diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index fe6dff7ff1b63..959cf9fa51399 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -3376,10 +3376,15 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
         let (sugg_span, suggestion) = match tcx.sess.source_map().span_to_snippet(args_span) {
             Ok(string) => {
-                let coro_prefix = if string.starts_with("async") {
-                    // `async` is 5 chars long. Not using `.len()` to avoid the cast from `usize`
-                    // to `u32`.
-                    Some(5)
+                let coro_prefix = if let Some(sub) = string.strip_prefix("async") {
+                    let trimmed_sub = sub.trim_end();
+                    if trimmed_sub.ends_with("gen") {
+                        // `async` is 5 chars long.
+                        Some((trimmed_sub.len() + 5) as _)
+                    } else {
+                        // `async` is 5 chars long.
+                        Some(5)
+                    }
                 } else if string.starts_with("gen") {
                     // `gen` is 3 chars long
                     Some(3)
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
index 72f219bfeb802..3759a224ff75b 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
@@ -204,8 +204,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             .iter()
             .flat_map(|trait_def_id| tcx.associated_items(*trait_def_id).in_definition_order())
             .filter_map(|item| {
-                (!item.is_impl_trait_in_trait() && item.as_tag() == assoc_tag)
-                    .then_some(item.name())
+                (!item.is_impl_trait_in_trait() && item.as_tag() == assoc_tag).then(|| item.name())
             })
             .collect();
 
diff --git a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
index 448fad2dc3ece..c436b8c0fb019 100644
--- a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
@@ -122,7 +122,7 @@ impl RustcMirAttrs {
                 })
             } else if attr.has_name(sym::borrowck_graphviz_format) {
                 Self::set_field(&mut ret.formatter, tcx, &attr, |s| match s {
-                    sym::gen_kill | sym::two_phase => Ok(s),
+                    sym::two_phase => Ok(s),
                     _ => {
                         tcx.dcx().emit_err(UnknownFormatter { span: attr.span() });
                         Err(())
diff --git a/compiler/rustc_session/src/code_stats.rs b/compiler/rustc_session/src/code_stats.rs
index b4597ae2515d4..6b18d450e9e5e 100644
--- a/compiler/rustc_session/src/code_stats.rs
+++ b/compiler/rustc_session/src/code_stats.rs
@@ -72,7 +72,7 @@ pub struct TypeSizeInfo {
 
 #[derive(Default)]
 pub struct CodeStats {
-    type_sizes: Lock<FxHashSet<TypeSizeInfo>>,
+    pub type_sizes: Lock<FxHashSet<TypeSizeInfo>>,
 }
 
 impl CodeStats {
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index fc05470d941c4..202378560eed7 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -14,6 +14,7 @@ use std::str::{self, FromStr};
 use std::sync::LazyLock;
 use std::{cmp, fmt, fs, iter};
 
+use externs::{ExternOpt, split_extern_opt};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::stable_hasher::{StableOrd, ToStableHashKey};
 use rustc_errors::emitter::HumanReadableErrorType;
@@ -39,6 +40,7 @@ use crate::utils::CanonicalizedPath;
 use crate::{EarlyDiagCtxt, HashStableContext, Session, filesearch, lint};
 
 mod cfg;
+mod externs;
 mod native_libs;
 pub mod sigpipe;
 
@@ -2205,44 +2207,13 @@ pub fn parse_externs(
     matches: &getopts::Matches,
     unstable_opts: &UnstableOptions,
 ) -> Externs {
-    fn is_ascii_ident(string: &str) -> bool {
-        let mut chars = string.chars();
-        if let Some(start) = chars.next()
-            && (start.is_ascii_alphabetic() || start == '_')
-        {
-            chars.all(|char| char.is_ascii_alphanumeric() || char == '_')
-        } else {
-            false
-        }
-    }
-
     let is_unstable_enabled = unstable_opts.unstable_options;
     let mut externs: BTreeMap<String, ExternEntry> = BTreeMap::new();
     for arg in matches.opt_strs("extern") {
-        let (name, path) = match arg.split_once('=') {
-            None => (arg, None),
-            Some((name, path)) => (name.to_string(), Some(Path::new(path))),
-        };
-        let (options, name) = match name.split_once(':') {
-            None => (None, name),
-            Some((opts, name)) => (Some(opts), name.to_string()),
-        };
-
-        if !is_ascii_ident(&name) {
-            let mut error = early_dcx.early_struct_fatal(format!(
-                "crate name `{name}` passed to `--extern` is not a valid ASCII identifier"
-            ));
-            let adjusted_name = name.replace('-', "_");
-            if is_ascii_ident(&adjusted_name) {
-                #[allow(rustc::diagnostic_outside_of_impl)] // FIXME
-                error.help(format!(
-                    "consider replacing the dashes with underscores: `{adjusted_name}`"
-                ));
-            }
-            error.emit();
-        }
+        let ExternOpt { crate_name: name, path, options } =
+            split_extern_opt(early_dcx, unstable_opts, &arg).unwrap_or_else(|e| e.emit());
 
