New lint: default_numeric_fallback

1 files changed, 388 insertions, 0 deletions

diff --git a/clippy_lints/src/default_numeric_fallback.rs b/clippy_lints/src/default_numeric_fallback.rs
new file mode 100644
index 00000000000..f049e64d0fb
--- /dev/null
+++ b/clippy_lints/src/default_numeric_fallback.rs
@@ -0,0 +1,388 @@
+use rustc_ast::ast::{Label, LitFloatType, LitIntType, LitKind};
+use rustc_hir::{
+    self as hir,
+    intravisit::{walk_expr, walk_stmt, walk_ty, FnKind, NestedVisitorMap, Visitor},
+    Body, Expr, ExprKind, FnDecl, FnRetTy, Guard, HirId, Lit, Stmt, StmtKind,
+};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::{
+    hir::map::Map,
+    ty::{self, subst::GenericArgKind, FloatTy, IntTy, Ty, TyCtxt},
+};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::Span;
+use rustc_typeck::hir_ty_to_ty;
+
+use if_chain::if_chain;
+
+use crate::utils::span_lint_and_help;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for usage of unconstrained numeric literals which may cause default numeric fallback in type
+    /// inference.
+    ///
+    /// Default numeric fallback means that if numeric types have not yet been bound to concrete
+    /// types at the end of type inference, then integer type is bound to `i32`, and similarly
+    /// floating type is bound to `f64`.
+    ///
+    /// See [RFC0212](https://github.com/rust-lang/rfcs/blob/master/text/0212-restore-int-fallback.md) for more information about the fallback.
+    ///
+    /// **Why is this bad?** For those who are very careful about types, default numeric fallback
+    /// can be a pitfall that cause unexpected runtime behavior.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// let i = 10;
+    /// let f = 1.23;
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// let i = 10i32;
+    /// let f = 1.23f64;
+    /// ```
+    pub DEFAULT_NUMERIC_FALLBACK,
+    restriction,
+    "usage of unconstrained numeric literals which may cause default numeric fallback."
+}
+
+declare_lint_pass!(DefaultNumericFallback => [DEFAULT_NUMERIC_FALLBACK]);
+
+fn enclosing_body_owner_opt(tcx: TyCtxt<'_>, hir_id: HirId) -> Option<HirId> {
+    let hir_map = tcx.hir();
+    for (parent, _) in hir_map.parent_iter(hir_id) {
+        if let Some(body) = hir_map.maybe_body_owned_by(parent) {
+            return Some(hir_map.body_owner(body));
+        }
+    }
+    None
+}
+
+impl LateLintPass<'_> for DefaultNumericFallback {
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        _: FnKind<'tcx>,
+        fn_decl: &'tcx FnDecl<'_>,
+        body: &'tcx Body<'_>,
+        _: Span,
+        hir_id: HirId,
+    ) {
+        let ret_ty_bound = match fn_decl.output {
+            FnRetTy::DefaultReturn(_) => None,
+            FnRetTy::Return(ty) => Some(ty),
+        }
+        .and_then(|ty| {
+            let mut infer_ty_finder = InferTyFinder::new();
+            infer_ty_finder.visit_ty(ty);
+            if infer_ty_finder.found {
+                None
+            } else if enclosing_body_owner_opt(cx.tcx, hir_id).is_some() {
+                cx.typeck_results().node_type_opt(ty.hir_id)
+            } else {
+                Some(hir_ty_to_ty(cx.tcx, ty))
+            }
+        });
+
+        let mut visitor = NumericFallbackVisitor::new(ret_ty_bound, cx);
+        visitor.visit_body(body);
+    }
+}
+
+struct NumericFallbackVisitor<'a, 'tcx> {
+    /// Stack manages type bound of exprs. The top element holds current expr type.
+    ty_bounds: Vec<Option<Ty<'tcx>>>,
+
+    /// Ret type bound.
+    ret_ty_bound: Option<Ty<'tcx>>,
+
+    /// Break type bounds.
+    break_ty_bounds: Vec<(Option<Label>, Option<Ty<'tcx>>)>,
+
+    cx: &'a LateContext<'tcx>,
+}
+
+impl<'a, 'tcx> NumericFallbackVisitor<'a, 'tcx> {
+    fn new(ret_ty_bound: Option<Ty<'tcx>>, cx: &'a LateContext<'tcx>) -> Self {
+        Self {
+            ty_bounds: vec![ret_ty_bound],
+            ret_ty_bound,
+            break_ty_bounds: vec![],
+            cx,
+        }
+    }
+
+    /// Check whether lit cause fallback or not.
