new lint: [useless_pathbuf_conversion]

CHANGELOG.md

@@ -6791,6 +6791,7 @@ Released 2018-09-13
 [`useless_format`]: https://rust-lang.github.io/rust-clippy/master/index.html#useless_format
 [`useless_let_if_seq`]: https://rust-lang.github.io/rust-clippy/master/index.html#useless_let_if_seq
 [`useless_nonzero_new_unchecked`]: https://rust-lang.github.io/rust-clippy/master/index.html#useless_nonzero_new_unchecked
+[`useless_pathbuf_conversion`]: https://rust-lang.github.io/rust-clippy/master/index.html#useless_pathbuf_conversion
 [`useless_transmute`]: https://rust-lang.github.io/rust-clippy/master/index.html#useless_transmute
 [`useless_vec`]: https://rust-lang.github.io/rust-clippy/master/index.html#useless_vec
 [`vec_box`]: https://rust-lang.github.io/rust-clippy/master/index.html#vec_box

clippy_lints/src/declared_lints.rs

@@ -775,6 +775,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::use_self::USE_SELF_INFO,
     crate::useless_concat::USELESS_CONCAT_INFO,
     crate::useless_conversion::USELESS_CONVERSION_INFO,
+    crate::useless_pathbuf_conversion::USELESS_PATHBUF_CONVERSION_INFO,
     crate::vec::USELESS_VEC_INFO,
     crate::vec_init_then_push::VEC_INIT_THEN_PUSH_INFO,
     crate::visibility::NEEDLESS_PUB_SELF_INFO,

clippy_lints/src/lib.rs

@@ -397,6 +397,7 @@ mod upper_case_acronyms;
 mod use_self;
 mod useless_concat;
 mod useless_conversion;
+mod useless_pathbuf_conversion;
 mod vec;
 mod vec_init_then_push;
 mod visibility;
@@ -580,6 +581,7 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
     store.register_late_pass(|_| Box::new(infinite_iter::InfiniteIter));
     store.register_late_pass(|_| Box::new(inline_fn_without_body::InlineFnWithoutBody));
     store.register_late_pass(|_| Box::<useless_conversion::UselessConversion>::default());
+    store.register_late_pass(|_| Box::new(useless_pathbuf_conversion::UselessPathbufConversion));
     store.register_late_pass(|_| Box::new(implicit_hasher::ImplicitHasher));
     store.register_late_pass(|_| Box::new(fallible_impl_from::FallibleImplFrom));
     store.register_late_pass(move |_| Box::new(question_mark::QuestionMark::new(conf)));

clippy_lints/src/useless_pathbuf_conversion.rs

@@ -0,0 +1,63 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_path_diagnostic_item;
+use clippy_utils::source::snippet_with_context;
+use clippy_utils::ty::is_type_diagnostic_item;
+
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, QPath};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::declare_lint_pass;
+use rustc_span::symbol::sym;
+
+declare_clippy_lint! {
+    /// **What it does:** Detects unnecessary `&PathBuf::from(...)` when `&Path` would suffice.
+    ///
+    /// **Why is this bad?** `PathBuf::from` allocates a new heap buffer unnecessarily.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// fn use_path(p: &std::path::Path) {}
+    /// use_path(&std::path::PathBuf::from("abc"));
+    /// ```
+    /// Could be written as:
+    /// ```rust
+    /// fn use_path(p: &std::path::Path) {}
+    /// use_path(std::path::Path::new("abc"));
+    /// ```
+   #[clippy::version = "1.92.0"]
+    pub USELESS_PATHBUF_CONVERSION,
+    complexity,
+    "creating a `PathBuf` only to take a reference, where `Path::new` would suffice"
+}
+
+declare_lint_pass!(UselessPathbufConversion => [USELESS_PATHBUF_CONVERSION]);
+
+impl<'tcx> LateLintPass<'tcx> for UselessPathbufConversion {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if let ExprKind::AddrOf(_, _, inner) = &expr.kind
+            && let ExprKind::Call(func, [arg]) = &inner.kind
+            && let ExprKind::Path(ref qpath) = func.kind
+            && let QPath::TypeRelative(pathbuf, from) = qpath
+            && is_path_diagnostic_item(cx, *pathbuf, sym::PathBuf)
+            && from.ident.name == sym::from
+            && let expr_ty = cx.typeck_results().expr_ty_adjusted(expr)
+            && let rustc_middle::ty::Ref(_, inner_ty, _) = expr_ty.kind()
+            && is_type_diagnostic_item(cx, *inner_ty, sym::Path)
+        {
+            let mut app = Applicability::MachineApplicable;
+            let arg_snippet = snippet_with_context(cx, arg.span, inner.span.ctxt(), "..", &mut app).0;
+
+            let sugg = format!("Path::new({arg_snippet})");
+
+            span_lint_and_sugg(
+                cx,
+                USELESS_PATHBUF_CONVERSION,
+                expr.span,
+                "unnecessary `PathBuf::from` when a `&Path` is enough",
+                "consider using",
+                sugg,
+                app,
+            );
+        }
+    }
+}

clippy_utils/src/source.rs

@@ -653,6 +653,9 @@ pub fn snippet_block_with_context(
 /// would result in `box []`. If given the context of the address of expression, this function will
 /// correctly get a snippet of `vec![]`.
 ///
+/// NOTE: Typically the `outer` context should be taken from the parent node, not from the node
+/// itself.
+///
 /// This will also return whether or not the snippet is a macro call.
 pub fn snippet_with_context<'a>(
     sess: &impl HasSession,

tests/ui/unnecessary_to_owned.fixed

@@ -5,7 +5,8 @@
     clippy::needless_lifetimes,
     clippy::owned_cow,
     clippy::ptr_arg,
-    clippy::uninlined_format_args
+    clippy::uninlined_format_args,
+    clippy::useless_pathbuf_conversion
 )]
 #![warn(clippy::unnecessary_to_owned, clippy::redundant_clone)]
 

tests/ui/unnecessary_to_owned.rs

@@ -5,7 +5,8 @@
     clippy::needless_lifetimes,
     clippy::owned_cow,
     clippy::ptr_arg,
-    clippy::uninlined_format_args
+    clippy::uninlined_format_args,
+    clippy::useless_pathbuf_conversion
 )]
 #![warn(clippy::unnecessary_to_owned, clippy::redundant_clone)]