Merging upstream version 1.68.2+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

19 files changed, 756 insertions, 568 deletions

diff --git a/src/tools/tidy/Cargo.toml b/src/tools/tidy/Cargo.toml
index 97d038da7..cdf1dd366 100644
--- a/src/tools/tidy/Cargo.toml
+++ b/src/tools/tidy/Cargo.toml
@@ -6,11 +6,14 @@ autobins = false
 
 [dependencies]
 cargo_metadata = "0.14"
+cargo-platform = "0.1.2"
 regex = "1"
 miropt-test-tools = { path = "../miropt-test-tools" }
 lazy_static = "1"
 walkdir = "2"
 ignore = "0.4.18"
+semver = "1.0"
+termcolor = "1.1.3"
 
 [[bin]]
 name = "rust-tidy"
diff --git a/src/tools/tidy/src/debug_artifacts.rs b/src/tools/tidy/src/debug_artifacts.rs
index 9880a32ad..0dd9c1e16 100644
--- a/src/tools/tidy/src/debug_artifacts.rs
+++ b/src/tools/tidy/src/debug_artifacts.rs
@@ -1,14 +1,12 @@
 //! Tidy check to prevent creation of unnecessary debug artifacts while running tests.
 
 use crate::walk::{filter_dirs, walk};
-use std::path::{Path, PathBuf};
+use std::path::Path;
 
 const GRAPHVIZ_POSTFLOW_MSG: &str = "`borrowck_graphviz_postflow` attribute in test";
 
-pub fn check(path: &Path, bad: &mut bool) {
-    let test_dir: PathBuf = path.join("test");
-
-    walk(&test_dir, &mut filter_dirs, &mut |entry, contents| {
+pub fn check(test_dir: &Path, bad: &mut bool) {
+    walk(test_dir, &mut filter_dirs, &mut |entry, contents| {
         let filename = entry.path();
         let is_rust = filename.extension().map_or(false, |ext| ext == "rs");
         if !is_rust {
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 296db9dfb..bc2edf634 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -1,7 +1,7 @@
 //! Checks the licenses of third-party dependencies.
 
-use cargo_metadata::{Metadata, Package, PackageId, Resolve};
-use std::collections::{BTreeSet, HashSet};
+use cargo_metadata::{DepKindInfo, Metadata, Package, PackageId};
+use std::collections::HashSet;
 use std::path::Path;
 
 /// These are licenses that are allowed for all crates, including the runtime,
@@ -40,6 +40,8 @@ const EXCEPTIONS: &[(&str, &str)] = &[
     ("im-rc", "MPL-2.0+"),                                   // cargo
     ("sized-chunks", "MPL-2.0+"),                            // cargo via im-rc
     ("bitmaps", "MPL-2.0+"),                                 // cargo via im-rc
+    ("fiat-crypto", "MIT OR Apache-2.0 OR BSD-1-Clause"),    // cargo via pasetors
+    ("subtle", "BSD-3-Clause"),                              // cargo via pasetors
     ("instant", "BSD-3-Clause"), // rustc_driver/tracing-subscriber/parking_lot
     ("snap", "BSD-3-Clause"),    // rustc
     ("fluent-langneg", "Apache-2.0"), // rustc (fluent translations)
@@ -50,7 +52,6 @@ const EXCEPTIONS: &[(&str, &str)] = &[
     ("similar", "Apache-2.0"),       // cargo (dev dependency)
     ("normalize-line-endings", "Apache-2.0"), // cargo (dev dependency)
     ("dissimilar", "Apache-2.0"),    // rustdoc, rustc_lexer (few tests) via expect-test, (dev deps)
-    ("subtle", "BSD-3-Clause"),      // cargo
 ];
 
 const EXCEPTIONS_CRANELIFT: &[(&str, &str)] = &[
@@ -58,6 +59,7 @@ const EXCEPTIONS_CRANELIFT: &[(&str, &str)] = &[
     ("cranelift-codegen", "Apache-2.0 WITH LLVM-exception"),
     ("cranelift-codegen-meta", "Apache-2.0 WITH LLVM-exception"),
     ("cranelift-codegen-shared", "Apache-2.0 WITH LLVM-exception"),
+    ("cranelift-egraph", "Apache-2.0 WITH LLVM-exception"),
     ("cranelift-entity", "Apache-2.0 WITH LLVM-exception"),
     ("cranelift-frontend", "Apache-2.0 WITH LLVM-exception"),
     ("cranelift-isle", "Apache-2.0 WITH LLVM-exception"),
@@ -68,6 +70,7 @@ const EXCEPTIONS_CRANELIFT: &[(&str, &str)] = &[
     ("mach", "BSD-2-Clause"),
     ("regalloc2", "Apache-2.0 WITH LLVM-exception"),
     ("target-lexicon", "Apache-2.0 WITH LLVM-exception"),
+    ("wasmtime-jit-icache-coherence", "Apache-2.0 WITH LLVM-exception"),
 ];
 
 const EXCEPTIONS_BOOTSTRAP: &[(&str, &str)] = &[
@@ -101,7 +104,6 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "chalk-engine",
     "chalk-ir",
     "chalk-solve",
-    "chrono",
     "convert_case", // dependency of derive_more
     "compiler_builtins",
     "cpufeatures",
@@ -120,11 +122,9 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "dlmalloc",
     "either",
     "ena",
-    "env_logger",
     "expect-test",
     "fallible-iterator", // dependency of `thorin`
     "fastrand",
-    "filetime",
     "fixedbitset",
     "flate2",
     "fluent-bundle",
@@ -138,13 +138,11 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "gsgdt",
     "hashbrown",
     "hermit-abi",
-    "humantime",
     "icu_list",
     "icu_locid",
     "icu_provider",
     "icu_provider_adapters",
     "icu_provider_macros",
-    "if_chain",
     "indexmap",
     "instant",
     "intl-memoizer",
@@ -166,8 +164,6 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "memmap2",
     "memoffset",
     "miniz_oxide",
-    "num-integer",
-    "num-traits",
     "num_cpus",
     "object",
     "odht",
@@ -185,12 +181,10 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "proc-macro2",
     "psm",
     "punycode",
-    "quick-error",
     "quote",
     "rand",
     "rand_chacha",
     "rand_core",
-    "rand_hc",
     "rand_xorshift",
     "rand_xoshiro",
     "redox_syscall",
@@ -213,14 +207,15 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "serde",
     "serde_derive",
     "serde_json",
-    "sha-1",
+    "sha1",
     "sha2",
     "sharded-slab",
     "smallvec",
     "snap",
     "stable_deref_trait",
     "stacker",
-    "subtle",
+    "static_assertions",
+    "subtle", // dependency of cargo (via pasetors)
     "syn",
     "synstructure",
     "tempfile",
@@ -230,7 +225,6 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "thiserror-impl",
     "thorin-dwp",
     "thread_local",
-    "time",
     "tinystr",
     "tinyvec",
     "tinyvec_macros",
@@ -241,6 +235,7 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "tracing-log",
     "tracing-subscriber",
     "tracing-tree",
+    "twox-hash",
     "type-map",
     "typenum",
     "unic-char-property",
@@ -291,6 +286,7 @@ const PERMITTED_CRANELIFT_DEPENDENCIES: &[&str] = &[
     "cranelift-codegen",
     "cranelift-codegen-meta",
     "cranelift-codegen-shared",
+    "cranelift-egraph",
     "cranelift-entity",
     "cranelift-frontend",
     "cranelift-isle",
@@ -299,6 +295,7 @@ const PERMITTED_CRANELIFT_DEPENDENCIES: &[&str] = &[
     "cranelift-native",
     "cranelift-object",
     "crc32fast",
+    "fallible-iterator",
     "fxhash",
     "getrandom",
     "gimli",
@@ -315,9 +312,11 @@ const PERMITTED_CRANELIFT_DEPENDENCIES: &[&str] = &[
     "region",
     "slice-group-by",
     "smallvec",
+    "stable_deref_trait",
     "target-lexicon",
     "version_check",
     "wasi",
+    "wasmtime-jit-icache-coherence",
     "winapi",
     "winapi-i686-pc-windows-gnu",
     "winapi-x86_64-pc-windows-gnu",
@@ -468,75 +467,57 @@ fn check_permitted_dependencies(
     restricted_dependency_crates: &[&'static str],
     bad: &mut bool,
 ) {
+    let mut deps = HashSet::new();
+    for to_check in restricted_dependency_crates {
+        let to_check = pkg_from_name(metadata, to_check);
+        use cargo_platform::Cfg;
+        use std::str::FromStr;
+        // We don't expect the compiler to ever run on wasm32, so strip
+        // out those dependencies to avoid polluting the permitted list.
+        deps_of_filtered(metadata, &to_check.id, &mut deps, &|dep_kinds| {
+            dep_kinds.iter().any(|dep_kind| {
+                dep_kind
+                    .target
+                    .as_ref()
+                    .map(|target| {
+                        !target.matches(
+                            "wasm32-unknown-unknown",
+                            &[
+                                Cfg::from_str("target_arch=\"wasm32\"").unwrap(),
+                                Cfg::from_str("target_os=\"unknown\"").unwrap(),
+                            ],
+                        )
+                    })
+                    .unwrap_or(true)
+            })
+        });
+    }
+
     // Check that the PERMITTED_DEPENDENCIES does not have unused entries.
-    for name in permitted_dependencies {
-        if !metadata.packages.iter().any(|p| p.name == *name) {
+    for permitted in permitted_dependencies {
+        if !deps.iter().any(|dep_id| &pkg_from_id(metadata, dep_id).name == permitted) {
             tidy_error!(
                 bad,
-                "could not find allowed package `{}`\n\
+                "could not find allowed package `{permitted}`\n\
                 Remove from PERMITTED_DEPENDENCIES list if it is no longer used.",
-                name
             );
         }
     }
-    // Get the list in a convenient form.
-    let permitted_dependencies: HashSet<_> = permitted_dependencies.iter().cloned().collect();
 