-        let path = path.map(|p| CanonicalizedPath::new(p));
+        let path = path.map(|p| CanonicalizedPath::new(p.as_path()));
 
         let entry = externs.entry(name.to_owned());
 
diff --git a/compiler/rustc_session/src/config/externs.rs b/compiler/rustc_session/src/config/externs.rs
new file mode 100644
index 0000000000000..1420ee38bf214
--- /dev/null
+++ b/compiler/rustc_session/src/config/externs.rs
@@ -0,0 +1,79 @@
+//! This module contains code to help parse and manipulate `--extern` arguments.
+
+use std::path::PathBuf;
+
+use rustc_errors::{Diag, FatalAbort};
+
+use super::UnstableOptions;
+use crate::EarlyDiagCtxt;
+
+#[cfg(test)]
+mod tests;
+
+/// Represents the pieces of an `--extern` argument.
+pub(crate) struct ExternOpt {
+    pub(crate) crate_name: String,
+    pub(crate) path: Option<PathBuf>,
+    pub(crate) options: Option<String>,
+}
+
+/// Breaks out the major components of an `--extern` argument.
+///
+/// The options field will be a string containing comma-separated options that will need further
+/// parsing and processing.
+pub(crate) fn split_extern_opt<'a>(
+    early_dcx: &'a EarlyDiagCtxt,
+    unstable_opts: &UnstableOptions,
+    extern_opt: &str,
+) -> Result<ExternOpt, Diag<'a, FatalAbort>> {
+    let (name, path) = match extern_opt.split_once('=') {
+        None => (extern_opt.to_string(), None),
+        Some((name, path)) => (name.to_string(), Some(PathBuf::from(path))),
+    };
+    let (options, crate_name) = match name.split_once(':') {
+        None => (None, name),
+        Some((opts, crate_name)) => {
+            if unstable_opts.namespaced_crates && crate_name.starts_with(':') {
+                // If the name starts with `:`, we know this was actually something like `foo::bar` and
+                // not a set of options. We can just use the original name as the crate name.
+                (None, name)
+            } else {
+                (Some(opts.to_string()), crate_name.to_string())
+            }
+        }
+    };
+
+    if !valid_crate_name(&crate_name, unstable_opts) {
+        let mut error = early_dcx.early_struct_fatal(format!(
+            "crate name `{crate_name}` passed to `--extern` is not a valid ASCII identifier"
+        ));
+        let adjusted_name = crate_name.replace('-', "_");
+        if is_ascii_ident(&adjusted_name) {
+            #[allow(rustc::diagnostic_outside_of_impl)] // FIXME
+            error
+                .help(format!("consider replacing the dashes with underscores: `{adjusted_name}`"));
+        }
+        return Err(error);
+    }
+
+    Ok(ExternOpt { crate_name, path, options })
+}
+
+fn valid_crate_name(name: &str, unstable_opts: &UnstableOptions) -> bool {
+    match name.split_once("::") {
+        Some((a, b)) if unstable_opts.namespaced_crates => is_ascii_ident(a) && is_ascii_ident(b),
+        Some(_) => false,
+        None => is_ascii_ident(name),
+    }
+}
+
+fn is_ascii_ident(string: &str) -> bool {
+    let mut chars = string.chars();
+    if let Some(start) = chars.next()
+        && (start.is_ascii_alphabetic() || start == '_')
+    {
+        chars.all(|char| char.is_ascii_alphanumeric() || char == '_')
+    } else {
+        false
+    }
+}
diff --git a/compiler/rustc_session/src/config/externs/tests.rs b/compiler/rustc_session/src/config/externs/tests.rs
new file mode 100644
index 0000000000000..6544886951572
--- /dev/null
+++ b/compiler/rustc_session/src/config/externs/tests.rs
@@ -0,0 +1,92 @@
+use std::path::PathBuf;
+
+use super::split_extern_opt;
+use crate::EarlyDiagCtxt;
+use crate::config::UnstableOptions;
+
+/// Verifies split_extern_opt handles the supported cases.
+#[test]
+fn test_split_extern_opt() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions::default();
+
+    let extern_opt =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, None);
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, None);
+}
+
+/// Tests some invalid cases for split_extern_opt.
+#[test]
+fn test_split_extern_opt_invalid() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions::default();
+
+    // too many `:`s
+    let result = split_extern_opt(&early_dcx, unstable_opts, "priv:noprelude:foo=libbar.rlib");
+    assert!(result.is_err());
+    let _ = result.map_err(|e| e.cancel());
+
+    // can't nest externs without the unstable flag
+    let result = split_extern_opt(&early_dcx, unstable_opts, "noprelude:foo::bar=libbar.rlib");
+    assert!(result.is_err());
+    let _ = result.map_err(|e| e.cancel());
+}
+
+/// Tests some cases for split_extern_opt with nested crates like `foo::bar`.
+#[test]
+fn test_split_extern_opt_nested() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions { namespaced_crates: true, ..Default::default() };
+
+    let extern_opt =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo::bar=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo::bar").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo::bar=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, None);
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo::bar").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, None);
+}
+
+/// Tests some invalid cases for split_extern_opt with nested crates like `foo::bar`.
+#[test]
+fn test_split_extern_opt_nested_invalid() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions { namespaced_crates: true, ..Default::default() };
+
+    // crates can only be nested one deep.
+    let result =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo::bar::baz=libbar.rlib");
+    assert!(result.is_err());
+    let _ = result.map_err(|e| e.cancel());
+}
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index c70f1500d3930..bd66f835f1201 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -2331,6 +2331,8 @@ options! {
         "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: bool = (true, parse_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes)"),
+    namespaced_crates: bool = (false, parse_bool, [TRACKED],
+        "allow crates to be namespaced by other crates (default: no)"),
     next_solver: NextSolverConfig = (NextSolverConfig::default(), parse_next_solver_config, [TRACKED],
         "enable and configure the next generation trait solver used by rustc"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index d1f3eb16e4e4a..2af567f2ec502 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1068,7 +1068,6 @@ symbols! {
         ge,
         gen_blocks,
         gen_future,
-        gen_kill,
         generator_clone,
         generators,
         generic_arg_infer,
diff --git a/src/bootstrap/src/core/build_steps/compile.rs b/src/bootstrap/src/core/build_steps/compile.rs
index dab58fccf5e68..6a5b38dd50435 100644
--- a/src/bootstrap/src/core/build_steps/compile.rs
+++ b/src/bootstrap/src/core/build_steps/compile.rs
@@ -155,7 +155,7 @@ impl Step for Std {
 