+    fn check_lit(&self, lit: &Lit, lit_ty: Ty<'tcx>) {
+        let ty_bound = self.ty_bounds.last().unwrap();
+
+        let should_lint = match (&lit.node, lit_ty.kind()) {
+            (LitKind::Int(_, LitIntType::Unsuffixed), ty::Int(ty::IntTy::I32)) => {
+                // In case integer literal is explicitly bound to i32, then suppress lint.
+                ty_bound.map_or(true, |ty_bound| !matches!(ty_bound.kind(), ty::Int(IntTy::I32)))
+            },
+
+            (LitKind::Float(_, LitFloatType::Unsuffixed), ty::Float(ty::FloatTy::F64)) => {
+                // In case float literal is explicitly bound to f64, then suppress lint.
+                ty_bound.map_or(true, |ty_bound| !matches!(ty_bound.kind(), ty::Float(FloatTy::F64)))
+            },
+
+            _ => false,
+        };
+
+        if should_lint {
+            span_lint_and_help(
+                self.cx,
+                DEFAULT_NUMERIC_FALLBACK,
+                lit.span,
+                "default numeric fallback might occur",
+                None,
+                "consider adding suffix to avoid default numeric fallback",
+            );
+        }
+    }
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for NumericFallbackVisitor<'a, 'tcx> {
+    type Map = Map<'tcx>;
+
+    #[allow(clippy::too_many_lines)]
+    fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
+        match (&expr.kind, *self.ty_bounds.last().unwrap()) {
+            (ExprKind::Array(_), Some(last_bound)) => {
+                if let ty::Array(ty, _) = last_bound.kind() {
+                    self.ty_bounds.push(Some(ty))
+                } else {
+                    self.ty_bounds.push(None)
+                }
+            },
+
+            (ExprKind::Call(func, args), _) => {
+                if_chain! {
+                    if let ExprKind::Path(ref func_path) = func.kind;
+                    if let Some(def_id) = self.cx.qpath_res(func_path, func.hir_id).opt_def_id();
+                    then {
+                        let fn_sig = self.cx.tcx.fn_sig(def_id).skip_binder();
+                        for (expr, bound) in args.iter().zip(fn_sig.inputs().iter()) {
+                            // Push found arg type, then visit arg.
+                            self.ty_bounds.push(Some(bound));
+                            self.visit_expr(expr);
+                            self.ty_bounds.pop();
+                        }
+                        return;
+                    } else {
+                        self.ty_bounds.push(None)
+                    }
+                }
+            },
+
+            (ExprKind::MethodCall(_, _, args, _), _) => {
+                if let Some(def_id) = self.cx.typeck_results().type_dependent_def_id(expr.hir_id) {
+                    let fn_sig = self.cx.tcx.fn_sig(def_id).skip_binder();
+                    for (expr, bound) in args.iter().zip(fn_sig.inputs().iter()) {
+                        self.ty_bounds.push(Some(bound));
+                        self.visit_expr(expr);
+                        self.ty_bounds.pop();
+                    }
+                    return;
+                }
+
+                self.ty_bounds.push(None)
+            },
+
+            (ExprKind::Tup(exprs), Some(last_bound)) => {
+                if let ty::Tuple(tys) = last_bound.kind() {
+                    for (expr, bound) in exprs.iter().zip(tys.iter()) {
+                        if let GenericArgKind::Type(ty) = bound.unpack() {
+                            self.ty_bounds.push(Some(ty));
+                        } else {
+                            self.ty_bounds.push(None);
+                        }
+
+                        self.visit_expr(expr);
+                        self.ty_bounds.pop();
+                    }
+                    return;
+                }
+
+                self.ty_bounds.push(None)
+            },
+
+            (ExprKind::Lit(lit), _) => {
+                let ty = self.cx.typeck_results().expr_ty(expr);
+                self.check_lit(lit, ty);
+                return;
+            },
+
+            (ExprKind::If(cond, then, else_), last_bound) => {
+                // Cond has no type bound in any situation.
+                self.ty_bounds.push(None);
+                self.visit_expr(cond);
+                self.ty_bounds.pop();
+
+                // Propagate current bound to childs.
