Auto merge of #8025 - flip1995:rustup, r=flip1995

Rustup

Re-sync, because I didn't get to syncing things back to rustc.

r? `@ghost`

changelog: none

clippy_lints/src/loops/explicit_counter_loop.rs

@@ -1,6 +1,4 @@
-use super::{
-    get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor, EXPLICIT_COUNTER_LOOP,
-};
+use super::{make_iterator_snippet, IncrementVisitor, InitializeVisitor, EXPLICIT_COUNTER_LOOP};
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::{get_enclosing_block, is_integer_const};
@@ -38,15 +36,13 @@ pub(super) fn check<'tcx>(
                 then {
                     let mut applicability = Applicability::MachineApplicable;
 
-                    let for_span = get_span_of_entire_for_loop(expr);
-
                     let int_name = match ty.map(ty::TyS::kind) {
                         // usize or inferred
                         Some(ty::Uint(UintTy::Usize)) | None => {
                             span_lint_and_sugg(
                                 cx,
                                 EXPLICIT_COUNTER_LOOP,
-                                for_span.with_hi(arg.span.hi()),
+                                expr.span.with_hi(arg.span.hi()),
                                 &format!("the variable `{}` is used as a loop counter", name),
                                 "consider using",
                                 format!(
@@ -67,11 +63,11 @@ pub(super) fn check<'tcx>(
                     span_lint_and_then(
                         cx,
                         EXPLICIT_COUNTER_LOOP,
-                        for_span.with_hi(arg.span.hi()),
+                        expr.span.with_hi(arg.span.hi()),
                         &format!("the variable `{}` is used as a loop counter", name),
                         |diag| {
                             diag.span_suggestion(
-                                for_span.with_hi(arg.span.hi()),
+                                expr.span.with_hi(arg.span.hi()),
                                 "consider using",
                                 format!(
                                     "for ({}, {}) in (0_{}..).zip({})",

clippy_lints/src/loops/manual_memcpy.rs

@@ -1,4 +1,4 @@
-use super::{get_span_of_entire_for_loop, IncrementVisitor, InitializeVisitor, MANUAL_MEMCPY};
+use super::{IncrementVisitor, InitializeVisitor, MANUAL_MEMCPY};
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet;
 use clippy_utils::sugg::Sugg;
@@ -86,7 +86,7 @@ pub(super) fn check<'tcx>(
                 span_lint_and_sugg(
                     cx,
                     MANUAL_MEMCPY,
-                    get_span_of_entire_for_loop(expr),
+                    expr.span,
                     "it looks like you're manually copying between slices",
                     "try replacing the loop by",
                     big_sugg,

clippy_lints/src/loops/mod.rs

@@ -23,7 +23,7 @@ use rustc_hir::{Expr, ExprKind, LoopSource, Pat};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
-use utils::{get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor};
+use utils::{make_iterator_snippet, IncrementVisitor, InitializeVisitor};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -584,7 +584,15 @@ declare_lint_pass!(Loops => [
 impl<'tcx> LateLintPass<'tcx> for Loops {
     #[allow(clippy::too_many_lines)]
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if let Some(higher::ForLoop { pat, arg, body, span }) = higher::ForLoop::hir(expr) {
+        let for_loop = higher::ForLoop::hir(expr);
+        if let Some(higher::ForLoop {
+            pat,
+            arg,
+            body,
+            loop_id,
+            span,
+        }) = for_loop
+        {
             // we don't want to check expanded macros
             // this check is not at the top of the function
             // since higher::for_loop expressions are marked as expansions
@@ -592,6 +600,9 @@ impl<'tcx> LateLintPass<'tcx> for Loops {
                 return;
             }
             check_for_loop(cx, pat, arg, body, expr, span);
+            if let ExprKind::Block(block, _) = body.kind {
+                never_loop::check(cx, block, loop_id, span, for_loop.as_ref());
+            }
         }
 
