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