src/tools/clippy/clippy_lints/src/default_numeric_fallback.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::numeric_literal;
   3 use clippy_utils::source::snippet_opt;
   4 use if_chain::if_chain;
   5 use rustc_ast::ast::{LitFloatType, LitIntType, LitKind};
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{
   8     intravisit::{walk_expr, walk_stmt, NestedVisitorMap, Visitor},
   9     Body, Expr, ExprKind, HirId, Lit, Stmt, StmtKind,
  10 };
  11 use rustc_lint::{LateContext, LateLintPass, LintContext};
  12 use rustc_middle::{
  13     hir::map::Map,
  14     lint::in_external_macro,
  15     ty::{self, FloatTy, IntTy, PolyFnSig, Ty},
  16 };
  17 use rustc_session::{declare_lint_pass, declare_tool_lint};
  18 use std::iter;
  19
  20 declare_clippy_lint! {
  21     /// ### What it does
  22     /// Checks for usage of unconstrained numeric literals which may cause default numeric fallback in type
  23     /// inference.
  24     ///
  25     /// Default numeric fallback means that if numeric types have not yet been bound to concrete
  26     /// types at the end of type inference, then integer type is bound to `i32`, and similarly
  27     /// floating type is bound to `f64`.
  28     ///
  29     /// See [RFC0212](https://github.com/rust-lang/rfcs/blob/master/text/0212-restore-int-fallback.md) for more information about the fallback.
  30     ///
  31     /// ### Why is this bad?
  32     /// For those who are very careful about types, default numeric fallback
  33     /// can be a pitfall that cause unexpected runtime behavior.
  34     ///
  35     /// ### Known problems
  36     /// This lint can only be allowed at the function level or above.
  37     ///
  38     /// ### Example
  39     /// ```rust
  40     /// let i = 10;
  41     /// let f = 1.23;
  42     /// ```
  43     ///
  44     /// Use instead:
  45     /// ```rust
  46     /// let i = 10i32;
  47     /// let f = 1.23f64;
  48     /// ```
  49     #[clippy::version = "1.52.0"]
  50     pub DEFAULT_NUMERIC_FALLBACK,
  51     restriction,
  52     "usage of unconstrained numeric literals which may cause default numeric fallback."
  53 }
  54
  55 declare_lint_pass!(DefaultNumericFallback => [DEFAULT_NUMERIC_FALLBACK]);
  56
  57 impl LateLintPass<'_> for DefaultNumericFallback {
  58     fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
  59         let mut visitor = NumericFallbackVisitor::new(cx);
  60         visitor.visit_body(body);
  61     }
  62 }
  63
  64 struct NumericFallbackVisitor<'a, 'tcx> {
  65     /// Stack manages type bound of exprs. The top element holds current expr type.
  66     ty_bounds: Vec<TyBound<'tcx>>,
  67
  68     cx: &'a LateContext<'tcx>,
  69 }
  70
  71 impl<'a, 'tcx> NumericFallbackVisitor<'a, 'tcx> {
  72     fn new(cx: &'a LateContext<'tcx>) -> Self {
  73         Self {
  74             ty_bounds: vec![TyBound::Nothing],
  75             cx,
  76         }
  77     }
  78
  79     /// Check whether a passed literal has potential to cause fallback or not.
  80     fn check_lit(&self, lit: &Lit, lit_ty: Ty<'tcx>) {
  81         if_chain! {
  82                 if !in_external_macro(self.cx.sess(), lit.span);
  83                 if let Some(ty_bound) = self.ty_bounds.last();
  84                 if matches!(lit.node,
  85                             LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed));
  86                 if !ty_bound.is_numeric();
  87                 then {
  88                     let (suffix, is_float) = match lit_ty.kind() {
  89                         ty::Int(IntTy::I32) => ("i32", false),
  90                         ty::Float(FloatTy::F64) => ("f64", true),
  91                         // Default numeric fallback never results in other types.
  92                         _ => return,
  93                     };
  94
  95                     let src = if let Some(src) = snippet_opt(self.cx, lit.span) {
  96                         src
  97                     } else {
  98                         match lit.node {
  99                             LitKind::Int(src, _) => format!("{}", src),
 100                             LitKind::Float(src, _) => format!("{}", src),
 101                             _ => return,
 102                         }
 103                     };
 104                     let sugg = numeric_literal::format(&src, Some(suffix), is_float);
 105                     span_lint_and_sugg(
 106                         self.cx,
 107                         DEFAULT_NUMERIC_FALLBACK,
 108                         lit.span,
 109                         "default numeric fallback might occur",
 110                         "consider adding suffix",
 111                         sugg,
 112                         Applicability::MaybeIncorrect,
 113                     );
 114                 }
 115         }
 116     }
 117 }
 118
 119 impl<'a, 'tcx> Visitor<'tcx> for NumericFallbackVisitor<'a, 'tcx> {
 120     type Map = Map<'tcx>;
 121
 122     #[allow(clippy::too_many_lines)]
 123     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 124         match &expr.kind {
 125             ExprKind::Call(func, args) => {
 126                 if let Some(fn_sig) = fn_sig_opt(self.cx, func.hir_id) {
 127                     for (expr, bound) in iter::zip(*args, fn_sig.skip_binder().inputs()) {
 128                         // Push found arg type, then visit arg.
