Rollup merge of #91638 - scottmcm:less-inband-2-of-28, r=petrochenkov

Remove `in_band_lifetimes` from `rustc_mir_transform`

Like #91580, this was inspired by the conversation in #44524 about possibly removing the feature from the compiler.  This crate is a heavy `'tcx` user, so is a nice case study.

r? ``@petrochenkov``

Three interesting ones:

This one had the `'tcx` declared on the function, despite the trait taking a `'tcx`:
```diff
-impl Visitor<'_> for UsedLocals {
+impl<'tcx> Visitor<'tcx> for UsedLocals {
     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
```

This one use in-band for one, and underscore for the other:
```diff
-pub fn remove_dead_blocks(tcx: TyCtxt<'tcx>, body: &mut Body<'_>) {
+pub fn remove_dead_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
```

A spurious name, since there's no single-use-lifetime warning:
```diff
-pub fn run_passes(tcx: TyCtxt<'tcx>, body: &'mir mut Body<'tcx>, passes: &[&dyn MirPass<'tcx>]) {
+pub fn run_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, passes: &[&dyn MirPass<'tcx>]) {
```

compiler/rustc_mir_transform/src/add_retag.rs

@@ -34,7 +34,7 @@ fn is_stable(place: PlaceRef<'_>) -> bool {
 }
 
 /// Determine whether this type may be a reference (or box), and thus needs retagging.
-fn may_be_reference(ty: Ty<'tcx>) -> bool {
+fn may_be_reference(ty: Ty<'_>) -> bool {
     match ty.kind() {
         // Primitive types that are not references
         ty::Bool

compiler/rustc_mir_transform/src/check_const_item_mutation.rs

@@ -23,7 +23,7 @@ struct ConstMutationChecker<'a, 'tcx> {
     target_local: Option<Local>,
 }
 
-impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> {
+impl<'tcx> ConstMutationChecker<'_, 'tcx> {
     fn is_const_item(&self, local: Local) -> Option<DefId> {
         if let Some(box LocalInfo::ConstRef { def_id }) = self.body.local_decls[local].local_info {
             Some(def_id)
@@ -95,7 +95,7 @@ impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for ConstMutationChecker<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for ConstMutationChecker<'_, 'tcx> {
     fn visit_statement(&mut self, stmt: &Statement<'tcx>, loc: Location) {
         if let StatementKind::Assign(box (lhs, _)) = &stmt.kind {
             // Check for assignment to fields of a constant

compiler/rustc_mir_transform/src/check_packed_ref.rs

@@ -66,7 +66,7 @@ fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for PackedRefChecker<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
         // Make sure we know where in the MIR we are.
         self.source_info = terminator.source_info;

compiler/rustc_mir_transform/src/check_unsafety.rs

@@ -46,7 +46,7 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
         self.source_info = terminator.source_info;
         match terminator.kind {
@@ -244,7 +244,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
+impl<'tcx> UnsafetyChecker<'_, 'tcx> {
     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
         // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
         assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
@@ -397,7 +397,7 @@ struct UnusedUnsafeVisitor<'a> {
     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 }
 
-impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
+impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_> {
     type Map = intravisit::ErasedMap<'tcx>;
 
     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {

compiler/rustc_mir_transform/src/const_debuginfo.rs

@@ -89,7 +89,7 @@ fn find_optimization_oportunities<'tcx>(body: &Body<'tcx>) -> Vec<(Local, Consta
     eligable_locals
 }
 
-impl<'tcx> Visitor<'tcx> for LocalUseVisitor {
+impl Visitor<'_> for LocalUseVisitor {
     fn visit_local(&mut self, local: &Local, context: PlaceContext, location: Location) {
         if context.is_mutating_use() {
             self.local_mutating_uses[*local] = self.local_mutating_uses[*local].saturating_add(1);

compiler/rustc_mir_transform/src/const_goto.rs

@@ -54,7 +54,7 @@ impl<'tcx> MirPass<'tcx> for ConstGoto {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for ConstGotoOptimizationFinder<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for ConstGotoOptimizationFinder<'_, 'tcx> {
     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
         let _: Option<_> = try {
             let target = terminator.kind.as_goto()?;

compiler/rustc_mir_transform/src/const_prop.rs

@@ -171,7 +171,7 @@ struct ConstPropMachine<'mir, 'tcx> {
     can_const_prop: IndexVec<Local, ConstPropMode>,
 }
 
