Auto merge of rust-lang#8805 - Alexendoo:let-chain-docs, r=flip1995

Recommend let chains over if_chain in docs

Switches over bit_mask.rs to let chains in order to create a nice example

While the rustfmt thing isn't resolved yet, my rust-analyzer isn't a fan of large `if_chains!`s, it stops giving me hover info and such after some number of if statements

changelog: none

Author: bors

CONTRIBUTING.md

@@ -69,7 +69,7 @@ and resolved paths.
 To figure out how this syntax structure is encoded in the AST, it is recommended to run
 `rustc -Z unpretty=ast-tree` on an example of the structure and compare with the [nodes in the AST docs].
 Usually the lint will end up to be a nested series of matches and ifs, [like so][deep-nesting].
-But we can make it nest-less by using [if_chain] macro, [like this][nest-less].
+But we can make it nest-less by using [let chains], [like this][nest-less].
 
 [`E-medium`] issues are generally pretty easy too, though it's recommended you work on an [`good-first-issue`]
 first. Sometimes they are only somewhat involved code wise, but not difficult per-se.
@@ -87,9 +87,9 @@ an AST expression). `match_def_path()` in Clippy's `utils` module can also be us
 [`E-medium`]: https://github.com/rust-lang/rust-clippy/labels/E-medium
 [`ty`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty
 [nodes in the AST docs]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ast/
-[deep-nesting]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/mem_forget.rs#L29-L43
-[if_chain]: https://docs.rs/if_chain/*/if_chain
-[nest-less]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/bit_mask.rs#L124-L150
+[deep-nesting]: https://github.com/rust-lang/rust-clippy/blob/5e4f0922911536f80d9591180fa604229ac13939/clippy_lints/src/mem_forget.rs#L31-L45
+[let chains]: https://github.com/rust-lang/rust/pull/94927
+[nest-less]: https://github.com/rust-lang/rust-clippy/blob/5e4f0922911536f80d9591180fa604229ac13939/clippy_lints/src/bit_mask.rs#L133-L159
 
 ## Writing code
 

clippy_lints/src/bit_mask.rs

@@ -1,7 +1,6 @@
 use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
 use clippy_utils::sugg::Sugg;
-use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, Expr, ExprKind};
@@ -130,32 +129,33 @@ impl<'tcx> LateLintPass<'tcx> for BitMask {
                 }
             }
         }
-        if_chain! {
-            if let ExprKind::Binary(op, left, right) = &e.kind;
-            if BinOpKind::Eq == op.node;
-            if let ExprKind::Binary(op1, left1, right1) = &left.kind;
-            if BinOpKind::BitAnd == op1.node;
-            if let ExprKind::Lit(lit) = &right1.kind;
-            if let LitKind::Int(n, _) = lit.node;
-            if let ExprKind::Lit(lit1) = &right.kind;
-            if let LitKind::Int(0, _) = lit1.node;
-            if n.leading_zeros() == n.count_zeros();
-            if n > u128::from(self.verbose_bit_mask_threshold);
-            then {
-                span_lint_and_then(cx,
-                                   VERBOSE_BIT_MASK,
-                                   e.span,
-                                   "bit mask could be simplified with a call to `trailing_zeros`",
-                                   |diag| {
+
+        if let ExprKind::Binary(op, left, right) = &e.kind
+            && BinOpKind::Eq == op.node
+            && let ExprKind::Binary(op1, left1, right1) = &left.kind
+            && BinOpKind::BitAnd == op1.node
+            && let ExprKind::Lit(lit) = &right1.kind
+            && let LitKind::Int(n, _) = lit.node
+            && let ExprKind::Lit(lit1) = &right.kind
+            && let LitKind::Int(0, _) = lit1.node
+            && n.leading_zeros() == n.count_zeros()
+            && n > u128::from(self.verbose_bit_mask_threshold)
+        {
+            span_lint_and_then(
+                cx,
+                VERBOSE_BIT_MASK,
+                e.span,
+                "bit mask could be simplified with a call to `trailing_zeros`",
+                |diag| {
                     let sugg = Sugg::hir(cx, left1, "...").maybe_par();
                     diag.span_suggestion(
                         e.span,
                         "try",
                         format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
                         Applicability::MaybeIncorrect,
                     );
-                });
-            }
+                },
+            );
         }
     }
 }

doc/adding_lints.md

@@ -656,7 +656,7 @@ Here are some pointers to things you are likely going to need for every lint:
 * [Clippy utils][utils] - Various helper functions. Maybe the function you need
   is already in here ([`is_type_diagnostic_item`], [`implements_trait`], [`snippet`], etc)
 * [Clippy diagnostics][diagnostics]
-* [The `if_chain` macro][if_chain]
+* [Let chains][let-chains]
 * [`from_expansion`][from_expansion] and [`in_external_macro`][in_external_macro]
 * [`Span`][span]
 * [`Applicability`][applicability]
@@ -684,7 +684,7 @@ don't hesitate to ask on [Zulip] or in the issue/PR.
 [`is_type_diagnostic_item`]: https://doc.rust-lang.org/nightly/nightly-rustc/clippy_utils/ty/fn.is_type_diagnostic_item.html
 [`implements_trait`]: https://doc.rust-lang.org/nightly/nightly-rustc/clippy_utils/ty/fn.implements_trait.html
 [`snippet`]: https://doc.rust-lang.org/nightly/nightly-rustc/clippy_utils/source/fn.snippet.html
-[if_chain]: https://docs.rs/if_chain/*/if_chain/
+[let-chains]: https://github.com/rust-lang/rust/pull/94927
 [from_expansion]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/struct.Span.html#method.from_expansion
 [in_external_macro]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/lint/fn.in_external_macro.html
 [span]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/struct.Span.html

doc/common_tools_writing_lints.md

@@ -62,16 +62,14 @@ Starting with an `expr`, you can check whether it is calling a specific method `
 ```rust
 impl<'tcx> LateLintPass<'tcx> for MyStructLint {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
-        if_chain! {
-            // Check our expr is calling a method
-            if let hir::ExprKind::MethodCall(path, _, [_self_arg, ..]) = &expr.kind;
+        // Check our expr is calling a method
+        if let hir::ExprKind::MethodCall(path, _, [_self_arg, ..]) = &expr.kind
             // Check the name of this method is `some_method`
-            if path.ident.name == sym!(some_method);
+            && path.ident.name == sym!(some_method)
             // Optionally, check the type of the self argument.
             // - See "Checking for a specific type"
-            then {
+        {
                 // ...
-            }
         }
     }
 }
@@ -165,18 +163,16 @@ use clippy_utils::{is_type_diagnostic_item, return_ty};
 
 impl<'tcx> LateLintPass<'tcx> for MyTypeImpl {
     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) {
-        if_chain! {
-            // Check if item is a method/function
-            if let ImplItemKind::Fn(ref signature, _) = impl_item.kind;
+        // Check if item is a method/function
+        if let ImplItemKind::Fn(ref signature, _) = impl_item.kind
             // Check the method is named `some_method`
-            if impl_item.ident.name == sym!(some_method);
+            && impl_item.ident.name == sym!(some_method)
             // We can also check it has a parameter `self`
-            if signature.decl.implicit_self.has_implicit_self();
+            && signature.decl.implicit_self.has_implicit_self()
             // We can go further and even check if its return type is `String`
-            if is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id), sym!(string_type));
-            then {
-                // ...
-            }
+            && is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id), sym!(string_type))
+        {
+            // ...
         }
     }
 }