clippy_lints/src/default_numeric_fallback.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet;
   3 use if_chain::if_chain;
   4 use rustc_ast::ast::{LitFloatType, LitIntType, LitKind};
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{
   7     intravisit::{walk_expr, walk_stmt, NestedVisitorMap, Visitor},
   8     Body, Expr, ExprKind, HirId, Lit, Stmt, StmtKind,
   9 };
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_middle::{
  12     hir::map::Map,
  13     ty::{self, FloatTy, IntTy, PolyFnSig, Ty},
  14 };
  15 use rustc_session::{declare_lint_pass, declare_tool_lint};
  16
  17 declare_clippy_lint! {
  18     /// **What it does:** Checks for usage of unconstrained numeric literals which may cause default numeric fallback in type
  19     /// inference.
  20     ///
  21     /// Default numeric fallback means that if numeric types have not yet been bound to concrete
  22     /// types at the end of type inference, then integer type is bound to `i32`, and similarly
  23     /// floating type is bound to `f64`.
  24     ///
  25     /// See [RFC0212](https://github.com/rust-lang/rfcs/blob/master/text/0212-restore-int-fallback.md) for more information about the fallback.
  26     ///
  27     /// **Why is this bad?** For those who are very careful about types, default numeric fallback
  28     /// can be a pitfall that cause unexpected runtime behavior.
  29     ///
  30     /// **Known problems:** This lint can only be allowed at the function level or above.
  31     ///
  32     /// **Example:**
  33     /// ```rust
  34     /// let i = 10;
  35     /// let f = 1.23;
  36     /// ```
  37     ///
  38     /// Use instead:
  39     /// ```rust
  40     /// let i = 10i32;
  41     /// let f = 1.23f64;
  42     /// ```
  43     pub DEFAULT_NUMERIC_FALLBACK,
  44     restriction,
  45     "usage of unconstrained numeric literals which may cause default numeric fallback."
  46 }
  47
  48 declare_lint_pass!(DefaultNumericFallback => [DEFAULT_NUMERIC_FALLBACK]);
  49
  50 impl LateLintPass<'_> for DefaultNumericFallback {
  51     fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
  52         let mut visitor = NumericFallbackVisitor::new(cx);
  53         visitor.visit_body(body);
  54     }
  55 }
  56
  57 struct NumericFallbackVisitor<'a, 'tcx> {
  58     /// Stack manages type bound of exprs. The top element holds current expr type.
  59     ty_bounds: Vec<TyBound<'tcx>>,
  60
  61     cx: &'a LateContext<'tcx>,
  62 }
  63
  64 impl<'a, 'tcx> NumericFallbackVisitor<'a, 'tcx> {
  65     fn new(cx: &'a LateContext<'tcx>) -> Self {
  66         Self {
  67             ty_bounds: vec![TyBound::Nothing],
  68             cx,
  69         }
  70     }
  71
  72     /// Check whether a passed literal has potential to cause fallback or not.
  73     fn check_lit(&self, lit: &Lit, lit_ty: Ty<'tcx>) {
  74         if_chain! {
  75                 if let Some(ty_bound) = self.ty_bounds.last();
  76                 if matches!(lit.node,
  77                             LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed));
  78                 if !ty_bound.is_integral();
  79                 then {
  80                     let suffix = match lit_ty.kind() {
  81                         ty::Int(IntTy::I32) => "i32",
  82                         ty::Float(FloatTy::F64) => "f64",
  83                         // Default numeric fallback never results in other types.
  84                         _ => return,
  85                     };
  86
  87                     let sugg = format!("{}_{}", snippet(self.cx, lit.span, ""), suffix);
  88                     span_lint_and_sugg(
  89                         self.cx,
  90                         DEFAULT_NUMERIC_FALLBACK,
  91                         lit.span,
  92                         "default numeric fallback might occur",
  93                         "consider adding suffix",
  94                         sugg,
  95                         Applicability::MaybeIncorrect,
  96                     );
  97                 }
  98         }
  99     }
 100 }
 101
 102 impl<'a, 'tcx> Visitor<'tcx> for NumericFallbackVisitor<'a, 'tcx> {
 103     type Map = Map<'tcx>;
 104
 105     #[allow(clippy::too_many_lines)]
 106     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 107         match &expr.kind {
 108             ExprKind::Call(func, args) => {
 109                 if let Some(fn_sig) = fn_sig_opt(self.cx, func.hir_id) {
 110                     for (expr, bound) in args.iter().zip(fn_sig.skip_binder().inputs().iter()) {
 111                         // Push found arg type, then visit arg.