         // When using `download-rustc`, we already have artifacts for the host available. Don't
         // recompile them.
-        if builder.download_rustc() && builder.is_builder_target(target)
+        if builder.download_rustc() && builder.config.is_host_target(target)
             // NOTE: the beta compiler may generate different artifacts than the downloaded compiler, so
             // its artifacts can't be reused.
             && compiler.stage != 0
@@ -229,7 +229,7 @@ impl Step for Std {
         // The LLD wrappers and `rust-lld` are self-contained linking components that can be
         // necessary to link the stdlib on some targets. We'll also need to copy these binaries to
         // the `stage0-sysroot` to ensure the linker is found when bootstrapping on such a target.
-        if compiler.stage == 0 && builder.is_builder_target(compiler.host) {
+        if compiler.stage == 0 && builder.config.is_host_target(compiler.host) {
             trace!(
                 "(build == host) copying linking components to `stage0-sysroot` for bootstrapping"
             );
@@ -1374,7 +1374,7 @@ pub fn rustc_cargo_env(
 /// Pass down configuration from the LLVM build into the build of
 /// rustc_llvm and rustc_codegen_llvm.
 fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelection) {
-    if builder.is_rust_llvm(target) {
+    if builder.config.is_rust_llvm(target) {
         cargo.env("LLVM_RUSTLLVM", "1");
     }
     if builder.config.llvm_enzyme {
@@ -2182,7 +2182,7 @@ impl Step for Assemble {
         debug!("copying codegen backends to sysroot");
         copy_codegen_backends_to_sysroot(builder, build_compiler, target_compiler);
 
-        if builder.config.lld_enabled {
+        if builder.config.lld_enabled && !builder.config.is_system_llvm(target_compiler.host) {
             builder.ensure(crate::core::build_steps::tool::LldWrapper {
                 build_compiler,
                 target_compiler,
@@ -2532,7 +2532,9 @@ pub fn strip_debug(builder: &Builder<'_>, target: TargetSelection, path: &Path)
     // FIXME: to make things simpler for now, limit this to the host and target where we know
     // `strip -g` is both available and will fix the issue, i.e. on a x64 linux host that is not
     // cross-compiling. Expand this to other appropriate targets in the future.
-    if target != "x86_64-unknown-linux-gnu" || !builder.is_builder_target(target) || !path.exists()
+    if target != "x86_64-unknown-linux-gnu"
+        || !builder.config.is_host_target(target)
+        || !path.exists()
     {
         return;
     }
diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index 83f71aeed7204..ed90ede793622 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -612,7 +612,7 @@ impl Step for DebuggerScripts {
 fn skip_host_target_lib(builder: &Builder<'_>, compiler: Compiler) -> bool {
     // The only true set of target libraries came from the build triple, so
     // let's reduce redundant work by only producing archives from that host.
-    if !builder.is_builder_target(compiler.host) {
+    if !builder.config.is_host_target(compiler.host) {
         builder.info("\tskipping, not a build host");
         true
     } else {
@@ -671,7 +671,8 @@ fn copy_target_libs(
                 &self_contained_dst.join(path.file_name().unwrap()),
                 FileType::NativeLibrary,
             );
-        } else if dependency_type == DependencyType::Target || builder.is_builder_target(target) {
+        } else if dependency_type == DependencyType::Target || builder.config.is_host_target(target)
+        {
             builder.copy_link(&path, &dst.join(path.file_name().unwrap()), FileType::NativeLibrary);
         }
     }
@@ -824,7 +825,7 @@ impl Step for Analysis {
     fn run(self, builder: &Builder<'_>) -> Option<GeneratedTarball> {
         let compiler = self.compiler;
         let target = self.target;
-        if !builder.is_builder_target(compiler.host) {
+        if !builder.config.is_host_target(compiler.host) {
             return None;
         }
 
@@ -2118,7 +2119,7 @@ fn maybe_install_llvm(
     //
     // If the LLVM is coming from ourselves (just from CI) though, we
     // still want to install it, as it otherwise won't be available.
-    if builder.is_system_llvm(target) {
+    if builder.config.is_system_llvm(target) {
         trace!("system LLVM requested, no install");
         return false;
     }
diff --git a/src/bootstrap/src/core/build_steps/format.rs b/src/bootstrap/src/core/build_steps/format.rs
index b1a97bde97b5b..9da8b27a91778 100644
--- a/src/bootstrap/src/core/build_steps/format.rs
+++ b/src/bootstrap/src/core/build_steps/format.rs
@@ -81,14 +81,19 @@ fn update_rustfmt_version(build: &Builder<'_>) {
     let Some((version, stamp_file)) = get_rustfmt_version(build) else {
         return;
     };
-    t!(std::fs::write(stamp_file.path(), version))
+
+    t!(stamp_file.add_stamp(version).write());
 }
 
