compiler/rustc_lint/src/redundant_semicolon.rs

   1 use crate::{EarlyContext, EarlyLintPass, LintContext};
   2 use rustc_ast::{Block, StmtKind};
   3 use rustc_errors::Applicability;
   4 use rustc_span::Span;
   5
   6 declare_lint! {
   7     /// The `redundant_semicolons` lint detects unnecessary trailing
   8     /// semicolons.
   9     ///
  10     /// ### Example
  11     ///
  12     /// ```rust
  13     /// let _ = 123;;
  14     /// ```
  15     ///
  16     /// {{produces}}
  17     ///
  18     /// ### Explanation
  19     ///
  20     /// Extra semicolons are not needed, and may be removed to avoid confusion
  21     /// and visual clutter.
  22     pub REDUNDANT_SEMICOLONS,
  23     Warn,
  24     "detects unnecessary trailing semicolons"
  25 }
  26
  27 declare_lint_pass!(RedundantSemicolons => [REDUNDANT_SEMICOLONS]);
  28
  29 impl EarlyLintPass for RedundantSemicolons {
  30     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
  31         let mut after_item_stmt = false;
  32         let mut seq = None;
  33         for stmt in block.stmts.iter() {
  34             match (&stmt.kind, &mut seq) {
  35                 (StmtKind::Empty, None) => seq = Some((stmt.span, false)),
  36                 (StmtKind::Empty, Some(seq)) => *seq = (seq.0.to(stmt.span), true),
  37                 (_, seq) => {
  38                     maybe_lint_redundant_semis(cx, seq, after_item_stmt);
  39                     after_item_stmt = matches!(stmt.kind, StmtKind::Item(_));
  40                 }
  41             }
  42         }
  43         maybe_lint_redundant_semis(cx, &mut seq, after_item_stmt);
  44     }
  45 }
  46
  47 fn maybe_lint_redundant_semis(
  48     cx: &EarlyContext<'_>,
  49     seq: &mut Option<(Span, bool)>,
  50     after_item_stmt: bool,
  51 ) {
  52     if let Some((span, multiple)) = seq.take() {
  53         // FIXME: Find a better way of ignoring the trailing
  54         // semicolon from macro expansion
  55         if span == rustc_span::DUMMY_SP {
  56             return;
  57         }
  58
  59         // FIXME: Lint on semicolons after item statements
  60         // once doing so doesn't break bootstrapping
  61         if after_item_stmt {
  62             return;
  63         }
  64
  65         cx.struct_span_lint(REDUNDANT_SEMICOLONS, span, |lint| {
  66             let (msg, rem) = if multiple {
  67                 ("unnecessary trailing semicolons", "remove these semicolons")
  68             } else {
  69                 ("unnecessary trailing semicolon", "remove this semicolon")
  70             };
  71             lint.build(msg)
  72                 .span_suggestion(span, rem, String::new(), Applicability::MaybeIncorrect)
  73                 .emit();
  74         });
  75     }
  76 }