Update upstream source from tag 'upstream/1.52.1+dfsg1'

[rustc.git] / src / tools / clippy / clippy_lints / src / inherent_to_string.rs

diff --git a/src/tools/clippy/clippy_lints/src/inherent_to_string.rs b/src/tools/clippy/clippy_lints/src/inherent_to_string.rs
new file mode 100644 (file)
index 0000000..c1f3e1d
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/inherent_to_string.rs
@@ -0,0 +1,157 @@
+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 rustc_span::sym;
+
+use crate::utils::{
+    get_trait_def_id, implements_trait, is_type_diagnostic_item, paths, return_ty, span_lint_and_help,
+    trait_ref_of_method,
+};
+
+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;
+            if impl_item.generics.params.is_empty();
+
+            // 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 self_type = cx.tcx.fn_sig(item.def_id).input(0);
+    let self_type = self_type.skip_binder().peel_refs();
+
+    // 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()),
+        );
+    }
+}