         // we don't want to check expanded macros
@@ -600,7 +611,9 @@ impl<'tcx> LateLintPass<'tcx> for Loops {
         }
 
         // check for never_loop
-        never_loop::check(cx, expr);
+        if let ExprKind::Loop(block, ..) = expr.kind {
+            never_loop::check(cx, block, expr.hir_id, expr.span, None);
+        }
 
         // check for `loop { if let {} else break }` that could be `while let`
         // (also matches an explicit "match" instead of "if let")

clippy_lints/src/loops/never_loop.rs

@@ -4,35 +4,41 @@ use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher::ForLoop;
 use clippy_utils::source::snippet;
 use rustc_errors::Applicability;
-use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, LoopSource, Node, Pat, Stmt, StmtKind};
+use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, Pat, Stmt, StmtKind};
 use rustc_lint::LateContext;
+use rustc_span::Span;
 use std::iter::{once, Iterator};
 
-pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-    if let ExprKind::Loop(block, _, source, _) = expr.kind {
-        match never_loop_block(block, expr.hir_id) {
-            NeverLoopResult::AlwaysBreak => {
-                span_lint_and_then(cx, NEVER_LOOP, expr.span, "this loop never actually loops", |diag| {
-                    if_chain! {
-                        if source == LoopSource::ForLoop;
-                        if let Some((_, Node::Expr(parent_match))) = cx.tcx.hir().parent_iter(expr.hir_id).nth(1);
-                        if let Some(ForLoop { arg: iterator, pat, span: for_span, .. }) = ForLoop::hir(parent_match);
-                        then {
-                            // Suggests using an `if let` instead. This is `Unspecified` because the
-                            // loop may (probably) contain `break` statements which would be invalid
-                            // in an `if let`.
-                            diag.span_suggestion_verbose(
-                                for_span.with_hi(iterator.span.hi()),
-                                "if you need the first element of the iterator, try writing",
-                                for_to_if_let_sugg(cx, iterator, pat),
-                                Applicability::Unspecified,
-                            );
-                        }
-                    };
-                });
-            },
-            NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
-        }
+pub(super) fn check(
+    cx: &LateContext<'tcx>,
+    block: &'tcx Block<'_>,
+    loop_id: HirId,
+    span: Span,
+    for_loop: Option<&ForLoop<'_>>,
+) {
+    match never_loop_block(block, loop_id) {
+        NeverLoopResult::AlwaysBreak => {
+            span_lint_and_then(cx, NEVER_LOOP, span, "this loop never actually loops", |diag| {
+                if let Some(ForLoop {
+                    arg: iterator,
+                    pat,
+                    span: for_span,
+                    ..
+                }) = for_loop
+                {
+                    // Suggests using an `if let` instead. This is `Unspecified` because the
+                    // loop may (probably) contain `break` statements which would be invalid
+                    // in an `if let`.
+                    diag.span_suggestion_verbose(
+                        for_span.with_hi(iterator.span.hi()),
+                        "if you need the first element of the iterator, try writing",
+                        for_to_if_let_sugg(cx, iterator, pat),
+                        Applicability::Unspecified,
+                    );
+                }
+            });
+        },
+        NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
     }
 }
 

clippy_lints/src/loops/single_element_loop.rs

@@ -1,4 +1,4 @@
-use super::{get_span_of_entire_for_loop, SINGLE_ELEMENT_LOOP};
+use super::SINGLE_ELEMENT_LOOP;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::single_segment_path;
 use clippy_utils::source::{indent_of, snippet};
@@ -30,7 +30,6 @@ pub(super) fn check<'tcx>(
         if !block.stmts.is_empty();
 
         then {
-            let for_span = get_span_of_entire_for_loop(expr);
             let mut block_str = snippet(cx, block.span, "..").into_owned();
             block_str.remove(0);
             block_str.pop();
@@ -39,7 +38,7 @@ pub(super) fn check<'tcx>(
             span_lint_and_sugg(
                 cx,
                 SINGLE_ELEMENT_LOOP,
-                for_span,
+                expr.span,
                 "for loop over a single element",
                 "try",
                 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),

clippy_lints/src/loops/utils.rs

@@ -8,7 +8,6 @@ use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, HirIdMap, Local, M
 use rustc_lint::LateContext;
 use rustc_middle::hir::map::Map;
 use rustc_middle::ty::Ty;
-use rustc_span::source_map::Span;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_typeck::hir_ty_to_ty;
@@ -330,17 +329,6 @@ impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
     }
 }
 