-    // Check dependencies.
-    let mut visited = BTreeSet::new();
-    let mut unapproved = BTreeSet::new();
-    for &krate in restricted_dependency_crates.iter() {
-        let pkg = pkg_from_name(metadata, krate);
-        let mut bad =
-            check_crate_dependencies(&permitted_dependencies, metadata, &mut visited, pkg);
-        unapproved.append(&mut bad);
-    }
+    // Get in a convenient form.
+    let permitted_dependencies: HashSet<_> = permitted_dependencies.iter().cloned().collect();
 
-    if !unapproved.is_empty() {
-        tidy_error!(bad, "Dependencies for {} not explicitly permitted:", descr);
-        for dep in unapproved {
-            println!("* {dep}");
+    for dep in deps {
+        let dep = pkg_from_id(metadata, dep);
+        // If this path is in-tree, we don't require it to be explicitly permitted.
+        if dep.source.is_some() {
+            if !permitted_dependencies.contains(dep.name.as_str()) {
+                tidy_error!(bad, "Dependency for {descr} not explicitly permitted: {}", dep.id);
+            }
         }
     }
 }
 
-/// Checks the dependencies of the given crate from the given cargo metadata to see if they are on
-/// the list of permitted dependencies. Returns a list of disallowed dependencies.
-fn check_crate_dependencies<'a>(
-    permitted_dependencies: &'a HashSet<&'static str>,
-    metadata: &'a Metadata,
-    visited: &mut BTreeSet<&'a PackageId>,
-    krate: &'a Package,
-) -> BTreeSet<&'a PackageId> {
-    // This will contain bad deps.
-    let mut unapproved = BTreeSet::new();
-
-    // Check if we have already visited this crate.
-    if visited.contains(&krate.id) {
-        return unapproved;
-    }
-
-    visited.insert(&krate.id);
-
-    // If this path is in-tree, we don't require it to be explicitly permitted.
-    if krate.source.is_some() {
-        // If this dependency is not on `PERMITTED_DEPENDENCIES`, add to bad set.
-        if !permitted_dependencies.contains(krate.name.as_str()) {
-            unapproved.insert(&krate.id);
-        }
-    }
-
-    // Do a DFS in the crate graph.
-    let to_check = deps_of(metadata, &krate.id);
-
-    for dep in to_check {
-        let mut bad = check_crate_dependencies(permitted_dependencies, metadata, visited, dep);
-        unapproved.append(&mut bad);
-    }
-
-    unapproved
-}
-
 /// Prevents multiple versions of some expensive crates.
 fn check_crate_duplicate(
     metadata: &Metadata,
@@ -571,24 +552,6 @@ fn check_crate_duplicate(
     }
 }
 
-/// Returns a list of dependencies for the given package.
-fn deps_of<'a>(metadata: &'a Metadata, pkg_id: &'a PackageId) -> Vec<&'a Package> {
-    let resolve = metadata.resolve.as_ref().unwrap();
-    let node = resolve
-        .nodes
-        .iter()
-        .find(|n| &n.id == pkg_id)
-        .unwrap_or_else(|| panic!("could not find `{pkg_id}` in resolve"));
-    node.deps
-        .iter()
-        .map(|dep| {
-            metadata.packages.iter().find(|pkg| pkg.id == dep.pkg).unwrap_or_else(|| {
-                panic!("could not find dep `{}` for pkg `{}` in resolve", dep.pkg, pkg_id)
-            })
-        })
-        .collect()
-}
-
 /// Finds a package with the given name.
 fn pkg_from_name<'a>(metadata: &'a Metadata, name: &'static str) -> &'a Package {
     let mut i = metadata.packages.iter().filter(|p| p.name == name);
@@ -598,41 +561,57 @@ fn pkg_from_name<'a>(metadata: &'a Metadata, name: &'static str) -> &'a Package
     result
 }
 
+fn pkg_from_id<'a>(metadata: &'a Metadata, id: &PackageId) -> &'a Package {
+    metadata.packages.iter().find(|p| &p.id == id).unwrap()
+}
+
 /// Finds all the packages that are in the rust runtime.
 fn compute_runtime_crates<'a>(metadata: &'a Metadata) -> HashSet<&'a PackageId> {
-    let resolve = metadata.resolve.as_ref().unwrap();
     let mut result = HashSet::new();
     for name in RUNTIME_CRATES {
         let id = &pkg_from_name(metadata, name).id;
-        normal_deps_of_r(resolve, id, &mut result);
+        deps_of_filtered(metadata, id, &mut result, &|_| true);
     }
     result
 }
 
-/// Recursively find all normal dependencies.
-fn normal_deps_of_r<'a>(
-    resolve: &'a Resolve,
+/// Recursively find all dependencies.
+fn deps_of_filtered<'a>(
+    metadata: &'a Metadata,
     pkg_id: &'a PackageId,
     result: &mut HashSet<&'a PackageId>,
+    filter: &dyn Fn(&[DepKindInfo]) -> bool,
 ) {
     if !result.insert(pkg_id) {
         return;
     }
-    let node = resolve
+    let node = metadata
+        .resolve
+        .as_ref()
+        .unwrap()
         .nodes
         .iter()
         .find(|n| &n.id == pkg_id)
         .unwrap_or_else(|| panic!("could not find `{pkg_id}` in resolve"));
     for dep in &node.deps {
-        normal_deps_of_r(resolve, &dep.pkg, result);
+        if !filter(&dep.dep_kinds) {
+            continue;
+        }
+        deps_of_filtered(metadata, &dep.pkg, result, filter);
     }
 }
 