 112                         self.ty_bounds.push(TyBound::Ty(bound));
 113                         self.visit_expr(expr);
 114                         self.ty_bounds.pop();
 115                     }
 116                     return;
 117                 }
 118             },
 119
 120             ExprKind::MethodCall(_, _, args, _) => {
 121                 if let Some(def_id) = self.cx.typeck_results().type_dependent_def_id(expr.hir_id) {
 122                     let fn_sig = self.cx.tcx.fn_sig(def_id).skip_binder();
 123                     for (expr, bound) in args.iter().zip(fn_sig.inputs().iter()) {
 124                         self.ty_bounds.push(TyBound::Ty(bound));
 125                         self.visit_expr(expr);
 126                         self.ty_bounds.pop();
 127                     }
 128                     return;
 129                 }
 130             },
 131
 132             ExprKind::Struct(_, fields, base) => {
 133                 if_chain! {
 134                     let ty = self.cx.typeck_results().expr_ty(expr);
 135                     if let Some(adt_def) = ty.ty_adt_def();
 136                     if adt_def.is_struct();
 137                     if let Some(variant) = adt_def.variants.iter().next();
 138                     then {
 139                         let fields_def = &variant.fields;
 140
 141                         // Push field type then visit each field expr.
 142                         for field in fields.iter() {
 143                             let bound =
 144                                 fields_def
 145                                     .iter()
 146                                     .find_map(|f_def| {
 147                                         if f_def.ident == field.ident
 148                                             { Some(self.cx.tcx.type_of(f_def.did)) }
 149                                         else { None }
 150                                     });
 151                             self.ty_bounds.push(bound.into());
 152                             self.visit_expr(field.expr);
 153                             self.ty_bounds.pop();
 154                         }
 155
 156                         // Visit base with no bound.
 157                         if let Some(base) = base {
 158                             self.ty_bounds.push(TyBound::Nothing);
 159                             self.visit_expr(base);
 160                             self.ty_bounds.pop();
 161                         }
 162                         return;
 163                     }
 164                 }
 165             },
 166
 167             ExprKind::Lit(lit) => {
 168                 let ty = self.cx.typeck_results().expr_ty(expr);
 169                 self.check_lit(lit, ty);
 170                 return;
 171             },
 172
 173             _ => {},
 174         }
 175
 176         walk_expr(self, expr);
 177     }
 178
 179     fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
 180         match stmt.kind {
 181             StmtKind::Local(local) => {
 182                 if local.ty.is_some() {
 183                     self.ty_bounds.push(TyBound::Any)
 184                 } else {
 185                     self.ty_bounds.push(TyBound::Nothing)
 186                 }
 187             },
 188
 189             _ => self.ty_bounds.push(TyBound::Nothing),
 190         }
 191
 192         walk_stmt(self, stmt);
 193         self.ty_bounds.pop();
 194     }
 195
 196     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 197         NestedVisitorMap::None
 198     }
 199 }
 200
 201 fn fn_sig_opt<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<PolyFnSig<'tcx>> {
 202     let node_ty = cx.typeck_results().node_type_opt(hir_id)?;
 203     // We can't use `TyS::fn_sig` because it automatically performs substs, this may result in FNs.
 204     match node_ty.kind() {
 205         ty::FnDef(def_id, _) => Some(cx.tcx.fn_sig(*def_id)),
 206         ty::FnPtr(fn_sig) => Some(*fn_sig),
 207         _ => None,
 208     }
 209 }
 210
 211 #[derive(Debug, Clone, Copy)]
 212 enum TyBound<'tcx> {
 213     Any,
 214     Ty(Ty<'tcx>),
 215     Nothing,
 216 }
 217
 218 impl<'tcx> TyBound<'tcx> {
 219     fn is_integral(self) -> bool {
 220         match self {
 221             TyBound::Any => true,
 222             TyBound::Ty(t) => t.is_integral(),
 223             TyBound::Nothing => false,
 224         }
 225     }
 226 }
 227
 228 impl<'tcx> From<Option<Ty<'tcx>>> for TyBound<'tcx> {
 229     fn from(v: Option<Ty<'tcx>>) -> Self {
 230         match v {
 231             Some(t) => TyBound::Ty(t),
 232             None => TyBound::Nothing,
 233         }
 234     }
 235 }