-impl<'mir, 'tcx> ConstPropMachine<'mir, 'tcx> {
+impl ConstPropMachine<'_, '_> {
     fn new(
         only_propagate_inside_block_locals: BitSet<Local>,
         can_const_prop: IndexVec<Local, ConstPropMode>,
@@ -308,14 +308,14 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
     }
 
     #[inline(always)]
-    fn stack(
+    fn stack<'a>(
         ecx: &'a InterpCx<'mir, 'tcx, Self>,
     ) -> &'a [Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>] {
         &ecx.machine.stack
     }
 
     #[inline(always)]
-    fn stack_mut(
+    fn stack_mut<'a>(
         ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
     ) -> &'a mut Vec<Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>> {
         &mut ecx.machine.stack
@@ -336,7 +336,7 @@ struct ConstPropagator<'mir, 'tcx> {
     source_info: Option<SourceInfo>,
 }
 
-impl<'mir, 'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'mir, 'tcx> {
+impl<'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'_, 'tcx> {
     type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
 
     #[inline]
@@ -345,21 +345,21 @@ impl<'mir, 'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'mir, 'tcx> {
     }
 }
 
-impl<'mir, 'tcx> HasDataLayout for ConstPropagator<'mir, 'tcx> {
+impl HasDataLayout for ConstPropagator<'_, '_> {
     #[inline]
     fn data_layout(&self) -> &TargetDataLayout {
         &self.tcx.data_layout
     }
 }
 
-impl<'mir, 'tcx> ty::layout::HasTyCtxt<'tcx> for ConstPropagator<'mir, 'tcx> {
+impl<'tcx> ty::layout::HasTyCtxt<'tcx> for ConstPropagator<'_, 'tcx> {
     #[inline]
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 }
 
-impl<'mir, 'tcx> ty::layout::HasParamEnv<'tcx> for ConstPropagator<'mir, 'tcx> {
+impl<'tcx> ty::layout::HasParamEnv<'tcx> for ConstPropagator<'_, 'tcx> {
     #[inline]
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.param_env
@@ -971,7 +971,7 @@ struct CanConstProp {
 
 impl CanConstProp {
     /// Returns true if `local` can be propagated
-    fn check(
+    fn check<'tcx>(
         tcx: TyCtxt<'tcx>,
         param_env: ParamEnv<'tcx>,
         body: &Body<'tcx>,
@@ -1019,7 +1019,7 @@ impl CanConstProp {
     }
 }
 
-impl<'tcx> Visitor<'tcx> for CanConstProp {
+impl Visitor<'_> for CanConstProp {
     fn visit_local(&mut self, &local: &Local, context: PlaceContext, _: Location) {
         use rustc_middle::mir::visit::PlaceContext::*;
         match context {
@@ -1079,7 +1079,7 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
     }
 }
 
-impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
+impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }

compiler/rustc_mir_transform/src/coverage/debug.rs

@@ -629,7 +629,7 @@ impl UsedExpressions {
 }
 
 /// Generates the MIR pass `CoverageSpan`-specific spanview dump file.
-pub(super) fn dump_coverage_spanview(
+pub(super) fn dump_coverage_spanview<'tcx>(
     tcx: TyCtxt<'tcx>,
     mir_body: &mir::Body<'tcx>,
     basic_coverage_blocks: &CoverageGraph,
@@ -651,7 +651,7 @@ pub(super) fn dump_coverage_spanview(
 }
 
 /// Converts the computed `BasicCoverageBlockData`s into `SpanViewable`s.
-fn span_viewables(
+fn span_viewables<'tcx>(
     tcx: TyCtxt<'tcx>,
     mir_body: &mir::Body<'tcx>,
     basic_coverage_blocks: &CoverageGraph,
@@ -670,7 +670,7 @@ fn span_viewables(
 }
 
 /// Generates the MIR pass coverage-specific graphviz dump file.
-pub(super) fn dump_coverage_graphviz(
+pub(super) fn dump_coverage_graphviz<'tcx>(
     tcx: TyCtxt<'tcx>,
     mir_body: &mir::Body<'tcx>,
     pass_name: &str,
@@ -750,7 +750,7 @@ pub(super) fn dump_coverage_graphviz(
         .expect("Unexpected error writing BasicCoverageBlock graphviz DOT file");
 }
 