+                self.ty_bounds.push(last_bound);
+                self.visit_expr(then);
+                if let Some(else_) = else_ {
+                    self.visit_expr(else_);
+                }
+                self.ty_bounds.pop();
+                return;
+            },
+
+            (ExprKind::Loop(_, label, ..), last_bound) => {
+                self.break_ty_bounds.push((*label, last_bound));
+                walk_expr(self, expr);
+                self.break_ty_bounds.pop();
+                return;
+            },
+
+            (ExprKind::Match(arg, arms, _), last_bound) => {
+                // Match argument has no type bound.
+                self.ty_bounds.push(None);
+                self.visit_expr(arg);
+                for arm in arms.iter() {
+                    self.visit_pat(arm.pat);
+                    if let Some(Guard::If(guard)) = arm.guard {
+                        self.visit_expr(guard);
+                    }
+                }
+                self.ty_bounds.pop();
+
+                // Propagate current bound.
+                self.ty_bounds.push(last_bound);
+                for arm in arms.iter() {
+                    self.visit_expr(arm.body);
+                }
+                self.ty_bounds.pop();
+                return;
+            },
+
+            (ExprKind::Block(..), last_bound) => self.ty_bounds.push(last_bound),
+
+            (ExprKind::Break(destination, _), _) => {
+                let ty = destination.label.map_or_else(
+                    || self.break_ty_bounds.last().unwrap().1,
+                    |dest_label| {
+                        self.break_ty_bounds
+                            .iter()
+                            .rev()
+                            .find_map(|(loop_label, ty)| {
+                                loop_label.map_or(None, |loop_label| {
+                                    if loop_label.ident == dest_label.ident {
+                                        Some(*ty)
+                                    } else {
+                                        None
+                                    }
+                                })
+                            })
+                            .unwrap()
+                    },
+                );
+                self.ty_bounds.push(ty);
+            },
+
+            (ExprKind::Ret(_), _) => self.ty_bounds.push(self.ret_ty_bound),
+
+            (ExprKind::Struct(qpath, fields, base), _) => {
+                if_chain! {
+                    if let Some(def_id) = self.cx.qpath_res(qpath, expr.hir_id).opt_def_id();
+                    let ty = self.cx.tcx.type_of(def_id);
+                    if let Some(adt_def) = ty.ty_adt_def();
+                    if adt_def.is_struct();
+                    if let Some(variant) = adt_def.variants.iter().next();
+                    then {
+                        let fields_def = &variant.fields;
+
+                        // Push field type then visit each field expr.
+                        for field in fields.iter() {
+                            let field_ty =
+                                fields_def
+                                    .iter()
+                                    .find_map(|f_def| {
+                                        if f_def.ident == field.ident
+                                            { Some(self.cx.tcx.type_of(f_def.did)) }
+                                        else { None }
+                                    });
+                            self.ty_bounds.push(field_ty);
+                            self.visit_expr(field.expr);
+                            self.ty_bounds.pop();
+                        }
+
+                        // Visit base with no bound.
+                        if let Some(base) = base {
+                            self.ty_bounds.push(None);
+                            self.visit_expr(base);
+                            self.ty_bounds.pop();
+                        }
+                        return;
+                    }
+                }
+                self.ty_bounds.push(None);
+            },
+
+            _ => self.ty_bounds.push(None),
+        }
+
+        walk_expr(self, expr);
+        self.ty_bounds.pop();
+    }
+
+    fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
+        match stmt.kind {
+            StmtKind::Local(local) => {
+                let ty = local.ty.and_then(|hir_ty| {
+                    let mut infer_ty_finder = InferTyFinder::new();
+                    infer_ty_finder.visit_ty(hir_ty);
+                    if infer_ty_finder.found {
+                        None
+                    } else {
+                        self.cx.typeck_results().node_type_opt(hir_ty.hir_id)
+                    }
+                });
+                self.ty_bounds.push(ty);
+            },
+
+            _ => self.ty_bounds.push(None),
+        }
+
+        walk_stmt(self, stmt);
+        self.ty_bounds.pop();
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}
+
+/// Find `hir::TyKind::Infer` is included in passed typed.
+struct InferTyFinder {
+    found: bool,
+}
+
+impl InferTyFinder {
+    fn new() -> Self {
+        Self { found: false }
+    }
+}
+
+impl<'tcx> Visitor<'tcx> for InferTyFinder {
+    type Map = Map<'tcx>;
+
+    fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
+        match ty.kind {
+            hir::TyKind::Infer => {
+                self.found = true;
+            },
+            _ => {
+                walk_ty(self, ty);
+            },
+        }
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}