clippy_lints/src/semicolon_if_nothing_returned.rs

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