Auto merge of #117228 - matthiaskrgr:rollup-23zzepv, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #116905 (refactor(compiler/resolve): simplify some code)
 - #117095 (Add way to differentiate argument locals from other locals in Stable MIR)
 - #117143 (Avoid unbounded O(n^2) when parsing nested type args)
 - #117194 (Minor improvements to `rustc_incremental`)
 - #117202 (Revert "Remove TaKO8Ki from reviewers")
 - #117207 (The value of `-Cinstrument-coverage=` doesn't need to be `Option`)
 - #117214 (Quietly fail if an error has already occurred)
 - #117221 (Rename type flag `HAS_TY_GENERATOR` to `HAS_TY_COROUTINE`)

r? `@ghost`
`@rustbot` modify labels: rollup

18 files changed, 132 insertions, 69 deletions

diff --git a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
index f22851d76b3..c84256f8ff3 100644
--- a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
+++ b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
@@ -8,7 +8,7 @@ use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::traits::query::OutlivesBound;
 use rustc_middle::ty::{self, RegionVid, Ty};
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::{ErrorGuaranteed, Span, DUMMY_SP};
 use rustc_trait_selection::traits::query::type_op::{self, TypeOp};
 use std::rc::Rc;
 use type_op::TypeOpOutput;
@@ -318,7 +318,8 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
             .param_env
             .and(type_op::implied_outlives_bounds::ImpliedOutlivesBounds { ty })
             .fully_perform(self.infcx, DUMMY_SP)
-            .unwrap_or_else(|_| bug!("failed to compute implied bounds {:?}", ty));
+            .map_err(|_: ErrorGuaranteed| debug!("failed to compute implied bounds {:?}", ty))
+            .ok()?;
         debug!(?bounds, ?constraints);
         self.add_outlives_bounds(bounds);
         constraints
diff --git a/compiler/rustc_incremental/src/lib.rs b/compiler/rustc_incremental/src/lib.rs
index bdae07a3946..dde138973b9 100644
--- a/compiler/rustc_incremental/src/lib.rs
+++ b/compiler/rustc_incremental/src/lib.rs
@@ -5,7 +5,6 @@
 #![cfg_attr(not(bootstrap), doc(rust_logo))]
 #![cfg_attr(not(bootstrap), feature(rustdoc_internals))]
 #![cfg_attr(not(bootstrap), allow(internal_features))]
-#![feature(never_type)]
 #![recursion_limit = "256"]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
@@ -19,15 +18,11 @@ mod assert_dep_graph;
 mod errors;
 mod persist;
 
-use assert_dep_graph::assert_dep_graph;
 pub use persist::copy_cgu_workproduct_to_incr_comp_cache_dir;
-pub use persist::delete_workproduct_files;
 pub use persist::finalize_session_directory;
-pub use persist::garbage_collect_session_directories;
 pub use persist::in_incr_comp_dir;
 pub use persist::in_incr_comp_dir_sess;
 pub use persist::load_query_result_cache;
-pub use persist::prepare_session_directory;
 pub use persist::save_dep_graph;
 pub use persist::save_work_product_index;
 pub use persist::setup_dep_graph;
diff --git a/compiler/rustc_incremental/src/persist/fs.rs b/compiler/rustc_incremental/src/persist/fs.rs
index db8ea2bfe48..f56fb0d0534 100644
--- a/compiler/rustc_incremental/src/persist/fs.rs
+++ b/compiler/rustc_incremental/src/persist/fs.rs
@@ -53,7 +53,7 @@
 //! ## Synchronization
 //!
 //! There is some synchronization needed in order for the compiler to be able to
-//! determine whether a given private session directory is not in used any more.
+//! determine whether a given private session directory is not in use any more.
 //! This is done by creating a lock file for each session directory and
 //! locking it while the directory is still being used. Since file locks have
 //! operating system support, we can rely on the lock being released if the
@@ -136,26 +136,29 @@ const QUERY_CACHE_FILENAME: &str = "query-cache.bin";
 const INT_ENCODE_BASE: usize = base_n::CASE_INSENSITIVE;
 
