clippy_lints/src/single_component_path_imports.rs

   1 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
   2 use clippy_utils::in_macro;
   3 use rustc_ast::{ptr::P, Crate, Item, ItemKind, ModKind, UseTreeKind};
   4 use rustc_errors::Applicability;
   5 use rustc_lint::{EarlyContext, EarlyLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::{edition::Edition, symbol::kw, Span, Symbol};
   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_crate(&mut self, cx: &EarlyContext<'_>, krate: &Crate) {
  41         if cx.sess.opts.edition < Edition::Edition2018 {
  42             return;
  43         }
  44         check_mod(cx, &krate.items);
  45     }
  46 }
  47
  48 fn check_mod(cx: &EarlyContext<'_>, items: &[P<Item>]) {
  49     // keep track of imports reused with `self` keyword,
  50     // such as `self::crypto_hash` in the example below
  51     // ```rust,ignore
  52     // use self::crypto_hash::{Algorithm, Hasher};
  53     // ```
  54     let mut imports_reused_with_self = Vec::new();
  55
  56     // keep track of single use statements
  57     // such as `crypto_hash` in the example below
  58     // ```rust,ignore
  59     // use crypto_hash;
  60     // ```
  61     let mut single_use_usages = Vec::new();
  62
  63     for item in items {
  64         track_uses(cx, &item, &mut imports_reused_with_self, &mut single_use_usages);
  65     }
  66
  67     for single_use in &single_use_usages {
  68         if !imports_reused_with_self.contains(&single_use.0) {
  69             let can_suggest = single_use.2;
  70             if can_suggest {
  71                 span_lint_and_sugg(
  72                     cx,
  73                     SINGLE_COMPONENT_PATH_IMPORTS,
  74                     single_use.1,
  75                     "this import is redundant",
  76                     "remove it entirely",
  77                     String::new(),
  78                     Applicability::MachineApplicable,
  79                 );
  80             } else {
  81                 span_lint_and_help(
  82                     cx,
  83                     SINGLE_COMPONENT_PATH_IMPORTS,
  84                     single_use.1,
  85                     "this import is redundant",
  86                     None,
  87                     "remove this import",
  88                 );
  89             }
  90         }
  91     }
  92 }
  93
  94 fn track_uses(
  95     cx: &EarlyContext<'_>,
  96     item: &Item,
  97     imports_reused_with_self: &mut Vec<Symbol>,
  98     single_use_usages: &mut Vec<(Symbol, Span, bool)>,
  99 ) {
 100     if in_macro(item.span) || item.vis.kind.is_pub() {
 101         return;
 102     }
 103
 104     match &item.kind {
 105         ItemKind::Mod(_, ModKind::Loaded(ref items, ..)) => {
 106             check_mod(cx, &items);
 107         },
 108         ItemKind::Use(use_tree) => {
 109             let segments = &use_tree.prefix.segments;
 110
 111             // keep track of `use some_module;` usages
 112             if segments.len() == 1 {
 113                 if let UseTreeKind::Simple(None, _, _) = use_tree.kind {
 114                     let ident = &segments[0].ident;
 115                     single_use_usages.push((ident.name, item.span, true));
 116                 }
 117                 return;
 118             }
 119
 120             if segments.is_empty() {
 121                 // keep track of `use {some_module, some_other_module};` usages
 122                 if let UseTreeKind::Nested(trees) = &use_tree.kind {
 123                     for tree in trees {
 124                         let segments = &tree.0.prefix.segments;
 125                         if segments.len() == 1 {
 126                             if let UseTreeKind::Simple(None, _, _) = tree.0.kind {
 127                                 let ident = &segments[0].ident;
 128                                 single_use_usages.push((ident.name, tree.0.span, false));
 129                             }
 130                         }
 131                     }
 132                 }
 133             } else {
 134                 // keep track of `use self::some_module` usages
 135                 if segments[0].ident.name == kw::SelfLower {
 136                     // simple case such as `use self::module::SomeStruct`
 137                     if segments.len() > 1 {
 138                         imports_reused_with_self.push(segments[1].ident.name);
 139                         return;
 140                     }
 141
 142                     // nested case such as `use self::{module1::Struct1, module2::Struct2}`
 143                     if let UseTreeKind::Nested(trees) = &use_tree.kind {
 144                         for tree in trees {
 145                             let segments = &tree.0.prefix.segments;
 146                             if !segments.is_empty() {
 147                                 imports_reused_with_self.push(segments[0].ident.name);
 148                             }
 149                         }
 150                     }
 151                 }
 152             }
 153         },
 154         _ => {},
 155     }
 156 }