+fn direct_deps_of<'a>(metadata: &'a Metadata, pkg_id: &'a PackageId) -> Vec<&'a Package> {
+    let resolve = metadata.resolve.as_ref().unwrap();
+    let node = resolve.nodes.iter().find(|n| &n.id == pkg_id).unwrap();
+    node.deps.iter().map(|dep| pkg_from_id(metadata, &dep.pkg)).collect()
+}
+
 fn check_rustfix(metadata: &Metadata, bad: &mut bool) {
     let cargo = pkg_from_name(metadata, "cargo");
     let compiletest = pkg_from_name(metadata, "compiletest");
-    let cargo_deps = deps_of(metadata, &cargo.id);
-    let compiletest_deps = deps_of(metadata, &compiletest.id);
+    let cargo_deps = direct_deps_of(metadata, &cargo.id);
+    let compiletest_deps = direct_deps_of(metadata, &compiletest.id);
     let cargo_rustfix = cargo_deps.iter().find(|p| p.name == "rustfix").unwrap();
     let compiletest_rustfix = compiletest_deps.iter().find(|p| p.name == "rustfix").unwrap();
     if cargo_rustfix.version != compiletest_rustfix.version {
diff --git a/src/tools/tidy/src/edition.rs b/src/tools/tidy/src/edition.rs
index 8a7c4460d..8172e3d29 100644
--- a/src/tools/tidy/src/edition.rs
+++ b/src/tools/tidy/src/edition.rs
@@ -11,7 +11,10 @@ fn is_edition_2021(mut line: &str) -> bool {
 pub fn check(path: &Path, bad: &mut bool) {
     walk(
         path,
-        &mut |path| filter_dirs(path) || path.ends_with("src/test"),
+        &mut |path| {
+            filter_dirs(path)
+                || (path.ends_with("tests") && path.join("COMPILER_TESTS.md").exists())
+        },
         &mut |entry, contents| {
             let file = entry.path();
             let filename = file.file_name().unwrap();
diff --git a/src/tools/tidy/src/error_codes.rs b/src/tools/tidy/src/error_codes.rs
new file mode 100644
index 000000000..5b84b51a0
--- /dev/null
+++ b/src/tools/tidy/src/error_codes.rs
@@ -0,0 +1,383 @@
+//! Tidy check to ensure error codes are properly documented and tested.
+//!
+//! Overview of check:
+//!
+//! 1. We create a list of error codes used by the compiler. Error codes are extracted from `compiler/rustc_error_codes/src/error_codes.rs`.
+//!
+//! 2. We check that the error code has a long-form explanation in `compiler/rustc_error_codes/src/error_codes/`.
+//!   - The explanation is expected to contain a `doctest` that fails with the correct error code. (`EXEMPT_FROM_DOCTEST` *currently* bypasses this check)
+//!   - Note that other stylistic conventions for markdown files are checked in the `style.rs` tidy check.
+//!
+//! 3. We check that the error code has a UI test in `tests/ui/error-codes/`.
+//!   - We ensure that there is both a `Exxxx.rs` file and a corresponding `Exxxx.stderr` file.
+//!   - We also ensure that the error code is used in the tests.
+//!   - *Currently*, it is possible to opt-out of this check with the `EXEMPTED_FROM_TEST` constant.
+//!
+//! 4. We check that the error code is actually emitted by the compiler.
+//!   - This is done by searching `compiler/` with a regex.
+
+use std::{ffi::OsStr, fs, path::Path};
+
+use regex::Regex;
+
+use crate::walk::{filter_dirs, walk, walk_many};
+
+const ERROR_CODES_PATH: &str = "compiler/rustc_error_codes/src/error_codes.rs";
+const ERROR_DOCS_PATH: &str = "compiler/rustc_error_codes/src/error_codes/";
+const ERROR_TESTS_PATH: &str = "tests/ui/error-codes/";
+
+// Error codes that (for some reason) can't have a doctest in their explanation. Error codes are still expected to provide a code example, even if untested.
+const IGNORE_DOCTEST_CHECK: &[&str] = &["E0464", "E0570", "E0601", "E0602", "E0640", "E0717"];
+
+// Error codes that don't yet have a UI test. This list will eventually be removed.
+const IGNORE_UI_TEST_CHECK: &[&str] =
+    &["E0461", "E0465", "E0476", "E0514", "E0523", "E0554", "E0640", "E0717", "E0729", "E0789"];
+
+macro_rules! verbose_print {
+    ($verbose:expr, $($fmt:tt)*) => {
+        if $verbose {
+            println!("{}", format_args!($($fmt)*));
+        }
+    };
+}
+
+pub fn check(root_path: &Path, search_paths: &[&Path], verbose: bool, bad: &mut bool) {
+    let mut errors = Vec::new();
+
+    // Stage 1: create list
+    let error_codes = extract_error_codes(root_path, &mut errors, verbose);
+    println!("Found {} error codes", error_codes.len());
+    println!("Highest error code: `{}`", error_codes.iter().max().unwrap());
+
+    // Stage 2: check list has docs
+    let no_longer_emitted = check_error_codes_docs(root_path, &error_codes, &mut errors, verbose);
+
+    // Stage 3: check list has UI tests
+    check_error_codes_tests(root_path, &error_codes, &mut errors, verbose, &no_longer_emitted);
+
+    // Stage 4: check list is emitted by compiler
+    check_error_codes_used(search_paths, &error_codes, &mut errors, &no_longer_emitted, verbose);
+
+    // Print any errors.
+    for error in errors {
+        tidy_error!(bad, "{}", error);
+    }
+}
+
+/// Stage 1: Parses a list of error codes from `error_codes.rs`.
+fn extract_error_codes(root_path: &Path, errors: &mut Vec<String>, verbose: bool) -> Vec<String> {
+    let path = root_path.join(Path::new(ERROR_CODES_PATH));
+    let file =
+        fs::read_to_string(&path).unwrap_or_else(|e| panic!("failed to read `{path:?}`: {e}"));
+
+    let mut error_codes = Vec::new();
+    let mut reached_undocumented_codes = false;
+
+    for line in file.lines() {
+        let line = line.trim();
+
+        if !reached_undocumented_codes && line.starts_with('E') {
+            let split_line = line.split_once(':');
+
+            // Extract the error code from the line, emitting a fatal error if it is not in a correct format.
+            let err_code = if let Some(err_code) = split_line {
+                err_code.0.to_owned()
+            } else {
+                errors.push(format!(
+                    "Expected a line with the format `Exxxx: include_str!(\"..\")`, but got \"{}\" \
+                    without a `:` delimiter",
+                    line,
+                ));
+                continue;
+            };
+
+            // If this is a duplicate of another error code, emit a fatal error.
+            if error_codes.contains(&err_code) {
+                errors.push(format!("Found duplicate error code: `{}`", err_code));
+                continue;
+            }
+
+            // Ensure that the line references the correct markdown file.
+            let expected_filename = format!(" include_str!(\"./error_codes/{}.md\"),", err_code);
+            if expected_filename != split_line.unwrap().1 {
+                errors.push(format!(
+                    "Error code `{}` expected to reference docs with `{}` but instead found `{}` in \
+                    `compiler/rustc_error_codes/src/error_codes.rs`",
+                    err_code,
+                    expected_filename,
+                    split_line.unwrap().1,
+                ));
+                continue;
+            }
+
+            error_codes.push(err_code);
+        } else if reached_undocumented_codes && line.starts_with('E') {
+            let err_code = match line.split_once(',') {
+                None => line,
+                Some((err_code, _)) => err_code,
+            }
+            .to_string();
+
+            verbose_print!(verbose, "warning: Error code `{}` is undocumented.", err_code);
+
+            if error_codes.contains(&err_code) {
+                errors.push(format!("Found duplicate error code: `{}`", err_code));
+            }
+
+            error_codes.push(err_code);
+        } else if line == ";" {
+            // Once we reach the undocumented error codes, adapt to different syntax.
+            reached_undocumented_codes = true;
+        }
+    }
+
+    error_codes
+}
+
+/// Stage 2: Checks that long-form error code explanations exist and have doctests.
+fn check_error_codes_docs(
+    root_path: &Path,
+    error_codes: &[String],
+    errors: &mut Vec<String>,
+    verbose: bool,
+) -> Vec<String> {
+    let docs_path = root_path.join(Path::new(ERROR_DOCS_PATH));
+
+    let mut no_longer_emitted_codes = Vec::new();
+
+    walk(&docs_path, &mut |_| false, &mut |entry, contents| {
+        let path = entry.path();
+
+        // Error if the file isn't markdown.
+        if path.extension() != Some(OsStr::new("md")) {
+            errors.push(format!(
+                "Found unexpected non-markdown file in error code docs directory: {}",
+                path.display()
+            ));
+            return;
+        }
+
+        // Make sure that the file is referenced in `error_codes.rs`
+        let filename = path.file_name().unwrap().to_str().unwrap().split_once('.');
+        let err_code = filename.unwrap().0; // `unwrap` is ok because we know the filename is in the correct format.
+
+        if error_codes.iter().all(|e| e != err_code) {
+            errors.push(format!(
+                "Found valid file `{}` in error code docs directory without corresponding \
+                entry in `error_code.rs`",
+                path.display()
+            ));
+            return;
+        }
+
+        let (found_code_example, found_proper_doctest, emit_ignore_warning, no_longer_emitted) =
+            check_explanation_has_doctest(&contents, &err_code);
+
+        if emit_ignore_warning {
+            verbose_print!(
+                verbose,
+                "warning: Error code `{err_code}` uses the ignore header. This should not be used, add the error code to the \
+                `IGNORE_DOCTEST_CHECK` constant instead."
+            );
+        }
+
+        if no_longer_emitted {
+            no_longer_emitted_codes.push(err_code.to_owned());
+        }
+
+        if !found_code_example {
+            verbose_print!(
+                verbose,
+                "warning: Error code `{err_code}` doesn't have a code example, all error codes are expected to have one \
+                (even if untested)."
+            );
+            return;
+        }
+
+        let test_ignored = IGNORE_DOCTEST_CHECK.contains(&&err_code);
+
+        // Check that the explanation has a doctest, and if it shouldn't, that it doesn't
+        if !found_proper_doctest && !test_ignored {
+            errors.push(format!(
+                "`{}` doesn't use its own error code in compile_fail example",
+                path.display(),
+            ));
+        } else if found_proper_doctest && test_ignored {
+            errors.push(format!(
+                "`{}` has a compile_fail doctest with its own error code, it shouldn't \
+                be listed in `IGNORE_DOCTEST_CHECK`",
+                path.display(),
+            ));
+        }
+    });
+
+    no_longer_emitted_codes
+}
+
+/// This function returns a tuple indicating whether the provided explanation:
+/// a) has a code example, tested or not.
+/// b) has a valid doctest
+fn check_explanation_has_doctest(explanation: &str, err_code: &str) -> (bool, bool, bool, bool) {
+    let mut found_code_example = false;
+    let mut found_proper_doctest = false;
+
+    let mut emit_ignore_warning = false;
+    let mut no_longer_emitted = false;
+
+    for line in explanation.lines() {
+        let line = line.trim();
+
+        if line.starts_with("```") {
+            found_code_example = true;
+
+            // Check for the `rustdoc` doctest headers.
+            if line.contains("compile_fail") && line.contains(err_code) {
+                found_proper_doctest = true;
+            }
+
+            if line.contains("ignore") {
+                emit_ignore_warning = true;
+                found_proper_doctest = true;
+            }
+        } else if line
+            .starts_with("#### Note: this error code is no longer emitted by the compiler")
+        {
+            no_longer_emitted = true;
+            found_code_example = true;
+            found_proper_doctest = true;
+        }
+    }
+
+    (found_code_example, found_proper_doctest, emit_ignore_warning, no_longer_emitted)
+}
+
+// Stage 3: Checks that each error code has a UI test in the correct directory
+fn check_error_codes_tests(
+    root_path: &Path,
+    error_codes: &[String],
+    errors: &mut Vec<String>,
+    verbose: bool,
+    no_longer_emitted: &[String],
+) {
+    let tests_path = root_path.join(Path::new(ERROR_TESTS_PATH));
+
+    for code in error_codes {
+        let test_path = tests_path.join(format!("{}.stderr", code));
+
+        if !test_path.exists() && !IGNORE_UI_TEST_CHECK.contains(&code.as_str()) {
+            verbose_print!(
+                verbose,
+                "warning: Error code `{code}` needs to have at least one UI test in the `tests/error-codes/` directory`!"
+            );
+            continue;
+        }
+        if IGNORE_UI_TEST_CHECK.contains(&code.as_str()) {
+            if test_path.exists() {
+                errors.push(format!(
+                    "Error code `{code}` has a UI test in `tests/ui/error-codes/{code}.rs`, it shouldn't be listed in `EXEMPTED_FROM_TEST`!"
+                ));
+            }
+            continue;
+        }
+
+        let file = match fs::read_to_string(&test_path) {
+            Ok(file) => file,
+            Err(err) => {
+                verbose_print!(
+                    verbose,
+                    "warning: Failed to read UI test file (`{}`) for `{code}` but the file exists. The test is assumed to work:\n{err}",
+                    test_path.display()
+                );
+                continue;
+            }
+        };
+
+        if no_longer_emitted.contains(code) {
+            // UI tests *can't* contain error codes that are no longer emitted.
+            continue;
+        }
+
+        let mut found_code = false;
+
+        for line in file.lines() {
+            let s = line.trim();
+            // Assuming the line starts with `error[E`, we can substring the error code out.
+            if s.starts_with("error[E") {
+                if &s[6..11] == code {
+                    found_code = true;
+                    break;
+                }
+            };
+        }
+
+        if !found_code {
+            verbose_print!(
+                verbose,
+                "warning: Error code {code}`` has a UI test file, but doesn't contain its own error code!"
+            );
+        }
+    }
+}
+
+/// Stage 4: Search `compiler/` and ensure that every error code is actually used by the compiler and that no undocumented error codes exist.
+fn check_error_codes_used(
+    search_paths: &[&Path],
+    error_codes: &[String],
+    errors: &mut Vec<String>,
+    no_longer_emitted: &[String],
+    verbose: bool,
+) {
+    // We want error codes which match the following cases:
+    //
+    // * foo(a, E0111, a)
+    // * foo(a, E0111)
+    // * foo(E0111, a)
+    // * #[error = "E0111"]
+    let regex = Regex::new(r#"[(,"\s](E\d{4})[,)"]"#).unwrap();
+
+    let mut found_codes = Vec::new();
+
+    walk_many(search_paths, &mut filter_dirs, &mut |entry, contents| {
+        let path = entry.path();
+
+        // Return early if we aren't looking at a source file.
+        if path.extension() != Some(OsStr::new("rs")) {
+            return;
+        }
+
+        for line in contents.lines() {
+            // We want to avoid parsing error codes in comments.
+            if line.trim_start().starts_with("//") {
+                continue;
+            }
+
+            for cap in regex.captures_iter(line) {
+                if let Some(error_code) = cap.get(1) {
+                    let error_code = error_code.as_str().to_owned();
+
+                    if !error_codes.contains(&error_code) {
+                        // This error code isn't properly defined, we must error.
+                        errors.push(format!("Error code `{}` is used in the compiler but not defined and documented in `compiler/rustc_error_codes/src/error_codes.rs`.", error_code));
+                        continue;
+                    }
+
+                    // This error code can now be marked as used.
+                    found_codes.push(error_code);
+                }
+            }
+        }
+    });
+
+    for code in error_codes {
