src/tools/clippy/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::{is_else_clause, 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             // Don't change `else if foo { panic!(..) }` to `else { assert!(foo, ..) }` as it just
  51             // shuffles the condition around.
  52             // Should this have a config value?
  53             if !is_else_clause(cx.tcx, expr);
  54             then {
  55                 let mut applicability = Applicability::MachineApplicable;
  56                 let format_args_snip = snippet_with_applicability(cx, format_args.inputs_span(), "..", &mut applicability);
  57                 let cond = cond.peel_drop_temps();
  58                 let mut comments = span_extract_comment(cx.sess().source_map(), expr.span);
  59                 if !comments.is_empty() {
  60                     comments += "\n";
  61                 }
  62                 let (cond, not) = match cond.kind {
  63                     ExprKind::Unary(UnOp::Not, e) => (e, ""),
  64                     _ => (cond, "!"),
  65                 };
  66                 let cond_sugg = sugg::Sugg::hir_with_applicability(cx, cond, "..", &mut applicability).maybe_par();
  67                 let sugg = format!("assert!({not}{cond_sugg}, {format_args_snip});");
  68                 // we show to the user the suggestion without the comments, but when applicating the fix, include the comments in the block
  69                 span_lint_and_then(
  70                     cx,
  71                     MANUAL_ASSERT,
  72                     expr.span,
  73                     "only a `panic!` in `if`-then statement",
  74                     |diag| {
  75                         // comments can be noisy, do not show them to the user
  76                         if !comments.is_empty() {
  77                             diag.tool_only_span_suggestion(
  78                                         expr.span.shrink_to_lo(),
  79                                         "add comments back",
  80                                         comments,
  81                                         applicability);
  82                         }
  83                         diag.span_suggestion(
  84                                     expr.span,
  85                                     "try instead",
  86                                     sugg,
  87                                     applicability);
  88                                      }
  89
  90                 );
  91             }
  92         }
  93     }
  94 }