4 - Make more use of `let_chains`

Continuation of #94376.

cc #53667

5 files changed, 63 insertions, 67 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 50310b28f9a..42c9753d6bd 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -732,43 +732,42 @@ impl<'a> Parser<'a> {
         mut e: DiagnosticBuilder<'a, ErrorReported>,
         expr: &mut P<Expr>,
     ) -> PResult<'a, ()> {
-        if let ExprKind::Binary(binop, _, _) = &expr.kind {
-            if let ast::BinOpKind::Lt = binop.node {
-                if self.eat(&token::Comma) {
-                    let x = self.parse_seq_to_before_end(
-                        &token::Gt,
-                        SeqSep::trailing_allowed(token::Comma),
-                        |p| p.parse_generic_arg(None),
-                    );
-                    match x {
-                        Ok((_, _, false)) => {
-                            if self.eat(&token::Gt) {
-                                e.span_suggestion_verbose(
-                                    binop.span.shrink_to_lo(),
-                                    TURBOFISH_SUGGESTION_STR,
-                                    "::".to_string(),
-                                    Applicability::MaybeIncorrect,
-                                )
-                                .emit();
-                                match self.parse_expr() {
-                                    Ok(_) => {
-                                        *expr =
-                                            self.mk_expr_err(expr.span.to(self.prev_token.span));
-                                        return Ok(());
-                                    }
-                                    Err(err) => {
-                                        *expr = self.mk_expr_err(expr.span);
-                                        err.cancel();
-                                    }
-                                }
+        if let ExprKind::Binary(binop, _, _) = &expr.kind
+            && let ast::BinOpKind::Lt = binop.node
+            && self.eat(&token::Comma)
+        {
+            let x = self.parse_seq_to_before_end(
+                &token::Gt,
+                SeqSep::trailing_allowed(token::Comma),
+                |p| p.parse_generic_arg(None),
+            );
+            match x {
+                Ok((_, _, false)) => {
+                    if self.eat(&token::Gt) {
+                        e.span_suggestion_verbose(
+                            binop.span.shrink_to_lo(),
+                            TURBOFISH_SUGGESTION_STR,
+                            "::".to_string(),
+                            Applicability::MaybeIncorrect,
+                        )
+                        .emit();
+                        match self.parse_expr() {
+                            Ok(_) => {
+                                *expr =
+                                    self.mk_expr_err(expr.span.to(self.prev_token.span));
+                                return Ok(());
+                            }
+                            Err(err) => {
+                                *expr = self.mk_expr_err(expr.span);
+                                err.cancel();
                             }
                         }
-                        Err(err) => {
-                            err.cancel();
-                        }
-                        _ => {}
                     }
                 }
+                Err(err) => {
+                    err.cancel();
+                }
+                _ => {}
             }
         }
         Err(e)
@@ -784,12 +783,13 @@ impl<'a> Parser<'a> {
         outer_op: &Spanned<AssocOp>,
     ) -> bool /* advanced the cursor */ {
         if let ExprKind::Binary(op, ref l1, ref r1) = inner_op.kind {
-            if let ExprKind::Field(_, ident) = l1.kind {
-                if ident.as_str().parse::<i32>().is_err() && !matches!(r1.kind, ExprKind::Lit(_)) {
-                    // The parser has encountered `foo.bar<baz`, the likelihood of the turbofish
-                    // suggestion being the only one to apply is high.
-                    return false;
-                }
+            if let ExprKind::Field(_, ident) = l1.kind
+                && ident.as_str().parse::<i32>().is_err()
+                && !matches!(r1.kind, ExprKind::Lit(_))
+            {
+                // The parser has encountered `foo.bar<baz`, the likelihood of the turbofish
+                // suggestion being the only one to apply is high.
+                return false;
             }
             let mut enclose = |left: Span, right: Span| {
                 err.multipart_suggestion(
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index bd349e89482..af5cc0e0948 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -102,14 +102,12 @@ impl<'a> Parser<'a> {
     ) -> PResult<'a, Option<Item>> {
         // Don't use `maybe_whole` so that we have precise control
         // over when we bump the parser
-        if let token::Interpolated(nt) = &self.token.kind {
-            if let token::NtItem(item) = &**nt {
-                let mut item = item.clone();
-                self.bump();
+        if let token::Interpolated(nt) = &self.token.kind && let token::NtItem(item) = &**nt {
+            let mut item = item.clone();
+            self.bump();
 
-                attrs.prepend_to_nt_inner(&mut item.attrs);
-                return Ok(Some(item.into_inner()));
-            }
+            attrs.prepend_to_nt_inner(&mut item.attrs);
+            return Ok(Some(item.into_inner()));
         };
 
         let mut unclosed_delims = vec![];
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index d8e6d5037bb..4d31de123b4 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -97,15 +97,15 @@ macro_rules! maybe_whole {
 #[macro_export]
 macro_rules! maybe_recover_from_interpolated_ty_qpath {
     ($self: expr, $allow_qpath_recovery: expr) => {
-        if $allow_qpath_recovery && $self.look_ahead(1, |t| t == &token::ModSep) {
-            if let token::Interpolated(nt) = &$self.token.kind {
-                if let token::NtTy(ty) = &**nt {
+        if $allow_qpath_recovery
+                    && $self.look_ahead(1, |t| t == &token::ModSep)
+                    && let token::Interpolated(nt) = &$self.token.kind
+                    && let token::NtTy(ty) = &**nt
+                {
                     let ty = ty.clone();
                     $self.bump();
                     return $self.maybe_recover_from_bad_qpath_stage_2($self.prev_token.span, ty);
                 }
-            }
-        }
     };
 }
 
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 0ffc9d09355..5e537d7b95c 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -658,13 +658,13 @@ impl<'a> Parser<'a> {
         &self,
         gen_arg: GenericArg,
     ) -> Result<(Ident, Option<GenericArgs>), GenericArg> {
-        if let GenericArg::Type(ty) = &gen_arg {
-            if let ast::TyKind::Path(qself, path) = &ty.kind {
-                if qself.is_none() && path.segments.len() == 1 {
-                    let seg = &path.segments[0];
-                    return Ok((seg.ident, seg.args.as_deref().cloned()));
-                }
-            }
+        if let GenericArg::Type(ty) = &gen_arg
+            && let ast::TyKind::Path(qself, path) = &ty.kind
+            && qself.is_none()
+            && path.segments.len() == 1
+        {
+            let seg = &path.segments[0];
+            return Ok((seg.ident, seg.args.as_deref().cloned()));
         }
         Err(gen_arg)
     }
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 6b195285243..2154c09f12a 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -48,15 +48,13 @@ impl<'a> Parser<'a> {
 
         // Don't use `maybe_whole` so that we have precise control
         // over when we bump the parser
-        if let token::Interpolated(nt) = &self.token.kind {
-            if let token::NtStmt(stmt) = &**nt {
-                let mut stmt = stmt.clone();
-                self.bump();
-                stmt.visit_attrs(|stmt_attrs| {
-                    attrs.prepend_to_nt_inner(stmt_attrs);
-                });
-                return Ok(Some(stmt));
-            }
+        if let token::Interpolated(nt) = &self.token.kind && let token::NtStmt(stmt) = &**nt {
+            let mut stmt = stmt.clone();
+            self.bump();
+            stmt.visit_attrs(|stmt_attrs| {
+                attrs.prepend_to_nt_inner(stmt_attrs);
+            });
+            return Ok(Some(stmt));
         }
 
         Ok(Some(if self.token.is_keyword(kw::Let) {