+        if !found_codes.contains(code) && !no_longer_emitted.contains(code) {
+            errors.push(format!("Error code `{code}` exists, but is not emitted by the compiler!"))
+        }
+
+        if found_codes.contains(code) && no_longer_emitted.contains(code) {
+            verbose_print!(
+                verbose,
+                "warning: Error code `{code}` is used when it's marked as \"no longer emitted\""
+            );
+        }
+    }
+}
diff --git a/src/tools/tidy/src/error_codes_check.rs b/src/tools/tidy/src/error_codes_check.rs
deleted file mode 100644
index 610e322e1..000000000
--- a/src/tools/tidy/src/error_codes_check.rs
+++ /dev/null
@@ -1,320 +0,0 @@
-//! Checks that all error codes have at least one test to prevent having error
-//! codes that are silently not thrown by the compiler anymore.
-
-use crate::walk::{filter_dirs, walk};
-use std::collections::{HashMap, HashSet};
-use std::ffi::OsStr;
-use std::fs::read_to_string;
-use std::path::Path;
-
-use regex::Regex;
-
-// A few of those error codes can't be tested but all the others can and *should* be tested!
-const EXEMPTED_FROM_TEST: &[&str] = &[
-    "E0313", "E0377", "E0461", "E0462", "E0465", "E0476", "E0490", "E0514", "E0519", "E0523",
-    "E0554", "E0640", "E0717", "E0729", "E0789",
-];
-
-// Some error codes don't have any tests apparently...
-const IGNORE_EXPLANATION_CHECK: &[&str] = &["E0464", "E0570", "E0601", "E0602", "E0729"];
-
-// If the file path contains any of these, we don't want to try to extract error codes from it.
-//
-// We need to declare each path in the windows version (with backslash).
-const PATHS_TO_IGNORE_FOR_EXTRACTION: &[&str] =
-    &["src/test/", "src\\test\\", "src/doc/", "src\\doc\\", "src/tools/", "src\\tools\\"];
-
-#[derive(Default, Debug)]
-struct ErrorCodeStatus {
-    has_test: bool,
-    has_explanation: bool,
-    is_used: bool,
-}
-
-fn check_error_code_explanation(
-    f: &str,
-    error_codes: &mut HashMap<String, ErrorCodeStatus>,
-    err_code: String,
-) -> bool {
-    let mut invalid_compile_fail_format = false;
-    let mut found_error_code = false;
-
-    for line in f.lines() {
-        let s = line.trim();
-        if s.starts_with("```") {
-            if s.contains("compile_fail") && s.contains('E') {
-                if !found_error_code {
-                    error_codes.get_mut(&err_code).map(|x| x.has_test = true);
-                    found_error_code = true;
-                }
-            } else if s.contains("compile-fail") {
-                invalid_compile_fail_format = true;
-            }
-        } else if s.starts_with("#### Note: this error code is no longer emitted by the compiler") {
-            if !found_error_code {
-                error_codes.get_mut(&err_code).map(|x| x.has_test = true);
-                found_error_code = true;
-            }
-        }
-    }
-    invalid_compile_fail_format
-}
-
-fn check_if_error_code_is_test_in_explanation(f: &str, err_code: &str) -> bool {
-    let mut ignore_found = false;
-
-    for line in f.lines() {
-        let s = line.trim();
-        if s.starts_with("#### Note: this error code is no longer emitted by the compiler") {
-            return true;
-        }
-        if s.starts_with("```") {
-            if s.contains("compile_fail") && s.contains(err_code) {
-                return true;
-            } else if s.contains("ignore") {
-                // It's very likely that we can't actually make it fail compilation...
-                ignore_found = true;
-            }
-        }
-    }
-    ignore_found
-}
-
-macro_rules! some_or_continue {
-    ($e:expr) => {
-        match $e {
-            Some(e) => e,
-            None => continue,
-        }
-    };
-}
-
-fn extract_error_codes(
-    f: &str,
-    error_codes: &mut HashMap<String, ErrorCodeStatus>,
-    path: &Path,
-    errors: &mut Vec<String>,
-) {
-    let mut reached_no_explanation = false;
-
-    for line in f.lines() {
-        let s = line.trim();
-        if !reached_no_explanation && s.starts_with('E') && s.contains("include_str!(\"") {
-            let err_code = s
-                .split_once(':')
-                .expect(
-                    format!(
-                        "Expected a line with the format `E0xxx: include_str!(\"..\")`, but got {} \
-                         without a `:` delimiter",
-                        s,
-                    )
-                    .as_str(),
-                )
-                .0
-                .to_owned();
-            error_codes.entry(err_code.clone()).or_default().has_explanation = true;
-
-            // Now we extract the tests from the markdown file!
-            let md_file_name = match s.split_once("include_str!(\"") {
-                None => continue,
-                Some((_, md)) => match md.split_once("\")") {
-                    None => continue,
-                    Some((file_name, _)) => file_name,
-                },
-            };
-            let path = some_or_continue!(path.parent())
-                .join(md_file_name)
-                .canonicalize()
-                .expect("failed to canonicalize error explanation file path");
-            match read_to_string(&path) {
-                Ok(content) => {
-                    let has_test = check_if_error_code_is_test_in_explanation(&content, &err_code);
-                    if !has_test && !IGNORE_EXPLANATION_CHECK.contains(&err_code.as_str()) {
-                        errors.push(format!(
-                            "`{}` doesn't use its own error code in compile_fail example",
-                            path.display(),
-                        ));
-                    } else if has_test && IGNORE_EXPLANATION_CHECK.contains(&err_code.as_str()) {
-                        errors.push(format!(
-                            "`{}` has a compile_fail example with its own error code, it shouldn't \
-                             be listed in IGNORE_EXPLANATION_CHECK!",
-                            path.display(),
-                        ));
-                    }
-                    if check_error_code_explanation(&content, error_codes, err_code) {
-                        errors.push(format!(
-                            "`{}` uses invalid tag `compile-fail` instead of `compile_fail`",
-                            path.display(),
-                        ));
-                    }
-                }
-                Err(e) => {
-                    eprintln!("Couldn't read `{}`: {}", path.display(), e);
-                }
-            }
-        } else if reached_no_explanation && s.starts_with('E') {
-            let err_code = match s.split_once(',') {
-                None => s,
-                Some((err_code, _)) => err_code,
-            }
-            .to_string();
-            if !error_codes.contains_key(&err_code) {
-                // this check should *never* fail!
-                error_codes.insert(err_code, ErrorCodeStatus::default());
-            }
-        } else if s == ";" {
-            reached_no_explanation = true;
-        }
-    }
-}
-
-fn extract_error_codes_from_tests(f: &str, error_codes: &mut HashMap<String, ErrorCodeStatus>) {
-    for line in f.lines() {
-        let s = line.trim();
-        if s.starts_with("error[E") || s.starts_with("warning[E") {
-            let err_code = match s.split_once(']') {
-                None => continue,
-                Some((err_code, _)) => match err_code.split_once('[') {
-                    None => continue,
-                    Some((_, err_code)) => err_code,
-                },
-            };
-            error_codes.entry(err_code.to_owned()).or_default().has_test = true;
-        }
-    }
-}
-
-fn extract_error_codes_from_source(
-    f: &str,
-    error_codes: &mut HashMap<String, ErrorCodeStatus>,
-    regex: &Regex,
-) {
-    for line in f.lines() {
-        if line.trim_start().starts_with("//") {
-            continue;
-        }
-        for cap in regex.captures_iter(line) {
-            if let Some(error_code) = cap.get(1) {
-                error_codes.entry(error_code.as_str().to_owned()).or_default().is_used = true;
-            }
-        }
-    }
-}
-
-pub fn check(paths: &[&Path], bad: &mut bool) {
-    let mut errors = Vec::new();
-    let mut found_explanations = 0;
-    let mut found_tests = 0;
-    let mut error_codes: HashMap<String, ErrorCodeStatus> = HashMap::new();
-    let mut explanations: HashSet<String> = HashSet::new();
-    // We want error codes which match the following cases:
-    //
-    // * foo(a, E0111, a)
-    // * foo(a, E0111)
-    // * foo(E0111, a)
-    // * #[error = "E0111"]
-    let regex = Regex::new(r#"[(,"\s](E\d{4})[,)"]"#).unwrap();
-
-    println!("Checking which error codes lack tests...");
-
-    for path in paths {
-        walk(path, &mut filter_dirs, &mut |entry, contents| {
-            let file_name = entry.file_name();
-            let entry_path = entry.path();
-
-            if file_name == "error_codes.rs" {
-                extract_error_codes(contents, &mut error_codes, entry.path(), &mut errors);
-                found_explanations += 1;
-            } else if entry_path.extension() == Some(OsStr::new("stderr")) {
-                extract_error_codes_from_tests(contents, &mut error_codes);
-                found_tests += 1;
-            } else if entry_path.extension() == Some(OsStr::new("rs")) {
-                let path = entry.path().to_string_lossy();
-                if PATHS_TO_IGNORE_FOR_EXTRACTION.iter().all(|c| !path.contains(c)) {
-                    extract_error_codes_from_source(contents, &mut error_codes, &regex);
-                }
-            } else if entry_path
-                .parent()
-                .and_then(|p| p.file_name())
-                .map(|p| p == "error_codes")
-                .unwrap_or(false)
-                && entry_path.extension() == Some(OsStr::new("md"))
-            {
-                explanations.insert(file_name.to_str().unwrap().replace(".md", ""));
-            }
-        });
-    }
-    if found_explanations == 0 {
-        eprintln!("No error code explanation was tested!");
-        *bad = true;
-    }
-    if found_tests == 0 {
-        eprintln!("No error code was found in compilation errors!");
-        *bad = true;
-    }
-    if explanations.is_empty() {
-        eprintln!("No error code explanation was found!");
-        *bad = true;
-    }
-    if errors.is_empty() {
-        println!("Found {} error codes", error_codes.len());
-
-        for (err_code, error_status) in &error_codes {
-            if !error_status.has_test && !EXEMPTED_FROM_TEST.contains(&err_code.as_str()) {
-                errors.push(format!("Error code {err_code} needs to have at least one UI test!"));
-            } else if error_status.has_test && EXEMPTED_FROM_TEST.contains(&err_code.as_str()) {
-                errors.push(format!(
-                    "Error code {} has a UI test, it shouldn't be listed into EXEMPTED_FROM_TEST!",
-                    err_code
-                ));
-            }
-            if !error_status.is_used && !error_status.has_explanation {
-                errors.push(format!(
-                    "Error code {} isn't used and doesn't have an error explanation, it should be \
-                     commented in error_codes.rs file",
-                    err_code
-                ));
-            }
-        }
-    }
-    if errors.is_empty() {
-        // Checking if local constants need to be cleaned.
-        for err_code in EXEMPTED_FROM_TEST {
-            match error_codes.get(err_code.to_owned()) {
-                Some(status) => {
-                    if status.has_test {
-                        errors.push(format!(
-                            "{} error code has a test and therefore should be \
-                            removed from the `EXEMPTED_FROM_TEST` constant",
-                            err_code
-                        ));
-                    }
-                }
-                None => errors.push(format!(
-                    "{} error code isn't used anymore and therefore should be removed \
-                        from `EXEMPTED_FROM_TEST` constant",
-                    err_code
-                )),
-            }
-        }
-    }
-    if errors.is_empty() {
-        for explanation in explanations {
-            if !error_codes.contains_key(&explanation) {
-                errors.push(format!(
-                    "{} error code explanation should be listed in `error_codes.rs`",
-                    explanation
-                ));
-            }
-        }
-    }
-    errors.sort();
-    for err in &errors {
-        eprintln!("{err}");
-    }
-    println!("Found {} error(s) in error codes", errors.len());
-    if !errors.is_empty() {
-        *bad = true;
-    }
-    println!("Done!");
-}
diff --git a/src/tools/tidy/src/errors.rs b/src/tools/tidy/src/errors.rs
deleted file mode 100644
index fe5fd72b9..000000000
--- a/src/tools/tidy/src/errors.rs
+++ /dev/null
@@ -1,77 +0,0 @@
-//! Tidy check to verify the validity of long error diagnostic codes.
-//!
-//! This ensures that error codes are used at most once and also prints out some
-//! statistics about the error codes.
-
-use crate::walk::{filter_dirs, walk};
-use std::collections::HashMap;
-use std::path::Path;
-
-pub fn check(path: &Path, bad: &mut bool) {
-    let mut map: HashMap<_, Vec<_>> = HashMap::new();
-    walk(
-        path,
-        &mut |path| filter_dirs(path) || path.ends_with("src/test"),
-        &mut |entry, contents| {
-            let file = entry.path();
-            let filename = file.file_name().unwrap().to_string_lossy();
-            if filename != "error_codes.rs" {
-                return;
-            }
-
-            // In the `register_long_diagnostics!` macro, entries look like this:
-            //
-            // ```
-            // EXXXX: r##"
-            // <Long diagnostic message>
-            // "##,
-            // ```
-            //
-            // and these long messages often have error codes themselves inside
-            // them, but we don't want to report duplicates in these cases. This
-            // variable keeps track of whether we're currently inside one of these
-            // long diagnostic messages.
-            let mut inside_long_diag = false;
-            for (num, line) in contents.lines().enumerate() {
-                if inside_long_diag {
-                    inside_long_diag = !line.contains("\"##");
-                    continue;
-                }
-
-                let mut search = line;
-                while let Some(i) = search.find('E') {
-                    search = &search[i + 1..];
-                    let code = if search.len() > 4 { search[..4].parse::<u32>() } else { continue };
-                    let code = match code {
-                        Ok(n) => n,
-                        Err(..) => continue,
-                    };
-                    map.entry(code).or_default().push((file.to_owned(), num + 1, line.to_owned()));
-                    break;
-                }
-
-                inside_long_diag = line.contains("r##\"");
-            }
-        },
-    );
-
-    let mut max = 0;
-    for (&code, entries) in map.iter() {
-        if code > max {
-            max = code;
-        }
-        if entries.len() == 1 {
-            continue;
-        }
-
-        tidy_error!(bad, "duplicate error code: {}", code);
-        for &(ref file, line_num, ref line) in entries.iter() {
-            tidy_error!(bad, "{}:{}: {}", file.display(), line_num, line);
-        }
-    }
-
-    if !*bad {
-        println!("* {} error codes", map.len());
-        println!("* highest error code: E{:04}", max);
-    }
-}
diff --git a/src/tools/tidy/src/features.rs b/src/tools/tidy/src/features.rs
index f10ecf5f2..af92e6eb8 100644
--- a/src/tools/tidy/src/features.rs
+++ b/src/tools/tidy/src/features.rs
@@ -82,6 +82,7 @@ pub fn collect_lib_features(base_src_path: &Path) -> Features {
 