 /// Returns the path to a session's dependency graph.
-pub fn dep_graph_path(sess: &Session) -> PathBuf {
+pub(crate) fn dep_graph_path(sess: &Session) -> PathBuf {
     in_incr_comp_dir_sess(sess, DEP_GRAPH_FILENAME)
 }
+
 /// Returns the path to a session's staging dependency graph.
 ///
 /// On the difference between dep-graph and staging dep-graph,
 /// see `build_dep_graph`.
-pub fn staging_dep_graph_path(sess: &Session) -> PathBuf {
+pub(crate) fn staging_dep_graph_path(sess: &Session) -> PathBuf {
     in_incr_comp_dir_sess(sess, STAGING_DEP_GRAPH_FILENAME)
 }
-pub fn work_products_path(sess: &Session) -> PathBuf {
+
+pub(crate) fn work_products_path(sess: &Session) -> PathBuf {
     in_incr_comp_dir_sess(sess, WORK_PRODUCTS_FILENAME)
 }
+
 /// Returns the path to a session's query cache.
 pub fn query_cache_path(sess: &Session) -> PathBuf {
     in_incr_comp_dir_sess(sess, QUERY_CACHE_FILENAME)
 }
 
 /// Locks a given session directory.
-pub fn lock_file_path(session_dir: &Path) -> PathBuf {
+fn lock_file_path(session_dir: &Path) -> PathBuf {
     let crate_dir = session_dir.parent().unwrap();
 
     let directory_name = session_dir.file_name().unwrap().to_string_lossy();
@@ -202,7 +205,7 @@ pub fn in_incr_comp_dir(incr_comp_session_dir: &Path, file_name: &str) -> PathBu
 /// The garbage collection will take care of it.
 ///
 /// [`rustc_interface::queries::dep_graph`]: ../../rustc_interface/struct.Queries.html#structfield.dep_graph
-pub fn prepare_session_directory(
+pub(crate) fn prepare_session_directory(
     sess: &Session,
     crate_name: Symbol,
     stable_crate_id: StableCrateId,
@@ -373,7 +376,7 @@ pub fn finalize_session_directory(sess: &Session, svh: Option<Svh>) {
     let _ = garbage_collect_session_directories(sess);
 }
 
-pub fn delete_all_session_dir_contents(sess: &Session) -> io::Result<()> {
+pub(crate) fn delete_all_session_dir_contents(sess: &Session) -> io::Result<()> {
     let sess_dir_iterator = sess.incr_comp_session_dir().read_dir()?;
     for entry in sess_dir_iterator {
         let entry = entry?;
@@ -621,7 +624,7 @@ fn is_old_enough_to_be_collected(timestamp: SystemTime) -> bool {
 }
 
 /// Runs garbage collection for the current session.
-pub fn garbage_collect_session_directories(sess: &Session) -> io::Result<()> {
+pub(crate) fn garbage_collect_session_directories(sess: &Session) -> io::Result<()> {
     debug!("garbage_collect_session_directories() - begin");
 
     let session_directory = sess.incr_comp_session_dir();
diff --git a/compiler/rustc_incremental/src/persist/load.rs b/compiler/rustc_incremental/src/persist/load.rs
index 2310d0b12ef..cbd55fe4205 100644
--- a/compiler/rustc_incremental/src/persist/load.rs
+++ b/compiler/rustc_incremental/src/persist/load.rs
@@ -1,4 +1,4 @@
-//! Code to save/load the dep-graph from files.
+//! Code to load the dep-graph from files.
 