 129                         self.ty_bounds.push(TyBound::Ty(bound));
 130                         self.visit_expr(expr);
 131                         self.ty_bounds.pop();
 132                     }
 133                     return;
 134                 }
 135             },
 136
 137             ExprKind::MethodCall(_, _, args, _) => {
 138                 if let Some(def_id) = self.cx.typeck_results().type_dependent_def_id(expr.hir_id) {
 139                     let fn_sig = self.cx.tcx.fn_sig(def_id).skip_binder();
 140                     for (expr, bound) in iter::zip(*args, fn_sig.inputs()) {
 141                         self.ty_bounds.push(TyBound::Ty(bound));
 142                         self.visit_expr(expr);
 143                         self.ty_bounds.pop();
 144                     }
 145                     return;
 146                 }
 147             },
 148
 149             ExprKind::Struct(_, fields, base) => {
 150                 let ty = self.cx.typeck_results().expr_ty(expr);
 151                 if_chain! {
 152                     if let Some(adt_def) = ty.ty_adt_def();
 153                     if adt_def.is_struct();
 154                     if let Some(variant) = adt_def.variants.iter().next();
 155                     then {
 156                         let fields_def = &variant.fields;
 157
 158                         // Push field type then visit each field expr.
 159                         for field in fields.iter() {
 160                             let bound =
 161                                 fields_def
 162                                     .iter()
 163                                     .find_map(|f_def| {
 164                                         if f_def.ident == field.ident
 165                                             { Some(self.cx.tcx.type_of(f_def.did)) }
 166                                         else { None }
 167                                     });
 168                             self.ty_bounds.push(bound.into());
 169                             self.visit_expr(field.expr);
 170                             self.ty_bounds.pop();
 171                         }
 172
 173                         // Visit base with no bound.
 174                         if let Some(base) = base {
 175                             self.ty_bounds.push(TyBound::Nothing);
 176                             self.visit_expr(base);
 177                             self.ty_bounds.pop();
 178                         }
 179                         return;
 180                     }
 181                 }
 182             },
 183
 184             ExprKind::Lit(lit) => {
 185                 let ty = self.cx.typeck_results().expr_ty(expr);
 186                 self.check_lit(lit, ty);
 187                 return;
 188             },
 189
 190             _ => {},
 191         }
 192
 193         walk_expr(self, expr);
 194     }
 195
 196     fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
 197         match stmt.kind {
 198             StmtKind::Local(local) => {
 199                 if local.ty.is_some() {
 200                     self.ty_bounds.push(TyBound::Any);
 201                 } else {
 202                     self.ty_bounds.push(TyBound::Nothing);
 203                 }
 204             },
 205
 206             _ => self.ty_bounds.push(TyBound::Nothing),
 207         }
 208
 209         walk_stmt(self, stmt);
 210         self.ty_bounds.pop();
 211     }
 212
 213     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 214         NestedVisitorMap::None
 215     }
 216 }
 217
 218 fn fn_sig_opt<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<PolyFnSig<'tcx>> {
 219     let node_ty = cx.typeck_results().node_type_opt(hir_id)?;
 220     // We can't use `TyS::fn_sig` because it automatically performs substs, this may result in FNs.
 221     match node_ty.kind() {
 222         ty::FnDef(def_id, _) => Some(cx.tcx.fn_sig(*def_id)),
 223         ty::FnPtr(fn_sig) => Some(*fn_sig),
 224         _ => None,
 225     }
 226 }
 227
 228 #[derive(Debug, Clone, Copy)]
 229 enum TyBound<'tcx> {
 230     Any,
 231     Ty(Ty<'tcx>),
 232     Nothing,
 233 }
 234
 235 impl<'tcx> TyBound<'tcx> {
 236     fn is_numeric(self) -> bool {
 237         match self {
 238             TyBound::Any => true,
 239             TyBound::Ty(t) => t.is_numeric(),
 240             TyBound::Nothing => false,
 241         }
 242     }
 243 }
 244
 245 impl<'tcx> From<Option<Ty<'tcx>>> for TyBound<'tcx> {
 246     fn from(v: Option<Ty<'tcx>>) -> Self {
 247         match v {
 248             Some(t) => TyBound::Ty(t),
 249             None => TyBound::Nothing,
 250         }
 251     }
 252 }