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

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

diff --git a/src/tools/clippy/clippy_lints/src/unused_self.rs b/src/tools/clippy/clippy_lints/src/unused_self.rs
new file mode 100644 (file)
index 0000000..812482c
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/unused_self.rs
@@ -0,0 +1,71 @@
+use if_chain::if_chain;
+use rustc_hir::{Impl, ImplItem, ImplItemKind, ItemKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+use crate::utils::span_lint_and_help;
+use crate::utils::visitors::LocalUsedVisitor;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks methods that contain a `self` argument but don't use it
+    ///
+    /// **Why is this bad?** It may be clearer to define the method as an associated function instead
+    /// of an instance method if it doesn't require `self`.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust,ignore
+    /// struct A;
+    /// impl A {
+    ///     fn method(&self) {}
+    /// }
+    /// ```
+    ///
+    /// Could be written:
+    ///
+    /// ```rust,ignore
+    /// struct A;
+    /// impl A {
+    ///     fn method() {}
+    /// }
+    /// ```
+    pub UNUSED_SELF,
+    pedantic,
+    "methods that contain a `self` argument but don't use it"
+}
+
+declare_lint_pass!(UnusedSelf => [UNUSED_SELF]);
+
+impl<'tcx> LateLintPass<'tcx> for UnusedSelf {
+    fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &ImplItem<'_>) {
+        if impl_item.span.from_expansion() {
+            return;
+        }
+        let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
+        let parent_item = cx.tcx.hir().expect_item(parent);
+        let assoc_item = cx.tcx.associated_item(impl_item.def_id);
+        if_chain! {
+            if let ItemKind::Impl(Impl { of_trait: None, .. }) = parent_item.kind;
+            if assoc_item.fn_has_self_parameter;
+            if let ImplItemKind::Fn(.., body_id) = &impl_item.kind;
+            let body = cx.tcx.hir().body(*body_id);
+            if !body.params.is_empty();
+            then {
+                let self_param = &body.params[0];
+                let self_hir_id = self_param.pat.hir_id;
+                if !LocalUsedVisitor::new(cx, self_hir_id).check_body(body) {
+                    span_lint_and_help(
+                        cx,
+                        UNUSED_SELF,
+                        self_param.span,
+                        "unused `self` argument",
+                        None,
+                        "consider refactoring to a associated function",
+                    );
+                    return;
+                }
+            }
+        }
+    }
+}