-// this function assumes the given expression is a `for` loop.
-pub(super) fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
-    // for some reason this is the only way to get the `Span`
-    // of the entire `for` loop
-    if let ExprKind::Match(_, arms, _) = &expr.kind {
-        arms[0].body.span
-    } else {
-        unreachable!()
-    }
-}
-
 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
 /// actual `Iterator` that the loop uses.
 pub(super) fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {

clippy_lints/src/misc.rs

@@ -20,8 +20,8 @@ use rustc_span::symbol::sym;
 use clippy_utils::consts::{constant, Constant};
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{
-    expr_path_res, get_item_name, get_parent_expr, higher, in_constant, is_diag_trait_item, is_integer_const,
-    iter_input_pats, last_path_segment, match_any_def_paths, paths, unsext, SpanlessEq,
+    expr_path_res, get_item_name, get_parent_expr, in_constant, is_diag_trait_item, is_integer_const, iter_input_pats,
+    last_path_segment, match_any_def_paths, paths, unsext, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -321,7 +321,6 @@ impl<'tcx> LateLintPass<'tcx> for MiscLints {
             if let StmtKind::Local(local) = stmt.kind;
             if let PatKind::Binding(an, .., name, None) = local.pat.kind;
             if let Some(init) = local.init;
-            if !higher::is_from_for_desugar(local);
             if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut;
             then {
                 // use the macro callsite when the init span (but not the whole local span)

clippy_lints/src/pattern_type_mismatch.rs

@@ -1,16 +1,12 @@
 use clippy_utils::diagnostics::span_lint_and_help;
-use clippy_utils::last_path_segment;
 use rustc_hir::{
-    intravisit, Body, Expr, ExprKind, FnDecl, HirId, LocalSource, MatchSource, Mutability, Pat, PatField, PatKind,
-    QPath, Stmt, StmtKind,
+    intravisit, Body, Expr, ExprKind, FnDecl, HirId, LocalSource, Mutability, Pat, PatKind, Stmt, StmtKind,
 };
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
-use rustc_middle::ty::subst::SubstsRef;
-use rustc_middle::ty::{AdtDef, FieldDef, Ty, TyKind, VariantDef};
+use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
-use std::iter;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -88,43 +84,28 @@ declare_lint_pass!(PatternTypeMismatch => [PATTERN_TYPE_MISMATCH]);
 impl<'tcx> LateLintPass<'tcx> for PatternTypeMismatch {
     fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
         if let StmtKind::Local(local) = stmt.kind {
-            if let Some(init) = &local.init {
-                if let Some(init_ty) = cx.typeck_results().node_type_opt(init.hir_id) {
-                    let pat = &local.pat;
-                    if in_external_macro(cx.sess(), pat.span) {
-                        return;
-                    }
-                    let deref_possible = match local.source {
-                        LocalSource::Normal => DerefPossible::Possible,
-                        _ => DerefPossible::Impossible,
-                    };
-                    apply_lint(cx, pat, init_ty, deref_possible);
-                }
+            if in_external_macro(cx.sess(), local.pat.span) {
+                return;
             }
+            let deref_possible = match local.source {
+                LocalSource::Normal => DerefPossible::Possible,
+                _ => DerefPossible::Impossible,
+            };
+            apply_lint(cx, local.pat, deref_possible);
         }
     }
 