-fn bcb_to_string_sections(
+fn bcb_to_string_sections<'tcx>(
     tcx: TyCtxt<'tcx>,
     mir_body: &mir::Body<'tcx>,
     debug_counters: &DebugCounters,
@@ -817,7 +817,7 @@ fn bcb_to_string_sections(
 
 /// Returns a simple string representation of a `TerminatorKind` variant, independent of any
 /// values it might hold.
-pub(super) fn term_type(kind: &TerminatorKind<'tcx>) -> &'static str {
+pub(super) fn term_type(kind: &TerminatorKind<'_>) -> &'static str {
     match kind {
         TerminatorKind::Goto { .. } => "Goto",
         TerminatorKind::SwitchInt { .. } => "SwitchInt",

compiler/rustc_mir_transform/src/coverage/graph.rs

@@ -27,7 +27,7 @@ pub(super) struct CoverageGraph {
 }
 
 impl CoverageGraph {
-    pub fn from_mir(mir_body: &mir::Body<'tcx>) -> Self {
+    pub fn from_mir(mir_body: &mir::Body<'_>) -> Self {
         let (bcbs, bb_to_bcb) = Self::compute_basic_coverage_blocks(mir_body);
 
         // Pre-transform MIR `BasicBlock` successors and predecessors into the BasicCoverageBlock
@@ -74,7 +74,7 @@ impl CoverageGraph {
     }
 
     fn compute_basic_coverage_blocks(
-        mir_body: &mir::Body<'tcx>,
+        mir_body: &mir::Body<'_>,
     ) -> (
         IndexVec<BasicCoverageBlock, BasicCoverageBlockData>,
         IndexVec<BasicBlock, Option<BasicCoverageBlock>>,
@@ -267,7 +267,7 @@ impl graph::WithSuccessors for CoverageGraph {
     }
 }
 
-impl graph::GraphPredecessors<'graph> for CoverageGraph {
+impl<'graph> graph::GraphPredecessors<'graph> for CoverageGraph {
     type Item = BasicCoverageBlock;
     type Iter = std::iter::Copied<std::slice::Iter<'graph, BasicCoverageBlock>>;
 }

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -443,7 +443,7 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
 }
 
 fn inject_edge_counter_basic_block(
-    mir_body: &mut mir::Body<'tcx>,
+    mir_body: &mut mir::Body<'_>,
     from_bb: BasicBlock,
     to_bb: BasicBlock,
 ) -> BasicBlock {
@@ -466,7 +466,7 @@ fn inject_edge_counter_basic_block(
 }
 
 fn inject_statement(
-    mir_body: &mut mir::Body<'tcx>,
+    mir_body: &mut mir::Body<'_>,
     counter_kind: CoverageKind,
     bb: BasicBlock,
     some_code_region: Option<CodeRegion>,
@@ -488,7 +488,7 @@ fn inject_statement(
 }
 
 // Non-code expressions are injected into the coverage map, without generating executable code.
-fn inject_intermediate_expression(mir_body: &mut mir::Body<'tcx>, expression: CoverageKind) {
+fn inject_intermediate_expression(mir_body: &mut mir::Body<'_>, expression: CoverageKind) {
     debug_assert!(matches!(expression, CoverageKind::Expression { .. }));
     debug!("  injecting non-code expression {:?}", expression);
     let inject_in_bb = mir::START_BLOCK;

compiler/rustc_mir_transform/src/coverage/query.rs

@@ -137,7 +137,7 @@ fn coverageinfo<'tcx>(tcx: TyCtxt<'tcx>, instance_def: ty::InstanceDef<'tcx>) ->
     coverage_visitor.info
 }
 
-fn covered_file_name<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Option<Symbol> {
+fn covered_file_name(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
     if tcx.is_mir_available(def_id) {
         let body = mir_body(tcx, def_id);
         for bb_data in body.basic_blocks().iter() {