 use crate::errors;
 use rustc_data_structures::memmap::Mmap;
diff --git a/compiler/rustc_incremental/src/persist/mod.rs b/compiler/rustc_incremental/src/persist/mod.rs
index fdecaca5a2d..94c05f4a2c8 100644
--- a/compiler/rustc_incremental/src/persist/mod.rs
+++ b/compiler/rustc_incremental/src/persist/mod.rs
@@ -11,14 +11,11 @@ mod save;
 mod work_product;
 
 pub use fs::finalize_session_directory;
-pub use fs::garbage_collect_session_directories;
 pub use fs::in_incr_comp_dir;
 pub use fs::in_incr_comp_dir_sess;
-pub use fs::prepare_session_directory;
 pub use load::load_query_result_cache;
 pub use load::setup_dep_graph;
 pub use load::LoadResult;
 pub use save::save_dep_graph;
 pub use save::save_work_product_index;
 pub use work_product::copy_cgu_workproduct_to_incr_comp_cache_dir;
-pub use work_product::delete_workproduct_files;
diff --git a/compiler/rustc_incremental/src/persist/save.rs b/compiler/rustc_incremental/src/persist/save.rs
index 210da751d95..fa21320be26 100644
--- a/compiler/rustc_incremental/src/persist/save.rs
+++ b/compiler/rustc_incremental/src/persist/save.rs
@@ -1,3 +1,4 @@
+use crate::assert_dep_graph::assert_dep_graph;
 use crate::errors;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync::join;
@@ -39,7 +40,7 @@ pub fn save_dep_graph(tcx: TyCtxt<'_>) {
         let dep_graph_path = dep_graph_path(sess);
         let staging_dep_graph_path = staging_dep_graph_path(sess);
 
-        sess.time("assert_dep_graph", || crate::assert_dep_graph(tcx));
+        sess.time("assert_dep_graph", || assert_dep_graph(tcx));
         sess.time("check_dirty_clean", || dirty_clean::check_dirty_clean_annotations(tcx));
 
         if sess.opts.unstable_opts.incremental_info {
diff --git a/compiler/rustc_incremental/src/persist/work_product.rs b/compiler/rustc_incremental/src/persist/work_product.rs
index bce5ca1e16b..fb96bed5a71 100644
--- a/compiler/rustc_incremental/src/persist/work_product.rs
+++ b/compiler/rustc_incremental/src/persist/work_product.rs
@@ -11,7 +11,8 @@ use rustc_session::Session;
 use std::fs as std_fs;
 use std::path::Path;
 
-/// Copies a CGU work product to the incremental compilation directory, so next compilation can find and reuse it.
+/// Copies a CGU work product to the incremental compilation directory, so next compilation can
+/// find and reuse it.
 pub fn copy_cgu_workproduct_to_incr_comp_cache_dir(
     sess: &Session,
     cgu_name: &str,
@@ -45,7 +46,7 @@ pub fn copy_cgu_workproduct_to_incr_comp_cache_dir(
 }
 
 /// Removes files for a given work product.
-pub fn delete_workproduct_files(sess: &Session, work_product: &WorkProduct) {
+pub(crate) fn delete_workproduct_files(sess: &Session, work_product: &WorkProduct) {
     for (_, path) in work_product.saved_files.items().into_sorted_stable_ord() {
         let path = in_incr_comp_dir_sess(sess, path);
         if let Err(err) = std_fs::remove_file(&path) {
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 750d49a1c2d..3d191669b1a 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -614,7 +614,7 @@ fn test_codegen_options_tracking_hash() {
     tracked!(force_frame_pointers, Some(false));
     tracked!(force_unwind_tables, Some(true));
     tracked!(inline_threshold, Some(0xf007ba11));
-    tracked!(instrument_coverage, Some(InstrumentCoverage::All));
+    tracked!(instrument_coverage, InstrumentCoverage::All);
     tracked!(link_dead_code, Some(true));
     tracked!(linker_plugin_lto, LinkerPluginLto::LinkerPluginAuto);
     tracked!(llvm_args, vec![String::from("1"), String::from("2")]);
diff --git a/compiler/rustc_middle/src/ty/flags.rs b/compiler/rustc_middle/src/ty/flags.rs
index d75315b7ac9..a348e9f608a 100644
--- a/compiler/rustc_middle/src/ty/flags.rs
+++ b/compiler/rustc_middle/src/ty/flags.rs
@@ -134,7 +134,7 @@ impl FlagComputation {
                 if should_remove_further_specializable {
                     self.flags -= TypeFlags::STILL_FURTHER_SPECIALIZABLE;
                 }
-                self.add_flags(TypeFlags::HAS_TY_GENERATOR);
+                self.add_flags(TypeFlags::HAS_TY_COROUTINE);
             }
 
