src/tools/clippy/clippy_lints/src/semicolon_if_nothing_returned.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_with_macro_callsite;
   3 use clippy_utils::{in_macro, sugg};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{Block, ExprKind};
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Looks for blocks of expressions and fires if the last expression returns
  12     /// `()` but is not followed by a semicolon.
  13     ///
  14     /// **Why is this bad?** The semicolon might be optional but when extending the block with new
  15     /// code, it doesn't require a change in previous last line.
  16     ///
  17     /// **Known problems:** None.
  18     ///
  19     /// **Example:**
  20     ///
  21     /// ```rust
  22     /// fn main() {
  23     ///     println!("Hello world")
  24     /// }
  25     /// ```
  26     /// Use instead:
  27     /// ```rust
  28     /// fn main() {
  29     ///     println!("Hello world");
  30     /// }
  31     /// ```
  32     pub SEMICOLON_IF_NOTHING_RETURNED,
  33     pedantic,
  34     "add a semicolon if nothing is returned"
  35 }
  36
  37 declare_lint_pass!(SemicolonIfNothingReturned => [SEMICOLON_IF_NOTHING_RETURNED]);
  38
  39 impl LateLintPass<'_> for SemicolonIfNothingReturned {
  40     fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx Block<'tcx>) {
  41         if_chain! {
  42             if !in_macro(block.span);
  43             if let Some(expr) = block.expr;
  44             let t_expr = cx.typeck_results().expr_ty(expr);
  45             if t_expr.is_unit();
  46             if let snippet = snippet_with_macro_callsite(cx, expr.span, "}");
  47             if !snippet.ends_with('}');
  48             then {
  49                 // filter out the desugared `for` loop
  50                 if let ExprKind::DropTemps(..) = &expr.kind {
  51                     return;
  52                 }
  53
  54                 let sugg = sugg::Sugg::hir_with_macro_callsite(cx, expr, "..");
  55                 let suggestion = format!("{0};", sugg);
  56                 span_lint_and_sugg(
  57                     cx,
  58                     SEMICOLON_IF_NOTHING_RETURNED,
  59                     expr.span.source_callsite(),
  60                     "consider adding a `;` to the last statement for consistent formatting",
  61                     "add a `;` here",
  62                     suggestion,
  63                     Applicability::MaybeIncorrect,
  64                 );
  65             }
  66         }
  67     }
  68 }