clippy_lints/src/semicolon_if_nothing_returned.rs

   1 use crate::utils::{in_macro, span_lint_and_sugg, sugg};
   2 use clippy_utils::source::snippet_with_macro_callsite;
   3 use if_chain::if_chain;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{Block, ExprKind};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Looks for blocks of expressions and fires if the last expression returns `()`
  11     /// but is not followed by a semicolon.
  12     ///
  13     /// **Why is this bad?** The semicolon might be optional but when
  14     /// extending the block with new code, it doesn't require a change in previous last line.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     ///
  20     /// ```rust
  21     /// fn main() {
  22     ///     println!("Hello world")
  23     /// }
  24     /// ```
  25     /// Use instead:
  26     /// ```rust
  27     /// fn main() {
  28     ///     println!("Hello world");
  29     /// }
  30     /// ```
  31     pub SEMICOLON_IF_NOTHING_RETURNED,
  32     restriction,
  33     "add a semicolon if nothing is returned"
  34 }
  35
  36 declare_lint_pass!(SemicolonIfNothingReturned => [SEMICOLON_IF_NOTHING_RETURNED]);
  37
  38 impl LateLintPass<'_> for SemicolonIfNothingReturned {
  39     fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx Block<'tcx>) {
  40         if_chain! {
  41             if !in_macro(block.span);
  42             if let Some(expr) = block.expr;
  43             let t_expr = cx.typeck_results().expr_ty(expr);
  44             if t_expr.is_unit();
  45             if let snippet = snippet_with_macro_callsite(cx, expr.span, "}");
  46             if !snippet.ends_with('}');
  47             then {
  48                 // filter out the desugared `for` loop
  49                 if let ExprKind::DropTemps(..) = &expr.kind {
  50                     return;
  51                 }
  52
  53                 let sugg = sugg::Sugg::hir_with_macro_callsite(cx, &expr, "..");
  54                 let suggestion = format!("{0};", sugg);
  55                 span_lint_and_sugg(
  56                     cx,
  57                     SEMICOLON_IF_NOTHING_RETURNED,
  58                     expr.span.source_callsite(),
  59                     "consider adding a `;` to the last statement for consistent formatting",
  60                     "add a `;` here",
  61                     suggestion,
  62                     Applicability::MaybeIncorrect,
  63                 );
  64             }
  65         }
  66     }
  67 }