clippy_lints/src/manual_assert.rs

   1 use crate::rustc_lint::LintContext;
   2 use clippy_utils::diagnostics::span_lint_and_then;
   3 use clippy_utils::macros::{root_macro_call, FormatArgsExpn};
   4 use clippy_utils::source::snippet_with_applicability;
   5 use clippy_utils::{peel_blocks_with_stmt, span_extract_comment, sugg};
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{Expr, ExprKind, UnOp};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::sym;
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Detects `if`-then-`panic!` that can be replaced with `assert!`.
  15     ///
  16     /// ### Why is this bad?
  17     /// `assert!` is simpler than `if`-then-`panic!`.
  18     ///
  19     /// ### Example
  20     /// ```rust
  21     /// let sad_people: Vec<&str> = vec![];
  22     /// if !sad_people.is_empty() {
  23     ///     panic!("there are sad people: {:?}", sad_people);
  24     /// }
  25     /// ```
  26     /// Use instead:
  27     /// ```rust
  28     /// let sad_people: Vec<&str> = vec![];
  29     /// assert!(sad_people.is_empty(), "there are sad people: {:?}", sad_people);
  30     /// ```
  31     #[clippy::version = "1.57.0"]
  32     pub MANUAL_ASSERT,
  33     pedantic,
  34     "`panic!` and only a `panic!` in `if`-then statement"
  35 }
  36
  37 declare_lint_pass!(ManualAssert => [MANUAL_ASSERT]);
  38
  39 impl<'tcx> LateLintPass<'tcx> for ManualAssert {
  40     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
  41         if_chain! {
  42             if let ExprKind::If(cond, then, None) = expr.kind;
  43             if !matches!(cond.kind, ExprKind::Let(_));
  44             if !expr.span.from_expansion();
  45             let then = peel_blocks_with_stmt(then);
  46             if let Some(macro_call) = root_macro_call(then.span);
  47             if cx.tcx.item_name(macro_call.def_id) == sym::panic;
  48             if !cx.tcx.sess.source_map().is_multiline(cond.span);
  49             if let Some(format_args) = FormatArgsExpn::find_nested(cx, then, macro_call.expn);
  50             then {
  51                 let mut applicability = Applicability::MachineApplicable;
  52                 let format_args_snip = snippet_with_applicability(cx, format_args.inputs_span(), "..", &mut applicability);
  53                 let cond = cond.peel_drop_temps();
  54                 let mut comments = span_extract_comment(cx.sess().source_map(), expr.span);
  55                 if !comments.is_empty() {
  56                     comments += "\n";
  57                 }
  58                 let (cond, not) = match cond.kind {
  59                     ExprKind::Unary(UnOp::Not, e) => (e, ""),
  60                     _ => (cond, "!"),
  61                 };
  62                 let cond_sugg = sugg::Sugg::hir_with_applicability(cx, cond, "..", &mut applicability).maybe_par();
  63                 let sugg = format!("assert!({not}{cond_sugg}, {format_args_snip});");
  64                 // we show to the user the suggestion without the comments, but when applicating the fix, include the comments in the block
  65                 span_lint_and_then(
  66                     cx,
  67                     MANUAL_ASSERT,
  68                     expr.span,
  69                     "only a `panic!` in `if`-then statement",
  70                     |diag| {
  71                         // comments can be noisy, do not show them to the user
  72                         if !comments.is_empty() {
  73                             diag.tool_only_span_suggestion(
  74                                         expr.span.shrink_to_lo(),
  75                                         "add comments back",
  76                                         comments,
  77                                         applicability);
  78                         }
  79                         diag.span_suggestion(
  80                                     expr.span,
  81                                     "try instead",
  82                                     sugg,
  83                                     applicability);
  84                                      }
  85
  86                 );
  87             }
  88         }
  89     }
  90 }