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

   1 use clippy_utils::diagnostics::span_lint_hir_and_then;
   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>, emit_hir_id: HirId) {
  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_hir_and_then(
 105                         self.cx,
 106                         DEFAULT_NUMERIC_FALLBACK,
 107                         emit_hir_id,
 108                         lit.span,
 109                         "default numeric fallback might occur",
 110                         |diag| {
 111                             diag.span_suggestion(lit.span, "consider adding suffix", sugg, Applicability::MaybeIncorrect);
 112                         }
 113                     );
 114                 }
 115         }
 116     }
 117 }
 118
 119 impl<'a, 'tcx> Visitor<'tcx> for NumericFallbackVisitor<'a, 'tcx> {
 120     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 121         match &expr.kind {
 122             ExprKind::Call(func, args) => {
 123                 if let Some(fn_sig) = fn_sig_opt(self.cx, func.hir_id) {
 124                     for (expr, bound) in iter::zip(*args, fn_sig.skip_binder().inputs()) {
 125                         // Push found arg type, then visit arg.
 126                         self.ty_bounds.push(TyBound::Ty(*bound));
 127                         self.visit_expr(expr);
 128                         self.ty_bounds.pop();
 129                     }
 130                     return;
 131                 }
 132             },
 133
 134             ExprKind::MethodCall(_, receiver, args, _) => {
 135                 if let Some(def_id) = self.cx.typeck_results().type_dependent_def_id(expr.hir_id) {
 136                     let fn_sig = self.cx.tcx.fn_sig(def_id).skip_binder();
 137                     for (expr, bound) in iter::zip(std::iter::once(*receiver).chain(args.iter()), fn_sig.inputs()) {
 138                         self.ty_bounds.push(TyBound::Ty(*bound));
 139                         self.visit_expr(expr);
 140                         self.ty_bounds.pop();
 141                     }
 142                     return;
 143                 }
 144             },
 145
 146             ExprKind::Struct(_, fields, base) => {
 147                 let ty = self.cx.typeck_results().expr_ty(expr);
 148                 if_chain! {
 149                     if let Some(adt_def) = ty.ty_adt_def();
 150                     if adt_def.is_struct();
 151                     if let Some(variant) = adt_def.variants().iter().next();
 152                     then {
 153                         let fields_def = &variant.fields;
 154
 155                         // Push field type then visit each field expr.
 156                         for field in fields.iter() {
 157                             let bound =
 158                                 fields_def
 159                                     .iter()
 160                                     .find_map(|f_def| {
 161                                         if f_def.ident(self.cx.tcx) == field.ident
 162                                             { Some(self.cx.tcx.type_of(f_def.did)) }
 163                                         else { None }
 164                                     });
 165                             self.ty_bounds.push(bound.into());
 166                             self.visit_expr(field.expr);
 167                             self.ty_bounds.pop();
 168                         }
 169
 170                         // Visit base with no bound.
 171                         if let Some(base) = base {
 172                             self.ty_bounds.push(TyBound::Nothing);
 173                             self.visit_expr(base);
 174                             self.ty_bounds.pop();
 175                         }
 176                         return;
 177                     }
 178                 }
 179             },
 180
 181             ExprKind::Lit(lit) => {
 182                 let ty = self.cx.typeck_results().expr_ty(expr);
 183                 self.check_lit(lit, ty, expr.hir_id);
 184                 return;
 185             },
 186
 187             _ => {},
 188         }
 189
 190         walk_expr(self, expr);
 191     }
 192
 193     fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
 194         match stmt.kind {
 195             StmtKind::Local(local) => {
 196                 if local.ty.is_some() {
 197                     self.ty_bounds.push(TyBound::Any);
 198                 } else {
 199                     self.ty_bounds.push(TyBound::Nothing);
 200                 }
 201             },
 202
 203             _ => self.ty_bounds.push(TyBound::Nothing),
 204         }
 205
 206         walk_stmt(self, stmt);
 207         self.ty_bounds.pop();
 208     }
 209 }
 210
 211 fn fn_sig_opt<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Option<PolyFnSig<'tcx>> {
 212     let node_ty = cx.typeck_results().node_type_opt(hir_id)?;
 213     // We can't use `Ty::fn_sig` because it automatically performs substs, this may result in FNs.
 214     match node_ty.kind() {
 215         ty::FnDef(def_id, _) => Some(cx.tcx.fn_sig(*def_id)),
 216         ty::FnPtr(fn_sig) => Some(*fn_sig),
 217         _ => None,
 218     }
 219 }
 220
 221 #[derive(Debug, Clone, Copy)]
 222 enum TyBound<'tcx> {
 223     Any,
 224     Ty(Ty<'tcx>),
 225     Nothing,
 226 }
 227
 228 impl<'tcx> TyBound<'tcx> {
 229     fn is_numeric(self) -> bool {
 230         match self {
 231             TyBound::Any => true,
 232             TyBound::Ty(t) => t.is_numeric(),
 233             TyBound::Nothing => false,
 234         }
 235     }
 236 }
 237
 238 impl<'tcx> From<Option<Ty<'tcx>>> for TyBound<'tcx> {
 239     fn from(v: Option<Ty<'tcx>>) -> Self {
 240         match v {
 241             Some(t) => TyBound::Ty(t),
 242             None => TyBound::Nothing,
 243         }
 244     }
 245 }