src/tools/clippy/clippy_lints/src/functions.rs

   1 use rustc::hir::intravisit;
   2 use rustc::hir;
   3 use rustc::lint::*;
   4 use rustc::ty;
   5 use std::collections::HashSet;
   6 use syntax::ast;
   7 use syntax::abi::Abi;
   8 use syntax::codemap::Span;
   9 use utils::{span_lint, type_is_unsafe_function, iter_input_pats};
  10
  11 /// **What it does:** Checks for functions with too many parameters.
  12 ///
  13 /// **Why is this bad?** Functions with lots of parameters are considered bad
  14 /// style and reduce readability (“what does the 5th parameter mean?”). Consider
  15 /// grouping some parameters into a new type.
  16 ///
  17 /// **Known problems:** None.
  18 ///
  19 /// **Example:**
  20 /// ```rust
  21 /// fn foo(x: u32, y: u32, name: &str, c: Color, w: f32, h: f32, a: f32, b:
  22 /// f32) { .. }
  23 /// ```
  24 declare_lint! {
  25     pub TOO_MANY_ARGUMENTS,
  26     Warn,
  27     "functions with too many arguments"
  28 }
  29
  30 /// **What it does:** Checks for public functions that dereferences raw pointer
  31 /// arguments but are not marked unsafe.
  32 ///
  33 /// **Why is this bad?** The function should probably be marked `unsafe`, since
  34 /// for an arbitrary raw pointer, there is no way of telling for sure if it is
  35 /// valid.
  36 ///
  37 /// **Known problems:**
  38 ///
  39 /// * It does not check functions recursively so if the pointer is passed to a
  40 /// private non-`unsafe` function which does the dereferencing, the lint won't
  41 /// trigger.
  42 /// * It only checks for arguments whose type are raw pointers, not raw pointers
  43 /// got from an argument in some other way (`fn foo(bar: &[*const u8])` or
  44 /// `some_argument.get_raw_ptr()`).
  45 ///
  46 /// **Example:**
  47 /// ```rust
  48 /// pub fn foo(x: *const u8) { println!("{}", unsafe { *x }); }
  49 /// ```
  50 declare_lint! {
  51     pub NOT_UNSAFE_PTR_ARG_DEREF,
  52     Warn,
  53     "public functions dereferencing raw pointer arguments but not marked `unsafe`"
  54 }
  55
  56 #[derive(Copy, Clone)]
  57 pub struct Functions {
  58     threshold: u64,
  59 }
  60
  61 impl Functions {
  62     pub fn new(threshold: u64) -> Self {
  63         Self { threshold: threshold }
  64     }
  65 }
  66
  67 impl LintPass for Functions {
  68     fn get_lints(&self) -> LintArray {
  69         lint_array!(TOO_MANY_ARGUMENTS, NOT_UNSAFE_PTR_ARG_DEREF)
  70     }
  71 }
  72
  73 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Functions {
  74     fn check_fn(
  75         &mut self,
  76         cx: &LateContext<'a, 'tcx>,
  77         kind: intravisit::FnKind<'tcx>,
  78         decl: &'tcx hir::FnDecl,
  79         body: &'tcx hir::Body,
  80         span: Span,
  81         nodeid: ast::NodeId,
  82     ) {
  83         use rustc::hir::map::Node::*;
  84
  85         let is_impl = if let Some(NodeItem(item)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(nodeid)) {
  86             matches!(item.node, hir::ItemImpl(_, _, _, _, Some(_), _, _) | hir::ItemDefaultImpl(..))