             &ty::Closure(_, args) => {
diff --git a/compiler/rustc_middle/src/ty/visit.rs b/compiler/rustc_middle/src/ty/visit.rs
index 15de9948644..ab0999b3f19 100644
--- a/compiler/rustc_middle/src/ty/visit.rs
+++ b/compiler/rustc_middle/src/ty/visit.rs
@@ -48,7 +48,7 @@ pub trait TypeVisitableExt<'tcx>: TypeVisitable<TyCtxt<'tcx>> {
         self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
     }
     fn has_coroutines(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_TY_GENERATOR)
+        self.has_type_flags(TypeFlags::HAS_TY_COROUTINE)
     }
     fn references_error(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_ERROR)
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 597303cae73..41b19ecb63a 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -159,8 +159,9 @@ pub struct Parser<'a> {
     /// appropriately.
     ///
     /// See the comments in the `parse_path_segment` function for more details.
-    unmatched_angle_bracket_count: u32,
-    max_angle_bracket_count: u32,
+    unmatched_angle_bracket_count: u16,
+    max_angle_bracket_count: u16,
+    angle_bracket_nesting: u16,
 
     last_unexpected_token_span: Option<Span>,
     /// If present, this `Parser` is not parsing Rust code but rather a macro call.
@@ -394,6 +395,7 @@ impl<'a> Parser<'a> {
             break_last_token: false,
             unmatched_angle_bracket_count: 0,
             max_angle_bracket_count: 0,
+            angle_bracket_nesting: 0,
             last_unexpected_token_span: None,
             subparser_name,
             capture_state: CaptureState {
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 2fcb9a78cfd..4969e672a72 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -487,10 +487,24 @@ impl<'a> Parser<'a> {
         // Take a snapshot before attempting to parse - we can restore this later.
         let snapshot = is_first_invocation.then(|| self.clone());
 
+        self.angle_bracket_nesting += 1;
         debug!("parse_generic_args_with_leading_angle_bracket_recovery: (snapshotting)");
         match self.parse_angle_args(ty_generics) {
-            Ok(args) => Ok(args),
+            Ok(args) => {
+                self.angle_bracket_nesting -= 1;
+                Ok(args)
+            }
+            Err(mut e) if self.angle_bracket_nesting > 10 => {
+                self.angle_bracket_nesting -= 1;
+                // When encountering severely malformed code where there are several levels of
+                // nested unclosed angle args (`f::<f::<f::<f::<...`), we avoid severe O(n^2)
+                // behavior by bailing out earlier (#117080).
+                e.emit();
+                rustc_errors::FatalError.raise();
+            }
             Err(e) if is_first_invocation && self.unmatched_angle_bracket_count > 0 => {
+                self.angle_bracket_nesting -= 1;
+
                 // Swap `self` with our backup of the parser state before attempting to parse
                 // generic arguments.
                 let snapshot = mem::replace(self, snapshot.unwrap());
@@ -520,8 +534,8 @@ impl<'a> Parser<'a> {
                     // Make a span over ${unmatched angle bracket count} characters.
                     // This is safe because `all_angle_brackets` ensures that there are only `<`s,
                     // i.e. no multibyte characters, in this range.
-                    let span =
-                        lo.with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count));
+                    let span = lo
+                        .with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count.into()));
                     self.sess.emit_err(errors::UnmatchedAngle {
                         span,
                         plural: snapshot.unmatched_angle_bracket_count > 1,
@@ -531,7 +545,10 @@ impl<'a> Parser<'a> {
                     self.parse_angle_args(ty_generics)
                 }
             }
-            Err(e) => Err(e),
+            Err(e) => {
+                self.angle_bracket_nesting -= 1;
+                Err(e)
+            }
         }
     }
 
