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Recommend let chains over if_chain in docs

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Alex Macleod 2022-05-09 14:23:16 +01:00
parent 5e4f092291
commit c9d88ef962
3 changed files with 17 additions and 21 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

4
doc/adding_lints.md
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@ -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))
{
// ...
}
}
}