clippy_lints/src/default_numeric_fallback.rs

   1 use rustc_ast::ast::{LitFloatType, LitIntType, LitKind};
   2 use rustc_errors::Applicability;
   3 use rustc_hir::{
   4     intravisit::{walk_expr, walk_stmt, NestedVisitorMap, Visitor},
   5     Body, Expr, ExprKind, HirId, Lit, Stmt, StmtKind,
   6 };
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::{
   9     hir::map::Map,
  10     ty::{self, FloatTy, IntTy, PolyFnSig, Ty},
  11 };
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13
  14 use if_chain::if_chain;
  15
  16 use crate::utils::{snippet, span_lint_and_sugg};
  17
  18 declare_clippy_lint! {
  19     /// **What it does:** Checks for usage of unconstrained numeric literals which may cause default numeric fallback in type
  20     /// inference.
  21     ///
  22     /// Default numeric fallback means that if numeric types have not yet been bound to concrete
  23     /// types at the end of type inference, then integer type is bound to `i32`, and similarly
  24     /// floating type is bound to `f64`.
  25     ///
  26     /// See [RFC0212](https://github.com/rust-lang/rfcs/blob/master/text/0212-restore-int-fallback.md) for more information about the fallback.
  27     ///
  28     /// **Why is this bad?** For those who are very careful about types, default numeric fallback
  29     /// can be a pitfall that cause unexpected runtime behavior.
  30     ///
  31     /// **Known problems:** This lint can only be allowed at the function level or above.
  32     ///
  33     /// **Example:**
  34     /// ```rust
  35     /// let i = 10;
  36     /// let f = 1.23;
  37     /// ```
  38     ///
  39     /// Use instead:
  40     /// ```rust
  41     /// let i = 10i32;
  42     /// let f = 1.23f64;
  43     /// ```
  44     pub DEFAULT_NUMERIC_FALLBACK,
  45     restriction,
  46     "usage of unconstrained numeric literals which may cause default numeric fallback."
  47 }
  48
  49 declare_lint_pass!(DefaultNumericFallback => [DEFAULT_NUMERIC_FALLBACK]);
  50
  51 impl LateLintPass<'_> for DefaultNumericFallback {
  52     fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
  53         let mut visitor = NumericFallbackVisitor::new(cx);
  54         visitor.visit_body(body);
  55     }
  56 }
  57
  58 struct NumericFallbackVisitor<'a, 'tcx> {
  59     /// Stack manages type bound of exprs. The top element holds current expr type.
  60     ty_bounds: Vec<TyBound<'tcx>>,
  61
  62     cx: &'a LateContext<'tcx>,
  63 }
  64
  65 impl<'a, 'tcx> NumericFallbackVisitor<'a, 'tcx> {
  66     fn new(cx: &'a LateContext<'tcx>) -> Self {
  67         Self {
  68             ty_bounds: vec![TyBound::Nothing],
  69             cx,
  70         }
  71     }
  72
  73     /// Check whether a passed literal has potential to cause fallback or not.
  74     fn check_lit(&self, lit: &Lit, lit_ty: Ty<'tcx>) {
  75         if_chain! {
  76                 if let Some(ty_bound) = self.ty_bounds.last();
  77                 if matches!(lit.node,
  78                             LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed));
  79                 if !ty_bound.is_integral();
  80                 then {
  81                     let suffix = match lit_ty.kind() {
  82                         ty::Int(IntTy::I32) => "i32",
  83                         ty::Float(FloatTy::F64) => "f64",
  84                         // Default numeric fallback never results in other types.
  85                         _ => return,
  86                     };
  87
  88                     let sugg = format!("{}_{}", snippet(self.cx, lit.span, ""), suffix);
  89                     span_lint_and_sugg(
  90                         self.cx,
  91                         DEFAULT_NUMERIC_FALLBACK,
  92                         lit.span,
  93                         "default numeric fallback might occur",
  94                         "consider adding suffix",
  95                         sugg,
  96                         Applicability::MaybeIncorrect,
  97                     );
  98                 }
  99         }
 100     }
 101 }
 102
 103 impl<'a, 'tcx> Visitor<'tcx> for NumericFallbackVisitor<'a, 'tcx> {
 104     type Map = Map<'tcx>;
 105
 106     #[allow(clippy::too_many_lines)]
 107     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 108         match &expr.kind {
 109             ExprKind::Call(func, args) => {
 110                 if let Some(fn_sig) = fn_sig_opt(self.cx, func.hir_id) {
 111                     for (expr, bound) in args.iter().zip(fn_sig.skip_binder().inputs().iter()) {
 112                         // Push found arg type, then visit arg.
