src/tools/clippy/clippy_lints/src/main_recursion.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::{is_entrypoint_fn, is_no_std_crate};
   4 use if_chain::if_chain;
   5 use rustc_hir::{Crate, Expr, ExprKind, QPath};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_tool_lint, impl_lint_pass};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for recursion using the entrypoint.
  11     ///
  12     /// **Why is this bad?** Apart from special setups (which we could detect following attributes like #![no_std]),
  13     /// recursing into main() seems like an unintuitive antipattern we should be able to detect.
  14     ///
  15     /// **Known problems:** None.
  16     ///
  17     /// **Example:**
  18     /// ```no_run
  19     /// fn main() {
  20     ///     main();
  21     /// }
  22     /// ```
  23     pub MAIN_RECURSION,
  24     style,
  25     "recursion using the entrypoint"
  26 }
  27
  28 #[derive(Default)]
  29 pub struct MainRecursion {
  30     has_no_std_attr: bool,
  31 }
  32
  33 impl_lint_pass!(MainRecursion => [MAIN_RECURSION]);
  34
  35 impl LateLintPass<'_> for MainRecursion {
  36     fn check_crate(&mut self, cx: &LateContext<'_>, _: &Crate<'_>) {
  37         self.has_no_std_attr = is_no_std_crate(cx);
  38     }
  39
  40     fn check_expr_post(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
  41         if self.has_no_std_attr {
  42             return;
  43         }
  44
  45         if_chain! {
  46             if let ExprKind::Call(func, _) = &expr.kind;
  47             if let ExprKind::Path(QPath::Resolved(_, path)) = &func.kind;
  48             if let Some(def_id) = path.res.opt_def_id();
  49             if is_entrypoint_fn(cx, def_id);
  50             then {
  51                 span_lint_and_help(
  52                     cx,
  53                     MAIN_RECURSION,
  54                     func.span,
  55                     &format!("recursing into entrypoint `{}`", snippet(cx, func.span, "main")),
  56                     None,
  57                     "consider using another function for this recursion"
  58                 )
  59             }
  60         }
  61     }
  62 }