src/tools/clippy/clippy_lints/src/single_component_path_imports.rs

   1 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
   2 use rustc_ast::node_id::{NodeId, NodeMap};
   3 use rustc_ast::{ptr::P, Crate, Item, ItemKind, MacroDef, ModKind, UseTreeKind};
   4 use rustc_errors::Applicability;
   5 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
   6 use rustc_session::{declare_tool_lint, impl_lint_pass};
   7 use rustc_span::{edition::Edition, symbol::kw, Span, Symbol};
   8
   9 declare_clippy_lint! {
  10     /// ### What it does
  11     /// Checking for imports with single component use path.
  12     ///
  13     /// ### Why is this bad?
  14     /// Import with single component use path such as `use cratename;`
  15     /// is not necessary, and thus should be removed.
  16     ///
  17     /// ### Example
  18     /// ```rust,ignore
  19     /// use regex;
  20     ///
  21     /// fn main() {
  22     ///     regex::Regex::new(r"^\d{4}-\d{2}-\d{2}$").unwrap();
  23     /// }
  24     /// ```
  25     /// Better as
  26     /// ```rust,ignore
  27     /// fn main() {
  28     ///     regex::Regex::new(r"^\d{4}-\d{2}-\d{2}$").unwrap();
  29     /// }
  30     /// ```
  31     #[clippy::version = "1.43.0"]
  32     pub SINGLE_COMPONENT_PATH_IMPORTS,
  33     style,
  34     "imports with single component path are redundant"
  35 }
  36
  37 #[derive(Default)]
  38 pub struct SingleComponentPathImports {
  39     /// Buffer found usages to emit when visiting that item so that `#[allow]` works as expected
  40     found: NodeMap<Vec<SingleUse>>,
  41 }
  42
  43 struct SingleUse {
  44     name: Symbol,
  45     span: Span,
  46     item_id: NodeId,
  47     can_suggest: bool,
  48 }
  49
  50 impl_lint_pass!(SingleComponentPathImports => [SINGLE_COMPONENT_PATH_IMPORTS]);
  51
  52 impl EarlyLintPass for SingleComponentPathImports {
  53     fn check_crate(&mut self, cx: &EarlyContext<'_>, krate: &Crate) {
  54         if cx.sess().opts.edition < Edition::Edition2018 {
  55             return;
  56         }
  57
  58         self.check_mod(cx, &krate.items);
  59     }
  60
  61     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
  62         for SingleUse { span, can_suggest, .. } in self.found.remove(&item.id).into_iter().flatten() {
  63             if can_suggest {
  64                 span_lint_and_sugg(
  65                     cx,
  66                     SINGLE_COMPONENT_PATH_IMPORTS,
  67                     span,
  68                     "this import is redundant",
  69                     "remove it entirely",
  70                     String::new(),
  71                     Applicability::MachineApplicable,
  72                 );
  73             } else {
  74                 span_lint_and_help(
  75                     cx,
  76                     SINGLE_COMPONENT_PATH_IMPORTS,
  77                     span,
  78                     "this import is redundant",
  79                     None,
  80                     "remove this import",
  81                 );
  82             }
  83         }
  84     }
  85 }
  86
  87 impl SingleComponentPathImports {
  88     fn check_mod(&mut self, cx: &EarlyContext<'_>, items: &[P<Item>]) {
  89         // keep track of imports reused with `self` keyword, such as `self::crypto_hash` in the example
  90         // below. Removing the `use crypto_hash;` would make this a compile error
  91         // ```
  92         // use crypto_hash;
  93         //
  94         // use self::crypto_hash::{Algorithm, Hasher};
  95         // ```
  96         let mut imports_reused_with_self = Vec::new();
  97
  98         // keep track of single use statements such as `crypto_hash` in the example below
  99         // ```
 100         // use crypto_hash;
 101         // ```
 102         let mut single_use_usages = Vec::new();
 103
 104         // keep track of macros defined in the module as we don't want it to trigger on this (#7106)
 105         // ```
 106         // macro_rules! foo { () => {} };
 107         // pub(crate) use foo;
 108         // ```
 109         let mut macros = Vec::new();
 110
 111         for item in items {
 112             self.track_uses(
 113                 cx,
 114                 item,
 115                 &mut imports_reused_with_self,
 116                 &mut single_use_usages,
 117                 &mut macros,
 118             );
 119         }
 120
 121         for usage in single_use_usages {
 122             if !imports_reused_with_self.contains(&usage.name) {
 123                 self.found.entry(usage.item_id).or_default().push(usage);
 124             }
 125         }
 126     }
 127
 128     fn track_uses(
 129         &mut self,
 130         cx: &EarlyContext<'_>,
 131         item: &Item,
 132         imports_reused_with_self: &mut Vec<Symbol>,
 133         single_use_usages: &mut Vec<SingleUse>,
 134         macros: &mut Vec<Symbol>,
 135     ) {
 136         if item.span.from_expansion() || item.vis.kind.is_pub() {
 137             return;
 138         }
 139
 140         match &item.kind {
 141             ItemKind::Mod(_, ModKind::Loaded(ref items, ..)) => {
 142                 self.check_mod(cx, items);
 143             },
 144             ItemKind::MacroDef(MacroDef { macro_rules: true, .. }) => {
 145                 macros.push(item.ident.name);
 146             },
 147             ItemKind::Use(use_tree) => {
 148                 let segments = &use_tree.prefix.segments;
 149
 150                 // keep track of `use some_module;` usages
 151                 if segments.len() == 1 {
 152                     if let UseTreeKind::Simple(None) = use_tree.kind {
 153                         let name = segments[0].ident.name;
 154                         if !macros.contains(&name) {
 155                             single_use_usages.push(SingleUse {
 156                                 name,
 157                                 span: item.span,
 158                                 item_id: item.id,
 159                                 can_suggest: true,
 160                             });
 161                         }
 162                     }
 163                     return;
 164                 }
 165
 166                 if segments.is_empty() {
 167                     // keep track of `use {some_module, some_other_module};` usages
 168                     if let UseTreeKind::Nested(trees) = &use_tree.kind {
 169                         for tree in trees {
 170                             let segments = &tree.0.prefix.segments;
 171                             if segments.len() == 1 {
 172                                 if let UseTreeKind::Simple(None) = tree.0.kind {
 173                                     let name = segments[0].ident.name;
 174                                     if !macros.contains(&name) {
 175                                         single_use_usages.push(SingleUse {
 176                                             name,
 177                                             span: tree.0.span,
 178                                             item_id: item.id,
 179                                             can_suggest: false,
 180                                         });
 181                                     }
 182                                 }
 183                             }
 184                         }
 185                     }
 186                 } else {
 187                     // keep track of `use self::some_module` usages
 188                     if segments[0].ident.name == kw::SelfLower {
 189                         // simple case such as `use self::module::SomeStruct`
 190                         if segments.len() > 1 {
 191                             imports_reused_with_self.push(segments[1].ident.name);
 192                             return;
 193                         }
 194
 195                         // nested case such as `use self::{module1::Struct1, module2::Struct2}`
 196                         if let UseTreeKind::Nested(trees) = &use_tree.kind {
 197                             for tree in trees {
 198                                 let segments = &tree.0.prefix.segments;
 199                                 if !segments.is_empty() {
 200                                     imports_reused_with_self.push(segments[0].ident.name);
 201                                 }
 202                             }
 203                         }
 204                     }
 205                 }
 206             },
 207             _ => {},
 208         }
 209     }
 210 }