New lint absolute_paths

clippy_lints/src/absolute_paths.rs

@@ -0,0 +1,100 @@
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::source::snippet_opt;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
+use rustc_hir::{HirId, ItemKind, Node, Path};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::symbol::kw;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of items through absolute paths, like `std::env::current_dir`.
+    ///
+    /// ### Why is this bad?
+    /// Many codebases have their own style when it comes to importing, but one that is seldom used
+    /// is using absolute paths *everywhere*. This is generally considered unidiomatic, and you
+    /// should add a `use` statement.
+    ///
+    /// The default maximum segments (2) is pretty strict, you may want to increase this in
+    /// `clippy.toml`.
+    ///
+    /// Note: One exception to this is code from macro expansion - this does not lint such cases, as
+    /// using absolute paths is the proper way of referencing items in one.
+    ///
+    /// ### Example
+    /// ```rust
+    /// let x = std::f64::consts::PI;
+    /// ```
+    /// Use any of the below instead, or anything else:
+    /// ```rust
+    /// use std::f64;
+    /// use std::f64::consts;
+    /// use std::f64::consts::PI;
+    /// let x = f64::consts::PI;
+    /// let x = consts::PI;
+    /// let x = PI;
+    /// use std::f64::consts as f64_consts;
+    /// let x = f64_consts::PI;
+    /// ```
+    #[clippy::version = "1.73.0"]
+    pub ABSOLUTE_PATHS,
+    restriction,
+    "checks for usage of an item without a `use` statement"
+}
+impl_lint_pass!(AbsolutePaths => [ABSOLUTE_PATHS]);
+
+pub struct AbsolutePaths {
+    pub absolute_paths_max_segments: u64,
+    pub absolute_paths_allowed_crates: FxHashSet<String>,
+}
+
+impl LateLintPass<'_> for AbsolutePaths {
+    // We should only lint `QPath::Resolved`s, but since `Path` is only used in `Resolved` and `UsePath`
+    // we don't need to use a visitor or anything as we can just check if the `Node` for `hir_id` isn't
+    // a `Use`
+    #[expect(clippy::cast_possible_truncation)]
+    fn check_path(&mut self, cx: &LateContext<'_>, path: &Path<'_>, hir_id: HirId) {
+        let Self {
+            absolute_paths_max_segments,
+            absolute_paths_allowed_crates,
+        } = self;
+
+        if !path.span.from_expansion()
+            && let Some(node) = cx.tcx.hir().find(hir_id)
+            && !matches!(node, Node::Item(item) if matches!(item.kind, ItemKind::Use(_, _)))
+            && let [first, rest @ ..] = path.segments
+            // Handle `::std`
+            && let (segment, len) = if first.ident.name == kw::PathRoot {
+                // Indexing is fine as `PathRoot` must be followed by another segment. `len() - 1`
+                // is fine here for the same reason
+                (&rest[0], path.segments.len() - 1)
+            } else {
+                (first, path.segments.len())
+            }
+            && len > *absolute_paths_max_segments as usize
+            && let Some(segment_snippet) = snippet_opt(cx, segment.ident.span)
+            && segment_snippet == segment.ident.as_str()
+        {
+            let is_abs_external =
+                matches!(segment.res, Res::Def(DefKind::Mod, DefId { index, .. }) if index == CRATE_DEF_INDEX);
+            let is_abs_crate = segment.ident.name == kw::Crate;
+
+            if is_abs_external && absolute_paths_allowed_crates.contains(segment.ident.name.as_str())
+                || is_abs_crate && absolute_paths_allowed_crates.contains("crate")
+            {
+                return;
+            }
+
+            if is_abs_external || is_abs_crate {
+                span_lint(
+                    cx,
+                    ABSOLUTE_PATHS,
+                    path.span,
+                    "consider bringing this path into scope with the `use` keyword",
+                );
+            }
+        }
+    }
+}