 113                         self.ty_bounds.push(TyBound::Ty(bound));
 114                         self.visit_expr(expr);
 115                         self.ty_bounds.pop();
 116                     }
 117                     return;
 118                 }
 119             },
 120
 121             ExprKind::MethodCall(_, _, args, _) => {
 122                 if let Some(def_id) = self.cx.typeck_results().type_dependent_def_id(expr.hir_id) {
 123                     let fn_sig = self.cx.tcx.fn_sig(def_id).skip_binder();
 124                     for (expr, bound) in args.iter().zip(fn_sig.inputs().iter()) {
 125                         self.ty_bounds.push(TyBound::Ty(bound));
 126                         self.visit_expr(expr);
 127                         self.ty_bounds.pop();
 128                     }
 129                     return;
 130                 }
 131             },
 132
 133             ExprKind::Struct(_, fields, base) => {
 134                 if_chain! {
 135                     let ty = self.cx.typeck_results().expr_ty(expr);
 136                     if let Some(adt_def) = ty.ty_adt_def();
 137                     if adt_def.is_struct();
 138                     if let Some(variant) = adt_def.variants.iter().next();
 139                     then {
 140                         let fields_def = &variant.fields;
 141
 142                         // Push field type then visit each field expr.
 143                         for field in fields.iter() {
 144                             let bound =
 145                                 fields_def
 146                                     .iter()
 147                                     .find_map(|f_def| {
 148                                         if f_def.ident == field.ident
 149                                             { Some(self.cx.tcx.type_of(f_def.did)) }
 150                                         else { None }
 151                                     });
 152                             self.ty_bounds.push(bound.into());
 153                             self.visit_expr(field.expr);
 154                             self.ty_bounds.pop();
 155                         }
 156
 157                         // Visit base with no bound.
 158                         if let Some(base) = base {
 159                             self.ty_bounds.push(TyBound::Nothing);
 160                             self.visit_expr(base);
 161                             self.ty_bounds.pop();
 162                         }
 163                         return;
 164                     }
 165                 }
 166             },
 167
 168             ExprKind::Lit(lit) => {
 169                 let ty = self.cx.typeck_results().expr_ty(expr);
 170                 self.check_lit(lit, ty);
 171                 return;
 172             },
 173
 174             _ => {},
 175         }
 176
 177         walk_expr(self, expr);
 178     }
 179
 180     fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
 181         match stmt.kind {
 182             StmtKind::Local(local) => {
 183                 if local.ty.is_some() {
 184                     self.ty_bounds.push(TyBound::Any)
 185                 } else {
 186                     self.ty_bounds.push(TyBound::Nothing)
 187                 }
 188             },
 189
 190             _ => self.ty_bounds.push(TyBound::Nothing),
 191         }
 192
 193         walk_stmt(self, stmt);
 194         self.ty_bounds.pop();
 195     }
 196
 197     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 198         NestedVisitorMap::None
 199     }
 200 }
 201
 202 fn fn_sig_opt<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<PolyFnSig<'tcx>> {
 203     let node_ty = cx.typeck_results().node_type_opt(hir_id)?;
 204     // We can't use `TyS::fn_sig` because it automatically performs substs, this may result in FNs.
 205     match node_ty.kind() {
 206         ty::FnDef(def_id, _) => Some(cx.tcx.fn_sig(*def_id)),
 207         ty::FnPtr(fn_sig) => Some(*fn_sig),
 208         _ => None,
 209     }
 210 }
 211
 212 #[derive(Debug, Clone, Copy)]
 213 enum TyBound<'tcx> {
 214     Any,
 215     Ty(Ty<'tcx>),
 216     Nothing,
 217 }
 218
 219 impl<'tcx> TyBound<'tcx> {
 220     fn is_integral(self) -> bool {
 221         match self {
 222             TyBound::Any => true,
 223             TyBound::Ty(t) => t.is_integral(),
 224             TyBound::Nothing => false,
 225         }
 226     }
 227 }
 228
 229 impl<'tcx> From<Option<Ty<'tcx>>> for TyBound<'tcx> {
 230     fn from(v: Option<Ty<'tcx>>) -> Self {
 231         match v {
 232             Some(t) => TyBound::Ty(t),
 233             None => TyBound::Nothing,
 234         }
 235     }
 236 }