clippy_lints/src/single_component_path_imports.rs

   1 use crate::utils::span_lint_and_sugg;
   2 use if_chain::if_chain;
   3 use rustc_errors::Applicability;
   4 use rustc_lint::{EarlyContext, EarlyLintPass};
   5 use rustc_session::{declare_lint_pass, declare_tool_lint};
   6 use rustc_span::edition::Edition;
   7 use syntax::ast::{Item, ItemKind, UseTreeKind};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checking for imports with single component use path.
  11     ///
  12     /// **Why is this bad?** Import with single component use path such as `use cratename;`
  13     /// is not necessary, and thus should be removed.
  14     ///
  15     /// **Known problems:** None.
  16     ///
  17     /// **Example:**
  18     ///
  19     /// ```rust, ignore
  20     /// use regex;
  21     ///
  22     /// fn main() {
  23     ///     regex::Regex::new(r"^\d{4}-\d{2}-\d{2}$").unwrap();
  24     /// }
  25     /// ```
  26     /// Better as
  27     /// ```rust, ignore
  28     /// fn main() {
  29     ///     regex::Regex::new(r"^\d{4}-\d{2}-\d{2}$").unwrap();
  30     /// }
  31     /// ```
  32     pub SINGLE_COMPONENT_PATH_IMPORTS,
  33     style,
  34     "imports with single component path are redundant"
  35 }
  36
  37 declare_lint_pass!(SingleComponentPathImports => [SINGLE_COMPONENT_PATH_IMPORTS]);
  38
  39 impl EarlyLintPass for SingleComponentPathImports {
  40     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
  41         if_chain! {
  42             if cx.sess.opts.edition == Edition::Edition2018;
  43             if !item.vis.node.is_pub();
  44             if let ItemKind::Use(use_tree) = &item.kind;
  45             if let segments = &use_tree.prefix.segments;
  46             if segments.len() == 1;
  47             if let UseTreeKind::Simple(None, _, _) = use_tree.kind;
  48             then {
  49                 span_lint_and_sugg(
  50                     cx,
  51                     SINGLE_COMPONENT_PATH_IMPORTS,
  52                     item.span,
  53                     "this import is redundant",
  54                     "remove it entirely",
  55                     String::new(),
  56                     Applicability::MachineApplicable
  57                 );
  58             }
  59         }
  60     }
  61 }