-/// Returns the Rust files modified between the `merge-base` of HEAD and
-/// rust-lang/master and what is now on the disk. Does not include removed files.
+/// Returns the Rust files modified between the last merge commit and what is now on the disk.
+/// Does not include removed files.
 ///
 /// Returns `None` if all files should be formatted.
 fn get_modified_rs_files(build: &Builder<'_>) -> Result<Option<Vec<String>>, String> {
+    // In CI `get_git_modified_files` returns something different to normal environment.
+    // This shouldn't be called in CI anyway.
+    assert!(!build.config.is_running_on_ci);
+
     if !verify_rustfmt_version(build) {
         return Ok(None);
     }
@@ -103,7 +108,7 @@ struct RustfmtConfig {
 
 // Prints output describing a collection of paths, with lines such as "formatted modified file
 // foo/bar/baz" or "skipped 20 untracked files".
-fn print_paths(build: &Builder<'_>, verb: &str, adjective: Option<&str>, paths: &[String]) {
+fn print_paths(verb: &str, adjective: Option<&str>, paths: &[String]) {
     let len = paths.len();
     let adjective =
         if let Some(adjective) = adjective { format!("{adjective} ") } else { String::new() };
@@ -114,9 +119,6 @@ fn print_paths(build: &Builder<'_>, verb: &str, adjective: Option<&str>, paths:
     } else {
         println!("fmt: {verb} {len} {adjective}files");
     }
-    if len > 1000 && !build.config.is_running_on_ci {
-        println!("hint: if this number seems too high, try running `git fetch origin master`");
-    }
 }
 
 pub fn format(build: &Builder<'_>, check: bool, all: bool, paths: &[PathBuf]) {
@@ -189,7 +191,7 @@ pub fn format(build: &Builder<'_>, check: bool, all: bool, paths: &[PathBuf]) {
                 )
                 .map(|x| x.to_string())
                 .collect();
-            print_paths(build, "skipped", Some("untracked"), &untracked_paths);
+            print_paths("skipped", Some("untracked"), &untracked_paths);
 
             for untracked_path in untracked_paths {
                 // The leading `/` makes it an exact match against the
@@ -212,7 +214,13 @@ pub fn format(build: &Builder<'_>, check: bool, all: bool, paths: &[PathBuf]) {
                             override_builder.add(&format!("/{file}")).expect(&file);
                         }
                     }
-                    Ok(None) => {}
+                    Ok(None) => {
+                        // NOTE: `Ok(None)` signifies that we need to format all files.
+                        // The tricky part here is that if `override_builder` isn't given any white
+                        // list files (i.e. files to be formatted, added without leading `!`), it
+                        // will instead look for *all* files. So, by doing nothing here, we are
+                        // actually making it so we format all files.
+                    }
                     Err(err) => {
                         eprintln!("fmt warning: Something went wrong running git commands:");
                         eprintln!("fmt warning: {err}");
@@ -318,7 +326,7 @@ pub fn format(build: &Builder<'_>, check: bool, all: bool, paths: &[PathBuf]) {
     });
     let mut paths = formatted_paths.into_inner().unwrap();
     paths.sort();
-    print_paths(build, if check { "checked" } else { "formatted" }, adjective, &paths);
+    print_paths(if check { "checked" } else { "formatted" }, adjective, &paths);
 
     drop(tx);
 
@@ -328,7 +336,10 @@ pub fn format(build: &Builder<'_>, check: bool, all: bool, paths: &[PathBuf]) {
         crate::exit!(1);
     }
 
-    if !check {
-        update_rustfmt_version(build);
-    }
+    // Update `build/.rustfmt-stamp`, allowing this code to ignore files which have not been changed
+    // since last merge.
+    //
+    // NOTE: Because of the exit above, this is only reachable if formatting / format checking
+    // succeeded. So we are not commiting the version if formatting was not good.
+    update_rustfmt_version(build);
 }
diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index 69a8bd59f16ca..0c82cb16348e6 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -485,7 +485,7 @@ impl Step for Llvm {
         }
 
         // https://llvm.org/docs/HowToCrossCompileLLVM.html
-        if !builder.is_builder_target(target) {
+        if !builder.config.is_host_target(target) {
             let LlvmResult { llvm_config, .. } =
                 builder.ensure(Llvm { target: builder.config.build });
             if !builder.config.dry_run() {
@@ -637,7 +637,7 @@ fn configure_cmake(
     }
     cfg.target(&target.triple).host(&builder.config.build.triple);
 
-    if !builder.is_builder_target(target) {
+    if !builder.config.is_host_target(target) {
         cfg.define("CMAKE_CROSSCOMPILING", "True");
 
         // NOTE: Ideally, we wouldn't have to do this, and `cmake-rs` would just handle it for us.
@@ -1098,7 +1098,7 @@ impl Step for Lld {
             .define("LLVM_CMAKE_DIR", llvm_cmake_dir)
             .define("LLVM_INCLUDE_TESTS", "OFF");
 
-        if !builder.is_builder_target(target) {
+        if !builder.config.is_host_target(target) {
             // Use the host llvm-tblgen binary.
             cfg.define(
                 "LLVM_TABLEGEN_EXE",
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index b1a3bba08871d..096f7de65975a 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -1894,7 +1894,7 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
                     .arg(llvm_components.trim());
                 llvm_components_passed = true;
             }
-            if !builder.is_rust_llvm(target) {
+            if !builder.config.is_rust_llvm(target) {
                 cmd.arg("--system-llvm");
             }
 
