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

   1 use crate::rustc_lint::LintContext;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::source::snippet_with_macro_callsite;
   4 use clippy_utils::sugg;
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{Block, ExprKind};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10
  11 declare_clippy_lint! {
  12     /// ### What it does
  13     /// Looks for blocks of expressions and fires if the last expression returns
  14     /// `()` but is not followed by a semicolon.
  15     ///
  16     /// ### Why is this bad?
  17     /// The semicolon might be optional but when extending the block with new
  18     /// code, it doesn't require a change in previous last line.
  19     ///
  20     /// ### Example
  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 !block.span.from_expansion();
  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             if cx.sess().source_map().is_multiline(block.span);
  49             then {
  50                 // filter out the desugared `for` loop
  51                 if let ExprKind::DropTemps(..) = &expr.kind {
  52                     return;
  53                 }
  54
  55                 let sugg = sugg::Sugg::hir_with_macro_callsite(cx, expr, "..");
  56                 let suggestion = format!("{0};", sugg);
  57                 span_lint_and_sugg(
  58                     cx,
  59                     SEMICOLON_IF_NOTHING_RETURNED,
  60                     expr.span.source_callsite(),
  61                     "consider adding a `;` to the last statement for consistent formatting",
  62                     "add a `;` here",
  63                     suggestion,
  64                     Applicability::MaybeIncorrect,
  65                 );
  66             }
  67         }
  68     }
  69 }