diff options
| -rw-r--r-- | doc/common_tools_writing_lints.md | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/doc/common_tools_writing_lints.md b/doc/common_tools_writing_lints.md index ed33b37c6bd..dbc43450594 100644 --- a/doc/common_tools_writing_lints.md +++ b/doc/common_tools_writing_lints.md @@ -4,7 +4,9 @@ You may need following tooltips to catch up with common operations. - [Common tools for writing lints](#common-tools-for-writing-lints) - [Retrieving the type of an expression](#retrieving-the-type-of-an-expression) + - [Checking if an expression is calling a specific method](#checking-if-an-expr-is-calling-a-specific-method) - [Checking if a type implements a specific trait](#checking-if-a-type-implements-a-specific-trait) + - [Checking if a type defines a method](#checking-if-a-type-defines-a-method) - [Dealing with macros](#dealing-with-macros) Useful Rustc dev guide links: @@ -49,6 +51,26 @@ Two noticeable items here: - `tables` is [`TypeckTables`][TypeckTables] and is created by type checking step, it includes useful information such as types of expressions, ways to resolve methods and so on. +# Checking if an expr is calling a specific method + +Starting with an `expr`, you can check whether it is calling a specific method `some_method`: + +```rust +impl LateLintPass<'_, '_> for MyStructLint { + fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<'_>) { + if_chain! { + // Check our expr is calling a method + if let hir::ExprKind::MethodCall(path, _, _args) = &expr.kind; + // Check the name of this method is `some_method` + if path.ident.name == sym!(some_method); + then { + // ... + } + } + } +} +``` + # Checking if a type implements a specific trait There are two ways to do this, depending if the target trait is part of lang items. @@ -83,6 +105,32 @@ A list of defined paths for Clippy can be found in [paths.rs][paths] We access lang items through the type context `tcx`. `tcx` is of type [`TyCtxt`][TyCtxt] and is defined in the `rustc_middle` crate. +# Checking if a type defines a specific method + +To check if our type defines a method called `some_method`: + +```rust +use crate::utils::{is_type_diagnostic_item, return_ty}; + +impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MyTypeImpl { + fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx ImplItem<'_>) { + if_chain! { + // 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); + // We can also check it has a parameter `self` + if 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 { + // ... + } + } + } +} +``` + # Dealing with macros There are several helpers in Clippy's utils to deal with macros: |