@@ -2668,7 +2668,7 @@ impl Step for Crate {
             cargo
         } else {
             // Also prepare a sysroot for the target.
-            if !builder.is_builder_target(target) {
+            if !builder.config.is_host_target(target) {
                 builder.ensure(compile::Std::new(compiler, target).force_recompile(true));
                 builder.ensure(RemoteCopyLibs { compiler, target });
             }
diff --git a/src/bootstrap/src/core/builder/tests.rs b/src/bootstrap/src/core/builder/tests.rs
index fd3b28e4e6ab2..5de824ebab238 100644
--- a/src/bootstrap/src/core/builder/tests.rs
+++ b/src/bootstrap/src/core/builder/tests.rs
@@ -1107,8 +1107,8 @@ fn test_is_builder_target() {
         let build = Build::new(config);
         let builder = Builder::new(&build);
 
-        assert!(builder.is_builder_target(target1));
-        assert!(!builder.is_builder_target(target2));
+        assert!(builder.config.is_host_target(target1));
+        assert!(!builder.config.is_host_target(target2));
     }
 }
 
diff --git a/src/bootstrap/src/core/config/config.rs b/src/bootstrap/src/core/config/config.rs
index 25ec64f90b53d..0333c00d98be5 100644
--- a/src/bootstrap/src/core/config/config.rs
+++ b/src/bootstrap/src/core/config/config.rs
@@ -2397,6 +2397,10 @@ impl Config {
             );
         }
 
+        if config.lld_enabled && config.is_system_llvm(config.build) {
+            panic!("Cannot enable LLD when using external llvm-config.");
+        }
+
         let default_std_features = BTreeSet::from([String::from("panic-unwind")]);
         config.rust_std_features = std_features.unwrap_or(default_std_features);
 
@@ -2888,6 +2892,13 @@ impl Config {
 
         let absolute_path = self.src.join(relative_path);
 
+        // NOTE: This check is required because `jj git clone` doesn't create directories for
+        // submodules, they are completely ignored. The code below assumes this directory exists,
+        // so create it here.
+        if !absolute_path.exists() {
+            t!(fs::create_dir_all(&absolute_path));
+        }
+
         // NOTE: The check for the empty directory is here because when running x.py the first time,
         // the submodule won't be checked out. Check it out now so we can build it.
         if !GitInfo::new(false, &absolute_path).is_managed_git_subrepository()
@@ -3233,6 +3244,42 @@ impl Config {
 
         Some(commit.to_string())
     }
+
+    /// Checks if the given target is the same as the host target.
+    pub fn is_host_target(&self, target: TargetSelection) -> bool {
+        self.build == target
+    }
+
+    /// Returns `true` if this is an external version of LLVM not managed by bootstrap.
+    /// In particular, we expect llvm sources to be available when this is false.
+    ///
+    /// NOTE: this is not the same as `!is_rust_llvm` when `llvm_has_patches` is set.
+    pub fn is_system_llvm(&self, target: TargetSelection) -> bool {
+        match self.target_config.get(&target) {
+            Some(Target { llvm_config: Some(_), .. }) => {
+                let ci_llvm = self.llvm_from_ci && self.is_host_target(target);
+                !ci_llvm
+            }
+            // We're building from the in-tree src/llvm-project sources.
+            Some(Target { llvm_config: None, .. }) => false,
+            None => false,
+        }
+    }
+
+    /// Returns `true` if this is our custom, patched, version of LLVM.
+    ///
+    /// This does not necessarily imply that we're managing the `llvm-project` submodule.
+    pub fn is_rust_llvm(&self, target: TargetSelection) -> bool {
+        match self.target_config.get(&target) {
+            // We're using a user-controlled version of LLVM. The user has explicitly told us whether the version has our patches.
+            // (They might be wrong, but that's not a supported use-case.)
+            // In particular, this tries to support `submodules = false` and `patches = false`, for using a newer version of LLVM that's not through `rust-lang/llvm-project`.
+            Some(Target { llvm_has_rust_patches: Some(patched), .. }) => *patched,
+            // The user hasn't promised the patches match.
+            // This only has our patches if it's downloaded from CI or built from source.
+            _ => !self.is_system_llvm(target),
+        }
+    }
 }
 
 /// Compares the current `Llvm` options against those in the CI LLVM builder and detects any incompatible options.
diff --git a/src/bootstrap/src/core/sanity.rs b/src/bootstrap/src/core/sanity.rs
index 891340add908e..4b020a7edb7ba 100644
--- a/src/bootstrap/src/core/sanity.rs
+++ b/src/bootstrap/src/core/sanity.rs
@@ -325,7 +325,7 @@ than building it.
         if target.contains("musl") && !target.contains("unikraft") {
             // If this is a native target (host is also musl) and no musl-root is given,
             // fall back to the system toolchain in /usr before giving up
-            if build.musl_root(*target).is_none() && build.is_builder_target(*target) {
+            if build.musl_root(*target).is_none() && build.config.is_host_target(*target) {
                 let target = build.config.target_config.entry(*target).or_default();
                 target.musl_root = Some("/usr".into());
             }
diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
index 1a513a240e173..88d181532a7ff 100644
--- a/src/bootstrap/src/lib.rs
+++ b/src/bootstrap/src/lib.rs
@@ -35,7 +35,7 @@ use utils::channel::GitInfo;
 
 use crate::core::builder;
 use crate::core::builder::Kind;
-use crate::core::config::{DryRun, LldMode, LlvmLibunwind, Target, TargetSelection, flags};
+use crate::core::config::{DryRun, LldMode, LlvmLibunwind, TargetSelection, flags};
 use crate::utils::exec::{BehaviorOnFailure, BootstrapCommand, CommandOutput, OutputMode, command};
 use crate::utils::helpers::{
     self, dir_is_empty, exe, libdir, output, set_file_times, split_debuginfo, symlink_dir,
@@ -803,7 +803,7 @@ impl Build {
     /// Note that if LLVM is configured externally then the directory returned
     /// will likely be empty.
     fn llvm_out(&self, target: TargetSelection) -> PathBuf {
-        if self.config.llvm_from_ci && self.is_builder_target(target) {
+        if self.config.llvm_from_ci && self.config.is_host_target(target) {
             self.config.ci_llvm_root()
         } else {
             self.out.join(target).join("llvm")
@@ -851,37 +851,6 @@ impl Build {
         if self.config.vendor { Some(self.src.join(VENDOR_DIR)) } else { None }
     }
 
