src/tools/clippy/clippy_lints/src/empty_structs_with_brackets.rs

   1 use clippy_utils::{diagnostics::span_lint_and_then, source::snippet_opt};
   2 use rustc_ast::ast::{Item, ItemKind, VariantData};
   3 use rustc_errors::Applicability;
   4 use rustc_lexer::TokenKind;
   5 use rustc_lint::{EarlyContext, EarlyLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::Span;
   8
   9 declare_clippy_lint! {
  10     /// ### What it does
  11     /// Finds structs without fields (a so-called "empty struct") that are declared with brackets.
  12     ///
  13     /// ### Why is this bad?
  14     /// Empty brackets after a struct declaration can be omitted.
  15     ///
  16     /// ### Example
  17     /// ```rust
  18     /// struct Cookie {}
  19     /// ```
  20     /// Use instead:
  21     /// ```rust
  22     /// struct Cookie;
  23     /// ```
  24     #[clippy::version = "1.62.0"]
  25     pub EMPTY_STRUCTS_WITH_BRACKETS,
  26     restriction,
  27     "finds struct declarations with empty brackets"
  28 }
  29 declare_lint_pass!(EmptyStructsWithBrackets => [EMPTY_STRUCTS_WITH_BRACKETS]);
  30
  31 impl EarlyLintPass for EmptyStructsWithBrackets {
  32     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
  33         let span_after_ident = item.span.with_lo(item.ident.span.hi());
  34
  35         if let ItemKind::Struct(var_data, _) = &item.kind
  36             && has_brackets(var_data)
  37             && has_no_fields(cx, var_data, span_after_ident) {
  38             span_lint_and_then(
  39                 cx,
  40                 EMPTY_STRUCTS_WITH_BRACKETS,
  41                 span_after_ident,
  42                 "found empty brackets on struct declaration",
  43                 |diagnostic| {
  44                     diagnostic.span_suggestion_hidden(
  45                         span_after_ident,
  46                         "remove the brackets",
  47                         ";",
  48                         Applicability::MachineApplicable);
  49                     },
  50             );
  51         }
  52     }
  53 }
  54
  55 fn has_no_ident_token(braces_span_str: &str) -> bool {
  56     !rustc_lexer::tokenize(braces_span_str).any(|t| t.kind == TokenKind::Ident)
  57 }
  58
  59 fn has_brackets(var_data: &VariantData) -> bool {
  60     !matches!(var_data, VariantData::Unit(_))
  61 }
  62
  63 fn has_no_fields(cx: &EarlyContext<'_>, var_data: &VariantData, braces_span: Span) -> bool {
  64     if !var_data.fields().is_empty() {
  65         return false;
  66     }
  67
  68     // there might still be field declarations hidden from the AST
  69     // (conditionally compiled code using #[cfg(..)])
  70
  71     let Some(braces_span_str) = snippet_opt(cx, braces_span) else {
  72         return false;
  73     };
  74
  75     has_no_ident_token(braces_span_str.as_ref())
  76 }
  77
  78 #[cfg(test)]
  79 mod unit_test {
  80     use super::*;
  81
  82     #[test]
  83     fn test_has_no_ident_token() {
  84         let input = "{ field: u8 }";
  85         assert!(!has_no_ident_token(input));
  86
  87         let input = "(u8, String);";
  88         assert!(!has_no_ident_token(input));
  89
  90         let input = " {
  91                 // test = 5
  92         }
  93         ";
  94         assert!(has_no_ident_token(input));
  95
  96         let input = " ();";
  97         assert!(has_no_ident_token(input));
  98     }
  99 }