 pub fn check(
     src_path: &Path,
+    tests_path: &Path,
     compiler_path: &Path,
     lib_path: &Path,
     bad: &mut bool,
@@ -95,10 +96,10 @@ pub fn check(
 
     walk_many(
         &[
-            &src_path.join("test/ui"),
-            &src_path.join("test/ui-fulldeps"),
-            &src_path.join("test/rustdoc-ui"),
-            &src_path.join("test/rustdoc"),
+            &tests_path.join("ui"),
+            &tests_path.join("ui-fulldeps"),
+            &tests_path.join("rustdoc-ui"),
+            &tests_path.join("rustdoc"),
         ],
         &mut filter_dirs,
         &mut |entry, contents| {
@@ -480,7 +481,7 @@ fn map_lib_features(
 ) {
     walk(
         base_src_path,
-        &mut |path| filter_dirs(path) || path.ends_with("src/test"),
+        &mut |path| filter_dirs(path) || path.ends_with("tests"),
         &mut |entry, contents| {
             let file = entry.path();
             let filename = file.file_name().unwrap().to_string_lossy();
diff --git a/src/tools/tidy/src/features/version/tests.rs b/src/tools/tidy/src/features/version/tests.rs
index 31224fdf1..7701dce2d 100644
--- a/src/tools/tidy/src/features/version/tests.rs
+++ b/src/tools/tidy/src/features/version/tests.rs
@@ -12,8 +12,8 @@ fn test_try_from_invalid_version() {
 