-    /// Returns `true` if this is an external version of LLVM not managed by bootstrap.
-    /// In particular, we expect llvm sources to be available when this is false.
-    ///
-    /// NOTE: this is not the same as `!is_rust_llvm` when `llvm_has_patches` is set.
-    fn is_system_llvm(&self, target: TargetSelection) -> bool {
-        match self.config.target_config.get(&target) {
-            Some(Target { llvm_config: Some(_), .. }) => {
-                let ci_llvm = self.config.llvm_from_ci && self.is_builder_target(target);
-                !ci_llvm
-            }
-            // We're building from the in-tree src/llvm-project sources.
-            Some(Target { llvm_config: None, .. }) => false,
-            None => false,
-        }
-    }
-
-    /// Returns `true` if this is our custom, patched, version of LLVM.
-    ///
-    /// This does not necessarily imply that we're managing the `llvm-project` submodule.
-    fn is_rust_llvm(&self, target: TargetSelection) -> bool {
-        match self.config.target_config.get(&target) {
-            // We're using a user-controlled version of LLVM. The user has explicitly told us whether the version has our patches.
-            // (They might be wrong, but that's not a supported use-case.)
-            // In particular, this tries to support `submodules = false` and `patches = false`, for using a newer version of LLVM that's not through `rust-lang/llvm-project`.
-            Some(Target { llvm_has_rust_patches: Some(patched), .. }) => *patched,
-            // The user hasn't promised the patches match.
-            // This only has our patches if it's downloaded from CI or built from source.
-            _ => !self.is_system_llvm(target),
-        }
-    }
-
     /// Returns the path to `FileCheck` binary for the specified target
     fn llvm_filecheck(&self, target: TargetSelection) -> PathBuf {
         let target_config = self.config.target_config.get(&target);
@@ -1356,7 +1325,7 @@ Executed at: {executed_at}"#,
             // need to use CXX compiler as linker to resolve the exception functions
             // that are only existed in CXX libraries
             Some(self.cxx.borrow()[&target].path().into())
-        } else if !self.is_builder_target(target)
+        } else if !self.config.is_host_target(target)
             && helpers::use_host_linker(target)
             && !target.is_msvc()
         {
@@ -2025,11 +1994,6 @@ to download LLVM rather than building it.
         stream.reset().unwrap();
         result
     }
-
-    /// Checks if the given target is the same as the builder target.
-    fn is_builder_target(&self, target: TargetSelection) -> bool {
-        self.config.build == target
-    }
 }
 
 #[cfg(unix)]
diff --git a/src/build_helper/src/git.rs b/src/build_helper/src/git.rs
index 693e0fc8f46d8..f5347c3082410 100644
--- a/src/build_helper/src/git.rs
+++ b/src/build_helper/src/git.rs
@@ -114,7 +114,9 @@ fn git_upstream_merge_base(
     Ok(output_result(git.arg("merge-base").arg(&updated_master).arg("HEAD"))?.trim().to_owned())
 }
 
-/// Searches for the nearest merge commit in the repository that also exists upstream.
+/// Searches for the nearest merge commit in the repository.
+///
+/// **In CI** finds the nearest merge commit that *also exists upstream*.
 ///
 /// It looks for the most recent commit made by the merge bot by matching the author's email
 /// address with the merge bot's email.
@@ -165,7 +167,7 @@ pub fn get_closest_merge_commit(
     Ok(output_result(&mut git)?.trim().to_owned())
 }
 
-/// Returns the files that have been modified in the current branch compared to the master branch.
+/// Returns the files that have been modified in the current branch compared to the last merge.
 /// The `extensions` parameter can be used to filter the files by their extension.
 /// Does not include removed files.
 /// If `extensions` is empty, all files will be returned.
diff --git a/src/doc/book b/src/doc/book
index 45f05367360f0..d33916341d480 160000
--- a/src/doc/book
+++ b/src/doc/book
@@ -1 +1 @@
-Subproject commit 45f05367360f033f89235eacbbb54e8d73ce6b70
+Subproject commit d33916341d480caede1d0ae57cbeae23aab23e88
diff --git a/src/doc/edition-guide b/src/doc/edition-guide
index 1e27e5e6d5133..467f45637b73e 160000
--- a/src/doc/edition-guide
+++ b/src/doc/edition-guide
@@ -1 +1 @@
-Subproject commit 1e27e5e6d5133ae4612f5cc195c15fc8d51b1c9c
+Subproject commit 467f45637b73ec6aa70fb36bc3054bb50b8967ea
diff --git a/src/doc/nomicon b/src/doc/nomicon
index b4448fa406a6d..0c10c30cc5473 160000
--- a/src/doc/nomicon
+++ b/src/doc/nomicon
@@ -1 +1 @@
-Subproject commit b4448fa406a6dccde62d1e2f34f70fc51814cdcc
+Subproject commit 0c10c30cc54736c5c194ce98c50e2de84eeb6e79
diff --git a/src/doc/reference b/src/doc/reference
index 46435cd4eba11..3340922df189b 160000
--- a/src/doc/reference
+++ b/src/doc/reference
@@ -1 +1 @@
-Subproject commit 46435cd4eba11b66acaa42c01da5c80ad88aee4b
+Subproject commit 3340922df189bddcbaad17dc3927d51a76bcd5ed
diff --git a/src/doc/rustc-dev-guide/src/compiler-debugging.md b/src/doc/rustc-dev-guide/src/compiler-debugging.md
index 47f3976202228..102e20207792e 100644
--- a/src/doc/rustc-dev-guide/src/compiler-debugging.md
+++ b/src/doc/rustc-dev-guide/src/compiler-debugging.md
@@ -301,7 +301,8 @@ Right below you can find elaborate explainers on a selected few.
 
