| use if_chain::if_chain; |
| use rustc_hir::{ImplItem, ImplItemKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| |
| use crate::utils::{ |
| get_trait_def_id, implements_trait, is_type_diagnostic_item, paths, return_ty, span_lint_and_help, |
| trait_ref_of_method, walk_ptrs_ty, |
| }; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String`. |
| /// |
| /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. As the functionality of `Display` is much more versatile, it should be preferred. |
| /// |
| /// **Known problems:** None |
| /// |
| /// ** Example:** |
| /// |
| /// ```rust |
| /// // Bad |
| /// pub struct A; |
| /// |
| /// impl A { |
| /// pub fn to_string(&self) -> String { |
| /// "I am A".to_string() |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// ```rust |
| /// // Good |
| /// use std::fmt; |
| /// |
| /// pub struct A; |
| /// |
| /// impl fmt::Display for A { |
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| /// write!(f, "I am A") |
| /// } |
| /// } |
| /// ``` |
| pub INHERENT_TO_STRING, |
| style, |
| "type implements inherent method `to_string()`, but should instead implement the `Display` trait" |
| } |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String` and if the type implementing this method also implements the `Display` trait. |
| /// |
| /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. The less versatile inherent method will then shadow the implementation introduced by `Display`. |
| /// |
| /// **Known problems:** None |
| /// |
| /// ** Example:** |
| /// |
| /// ```rust |
| /// // Bad |
| /// use std::fmt; |
| /// |
| /// pub struct A; |
| /// |
| /// impl A { |
| /// pub fn to_string(&self) -> String { |
| /// "I am A".to_string() |
| /// } |
| /// } |
| /// |
| /// impl fmt::Display for A { |
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| /// write!(f, "I am A, too") |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// ```rust |
| /// // Good |
| /// use std::fmt; |
| /// |
| /// pub struct A; |
| /// |
| /// impl fmt::Display for A { |
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| /// write!(f, "I am A") |
| /// } |
| /// } |
| /// ``` |
| pub INHERENT_TO_STRING_SHADOW_DISPLAY, |
| correctness, |
| "type implements inherent method `to_string()`, which gets shadowed by the implementation of the `Display` trait" |
| } |
| |
| declare_lint_pass!(InherentToString => [INHERENT_TO_STRING, INHERENT_TO_STRING_SHADOW_DISPLAY]); |
| |
| impl<'tcx> LateLintPass<'tcx> for InherentToString { |
| fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) { |
| if impl_item.span.from_expansion() { |
| return; |
| } |
| |
| if_chain! { |
| // Check if item is a method, called to_string and has a parameter 'self' |
| if let ImplItemKind::Fn(ref signature, _) = impl_item.kind; |
| if impl_item.ident.name.as_str() == "to_string"; |
| let decl = &signature.decl; |
| if decl.implicit_self.has_implicit_self(); |
| if decl.inputs.len() == 1; |
| |
| // Check if return type is String |
| if is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id), sym!(string_type)); |
| |
| // Filters instances of to_string which are required by a trait |
| if trait_ref_of_method(cx, impl_item.hir_id).is_none(); |
| |
| then { |
| show_lint(cx, impl_item); |
| } |
| } |
| } |
| } |
| |
| fn show_lint(cx: &LateContext<'_>, item: &ImplItem<'_>) { |
| let display_trait_id = get_trait_def_id(cx, &paths::DISPLAY_TRAIT).expect("Failed to get trait ID of `Display`!"); |
| |
| // Get the real type of 'self' |
| let fn_def_id = cx.tcx.hir().local_def_id(item.hir_id); |
| let self_type = cx.tcx.fn_sig(fn_def_id).input(0); |
| let self_type = walk_ptrs_ty(self_type.skip_binder()); |
| |
| // Emit either a warning or an error |
| if implements_trait(cx, self_type, display_trait_id, &[]) { |
| span_lint_and_help( |
| cx, |
| INHERENT_TO_STRING_SHADOW_DISPLAY, |
| item.span, |
| &format!( |
| "type `{}` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`", |
| self_type.to_string() |
| ), |
| None, |
| &format!("remove the inherent method from type `{}`", self_type.to_string()) |
| ); |
| } else { |
| span_lint_and_help( |
| cx, |
| INHERENT_TO_STRING, |
| item.span, |
| &format!( |
| "implementation of inherent method `to_string(&self) -> String` for type `{}`", |
| self_type.to_string() |
| ), |
| None, |
| &format!("implement trait `Display` for type `{}` instead", self_type.to_string()), |
| ); |
| } |
| } |