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if let ExprKind::Match(scrutinee, arms, MatchSource::Normal) = expr.kind {
-            if let Some(expr_ty) = cx.typeck_results().node_type_opt(scrutinee.hir_id) {
-                'pattern_checks: for arm in arms {
-                    let pat = &arm.pat;
-                    if in_external_macro(cx.sess(), pat.span) {
-                        continue 'pattern_checks;
-                    }
-                    if apply_lint(cx, pat, expr_ty, DerefPossible::Possible) {
-                        break 'pattern_checks;
-                    }
+        if let ExprKind::Match(_, arms, _) = expr.kind {
+            for arm in arms {
+                let pat = &arm.pat;
+                if apply_lint(cx, pat, DerefPossible::Possible) {
+                    break;
                 }
             }
         }
-        if let ExprKind::Let(let_pat, let_expr, _) = expr.kind {
-            if let Some(expr_ty) = cx.typeck_results().node_type_opt(let_expr.hir_id) {
-                if in_external_macro(cx.sess(), let_pat.span) {
-                    return;
-                }
-                apply_lint(cx, let_pat, expr_ty, DerefPossible::Possible);
-            }
+        if let ExprKind::Let(let_pat, ..) = expr.kind {
+            apply_lint(cx, let_pat, DerefPossible::Possible);
         }
     }
 
@@ -135,12 +116,10 @@ impl<'tcx> LateLintPass<'tcx> for PatternTypeMismatch {
         _: &'tcx FnDecl<'_>,
         body: &'tcx Body<'_>,
         _: Span,
-        hir_id: HirId,
+        _: HirId,
     ) {
-        if let Some(fn_sig) = cx.typeck_results().liberated_fn_sigs().get(hir_id) {
-            for (param, ty) in iter::zip(body.params, fn_sig.inputs()) {
-                apply_lint(cx, param.pat, ty, DerefPossible::Impossible);
-            }
+        for param in body.params {
+            apply_lint(cx, param.pat, DerefPossible::Impossible);
         }
     }
 }
@@ -151,8 +130,8 @@ enum DerefPossible {
     Impossible,
 }
 
-fn apply_lint<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>, expr_ty: Ty<'tcx>, deref_possible: DerefPossible) -> bool {
-    let maybe_mismatch = find_first_mismatch(cx, pat, expr_ty, Level::Top);
+fn apply_lint<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>, deref_possible: DerefPossible) -> bool {
+    let maybe_mismatch = find_first_mismatch(cx, pat);
     if let Some((span, mutability, level)) = maybe_mismatch {
         span_lint_and_help(
             cx,
@@ -185,132 +164,32 @@ enum Level {
 }
 