 Some compiler options for debugging specific features yield graphviz graphs -
 e.g. the `#[rustc_mir(borrowck_graphviz_postflow="suffix.dot")]` attribute
-dumps various borrow-checker dataflow graphs.
+on a function dumps various borrow-checker dataflow graphs in conjunction with
+`-Zdump-mir-dataflow`.
 
 These all produce `.dot` files. To view these files, install graphviz (e.g.
 `apt-get install graphviz`) and then run the following commands:
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 24fc2ddb74104..eb298060b2ece 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -2378,12 +2378,19 @@ impl<'test> TestCx<'test> {
         // eg.
         // /home/user/rust/build/x86_64-unknown-linux-gnu/test/ui/<test_dir>/$name.$revision.$mode/
         normalize_path(&self.output_base_dir(), "$TEST_BUILD_DIR");
+        // Same as above, but with a canonicalized path.
+        // This is required because some tests print canonical paths inside test build directory,
+        // so if the build directory is a symlink, normalization doesn't help.
+        //
+        // NOTE: There are also tests which print the non-canonical name, so we need both this and
+        // the above normalizations.
+        normalize_path(&self.output_base_dir().canonicalize_utf8().unwrap(), "$TEST_BUILD_DIR");
         // eg. /home/user/rust/build
         normalize_path(&self.config.build_root, "$BUILD_DIR");
 
         if json {
             // escaped newlines in json strings should be readable
-            // in the stderr files. There's no point int being correct,
+            // in the stderr files. There's no point in being correct,
             // since only humans process the stderr files.
             // Thus we just turn escaped newlines back into newlines.
             normalized = normalized.replace("\\n", "\n");
diff --git a/src/tools/rustbook/Cargo.lock b/src/tools/rustbook/Cargo.lock
index e0939afc09bb7..c14372dd6aec4 100644
--- a/src/tools/rustbook/Cargo.lock
+++ b/src/tools/rustbook/Cargo.lock
@@ -951,6 +951,7 @@ dependencies = [
  "once_cell",
  "pathdiff",
  "pulldown-cmark 0.10.3",
+ "railroad",
  "regex",
  "semver",
  "serde_json",
@@ -1300,6 +1301,15 @@ version = "5.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "74765f6d916ee2faa39bc8e68e4f3ed8949b48cccdac59983d287a7cb71ce9c5"
 
+[[package]]
+name = "railroad"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ecedffc46c1b2cb04f4b80e094eae6b3f3f470a9635f1f396dd5206428f6b58"
+dependencies = [
+ "unicode-width",
+]
+
 [[package]]
 name = "rand"
 version = "0.8.5"
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 88c2a02798ace..46e55859a5785 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -682,8 +682,10 @@ pub static CRATES: &[&str] = &[
 pub fn has_missing_submodule(root: &Path, submodules: &[&str]) -> bool {
     !CiEnv::is_ci()
         && submodules.iter().any(|submodule| {
+            let path = root.join(submodule);
+            !path.exists()
             // If the directory is empty, we can consider it as an uninitialized submodule.
-            read_dir(root.join(submodule)).unwrap().next().is_none()
+            || read_dir(path).unwrap().next().is_none()
         })
 }
 
