src/tools/clippy/clippy_lints/src/loops/while_immutable_condition.rs

   1 use super::WHILE_IMMUTABLE_CONDITION;
   2 use clippy_utils::consts::constant;
   3 use clippy_utils::diagnostics::span_lint_and_then;
   4 use clippy_utils::usage::mutated_variables;
   5 use if_chain::if_chain;
   6 use rustc_hir::def::{DefKind, Res};
   7 use rustc_hir::def_id::DefIdMap;
   8 use rustc_hir::intravisit::{walk_expr, Visitor};
   9 use rustc_hir::HirIdSet;
  10 use rustc_hir::{Expr, ExprKind, QPath};
  11 use rustc_lint::LateContext;
  12
  13 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
  14     if constant(cx, cx.typeck_results(), cond).is_some() {
  15         // A pure constant condition (e.g., `while false`) is not linted.
  16         return;
  17     }
  18
  19     let mut var_visitor = VarCollectorVisitor {
  20         cx,
  21         ids: HirIdSet::default(),
  22         def_ids: DefIdMap::default(),
  23         skip: false,
  24     };
  25     var_visitor.visit_expr(cond);
  26     if var_visitor.skip {
  27         return;
  28     }
  29     let used_in_condition = &var_visitor.ids;
  30     let mutated_in_body = mutated_variables(expr, cx);
  31     let mutated_in_condition = mutated_variables(cond, cx);
  32     let no_cond_variable_mutated =
  33         if let (Some(used_mutably_body), Some(used_mutably_cond)) = (mutated_in_body, mutated_in_condition) {
  34             used_in_condition.is_disjoint(&used_mutably_body) && used_in_condition.is_disjoint(&used_mutably_cond)
  35         } else {
  36             return;
  37         };
  38     let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
  39
  40     let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
  41         has_break_or_return: false,
  42     };
  43     has_break_or_return_visitor.visit_expr(expr);
  44     let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
  45
  46     if no_cond_variable_mutated && !mutable_static_in_cond {
  47         span_lint_and_then(
  48             cx,
  49             WHILE_IMMUTABLE_CONDITION,
  50             cond.span,
  51             "variables in the condition are not mutated in the loop body",
  52             |diag| {
  53                 diag.note("this may lead to an infinite or to a never running loop");
  54
  55                 if has_break_or_return {
  56                     diag.note("this loop contains `return`s or `break`s");
  57                     diag.help("rewrite it as `if cond { loop { } }`");
  58                 }
  59             },
  60         );
  61     }
  62 }
  63
  64 struct HasBreakOrReturnVisitor {
  65     has_break_or_return: bool,
  66 }
  67
  68 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
  69     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
  70         if self.has_break_or_return {
  71             return;
  72         }
  73
  74         match expr.kind {
  75             ExprKind::Ret(_) | ExprKind::Break(_, _) => {
  76                 self.has_break_or_return = true;
  77                 return;
  78             },
  79             _ => {},
  80         }
  81
  82         walk_expr(self, expr);
  83     }
  84 }
  85
  86 /// Collects the set of variables in an expression
  87 /// Stops analysis if a function call is found
  88 /// Note: In some cases such as `self`, there are no mutable annotation,
  89 /// All variables definition IDs are collected
  90 struct VarCollectorVisitor<'a, 'tcx> {
  91     cx: &'a LateContext<'tcx>,
  92     ids: HirIdSet,
  93     def_ids: DefIdMap<bool>,
  94     skip: bool,
  95 }
  96
  97 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
  98     fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
  99         if_chain! {
 100             if let ExprKind::Path(ref qpath) = ex.kind;
 101             if let QPath::Resolved(None, _) = *qpath;
 102             then {
 103                 match self.cx.qpath_res(qpath, ex.hir_id) {
 104                     Res::Local(hir_id) => {
 105                         self.ids.insert(hir_id);
 106                     },
 107                     Res::Def(DefKind::Static, def_id) => {
 108                         let mutable = self.cx.tcx.is_mutable_static(def_id);
 109                         self.def_ids.insert(def_id, mutable);
 110                     },
 111                     _ => {},
 112                 }
 113             }
 114         }
 115     }
 116 }
 117
 118 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
 119     fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
 120         match ex.kind {
 121             ExprKind::Path(_) => self.insert_def_id(ex),
 122             // If there is any function/method call… we just stop analysis
 123             ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
 124
 125             _ => walk_expr(self, ex),
 126         }
 127     }
 128 }