src/tools/clippy/clippy_lints/src/unnecessary_self_imports.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use if_chain::if_chain;
   3 use rustc_ast::{Item, ItemKind, 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::symbol::kw;
   8
   9 declare_clippy_lint! {
  10     /// ### What it does
  11     /// Checks for imports ending in `::{self}`.
  12     ///
  13     /// ### Why is this bad?
  14     /// In most cases, this can be written much more cleanly by omitting `::{self}`.
  15     ///
  16     /// ### Known problems
  17     /// Removing `::{self}` will cause any non-module items at the same path to also be imported.
  18     /// This might cause a naming conflict (https://github.com/rust-lang/rustfmt/issues/3568). This lint makes no attempt
  19     /// to detect this scenario and that is why it is a restriction lint.
  20     ///
  21     /// ### Example
  22     /// ```rust
  23     /// use std::io::{self};
  24     /// ```
  25     /// Use instead:
  26     /// ```rust
  27     /// use std::io;
  28     /// ```
  29     pub UNNECESSARY_SELF_IMPORTS,
  30     restriction,
  31     "imports ending in `::{self}`, which can be omitted"
  32 }
  33
  34 declare_lint_pass!(UnnecessarySelfImports => [UNNECESSARY_SELF_IMPORTS]);
  35
  36 impl EarlyLintPass for UnnecessarySelfImports {
  37     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
  38         if_chain! {
  39             if let ItemKind::Use(use_tree) = &item.kind;
  40             if let UseTreeKind::Nested(nodes) = &use_tree.kind;
  41             if let [(self_tree, _)] = &**nodes;
  42             if let [self_seg] = &*self_tree.prefix.segments;
  43             if self_seg.ident.name == kw::SelfLower;
  44             if let Some(last_segment) = use_tree.prefix.segments.last();
  45
  46             then {
  47                 span_lint_and_then(
  48                     cx,
  49                     UNNECESSARY_SELF_IMPORTS,
  50                     item.span,
  51                     "import ending with `::{self}`",
  52                     |diag| {
  53                         diag.span_suggestion(
  54                             last_segment.span().with_hi(item.span.hi()),
  55                             "consider omitting `::{self}`",
  56                             format!(
  57                                 "{}{};",
  58                                 last_segment.ident,
  59                                 if let UseTreeKind::Simple(Some(alias), ..) = self_tree.kind { format!(" as {}", alias) } else { String::new() },
  60                             ),
  61                             Applicability::MaybeIncorrect,
  62                         );
  63                         diag.note("this will slightly change semantics; any non-module items at the same path will also be imported");
  64                     },
  65                 );
  66             }
  67         }
  68     }
  69 }