diff --git a/tests/ui/async-await/async-gen-move-suggestion.fixed b/tests/ui/async-await/async-gen-move-suggestion.fixed
new file mode 100644
index 0000000000000..d802076552895
--- /dev/null
+++ b/tests/ui/async-await/async-gen-move-suggestion.fixed
@@ -0,0 +1,35 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/139839>.
+// It ensures that the "add `move` keyword" suggestion is valid.
+
+//@ run-rustfix
+//@ edition:2024
+
+#![feature(coroutines)]
+#![feature(gen_blocks)]
+#![feature(async_iterator)]
+
+use std::async_iter::AsyncIterator;
+
+#[allow(dead_code)]
+fn moved() -> impl AsyncIterator<Item = u32> {
+    let mut x = "foo".to_string();
+
+    async gen move { //~ ERROR
+        x.clear();
+        for x in 3..6 { yield x }
+    }
+}
+
+#[allow(dead_code)]
+fn check_with_whitespace_chars() -> impl AsyncIterator<Item = u32> {
+    let mut x = "foo".to_string();
+
+    async // Just to check that whitespace characters are correctly handled
+    gen move { //~^ ERROR
+        x.clear();
+        for x in 3..6 { yield x }
+    }
+}
+
+fn main() {
+}
diff --git a/tests/ui/async-await/async-gen-move-suggestion.rs b/tests/ui/async-await/async-gen-move-suggestion.rs
new file mode 100644
index 0000000000000..825fb0fd1898c
--- /dev/null
+++ b/tests/ui/async-await/async-gen-move-suggestion.rs
@@ -0,0 +1,35 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/139839>.
+// It ensures that the "add `move` keyword" suggestion is valid.
+
+//@ run-rustfix
+//@ edition:2024
+
+#![feature(coroutines)]
+#![feature(gen_blocks)]
+#![feature(async_iterator)]
+
+use std::async_iter::AsyncIterator;
+
+#[allow(dead_code)]
+fn moved() -> impl AsyncIterator<Item = u32> {
+    let mut x = "foo".to_string();
+
+    async gen { //~ ERROR
+        x.clear();
+        for x in 3..6 { yield x }
+    }
+}
+
+#[allow(dead_code)]
+fn check_with_whitespace_chars() -> impl AsyncIterator<Item = u32> {
+    let mut x = "foo".to_string();
+
+    async // Just to check that whitespace characters are correctly handled
+    gen { //~^ ERROR
+        x.clear();
+        for x in 3..6 { yield x }
+    }
+}
+
+fn main() {
+}
diff --git a/tests/ui/async-await/async-gen-move-suggestion.stderr b/tests/ui/async-await/async-gen-move-suggestion.stderr
new file mode 100644
index 0000000000000..b8cdb8be7a4ae
--- /dev/null
+++ b/tests/ui/async-await/async-gen-move-suggestion.stderr
@@ -0,0 +1,47 @@
+error[E0373]: async gen block may outlive the current function, but it borrows `x`, which is owned by the current function
+  --> $DIR/async-gen-move-suggestion.rs:17:5
+   |
+LL |     async gen {
+   |     ^^^^^^^^^ may outlive borrowed value `x`
+LL |         x.clear();
+   |         - `x` is borrowed here
+   |
+note: async gen block is returned here
+  --> $DIR/async-gen-move-suggestion.rs:17:5
+   |
+LL | /     async gen {
+LL | |         x.clear();
+LL | |         for x in 3..6 { yield x }
+LL | |     }
+   | |_____^
+help: to force the async gen block to take ownership of `x` (and any other referenced variables), use the `move` keyword
+   |
+LL |     async gen move {
+   |               ++++
+
+error[E0373]: async gen block may outlive the current function, but it borrows `x`, which is owned by the current function
+  --> $DIR/async-gen-move-suggestion.rs:27:5
+   |
+LL | /     async // Just to check that whitespace characters are correctly handled
+LL | |     gen {
+   | |_______^ may outlive borrowed value `x`
+LL |           x.clear();
+   |           - `x` is borrowed here
+   |
+note: async gen block is returned here
+  --> $DIR/async-gen-move-suggestion.rs:27:5
+   |
+LL | /     async // Just to check that whitespace characters are correctly handled
+LL | |     gen {
+LL | |         x.clear();
+LL | |         for x in 3..6 { yield x }
+LL | |     }
+   | |_____^
+help: to force the async gen block to take ownership of `x` (and any other referenced variables), use the `move` keyword
+   |
+LL |     gen move {
+   |         ++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0373`.
diff --git a/tests/ui/consts/const-blocks/const-block-in-array-size.rs b/tests/ui/consts/const-blocks/const-block-in-array-size.rs
new file mode 100644
index 0000000000000..ecab24322869c
--- /dev/null
+++ b/tests/ui/consts/const-blocks/const-block-in-array-size.rs
@@ -0,0 +1,5 @@
+//@ check-pass
+
+type A = [u32; const { 2 }];
+
+fn main() {}
diff --git a/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name.rs b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name.rs
new file mode 100644
index 0000000000000..450f41e209dfb
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name.rs
@@ -0,0 +1,12 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/139873>.
+
+// Test that we don't try to get the (nonexistent) name of the RPITIT in `Trait::foo`
+// when emitting an error for a missing associated item `Trait::Output`.
+
+trait Trait {
+    fn foo() -> impl Sized;
+    fn bar() -> Self::Output;
+    //~^ ERROR associated type `Output` not found for `Self`
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name.stderr b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name.stderr
new file mode 100644
index 0000000000000..74e15785af19c
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/dont-probe-missing-item-name.stderr
@@ -0,0 +1,9 @@
+error[E0220]: associated type `Output` not found for `Self`
+  --> $DIR/dont-probe-missing-item-name.rs:8:23
+   |
+LL |     fn bar() -> Self::Output;
+   |                       ^^^^^^ associated type `Output` not found
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0220`.
diff --git a/tests/ui/mir-dataflow/README.md b/tests/ui/mir-dataflow/README.md
index a3ab14b23c7db..886020226d031 100644
--- a/tests/ui/mir-dataflow/README.md
+++ b/tests/ui/mir-dataflow/README.md
@@ -42,12 +42,3 @@ each generated output path.
    on *entry* to each block, as well as the gen- and kill-sets that
    were so-called "transfer functions" summarizing the effect of each
    basic block.
-
- * (In addition to the `borrowck_graphviz_postflow` attribute-key
-   noted above, there is also `borrowck_graphviz_preflow`; it has the
-   same interface and generates the same set of files, but it renders
-   the dataflow state after building the gen- and kill-sets but
-   *before* running the dataflow analysis itself, so each entry-set is
-   just the initial default state for that dataflow analysis. This is
-   less useful for understanding the error message output in these
-   tests.)