 #[allow(rustc::usage_of_ty_tykind)]
-fn find_first_mismatch<'tcx>(
-    cx: &LateContext<'tcx>,
-    pat: &Pat<'_>,
-    ty: Ty<'tcx>,
-    level: Level,
-) -> Option<(Span, Mutability, Level)> {
-    if let PatKind::Ref(sub_pat, _) = pat.kind {
-        if let TyKind::Ref(_, sub_ty, _) = ty.kind() {
-            return find_first_mismatch(cx, sub_pat, sub_ty, Level::Lower);
+fn find_first_mismatch<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>) -> Option<(Span, Mutability, Level)> {
+    let mut result = None;
+    pat.walk(|p| {
+        if result.is_some() {
+            return false;
         }
-    }
-
-    if let TyKind::Ref(_, _, mutability) = *ty.kind() {
-        if is_non_ref_pattern(&pat.kind) {
-            return Some((pat.span, mutability, level));
+        if in_external_macro(cx.sess(), p.span) {
+            return true;
         }
-    }
-
-    if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
-        if let TyKind::Adt(adt_def, substs_ref) = ty.kind() {
-            if let Some(variant) = get_variant(adt_def, qpath) {
-                let field_defs = &variant.fields;
-                return find_first_mismatch_in_struct(cx, field_pats, field_defs, substs_ref);
-            }
-        }
-    }
-
-    if let PatKind::TupleStruct(ref qpath, pats, _) = pat.kind {
-        if let TyKind::Adt(adt_def, substs_ref) = ty.kind() {
-            if let Some(variant) = get_variant(adt_def, qpath) {
-                let field_defs = &variant.fields;
-                let ty_iter = field_defs.iter().map(|field_def| field_def.ty(cx.tcx, substs_ref));
-                return find_first_mismatch_in_tuple(cx, pats, ty_iter);
-            }
-        }
-    }
-
-    if let PatKind::Tuple(pats, _) = pat.kind {
-        if let TyKind::Tuple(..) = ty.kind() {
-            return find_first_mismatch_in_tuple(cx, pats, ty.tuple_fields());
-        }
-    }
-
-    if let PatKind::Or(sub_pats) = pat.kind {
-        for pat in sub_pats {
-            let maybe_mismatch = find_first_mismatch(cx, pat, ty, level);
-            if let Some(mismatch) = maybe_mismatch {
-                return Some(mismatch);
-            }
-        }
-    }
-
-    None
-}
-
-fn get_variant<'a>(adt_def: &'a AdtDef, qpath: &QPath<'_>) -> Option<&'a VariantDef> {
-    if adt_def.is_struct() {
-        if let Some(variant) = adt_def.variants.iter().next() {
-            return Some(variant);
-        }
-    }
-
-    if adt_def.is_enum() {
-        let pat_ident = last_path_segment(qpath).ident;
-        for variant in &adt_def.variants {
-            if variant.ident == pat_ident {
-                return Some(variant);
-            }
-        }
-    }
-
-    None
-}
-
-fn find_first_mismatch_in_tuple<'tcx, I>(
-    cx: &LateContext<'tcx>,
-    pats: &[Pat<'_>],
-    ty_iter_src: I,
-) -> Option<(Span, Mutability, Level)>
-where
-    I: IntoIterator<Item = Ty<'tcx>>,
-{
-    let mut field_tys = ty_iter_src.into_iter();
-    'fields: for pat in pats {
-        let field_ty = if let Some(ty) = field_tys.next() {
-            ty
-        } else {
-            break 'fields;
+        let adjust_pat = match p.kind {
+            PatKind::Or([p, ..]) => p,
+            _ => p,
         };
-
-        let maybe_mismatch = find_first_mismatch(cx, pat, field_ty, Level::Lower);
-        if let Some(mismatch) = maybe_mismatch {
-            return Some(mismatch);
-        }
-    }
-
-    None
-}
-
-fn find_first_mismatch_in_struct<'tcx>(
-    cx: &LateContext<'tcx>,
-    field_pats: &[PatField<'_>],
-    field_defs: &[FieldDef],
-    substs_ref: SubstsRef<'tcx>,
-) -> Option<(Span, Mutability, Level)> {
-    for field_pat in field_pats {
-        'definitions: for field_def in field_defs {
-            if field_pat.ident == field_def.ident {
-                let field_ty = field_def.ty(cx.tcx, substs_ref);
-                let pat = &field_pat.pat;
-                let maybe_mismatch = find_first_mismatch(cx, pat, field_ty, Level::Lower);
-                if let Some(mismatch) = maybe_mismatch {
-                    return Some(mismatch);
+        if let Some(adjustments) = cx.typeck_results().pat_adjustments().get(adjust_pat.hir_id) {
+            if let [first, ..] = **adjustments {
+                if let ty::Ref(.., mutability) = *first.kind() {
+                    let level = if p.hir_id == pat.hir_id {
+                        Level::Top
+                    } else {
+                        Level::Lower
+                    };
+                    result = Some((p.span, mutability, level));
                 }
-                break 'definitions;
             }
         }
-    }
-
-    None
-}
-
-fn is_non_ref_pattern(pat_kind: &PatKind<'_>) -> bool {
-    match pat_kind {
-        PatKind::Struct(..) | PatKind::Tuple(..) | PatKind::TupleStruct(..) | PatKind::Path(..) => true,
-        PatKind::Or(sub_pats) => sub_pats.iter().any(|pat| is_non_ref_pattern(&pat.kind)),
-        _ => false,
-    }
+        result.is_none()
+    });
+    result
 }

