn as_start(&self) -> Annotation {
         Annotation {
             start_col: self.start_col,
             end_col: AnnotationColumn {
@@ -76,7 +76,7 @@ impl MultilineAnnotation {
         }
     }
 
-    pub fn as_end(&self) -> Annotation {
+    pub(crate) fn as_end(&self) -> Annotation {
         Annotation {
             start_col: AnnotationColumn {
                 // these might not correspond to the same place anymore,
@@ -91,7 +91,7 @@ impl MultilineAnnotation {
         }
     }
 
-    pub fn as_line(&self) -> Annotation {
+    pub(crate) fn as_line(&self) -> Annotation {
         Annotation {
             start_col: Default::default(),
             end_col: Default::default(),
@@ -103,7 +103,7 @@ impl MultilineAnnotation {
 }
 
 #[derive(Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
-pub enum AnnotationType {
+pub(crate) enum AnnotationType {
     /// Annotation under a single line of code
     Singleline,
 
@@ -129,7 +129,7 @@ pub enum AnnotationType {
 }
 
 #[derive(Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
-pub struct Annotation {
+pub(crate) struct Annotation {
     /// Start column.
     /// Note that it is important that this field goes
     /// first, so that when we sort, we sort orderings by start
@@ -152,12 +152,12 @@ pub struct Annotation {
 
 impl Annotation {
     /// Whether this annotation is a vertical line placeholder.
-    pub fn is_line(&self) -> bool {
+    pub(crate) fn is_line(&self) -> bool {
         matches!(self.annotation_type, AnnotationType::MultilineLine(_))
     }
 
     /// Length of this annotation as displayed in the stderr output
-    pub fn len(&self) -> usize {
+    pub(crate) fn len(&self) -> usize {
         // Account for usize underflows
         if self.end_col.display > self.start_col.display {
             self.end_col.display - self.start_col.display
@@ -166,7 +166,7 @@ impl Annotation {
         }
     }
 
-    pub fn has_label(&self) -> bool {
+    pub(crate) fn has_label(&self) -> bool {
         if let Some(ref label) = self.label {
             // Consider labels with no text as effectively not being there
             // to avoid weird output with unnecessary vertical lines, like:
@@ -184,7 +184,7 @@ impl Annotation {
         }
     }
 
-    pub fn takes_space(&self) -> bool {
+    pub(crate) fn takes_space(&self) -> bool {
         // Multiline annotations always have to keep vertical space.
         matches!(
             self.annotation_type,
@@ -194,7 +194,7 @@ impl Annotation {
 }
 
 #[derive(Debug)]
-pub struct StyledString {
+pub(crate) struct StyledString {
     pub text: String,
     pub style: Style,
 }
diff --git a/compiler/rustc_errors/src/styled_buffer.rs b/compiler/rustc_errors/src/styled_buffer.rs
index 9aa14e1f214..5ca9e9b18f3 100644
--- a/compiler/rustc_errors/src/styled_buffer.rs
+++ b/compiler/rustc_errors/src/styled_buffer.rs
@@ -3,7 +3,7 @@
 use crate::snippet::{Style, StyledString};
 
 #[derive(Debug)]
-pub struct StyledBuffer {
+pub(crate) struct StyledBuffer {
     lines: Vec<Vec<StyledChar>>,
 }
 
@@ -22,12 +22,12 @@ impl StyledChar {
 }
 
 impl StyledBuffer {
-    pub fn new() -> StyledBuffer {
+    pub(crate) fn new() -> StyledBuffer {
         StyledBuffer { lines: vec![] }
     }
 
     /// Returns content of `StyledBuffer` split by lines and line styles
-    pub fn render(&self) -> Vec<Vec<StyledString>> {
+    pub(crate) fn render(&self) -> Vec<Vec<StyledString>> {
         // Tabs are assumed to have been replaced by spaces in calling code.
         debug_assert!(self.lines.iter().all(|r| !r.iter().any(|sc| sc.chr == '\t')));
 
@@ -70,7 +70,7 @@ impl StyledBuffer {
     /// Sets `chr` with `style` for given `line`, `col`.
     /// If `line` does not exist in our buffer, adds empty lines up to the given
     /// and fills the last line with unstyled whitespace.
-    pub fn putc(&mut self, line: usize, col: usize, chr: char, style: Style) {
+    pub(crate) fn putc(&mut self, line: usize, col: usize, chr: char, style: Style) {
         self.ensure_lines(line);
         if col >= self.lines[line].len() {
             self.lines[line].resize(col + 1, StyledChar::SPACE);
@@ -81,7 +81,7 @@ impl StyledBuffer {
     /// Sets `string` with `style` for given `line`, starting from `col`.
     /// If `line` does not exist in our buffer, adds empty lines up to the given
     /// and fills the last line with unstyled whitespace.
-    pub fn puts(&mut self, line: usize, col: usize, string: &str, style: Style) {
+    pub(crate) fn puts(&mut self, line: usize, col: usize, string: &str, style: Style) {
         let mut n = col;
         for c in string.chars() {
             self.putc(line, n, c, style);
@@ -91,7 +91,7 @@ impl StyledBuffer {
 
     /// For given `line` inserts `string` with `style` before old content of that line,
     /// adding lines if needed
-    pub fn prepend(&mut self, line: usize, string: &str, style: Style) {
+    pub(crate) fn prepend(&mut self, line: usize, string: &str, style: Style) {
         self.ensure_lines(line);
         let string_len = string.chars().count();
 
@@ -107,7 +107,7 @@ impl StyledBuffer {
 
     /// For given `line` inserts `string` with `style` after old content of that line,
     /// adding lines if needed
-    pub fn append(&mut self, line: usize, string: &str, style: Style) {
+    pub(crate) fn append(&mut self, line: usize, string: &str, style: Style) {
         if line >= self.lines.len() {
             self.puts(line, 0, string, style);
         } else {
@@ -116,14 +116,14 @@ impl StyledBuffer {
         }
     }
 
-    pub fn num_lines(&self) -> usize {
+    pub(crate) fn num_lines(&self) -> usize {
         self.lines.len()
     }
 
     /// Set `style` for `line`, `col_start..col_end` range if:
     /// 1. That line and column range exist in `StyledBuffer`
     /// 2. `overwrite` is `true` or existing style is `Style::NoStyle` or `Style::Quotation`
-    pub fn set_style_range(
+    pub(crate) fn set_style_range(
         &mut self,
         line: usize,
         col_start: usize,
@@ -139,7 +139,7 @@ impl StyledBuffer {
     /// Set `style` for `line`, `col` if:
     /// 1. That line and column exist in `StyledBuffer`
     /// 2. `overwrite` is `true` or existing style is `Style::NoStyle` or `Style::Quotation`
-    pub fn set_style(&mut self, line: usize, col: usize, style: Style, overwrite: bool) {
+    fn set_style(&mut self, line: usize, col: usize, style: Style, overwrite: bool) {
         if let Some(ref mut line) = self.lines.get_mut(line) {
             if let Some(StyledChar { style: s, .. }) = line.get_mut(col) {
                 if overwrite || matches!(s, Style::NoStyle | Style::Quotation) {