clippy_lints/src/declared_lints.rs

@@ -37,6 +37,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::utils::internal_lints::produce_ice::PRODUCE_ICE_INFO,
     #[cfg(feature = "internal")]
     crate::utils::internal_lints::unnecessary_def_path::UNNECESSARY_DEF_PATH_INFO,
+    crate::absolute_paths::ABSOLUTE_PATHS_INFO,
     crate::allow_attributes::ALLOW_ATTRIBUTES_INFO,
     crate::almost_complete_range::ALMOST_COMPLETE_RANGE_INFO,
     crate::approx_const::APPROX_CONSTANT_INFO,

clippy_lints/src/lib.rs

@@ -65,6 +65,7 @@ mod declared_lints;
 mod renamed_lints;
 
 // begin lints modules, do not remove this comment, it’s used in `update_lints`
+mod absolute_paths;
 mod allow_attributes;
 mod almost_complete_range;
 mod approx_const;
@@ -1082,6 +1083,14 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(manual_float_methods::ManualFloatMethods));
     store.register_late_pass(|_| Box::new(four_forward_slashes::FourForwardSlashes));
     store.register_late_pass(|_| Box::new(error_impl_error::ErrorImplError));
+    let absolute_paths_max_segments = conf.absolute_paths_max_segments;
+    let absolute_paths_allowed_crates = conf.absolute_paths_allowed_crates.clone();
+    store.register_late_pass(move |_| {
+        Box::new(absolute_paths::AbsolutePaths {
+            absolute_paths_max_segments,
+            absolute_paths_allowed_crates: absolute_paths_allowed_crates.clone(),
+        })
+    });
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/lifetimes.rs

@@ -15,6 +15,7 @@ use rustc_hir::{
     PredicateOrigin, TraitFn, TraitItem, TraitItemKind, Ty, TyKind, WherePredicate,
 };
 use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::hir::map::Map;
 use rustc_middle::hir::nested_filter as middle_nested_filter;
 use rustc_middle::lint::in_external_macro;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -620,7 +621,7 @@ impl<'cx, 'tcx, F> Visitor<'tcx> for LifetimeChecker<'cx, 'tcx, F>
 where
     F: NestedFilter<'tcx>,
 {
-    type Map = rustc_middle::hir::map::Map<'tcx>;
+    type Map = Map<'tcx>;
     type NestedFilter = F;
 
     // for lifetimes as parameters of generics

clippy_lints/src/redundant_static_lifetimes.rs

@@ -5,6 +5,7 @@ use rustc_ast::ast::{ConstItem, Item, ItemKind, StaticItem, Ty, TyKind};
 use rustc_errors::Applicability;
 use rustc_lint::{EarlyContext, EarlyLintPass};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::symbol::kw;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -64,7 +65,7 @@ impl RedundantStaticLifetimes {
                 if let Some(lifetime) = *optional_lifetime {
                     match borrow_type.ty.kind {
                         TyKind::Path(..) | TyKind::Slice(..) | TyKind::Array(..) | TyKind::Tup(..) => {
-                            if lifetime.ident.name == rustc_span::symbol::kw::StaticLifetime {
+                            if lifetime.ident.name == kw::StaticLifetime {
                                 let snip = snippet(cx, borrow_type.ty.span, "<type>");
                                 let sugg = format!("&{}{snip}", borrow_type.mutbl.prefix_str());
                                 span_lint_and_then(

clippy_lints/src/utils/conf.rs

@@ -551,6 +551,16 @@ define_Conf! {
     ///
     /// Whether to allow `r#""#` when `r""` can be used
     (allow_one_hash_in_raw_strings: bool = false),
+    /// Lint: ABSOLUTE_PATHS.
+    ///
+    /// The maximum number of segments a path can have before being linted, anything above this will
+    /// be linted.
+    (absolute_paths_max_segments: u64 = 2),
+    /// Lint: ABSOLUTE_PATHS.
+    ///
+    /// Which crates to allow absolute paths from
+    (absolute_paths_allowed_crates: rustc_data_structures::fx::FxHashSet<String> =
+        rustc_data_structures::fx::FxHashSet::default()),
 }
 
 /// Search for the configuration file.