clippy_lints/src/types/borrowed_box.rs

@@ -3,10 +3,8 @@ use clippy_utils::source::snippet;
 use clippy_utils::{match_def_path, paths};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
-use rustc_hir::{
-    self as hir, GenericArg, GenericBounds, GenericParamKind, HirId, Lifetime, MutTy, Mutability, Node, QPath,
-    SyntheticTyParamKind, TyKind,
-};
+use rustc_hir::{self as hir, GenericArg, GenericBounds, GenericParamKind};
+use rustc_hir::{HirId, Lifetime, MutTy, Mutability, Node, QPath, TyKind};
 use rustc_lint::LateContext;
 
 use super::BORROWED_BOX;
@@ -105,7 +103,7 @@ fn get_bounds_if_impl_trait<'tcx>(cx: &LateContext<'tcx>, qpath: &QPath<'_>, id:
         if let Some(did) = cx.qpath_res(qpath, id).opt_def_id();
         if let Some(Node::GenericParam(generic_param)) = cx.tcx.hir().get_if_local(did);
         if let GenericParamKind::Type { synthetic, .. } = generic_param.kind;
-        if synthetic == Some(SyntheticTyParamKind::ImplTrait);
+        if synthetic;
         then {
             Some(generic_param.bounds)
         } else {

clippy_lints/src/unit_types/let_unit_value.rs

@@ -1,5 +1,4 @@
 use clippy_utils::diagnostics::span_lint_and_then;
-use clippy_utils::higher;
 use clippy_utils::source::snippet_with_macro_callsite;
 use rustc_errors::Applicability;
 use rustc_hir::{Stmt, StmtKind};
@@ -14,9 +13,6 @@ pub(super) fn check(cx: &LateContext<'_>, stmt: &Stmt<'_>) {
             if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
                 return;
             }
-            if higher::is_from_for_desugar(local) {
-                return;
-            }
             span_lint_and_then(
                 cx,
                 LET_UNIT_VALUE,

clippy_utils/src/higher.rs

@@ -22,31 +22,31 @@ pub struct ForLoop<'tcx> {
     pub arg: &'tcx hir::Expr<'tcx>,
     /// `for` loop body
     pub body: &'tcx hir::Expr<'tcx>,
+    /// Compare this against `hir::Destination.target`
+    pub loop_id: HirId,
     /// entire `for` loop span
     pub span: Span,
 }
 
 impl<'tcx> ForLoop<'tcx> {
-    #[inline]
     /// Parses a desugared `for` loop
     pub fn hir(expr: &Expr<'tcx>) -> Option<Self> {
         if_chain! {
-            if let hir::ExprKind::Match(iterexpr, arms, hir::MatchSource::ForLoopDesugar) = expr.kind;
-            if let Some(first_arm) = arms.get(0);
-            if let hir::ExprKind::Call(_, iterargs) = iterexpr.kind;
-            if let Some(first_arg) = iterargs.get(0);
-            if iterargs.len() == 1 && arms.len() == 1 && first_arm.guard.is_none();
-            if let hir::ExprKind::Loop(block, ..) = first_arm.body.kind;
-            if block.expr.is_none();
-            if let [ _, _, ref let_stmt, ref body ] = *block.stmts;
-            if let hir::StmtKind::Local(local) = let_stmt.kind;
-            if let hir::StmtKind::Expr(body_expr) = body.kind;
+            if let hir::ExprKind::DropTemps(e) = expr.kind;
+            if let hir::ExprKind::Match(iterexpr, [arm], hir::MatchSource::ForLoopDesugar) = e.kind;
+            if let hir::ExprKind::Call(_, [arg]) = iterexpr.kind;
+            if let hir::ExprKind::Loop(block, ..) = arm.body.kind;
+            if let [stmt] = &*block.stmts;
+            if let hir::StmtKind::Expr(e) = stmt.kind;
+            if let hir::ExprKind::Match(_, [_, some_arm], _) = e.kind;
+            if let hir::PatKind::Struct(_, [field], _) = some_arm.pat.kind;
             then {
                 return Some(Self {
-                    pat: &*local.pat,
-                    arg: first_arg,
-                    body: body_expr,
-                    span: first_arm.span
+                    pat: field.pat,
+                    arg,
+                    body: some_arm.body,
+                    loop_id: arm.body.hir_id,
+                    span: expr.span.ctxt().outer_expn_data().call_site,
                 });
             }
         }
@@ -678,38 +678,6 @@ impl<'tcx> FormatArgsArg<'tcx> {
     }
 }
 