diff --git a/compiler/rustc_resolve/src/check_unused.rs b/compiler/rustc_resolve/src/check_unused.rs
index 352bf98d01f..3b1f957c890 100644
--- a/compiler/rustc_resolve/src/check_unused.rs
+++ b/compiler/rustc_resolve/src/check_unused.rs
@@ -335,7 +335,7 @@ impl Resolver<'_, '_> {
 
         for unused in visitor.unused_imports.values() {
             let mut fixes = Vec::new();
-            let mut spans = match calc_unused_spans(unused, unused.use_tree, unused.use_tree_id) {
+            let spans = match calc_unused_spans(unused, unused.use_tree, unused.use_tree_id) {
                 UnusedSpanResult::Used => continue,
                 UnusedSpanResult::FlatUnused(span, remove) => {
                     fixes.push((remove, String::new()));
@@ -353,20 +353,19 @@ impl Resolver<'_, '_> {
                 }
             };
 
-            let len = spans.len();
-            spans.sort();
-            let ms = MultiSpan::from_spans(spans.clone());
-            let mut span_snippets = spans
+            let ms = MultiSpan::from_spans(spans);
+
+            let mut span_snippets = ms
+                .primary_spans()
                 .iter()
-                .filter_map(|s| match tcx.sess.source_map().span_to_snippet(*s) {
-                    Ok(s) => Some(format!("`{s}`")),
-                    _ => None,
-                })
+                .filter_map(|span| tcx.sess.source_map().span_to_snippet(*span).ok())
+                .map(|s| format!("`{s}`"))
                 .collect::<Vec<String>>();
             span_snippets.sort();
+
             let msg = format!(
                 "unused import{}{}",
-                pluralize!(len),
+                pluralize!(ms.primary_spans().len()),
                 if !span_snippets.is_empty() {
                     format!(": {}", span_snippets.join(", "))
                 } else {
@@ -376,7 +375,7 @@ impl Resolver<'_, '_> {
 
             let fix_msg = if fixes.len() == 1 && fixes[0].0 == unused.item_span {
                 "remove the whole `use` item"
-            } else if spans.len() > 1 {
+            } else if ms.primary_spans().len() > 1 {
                 "remove the unused imports"
             } else {
                 "remove the unused import"
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 78e410488c3..7aced414ed6 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -2743,13 +2743,11 @@ pub fn build_session_options(
     // This is what prevents them from being used on stable compilers.
     match cg.instrument_coverage {
         // Stable values:
-        Some(InstrumentCoverage::All | InstrumentCoverage::Off) | None => {}
+        InstrumentCoverage::All | InstrumentCoverage::Off => {}
         // Unstable values:
-        Some(
-            InstrumentCoverage::Branch
-            | InstrumentCoverage::ExceptUnusedFunctions
-            | InstrumentCoverage::ExceptUnusedGenerics,
-        ) => {
+        InstrumentCoverage::Branch
+        | InstrumentCoverage::ExceptUnusedFunctions
+        | InstrumentCoverage::ExceptUnusedGenerics => {
             if !unstable_opts.unstable_options {
                 handler.early_error(
                     "`-C instrument-coverage=branch` and `-C instrument-coverage=except-*` \
@@ -2759,7 +2757,7 @@ pub fn build_session_options(
         }
     }
 