 #[test]
 fn test_try_from_single() {
-    assert_eq!("1.32.0".parse(), Ok(Version { parts: [1, 32, 0] }));
-    assert_eq!("1.0.0".parse(), Ok(Version { parts: [1, 0, 0] }));
+    assert_eq!("1.32.0".parse(), Ok(Version::Explicit { parts: [1, 32, 0] }));
+    assert_eq!("1.0.0".parse(), Ok(Version::Explicit { parts: [1, 0, 0] }));
 }
 
 #[test]
diff --git a/src/tools/tidy/src/lib.rs b/src/tools/tidy/src/lib.rs
index 698e4850b..35000320d 100644
--- a/src/tools/tidy/src/lib.rs
+++ b/src/tools/tidy/src/lib.rs
@@ -3,6 +3,10 @@
 //! This library contains the tidy lints and exposes it
 //! to be used by tools.
 
+use std::fmt::Display;
+
+use termcolor::WriteColor;
+
 /// A helper macro to `unwrap` a result except also print out details like:
 ///
 /// * The expression that failed
@@ -26,33 +30,44 @@ macro_rules! t {
 }
 
 macro_rules! tidy_error {
-    ($bad:expr, $fmt:expr) => ({
-        *$bad = true;
-        eprint!("tidy error: ");
-        eprintln!($fmt);
-    });
-    ($bad:expr, $fmt:expr, $($arg:tt)*) => ({
-        *$bad = true;
-        eprint!("tidy error: ");
-        eprintln!($fmt, $($arg)*);
+    ($bad:expr, $($fmt:tt)*) => ({
+        $crate::tidy_error($bad, format_args!($($fmt)*)).expect("failed to output error");
     });
 }
 
+fn tidy_error(bad: &mut bool, args: impl Display) -> std::io::Result<()> {
+    use std::io::Write;
+    use termcolor::{Color, ColorChoice, ColorSpec, StandardStream};
+
+    *bad = true;
+
+    let mut stderr = StandardStream::stdout(ColorChoice::Auto);
+    stderr.set_color(ColorSpec::new().set_fg(Some(Color::Red)))?;
+
+    write!(&mut stderr, "tidy error")?;
+    stderr.set_color(&ColorSpec::new())?;
+
+    writeln!(&mut stderr, ": {args}")?;
+    Ok(())
+}
+
 pub mod alphabetical;
 pub mod bins;
 pub mod debug_artifacts;
 pub mod deps;
 pub mod edition;
-pub mod error_codes_check;
-pub mod errors;
+pub mod error_codes;
 pub mod extdeps;
 pub mod features;
 pub mod mir_opt_tests;
 pub mod pal;
 pub mod primitive_docs;
+pub mod rustdoc_gui_tests;
 pub mod style;
 pub mod target_specific_tests;
+pub mod tests_placement;
 pub mod ui_tests;
 pub mod unit_tests;
 pub mod unstable_book;
 pub mod walk;
+pub mod x_version;
diff --git a/src/tools/tidy/src/main.rs b/src/tools/tidy/src/main.rs
index b0b11cafc..505f9d724 100644
--- a/src/tools/tidy/src/main.rs
+++ b/src/tools/tidy/src/main.rs
@@ -25,8 +25,10 @@ fn main() {
             .expect("concurrency must be a number");
 
     let src_path = root_path.join("src");
+    let tests_path = root_path.join("tests");
     let library_path = root_path.join("library");
     let compiler_path = root_path.join("compiler");
+    let librustdoc_path = src_path.join("librustdoc");
 
     let args: Vec<String> = env::args().skip(1).collect();
 
@@ -35,19 +37,30 @@ fn main() {
 
     let bad = std::sync::Arc::new(AtomicBool::new(false));
 
+    let drain_handles = |handles: &mut VecDeque<ScopedJoinHandle<'_, ()>>| {
+        // poll all threads for completion before awaiting the oldest one
+        for i in (0..handles.len()).rev() {
+            if handles[i].is_finished() {
+                handles.swap_remove_back(i).unwrap().join().unwrap();
+            }
+        }
+
+        while handles.len() >= concurrency.get() {
+            handles.pop_front().unwrap().join().unwrap();
+        }
+    };
+
     scope(|s| {
         let mut handles: VecDeque<ScopedJoinHandle<'_, ()>> =
             VecDeque::with_capacity(concurrency.get());
 
         macro_rules! check {
             ($p:ident $(, $args:expr)* ) => {
-                while handles.len() >= concurrency.get() {
-                    handles.pop_front().unwrap().join().unwrap();
-                }
+                drain_handles(&mut handles);
 
                 let handle = s.spawn(|| {
                     let mut flag = false;
-                    $p::check($($args),* , &mut flag);
+                    $p::check($($args, )* &mut flag);
                     if (flag) {
                         bad.store(true, Ordering::Relaxed);
                     }
@@ -56,20 +69,21 @@ fn main() {
             }
         }
 
-        check!(target_specific_tests, &src_path);
+        check!(target_specific_tests, &tests_path);
 
         // Checks that are done on the cargo workspace.
         check!(deps, &root_path, &cargo);
         check!(extdeps, &root_path);
 
         // Checks over tests.
-        check!(debug_artifacts, &src_path);
-        check!(ui_tests, &src_path);
-        check!(mir_opt_tests, &src_path, bless);
+        check!(tests_placement, &root_path);
+        check!(debug_artifacts, &tests_path);
+        check!(ui_tests, &tests_path);
+        check!(mir_opt_tests, &tests_path, bless);
+        check!(rustdoc_gui_tests, &tests_path);
 
         // Checks that only make sense for the compiler.
-        check!(errors, &compiler_path);
-        check!(error_codes_check, &[&src_path, &compiler_path]);
+        check!(error_codes, &root_path, &[&compiler_path, &librustdoc_path], verbose);
 
         // Checks that only make sense for the std libs.
         check!(pal, &library_path);
@@ -77,6 +91,7 @@ fn main() {
 
         // Checks that need to be done for both the compiler and std libraries.
         check!(unit_tests, &src_path);
+        check!(unit_tests, &tests_path);
         check!(unit_tests, &compiler_path);
         check!(unit_tests, &library_path);
 
@@ -85,23 +100,34 @@ fn main() {
         }
 
         check!(style, &src_path);
+        check!(style, &tests_path);
         check!(style, &compiler_path);
         check!(style, &library_path);
 
         check!(edition, &src_path);
         check!(edition, &compiler_path);
         check!(edition, &library_path);
+        check!(edition, &tests_path);
 
         check!(alphabetical, &src_path);
+        check!(alphabetical, &tests_path);
         check!(alphabetical, &compiler_path);
         check!(alphabetical, &library_path);
 
+        check!(x_version, &root_path, &cargo);
+
         let collected = {
-            while handles.len() >= concurrency.get() {
-                handles.pop_front().unwrap().join().unwrap();
-            }
+            drain_handles(&mut handles);
+
             let mut flag = false;
-            let r = features::check(&src_path, &compiler_path, &library_path, &mut flag, verbose);
+            let r = features::check(
+                &src_path,
+                &tests_path,
+                &compiler_path,
+                &library_path,
+                &mut flag,
+                verbose,
+            );
             if flag {
                 bad.store(true, Ordering::Relaxed);
             }
diff --git a/src/tools/tidy/src/mir_opt_tests.rs b/src/tools/tidy/src/mir_opt_tests.rs
index 018573284..2a9dcac2e 100644
--- a/src/tools/tidy/src/mir_opt_tests.rs
+++ b/src/tools/tidy/src/mir_opt_tests.rs
@@ -6,7 +6,7 @@ use std::path::{Path, PathBuf};
 fn check_unused_files(path: &Path, bless: bool, bad: &mut bool) {
     let mut rs_files = Vec::<PathBuf>::new();
     let mut output_files = HashSet::<PathBuf>::new();
-    let files = walkdir::WalkDir::new(&path.join("test/mir-opt")).into_iter();
+    let files = walkdir::WalkDir::new(&path.join("mir-opt")).into_iter();
 
     for file in files.filter_map(Result::ok).filter(|e| e.file_type().is_file()) {
         let filepath = file.path();
@@ -41,7 +41,7 @@ fn check_unused_files(path: &Path, bless: bool, bad: &mut bool) {
 }
 