-/// Checks if a `let` statement is from a `for` loop desugaring.
-pub fn is_from_for_desugar(local: &hir::Local<'_>) -> bool {
-    // This will detect plain for-loops without an actual variable binding:
-    //
-    // ```
-    // for x in some_vec {
-    //     // do stuff
-    // }
-    // ```
-    if_chain! {
-        if let Some(expr) = local.init;
-        if let hir::ExprKind::Match(_, _, hir::MatchSource::ForLoopDesugar) = expr.kind;
-        then {
-            return true;
-        }
-    }
-
-    // This detects a variable binding in for loop to avoid `let_unit_value`
-    // lint (see issue #1964).
-    //
-    // ```
-    // for _ in vec![()] {
-    //     // anything
-    // }
-    // ```
-    if let hir::LocalSource::ForLoopDesugar = local.source {
-        return true;
-    }
-
-    false
-}
-
 /// A parsed `panic!` expansion
 pub struct PanicExpn<'tcx> {
     /// Span of `panic!(..)`

rust-toolchain

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2021-11-18"
+channel = "nightly-2021-11-23"
 components = ["cargo", "llvm-tools-preview", "rust-src", "rust-std", "rustc", "rustc-dev", "rustfmt"]

tests/ui/author/loop.stdout

@@ -1,6 +1,5 @@
 if_chain! {
-    if let ExprKind::DropTemps(expr1) = expr.kind;
-    if let Some(higher::ForLoop { pat: pat, arg: arg, body: body, .. }) = higher::ForLoop::hir(expr1);
+    if let Some(higher::ForLoop { pat: pat, arg: arg, body: body, .. }) = higher::ForLoop::hir(expr);
     if let PatKind::Binding(BindingAnnotation::Unannotated, _, name, None) = pat.kind;
     if name.as_str() == "y";
     if let ExprKind::Struct(qpath, fields, None) = arg.kind;
@@ -26,8 +25,7 @@ if_chain! {
     }
 }
 if_chain! {
-    if let ExprKind::DropTemps(expr1) = expr.kind;
-    if let Some(higher::ForLoop { pat: pat, arg: arg, body: body, .. }) = higher::ForLoop::hir(expr1);
+    if let Some(higher::ForLoop { pat: pat, arg: arg, body: body, .. }) = higher::ForLoop::hir(expr);
     if let PatKind::Wild = pat.kind;
     if let ExprKind::Struct(qpath, fields, None) = arg.kind;
     if matches!(qpath, QPath::LangItem(LangItem::Range, _));
@@ -49,8 +47,7 @@ if_chain! {
     }
 }
 if_chain! {
-    if let ExprKind::DropTemps(expr1) = expr.kind;
-    if let Some(higher::ForLoop { pat: pat, arg: arg, body: body, .. }) = higher::ForLoop::hir(expr1);
+    if let Some(higher::ForLoop { pat: pat, arg: arg, body: body, .. }) = higher::ForLoop::hir(expr);
     if let PatKind::Wild = pat.kind;
     if let ExprKind::Struct(qpath, fields, None) = arg.kind;
     if matches!(qpath, QPath::LangItem(LangItem::Range, _));