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

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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
This commit is contained in:
bors 2022-05-09 13:56:53 +00:00
commit c3f3c588b0
4 changed files with 37 additions and 41 deletions
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8
CONTRIBUTING.md
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@ -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

40
clippy_lints/src/bit_mask.rs
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@ -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};
@ -130,23 +129,24 @@ 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,
@ -154,8 +154,8 @@ impl<'tcx> LateLintPass<'tcx> for BitMask {
format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()),
Applicability::MaybeIncorrect,
);
});
}
},
);
}
}
}

4
doc/adding_lints.md
View File

@ -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

26
doc/common_tools_writing_lints.md
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@ -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))
{
// ...
}
}
}