 fn check_dash_files(path: &Path, bless: bool, bad: &mut bool) {
-    for file in walkdir::WalkDir::new(&path.join("test/mir-opt"))
+    for file in walkdir::WalkDir::new(&path.join("mir-opt"))
         .into_iter()
         .filter_map(Result::ok)
         .filter(|e| e.file_type().is_file())
diff --git a/src/tools/tidy/src/rustdoc_gui_tests.rs b/src/tools/tidy/src/rustdoc_gui_tests.rs
new file mode 100644
index 000000000..feb513df3
--- /dev/null
+++ b/src/tools/tidy/src/rustdoc_gui_tests.rs
@@ -0,0 +1,33 @@
+//! Tidy check to ensure that rustdoc GUI tests start with a small description.
+
+use std::path::Path;
+
+pub fn check(path: &Path, bad: &mut bool) {
+    crate::walk::walk(
+        &path.join("rustdoc-gui"),
+        &mut |p| {
+            // If there is no extension, it's very likely a folder and we want to go into it.
+            p.extension().map(|e| e != "goml").unwrap_or(false)
+        },
+        &mut |entry, content| {
+            for line in content.lines() {
+                if !line.starts_with("// ") {
+                    tidy_error!(
+                        bad,
+                        "{}: rustdoc-gui tests must start with a small description",
+                        entry.path().display(),
+                    );
+                    return;
+                } else if line.starts_with("// ") {
+                    let parts = line[2..].trim();
+                    // We ignore tidy comments.
+                    if parts.starts_with("// tidy-") {
+                        continue;
+                    }
+                    // All good!
+                    return;
+                }
+            }
+        },
+    );
+}
diff --git a/src/tools/tidy/src/style.rs b/src/tools/tidy/src/style.rs
index e3a094caf..6a0855405 100644
--- a/src/tools/tidy/src/style.rs
+++ b/src/tools/tidy/src/style.rs
@@ -15,15 +15,17 @@
 //!
 //! A number of these checks can be opted-out of with various directives of the form:
 //! `// ignore-tidy-CHECK-NAME`.
+// ignore-tidy-dbg
 
 use crate::walk::{filter_dirs, walk};
-use regex::Regex;
+use regex::{Regex, RegexSet};
 use std::path::Path;
 
 /// Error code markdown is restricted to 80 columns because they can be
 /// displayed on the console with --example.
 const ERROR_CODE_COLS: usize = 80;
 const COLS: usize = 100;
+const GOML_COLS: usize = 120;
 
 const LINES: usize = 3000;
 
@@ -43,6 +45,9 @@ C++ code used llvm_unreachable, which triggers undefined behavior
 when executed when assertions are disabled.
 Use llvm::report_fatal_error for increased robustness.";
 
+const DOUBLE_SPACE_AFTER_DOT: &str = r"\
+Use a single space after dots in comments.";
+
 const ANNOTATIONS_TO_IGNORE: &[&str] = &[
     "// @!has",
     "// @has",
@@ -63,6 +68,8 @@ const PROBLEMATIC_CONSTS: &[u32] = &[
     3735927486, 3735932941, 4027431614, 4276992702,
 ];
 
+const INTERNAL_COMPILER_DOCS_LINE: &str = "#### This error code is internal to the compiler and will not be emitted with normal Rust code.";
+
 /// Parser states for `line_is_url`.
 #[derive(Clone, Copy, PartialEq)]
 #[allow(non_camel_case_types)]
@@ -131,6 +138,8 @@ fn long_line_is_ok(extension: &str, is_error_code: bool, max_columns: usize, lin
         "ftl" => true,
         // non-error code markdown is allowed to be any length
         "md" if !is_error_code => true,
+        // HACK(Ezrashaw): there is no way to split a markdown header over multiple lines
+        "md" if line == INTERNAL_COMPILER_DOCS_LINE => true,
         _ => line_is_url(is_error_code, max_columns, line) || should_ignore(line),
     }
 }
@@ -225,10 +234,12 @@ pub fn check(path: &Path, bad: &mut bool) {
         .chain(PROBLEMATIC_CONSTS.iter().map(|v| format!("{:x}", v)))
         .chain(PROBLEMATIC_CONSTS.iter().map(|v| format!("{:X}", v)))
         .collect();
+    let problematic_regex = RegexSet::new(problematic_consts_strings.as_slice()).unwrap();
     walk(path, &mut skip, &mut |entry, contents| {
         let file = entry.path();
         let filename = file.file_name().unwrap().to_string_lossy();
-        let extensions = [".rs", ".py", ".js", ".sh", ".c", ".cpp", ".h", ".md", ".css", ".ftl"];
+        let extensions =
+            [".rs", ".py", ".js", ".sh", ".c", ".cpp", ".h", ".md", ".css", ".ftl", ".goml"];
         if extensions.iter().all(|e| !filename.ends_with(e)) || filename.starts_with(".#") {
             return;
         }
@@ -238,7 +249,7 @@ pub fn check(path: &Path, bad: &mut bool) {
             // This list should ideally be sourced from rustfmt.toml but we don't want to add a toml
             // parser to tidy.
             !file.ancestors().any(|a| {
-                a.ends_with("src/test") ||
+                (a.ends_with("tests") && a.join("COMPILER_TESTS.md").exists()) ||
                     a.ends_with("src/doc/book")
             });
 
@@ -253,8 +264,15 @@ pub fn check(path: &Path, bad: &mut bool) {
 
         let extension = file.extension().unwrap().to_string_lossy();
         let is_error_code = extension == "md" && is_in(file, "src", "error_codes");
+        let is_goml_code = extension == "goml";
 
-        let max_columns = if is_error_code { ERROR_CODE_COLS } else { COLS };
+        let max_columns = if is_error_code {
+            ERROR_CODE_COLS
+        } else if is_goml_code {
+            GOML_COLS
+        } else {
+            COLS
+        };
 
         let can_contain = contents.contains("// ignore-tidy-")
             || contents.contains("# ignore-tidy-")
@@ -264,6 +282,10 @@ pub fn check(path: &Path, bad: &mut bool) {
         if filename.contains("ignore-tidy") {
             return;
         }
+        // apfloat shouldn't be changed because of license problems
+        if is_in(file, "compiler", "rustc_apfloat") {
+            return;
+        }
         let mut skip_cr = contains_ignore_directive(can_contain, &contents, "cr");
         let mut skip_undocumented_unsafe =
             contains_ignore_directive(can_contain, &contents, "undocumented-unsafe");
@@ -277,14 +299,51 @@ pub fn check(path: &Path, bad: &mut bool) {
         let mut skip_leading_newlines =
             contains_ignore_directive(can_contain, &contents, "leading-newlines");
         let mut skip_copyright = contains_ignore_directive(can_contain, &contents, "copyright");
+        let mut skip_dbg = contains_ignore_directive(can_contain, &contents, "dbg");
         let mut leading_new_lines = false;
         let mut trailing_new_lines = 0;
         let mut lines = 0;
         let mut last_safety_comment = false;
+        let is_test = file.components().any(|c| c.as_os_str() == "tests");
+        // scanning the whole file for multiple needles at once is more efficient than
+        // executing lines times needles separate searches.
+        let any_problematic_line = problematic_regex.is_match(contents);
         for (i, line) in contents.split('\n').enumerate() {
+            if line.is_empty() {
+                if i == 0 {
+                    leading_new_lines = true;
+                }
+                trailing_new_lines += 1;
+                continue;
+            } else {
+                trailing_new_lines = 0;
+            }
+
+            let trimmed = line.trim();
+
+            if !trimmed.starts_with("//") {
+                lines += 1;
+            }
+
             let mut err = |msg: &str| {
                 tidy_error!(bad, "{}:{}: {}", file.display(), i + 1, msg);
             };
+
+            if trimmed.contains("dbg!")
+                && !trimmed.starts_with("//")
+                && !file.ancestors().any(|a| {
+                    (a.ends_with("tests") && a.join("COMPILER_TESTS.md").exists())
+                        || a.ends_with("library/alloc/tests")
+                })
+                && filename != "tests.rs"
+            {
+                suppressible_tidy_err!(
+                    err,
+                    skip_dbg,
+                    "`dbg!` macro is intended as a debugging tool. It should not be in version control."
+                )
+            }
+
             if !under_rustfmt
                 && line.chars().count() > max_columns
                 && !long_line_is_ok(&extension, is_error_code, max_columns, line)
@@ -308,28 +367,29 @@ pub fn check(path: &Path, bad: &mut bool) {
                 suppressible_tidy_err!(err, skip_cr, "CR character");
             }
             if filename != "style.rs" {
-                if line.contains("TODO") {
+                if trimmed.contains("TODO") {
                     err("TODO is deprecated; use FIXME")
                 }
-                if line.contains("//") && line.contains(" XXX") {
+                if trimmed.contains("//") && trimmed.contains(" XXX") {
                     err("XXX is deprecated; use FIXME")
                 }
-                for s in problematic_consts_strings.iter() {
-                    if line.contains(s) {
-                        err("Don't use magic numbers that spell things (consider 0x12345678)");
+                if any_problematic_line {
+                    for s in problematic_consts_strings.iter() {
+                        if trimmed.contains(s) {
+                            err("Don't use magic numbers that spell things (consider 0x12345678)");
+                        }
                     }
                 }
             }
-            let is_test = || file.components().any(|c| c.as_os_str() == "tests");
             // for now we just check libcore
-            if line.contains("unsafe {") && !line.trim().starts_with("//") && !last_safety_comment {
-                if file.components().any(|c| c.as_os_str() == "core") && !is_test() {
+            if trimmed.contains("unsafe {") && !trimmed.starts_with("//") && !last_safety_comment {
+                if file.components().any(|c| c.as_os_str() == "core") && !is_test {
                     suppressible_tidy_err!(err, skip_undocumented_unsafe, "undocumented unsafe");
                 }
             }
-            if line.contains("// SAFETY:") {
+            if trimmed.contains("// SAFETY:") {
                 last_safety_comment = true;
-            } else if line.trim().starts_with("//") || line.trim().is_empty() {
+            } else if trimmed.starts_with("//") || trimmed.is_empty() {
                 // keep previous value
             } else {
                 last_safety_comment = false;
@@ -337,7 +397,8 @@ pub fn check(path: &Path, bad: &mut bool) {
             if (line.starts_with("// Copyright")
                 || line.starts_with("# Copyright")
                 || line.starts_with("Copyright"))
-                && (line.contains("Rust Developers") || line.contains("Rust Project Developers"))
+                && (trimmed.contains("Rust Developers")
+                    || trimmed.contains("Rust Project Developers"))
             {
                 suppressible_tidy_err!(
                     err,
@@ -351,17 +412,18 @@ pub fn check(path: &Path, bad: &mut bool) {
             if filename.ends_with(".cpp") && line.contains("llvm_unreachable") {
                 err(LLVM_UNREACHABLE_INFO);
             }
-            if line.is_empty() {
-                if i == 0 {
-                    leading_new_lines = true;
-                }
-                trailing_new_lines += 1;
-            } else {
-                trailing_new_lines = 0;
-            }
 