-    if cg.instrument_coverage.is_some() && cg.instrument_coverage != Some(InstrumentCoverage::Off) {
+    if cg.instrument_coverage != InstrumentCoverage::Off {
         if cg.profile_generate.enabled() || cg.profile_use.is_some() {
             handler.early_error(
                 "option `-C instrument-coverage` is not compatible with either `-C profile-use` \
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 35c167837e5..fd473acbd3c 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -294,7 +294,7 @@ impl CodegenOptions {
     // JUSTIFICATION: defn of the suggested wrapper fn
     #[allow(rustc::bad_opt_access)]
     pub fn instrument_coverage(&self) -> InstrumentCoverage {
-        self.instrument_coverage.unwrap_or(InstrumentCoverage::Off)
+        self.instrument_coverage
     }
 }
 
@@ -913,23 +913,23 @@ mod parse {
     }
 
     pub(crate) fn parse_instrument_coverage(
-        slot: &mut Option<InstrumentCoverage>,
+        slot: &mut InstrumentCoverage,
         v: Option<&str>,
     ) -> bool {
         if v.is_some() {
-            let mut bool_arg = None;
-            if parse_opt_bool(&mut bool_arg, v) {
-                *slot = bool_arg.unwrap().then_some(InstrumentCoverage::All);
+            let mut bool_arg = false;
+            if parse_bool(&mut bool_arg, v) {
+                *slot = if bool_arg { InstrumentCoverage::All } else { InstrumentCoverage::Off };
                 return true;
             }
         }
 
         let Some(v) = v else {
-            *slot = Some(InstrumentCoverage::All);
+            *slot = InstrumentCoverage::All;
             return true;
         };
 
-        *slot = Some(match v {
+        *slot = match v {
             "all" => InstrumentCoverage::All,
             "branch" => InstrumentCoverage::Branch,
             "except-unused-generics" | "except_unused_generics" => {
@@ -940,7 +940,7 @@ mod parse {
             }
             "off" | "no" | "n" | "false" | "0" => InstrumentCoverage::Off,
             _ => return false,
-        });
+        };
         true
     }
 
@@ -1352,7 +1352,7 @@ options! {
     inline_threshold: Option<u32> = (None, parse_opt_number, [TRACKED],
         "set the threshold for inlining a function"),
     #[rustc_lint_opt_deny_field_access("use `Session::instrument_coverage` instead of this field")]
-    instrument_coverage: Option<InstrumentCoverage> = (None, parse_instrument_coverage, [TRACKED],
+    instrument_coverage: InstrumentCoverage = (InstrumentCoverage::Off, parse_instrument_coverage, [TRACKED],
         "instrument the generated code to support LLVM source-based code coverage \
         reports (note, the compiler build config must include `profiler = true`); \
         implies `-C symbol-mangling-version=v0`. Optional values are:
diff --git a/compiler/rustc_smir/src/rustc_smir/mod.rs b/compiler/rustc_smir/src/rustc_smir/mod.rs
index 928536721c9..86b49eed4d1 100644
--- a/compiler/rustc_smir/src/rustc_smir/mod.rs
+++ b/compiler/rustc_smir/src/rustc_smir/mod.rs
@@ -287,9 +287,8 @@ impl<'tcx> Stable<'tcx> for mir::Body<'tcx> {
     type T = stable_mir::mir::Body;
 
     fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
-        stable_mir::mir::Body {
-            blocks: self
-                .basic_blocks
+        stable_mir::mir::Body::new(
+            self.basic_blocks
                 .iter()
                 .map(|block| stable_mir::mir::BasicBlock {
                     terminator: block.terminator().stable(tables),
@@ -300,15 +299,15 @@ impl<'tcx> Stable<'tcx> for mir::Body<'tcx> {
                         .collect(),
                 })
                 .collect(),
-            locals: self
-                .local_decls
+            self.local_decls
                 .iter()
                 .map(|decl| stable_mir::mir::LocalDecl {
                     ty: decl.ty.stable(tables),
                     span: decl.source_info.span.stable(tables),
                 })
                 .collect(),
-        }
+            self.arg_count,
+        )
     }
 }
 
diff --git a/compiler/rustc_type_ir/src/flags.rs b/compiler/rustc_type_ir/src/flags.rs
index 2acb903c217..d5cadd4e83a 100644
--- a/compiler/rustc_type_ir/src/flags.rs
+++ b/compiler/rustc_type_ir/src/flags.rs
@@ -113,7 +113,7 @@ bitflags! {
         /// Does this value have `InferConst::Fresh`?
         const HAS_CT_FRESH                = 1 << 22;
 