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -21,7 +21,7 @@ pub(super) enum CoverageStatement {
 }
 
 impl CoverageStatement {
-    pub fn format(&self, tcx: TyCtxt<'tcx>, mir_body: &'a mir::Body<'tcx>) -> String {
+    pub fn format<'tcx>(&self, tcx: TyCtxt<'tcx>, mir_body: &mir::Body<'tcx>) -> String {
         match *self {
             Self::Statement(bb, span, stmt_index) => {
                 let stmt = &mir_body[bb].statements[stmt_index];
@@ -86,7 +86,7 @@ impl CoverageSpan {
     }
 
     pub fn for_statement(
-        statement: &Statement<'tcx>,
+        statement: &Statement<'_>,
         span: Span,
         expn_span: Span,
         bcb: BasicCoverageBlock,
@@ -151,18 +151,18 @@ impl CoverageSpan {
         self.bcb == other.bcb
     }
 
-    pub fn format(&self, tcx: TyCtxt<'tcx>, mir_body: &'a mir::Body<'tcx>) -> String {
+    pub fn format<'tcx>(&self, tcx: TyCtxt<'tcx>, mir_body: &mir::Body<'tcx>) -> String {
         format!(
             "{}\n    {}",
             source_range_no_file(tcx, &self.span),
             self.format_coverage_statements(tcx, mir_body).replace("\n", "\n    "),
         )
     }
 
-    pub fn format_coverage_statements(
+    pub fn format_coverage_statements<'tcx>(
         &self,
         tcx: TyCtxt<'tcx>,
-        mir_body: &'a mir::Body<'tcx>,
+        mir_body: &mir::Body<'tcx>,
     ) -> String {
         let mut sorted_coverage_statements = self.coverage_statements.clone();
         sorted_coverage_statements.sort_unstable_by_key(|covstmt| match *covstmt {
@@ -803,7 +803,7 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
 
 /// If the MIR `Statement` has a span contributive to computing coverage spans,
 /// return it; otherwise return `None`.
-pub(super) fn filtered_statement_span(statement: &'a Statement<'tcx>) -> Option<Span> {
+pub(super) fn filtered_statement_span(statement: &Statement<'_>) -> Option<Span> {
     match statement.kind {
         // These statements have spans that are often outside the scope of the executed source code
         // for their parent `BasicBlock`.
@@ -847,7 +847,7 @@ pub(super) fn filtered_statement_span(statement: &'a Statement<'tcx>) -> Option<
 
 /// If the MIR `Terminator` has a span contributive to computing coverage spans,
 /// return it; otherwise return `None`.
-pub(super) fn filtered_terminator_span(terminator: &'a Terminator<'tcx>) -> Option<Span> {
+pub(super) fn filtered_terminator_span(terminator: &Terminator<'_>) -> Option<Span> {
     match terminator.kind {
         // These terminators have spans that don't positively contribute to computing a reasonable
         // span of actually executed source code. (For example, SwitchInt terminators extracted from

compiler/rustc_mir_transform/src/coverage/tests.rs

@@ -180,7 +180,7 @@ impl<'tcx> MockBlocks<'tcx> {
     }
 }
 
-fn debug_basic_blocks(mir_body: &Body<'tcx>) -> String {
+fn debug_basic_blocks<'tcx>(mir_body: &Body<'tcx>) -> String {
     format!(
         "{:?}",
         mir_body
@@ -273,7 +273,7 @@ fn print_coverage_graphviz(
 }
 
 /// Create a mock `Body` with a simple flow.
-fn goto_switchint() -> Body<'a> {
+fn goto_switchint<'a>() -> Body<'a> {
     let mut blocks = MockBlocks::new();
     let start = blocks.call(None);
     let goto = blocks.goto(Some(start));
@@ -363,7 +363,7 @@ fn test_covgraph_goto_switchint() {
 }
 
 /// Create a mock `Body` with a loop.
-fn switchint_then_loop_else_return() -> Body<'a> {
+fn switchint_then_loop_else_return<'a>() -> Body<'a> {
     let mut blocks = MockBlocks::new();
     let start = blocks.call(None);
     let switchint = blocks.switchint(Some(start));
@@ -449,7 +449,7 @@ fn test_covgraph_switchint_then_loop_else_return() {
 }
 
 /// Create a mock `Body` with nested loops.
-fn switchint_loop_then_inner_loop_else_break() -> Body<'a> {
+fn switchint_loop_then_inner_loop_else_break<'a>() -> Body<'a> {
     let mut blocks = MockBlocks::new();
     let start = blocks.call(None);
     let switchint = blocks.switchint(Some(start));