-            if !line.trim().starts_with("//") {
-                lines += 1;
+            // For now only enforce in compiler
+            let is_compiler = || file.components().any(|c| c.as_os_str() == "compiler");
+            if is_compiler()
+                && line.contains("//")
+                && line
+                    .chars()
+                    .collect::<Vec<_>>()
+                    .windows(4)
+                    .any(|cs| matches!(cs, ['.', ' ', ' ', last] if last.is_alphabetic()))
+            {
+                err(DOUBLE_SPACE_AFTER_DOT)
             }
         }
         if leading_new_lines {
diff --git a/src/tools/tidy/src/target_specific_tests.rs b/src/tools/tidy/src/target_specific_tests.rs
index 8ba257056..d7a157672 100644
--- a/src/tools/tidy/src/target_specific_tests.rs
+++ b/src/tools/tidy/src/target_specific_tests.rs
@@ -35,9 +35,8 @@ struct RevisionInfo<'a> {
 }
 
 pub fn check(path: &Path, bad: &mut bool) {
-    let tests = path.join("test");
     crate::walk::walk(
-        &tests,
+        path,
         &mut |path| path.extension().map(|p| p == "rs") == Some(false),
         &mut |entry, content| {
             let file = entry.path().display();
diff --git a/src/tools/tidy/src/tests_placement.rs b/src/tools/tidy/src/tests_placement.rs
new file mode 100644
index 000000000..9d0057df8
--- /dev/null
+++ b/src/tools/tidy/src/tests_placement.rs
@@ -0,0 +1,15 @@
+use std::path::Path;
+
+const FORBIDDEN_PATH: &str = "src/test";
+const ALLOWED_PATH: &str = "tests";
+
+pub fn check(root_path: impl AsRef<Path>, bad: &mut bool) {
+    if root_path.as_ref().join(FORBIDDEN_PATH).exists() {
+        tidy_error!(
+            bad,
+            "Tests have been moved, please move them from {} to {}",
+            root_path.as_ref().join(FORBIDDEN_PATH).display(),
+            root_path.as_ref().join(ALLOWED_PATH).display()
+        )
+    }
+}
diff --git a/src/tools/tidy/src/ui_tests.rs b/src/tools/tidy/src/ui_tests.rs
index ee326e190..806e84025 100644
--- a/src/tools/tidy/src/ui_tests.rs
+++ b/src/tools/tidy/src/ui_tests.rs
@@ -10,16 +10,16 @@ use std::path::Path;
 const ENTRY_LIMIT: usize = 1000;
 // FIXME: The following limits should be reduced eventually.
 const ROOT_ENTRY_LIMIT: usize = 939;
-const ISSUES_ENTRY_LIMIT: usize = 2070;
+const ISSUES_ENTRY_LIMIT: usize = 1998;
 
 fn check_entries(path: &Path, bad: &mut bool) {
-    for dir in Walk::new(&path.join("test/ui")) {
+    for dir in Walk::new(&path.join("ui")) {
         if let Ok(entry) = dir {
             if entry.file_type().map(|ft| ft.is_dir()).unwrap_or(false) {
                 let dir_path = entry.path();
                 // Use special values for these dirs.
-                let is_root = path.join("test/ui") == dir_path;
-                let is_issues_dir = path.join("test/ui/issues") == dir_path;
+                let is_root = path.join("ui") == dir_path;
+                let is_issues_dir = path.join("ui/issues") == dir_path;
                 let limit = if is_root {
                     ROOT_ENTRY_LIMIT
                 } else if is_issues_dir {
@@ -53,7 +53,7 @@ fn check_entries(path: &Path, bad: &mut bool) {
 
 pub fn check(path: &Path, bad: &mut bool) {
     check_entries(&path, bad);
-    for path in &[&path.join("test/ui"), &path.join("test/ui-fulldeps")] {
+    for path in &[&path.join("ui"), &path.join("ui-fulldeps")] {
         crate::walk::walk_no_read(path, &mut |_| false, &mut |entry| {
             let file_path = entry.path();
             if let Some(ext) = file_path.extension() {
diff --git a/src/tools/tidy/src/unit_tests.rs b/src/tools/tidy/src/unit_tests.rs
index 2c23b6ebc..27f36c855 100644
--- a/src/tools/tidy/src/unit_tests.rs
+++ b/src/tools/tidy/src/unit_tests.rs
@@ -22,7 +22,7 @@ pub fn check(root_path: &Path, bad: &mut bool) {
         let file_name = path.file_name().unwrap_or_default();
         if path.is_dir() {
             filter_dirs(path)
-                || path.ends_with("src/test")
+                || path.ends_with("tests")
                 || path.ends_with("src/doc")
                 || (file_name == "tests" || file_name == "benches") && !is_core(path)
         } else {
diff --git a/src/tools/tidy/src/x_version.rs b/src/tools/tidy/src/x_version.rs
new file mode 100644
index 000000000..c470d502a
--- /dev/null
+++ b/src/tools/tidy/src/x_version.rs
@@ -0,0 +1,68 @@
+use semver::Version;
+use std::path::Path;
+use std::process::{Command, Stdio};
+
+pub fn check(root: &Path, cargo: &Path, bad: &mut bool) {
+    let cargo_list = Command::new(cargo).args(["install", "--list"]).stdout(Stdio::piped()).spawn();
+
+    let child = match cargo_list {
+        Ok(child) => child,
+        Err(e) => return tidy_error!(bad, "failed to run `cargo`: {}", e),
+    };
+
+    let cargo_list = child.wait_with_output().unwrap();
+
+    if cargo_list.status.success() {
+        let exe_list = String::from_utf8_lossy(&cargo_list.stdout);
+        let exe_list = exe_list.lines();
+
+        let mut installed: Option<Version> = None;
+
+        for line in exe_list {
+            let mut iter = line.split_whitespace();
+            if iter.next() == Some("x") {
+                if let Some(version) = iter.next() {
+                    // Check this is the rust-lang/rust x tool installation since it should be
+                    // installed at a path containing `src/tools/x`.
+                    if let Some(path) = iter.next() {
+                        if path.contains(&"src/tools/x") {
+                            let version = version.strip_prefix("v").unwrap();
+                            installed = Some(Version::parse(version).unwrap());
+                            break;
+                        }
+                    };
+                }
+            } else {
+                continue;
+            }
+        }
+        // Unwrap the some if x is installed, otherwise return because it's fine if x isn't installed.
+        let installed = if let Some(i) = installed { i } else { return };
+
+        if let Some(expected) = get_x_wrapper_version(root, cargo) {
+            if installed < expected {
+                return println!(
+                    "Current version of x is {installed}, but the latest version is {expected}\nConsider updating to the newer version of x by running `cargo install --path src/tools/x`"
+                );
+            }
+        } else {
+            return tidy_error!(
+                bad,
+                "Unable to parse the latest version of `x` at `src/tools/x/Cargo.toml`"
+            );
+        }
+    } else {
+        return tidy_error!(bad, "failed to check version of `x`: {}", cargo_list.status);
+    }
+}
+
+// Parse latest version out of `x` Cargo.toml
+fn get_x_wrapper_version(root: &Path, cargo: &Path) -> Option<Version> {
+    let mut cmd = cargo_metadata::MetadataCommand::new();
+    cmd.cargo_path(cargo)
+        .manifest_path(root.join("src/tools/x/Cargo.toml"))
+        .no_deps()
+        .features(cargo_metadata::CargoOpt::AllFeatures);
+    let mut metadata = t!(cmd.exec());
+    metadata.packages.pop().map(|x| x.version)
+}