implemeted lint, but the other lint now fails expectedly

Author: dbaranov34

CHANGELOG.md

@@ -6643,6 +6643,7 @@ 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_patbuf_conversion`]: https://rust-lang.github.io/rust-clippy/master/index.html#useless_patbuf_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

@@ -773,6 +773,7 @@ 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

@@ -398,6 +398,7 @@ 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;
@@ -581,6 +582,7 @@ 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 +1,66 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet;
+use clippy_utils::ty::is_type_diagnostic_item;
+use rustc_hir::{Expr, ExprKind};
+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 = "1.91.0"]
+    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<'_>) {
+        // Only care about &PathBuf::from(...)
+        if let ExprKind::AddrOf(_, _, inner) = &expr.kind {
+            if let ExprKind::Call(func, args) = &inner.kind {
+                if let ExprKind::Path(ref qpath) = func.kind {
+                    if let Some(def_id) = cx.qpath_res(qpath, func.hir_id).opt_def_id() {
+                        // check that the function is `from`
+                        if cx.tcx.item_name(def_id) != sym::from {
+                            return;
+                        }
+
+                        // get the type of the function's return value
+                        let ty = cx.typeck_results().expr_ty(inner);
+
+                        if is_type_diagnostic_item(cx, ty, sym::PathBuf) {
+                            if let Some(arg) = args.get(0) {
+                                let sugg = format!("Path::new({})", snippet(cx, arg.span, ".."));
+                                span_lint_and_sugg(
+                                    cx,
+                                    USELESS_PATHBUF_CONVERSION,
+                                    expr.span,
+                                    "unnecessary `PathBuf::from` when a `&Path` is enough",
+                                    "consider using",
+                                    sugg,
+                                    rustc_errors::Applicability::MachineApplicable,
+                                );
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

tests/ui/useless_pathbuf_conversion.fixed

@@ -0,0 +1,11 @@
+#![warn(clippy::useless_pathbuf_conversion)]
+use std::path::{Path, PathBuf};
+
+fn use_path(p: &Path) {}
+
+fn main() {
+    use_path(Path::new("abc"));
+    //~^ useless_pathbuf_conversion
+
+    use_path(Path::new("abc"));
+}

tests/ui/useless_pathbuf_conversion.rs

@@ -0,0 +1,11 @@
+#![warn(clippy::useless_pathbuf_conversion)]
+use std::path::{Path, PathBuf};
+
+fn use_path(p: &Path) {}
+
+fn main() {
+    use_path(&PathBuf::from("abc"));
+    //~^ useless_pathbuf_conversion
+
+    use_path(Path::new("abc"));
+}

tests/ui/useless_pathbuf_conversion.stderr

@@ -0,0 +1,11 @@
+error: unnecessary `PathBuf::from` when a `&Path` is enough
+  --> tests/ui/useless_pathbuf_conversion.rs:7:14
+   |
+LL |     use_path(&PathBuf::from("abc"));
+   |              ^^^^^^^^^^^^^^^^^^^^^ help: consider using: `Path::new("abc")`
+   |
+   = note: `-D clippy::useless-pathbuf-conversion` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::useless_pathbuf_conversion)]`
+
+error: aborting due to 1 previous error
+