  87         } else {
  88             false
  89         };
  90
  91         let unsafety = match kind {
  92             hir::intravisit::FnKind::ItemFn(_, _, unsafety, _, _, _, _) => unsafety,
  93             hir::intravisit::FnKind::Method(_, sig, _, _) => sig.unsafety,
  94             hir::intravisit::FnKind::Closure(_) => return,
  95         };
  96
  97         // don't warn for implementations, it's not their fault
  98         if !is_impl {
  99             // don't lint extern functions decls, it's not their fault either
 100             match kind {
 101                 hir::intravisit::FnKind::Method(_, &hir::MethodSig { abi: Abi::Rust, .. }, _, _) |
 102                 hir::intravisit::FnKind::ItemFn(_, _, _, _, Abi::Rust, _, _) => self.check_arg_number(cx, decl, span),
 103                 _ => {},
 104             }
 105         }
 106
 107         self.check_raw_ptr(cx, unsafety, decl, body, nodeid);
 108     }
 109
 110     fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::TraitItem) {
 111         if let hir::TraitItemKind::Method(ref sig, ref eid) = item.node {
 112             // don't lint extern functions decls, it's not their fault
 113             if sig.abi == Abi::Rust {
 114                 self.check_arg_number(cx, &sig.decl, item.span);
 115             }
 116
 117             if let hir::TraitMethod::Provided(eid) = *eid {
 118                 let body = cx.tcx.hir.body(eid);
 119                 self.check_raw_ptr(cx, sig.unsafety, &sig.decl, body, item.id);
 120             }
 121         }
 122     }
 123 }
 124
 125 impl<'a, 'tcx> Functions {
 126     fn check_arg_number(&self, cx: &LateContext, decl: &hir::FnDecl, span: Span) {
 127         let args = decl.inputs.len() as u64;
 128         if args > self.threshold {
 129             span_lint(
 130                 cx,
 131                 TOO_MANY_ARGUMENTS,
 132                 span,
 133                 &format!("this function has too many arguments ({}/{})", args, self.threshold),
 134             );
 135         }
 136     }
 137
 138     fn check_raw_ptr(
 139         &self,
 140         cx: &LateContext<'a, 'tcx>,
 141         unsafety: hir::Unsafety,
 142         decl: &'tcx hir::FnDecl,
 143         body: &'tcx hir::Body,
 144         nodeid: ast::NodeId,
 145     ) {
 146         let expr = &body.value;
 147         if unsafety == hir::Unsafety::Normal && cx.access_levels.is_exported(nodeid) {
 148             let raw_ptrs = iter_input_pats(decl, body)
 149                 .zip(decl.inputs.iter())
 150                 .filter_map(|(arg, ty)| raw_ptr_arg(arg, ty))
 151                 .collect::<HashSet<_>>();
 152
 153             if !raw_ptrs.is_empty() {
 154                 let tables = cx.tcx.body_tables(body.id());
 155                 let mut v = DerefVisitor {
 156                     cx: cx,
 157                     ptrs: raw_ptrs,
 158                     tables,
 159                 };
 160
 161                 hir::intravisit::walk_expr(&mut v, expr);
 162             }
 163         }
 164     }
 165 }
 166
 167 fn raw_ptr_arg(arg: &hir::Arg, ty: &hir::Ty) -> Option<hir::def_id::DefId> {
 168     if let (&hir::PatKind::Binding(_, def_id, _, _), &hir::TyPtr(_)) = (&arg.pat.node, &ty.node) {
 169         Some(def_id)
 170     } else {
 171         None
 172     }
 173 }
 174
 175 struct DerefVisitor<'a, 'tcx: 'a> {
 176     cx: &'a LateContext<'a, 'tcx>,
 177     ptrs: HashSet<hir::def_id::DefId>,
 178     tables: &'a ty::TypeckTables<'tcx>,
 179 }
 180
 181 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for DerefVisitor<'a, 'tcx> {
 182     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 183         match expr.node {
 184             hir::ExprCall(ref f, ref args) => {
 185                 let ty = self.tables.expr_ty(f);
 186
 187                 if type_is_unsafe_function(self.cx, ty) {
 188                     for arg in args {
 189                         self.check_arg(arg);
 190                     }
 191                 }
 192             },
 193             hir::ExprMethodCall(_, _, ref args) => {
 194                 let def_id = self.tables.type_dependent_defs()[expr.hir_id].def_id();
 195                 let base_type = self.cx.tcx.type_of(def_id);
 196
 197                 if type_is_unsafe_function(self.cx, base_type) {
 198                     for arg in args {
 199                         self.check_arg(arg);
 200                     }
 201                 }
 202             },
 203             hir::ExprUnary(hir::UnDeref, ref ptr) => self.check_arg(ptr),
 204             _ => (),
 205         }
 206
 207         hir::intravisit::walk_expr(self, expr);
 208     }
 209     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
 210         intravisit::NestedVisitorMap::None
 211     }
 212 }
 213
 214 impl<'a, 'tcx: 'a> DerefVisitor<'a, 'tcx> {
 215     fn check_arg(&self, ptr: &hir::Expr) {
 216         if let hir::ExprPath(ref qpath) = ptr.node {
 217             let def = self.cx.tables.qpath_def(qpath, ptr.hir_id);
 218             if self.ptrs.contains(&def.def_id()) {
 219                 span_lint(
 220                     self.cx,
 221                     NOT_UNSAFE_PTR_ARG_DEREF,
 222                     ptr.span,
 223                     "this public function dereferences a raw pointer but is not marked `unsafe`",
 224                 );
 225             }
 226         }
 227     }
 228 }