-        /// Does this have `Generator` or `GeneratorWitness`?
-        const HAS_TY_GENERATOR            = 1 << 23;
+        /// Does this have `Coroutine` or `CoroutineWitness`?
+        const HAS_TY_COROUTINE            = 1 << 23;
     }
 }
diff --git a/compiler/stable_mir/src/mir/body.rs b/compiler/stable_mir/src/mir/body.rs
index c2e79eaaf3f..50c37e8f910 100644
--- a/compiler/stable_mir/src/mir/body.rs
+++ b/compiler/stable_mir/src/mir/body.rs
@@ -2,10 +2,60 @@ use crate::ty::{AdtDef, ClosureDef, Const, CoroutineDef, GenericArgs, Movability
 use crate::Opaque;
 use crate::{ty::Ty, Span};
 
+/// The SMIR representation of a single function.
 #[derive(Clone, Debug)]
 pub struct Body {
     pub blocks: Vec<BasicBlock>,
-    pub locals: LocalDecls,
+
+    // Declarations of locals within the function.
+    //
+    // The first local is the return value pointer, followed by `arg_count`
+    // locals for the function arguments, followed by any user-declared
+    // variables and temporaries.
+    locals: LocalDecls,
+
+    // The number of arguments this function takes.
+    arg_count: usize,
+}
+
+impl Body {
+    /// Constructs a `Body`.
+    ///
+    /// A constructor is required to build a `Body` from outside the crate
+    /// because the `arg_count` and `locals` fields are private.
+    pub fn new(blocks: Vec<BasicBlock>, locals: LocalDecls, arg_count: usize) -> Self {
+        // If locals doesn't contain enough entries, it can lead to panics in
+        // `ret_local`, `arg_locals`, and `inner_locals`.
+        assert!(
+            locals.len() > arg_count,
+            "A Body must contain at least a local for the return value and each of the function's arguments"
+        );
+        Self { blocks, locals, arg_count }
+    }
+
+    /// Return local that holds this function's return value.
+    pub fn ret_local(&self) -> &LocalDecl {
+        &self.locals[0]
+    }
+
+    /// Locals in `self` that correspond to this function's arguments.
+    pub fn arg_locals(&self) -> &[LocalDecl] {
+        &self.locals[1..][..self.arg_count]
+    }
+
+    /// Inner locals for this function. These are the locals that are
+    /// neither the return local nor the argument locals.
+    pub fn inner_locals(&self) -> &[LocalDecl] {
+        &self.locals[self.arg_count + 1..]
+    }
+
+    /// Convenience function to get all the locals in this function.
+    ///
+    /// Locals are typically accessed via the more specific methods `ret_local`,
+    /// `arg_locals`, and `inner_locals`.
+    pub fn locals(&self) -> &[LocalDecl] {
+        &self.locals
+    }
 }
 
 type LocalDecls = Vec<LocalDecl>;
@@ -467,7 +517,7 @@ pub enum NullOp {
 }
 
 impl Operand {
-    pub fn ty(&self, locals: &LocalDecls) -> Ty {
+    pub fn ty(&self, locals: &[LocalDecl]) -> Ty {
         match self {
             Operand::Copy(place) | Operand::Move(place) => place.ty(locals),
             Operand::Constant(c) => c.ty(),
@@ -482,7 +532,7 @@ impl Constant {
 }
 
 impl Place {
-    pub fn ty(&self, locals: &LocalDecls) -> Ty {
+    pub fn ty(&self, locals: &[LocalDecl]) -> Ty {
         let _start_ty = locals[self.local].ty;
         todo!("Implement projection")
     }