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