src/tools/clippy/clippy_lints/src/functions.rs - toolchain/rustc - Git at Google

 use crate::utils::{
     attrs::is_proc_macro, iter_input_pats, match_def_path, qpath_res, return_ty, snippet, snippet_opt,
     span_help_and_lint, span_lint, span_lint_and_then, type_is_unsafe_function,
 };
 use matches::matches;
 use rustc::hir::{self, def::Res, def_id::DefId, intravisit};
 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
 use rustc::ty::{self, Ty};
 use rustc::{declare_tool_lint, impl_lint_pass};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
 use rustc_target::spec::abi::Abi;
 use syntax::ast::Attribute;
 use syntax::source_map::Span;

 declare_clippy_lint! {
     /// **What it does:** Checks for functions with too many parameters.
     ///
     /// **Why is this bad?** Functions with lots of parameters are considered bad
     /// style and reduce readability (“what does the 5th parameter mean?”). Consider
     /// grouping some parameters into a new type.
     ///
     /// **Known problems:** None.
     ///
     /// **Example:**
     /// ```rust
     /// # struct Color;
     /// fn foo(x: u32, y: u32, name: &str, c: Color, w: f32, h: f32, a: f32, b: f32) {
     ///     // ..
     /// }
     /// ```
     pub TOO_MANY_ARGUMENTS,
     complexity,
     "functions with too many arguments"
 }

 declare_clippy_lint! {
     /// **What it does:** Checks for functions with a large amount of lines.
     ///
     /// **Why is this bad?** Functions with a lot of lines are harder to understand
     /// due to having to look at a larger amount of code to understand what the
     /// function is doing. Consider splitting the body of the function into
     /// multiple functions.
     ///
     /// **Known problems:** None.
     ///
     /// **Example:**
     /// ``` rust
     /// fn im_too_long() {
     /// println!("");
     /// // ... 100 more LoC
     /// println!("");
     /// }
     /// ```
     pub TOO_MANY_LINES,
     pedantic,
     "functions with too many lines"
 }

 declare_clippy_lint! {
     /// **What it does:** Checks for public functions that dereference raw pointer
     /// arguments but are not marked unsafe.
     ///
     /// **Why is this bad?** The function should probably be marked `unsafe`, since
     /// for an arbitrary raw pointer, there is no way of telling for sure if it is
     /// valid.
     ///
     /// **Known problems:**
     ///
     /// * It does not check functions recursively so if the pointer is passed to a
     /// private non-`unsafe` function which does the dereferencing, the lint won't
     /// trigger.
     /// * It only checks for arguments whose type are raw pointers, not raw pointers
     /// got from an argument in some other way (`fn foo(bar: &[*const u8])` or
     /// `some_argument.get_raw_ptr()`).
     ///
     /// **Example:**
     /// ```rust
     /// pub fn foo(x: *const u8) {
     ///     println!("{}", unsafe { *x });
     /// }
     /// ```
     pub NOT_UNSAFE_PTR_ARG_DEREF,
     correctness,
     "public functions dereferencing raw pointer arguments but not marked `unsafe`"
 }

 declare_clippy_lint! {
     /// **What it does:** Checks for a [`#[must_use]`] attribute on
     /// unit-returning functions and methods.
     ///
     /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
     ///
     /// **Why is this bad?** Unit values are useless. The attribute is likely
     /// a remnant of a refactoring that removed the return type.
     ///
     /// **Known problems:** None.
     ///
     /// **Examples:**
     /// ```rust
     /// #[must_use]
     /// fn useless() { }
     /// ```
     pub MUST_USE_UNIT,
     style,
     "`#[must_use]` attribute on a unit-returning function / method"
 }

 declare_clippy_lint! {
     /// **What it does:** Checks for a [`#[must_use]`] attribute without
     /// further information on functions and methods that return a type already
     /// marked as `#[must_use]`.
     ///
     /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
     ///
     /// **Why is this bad?** The attribute isn't needed. Not using the result
     /// will already be reported. Alternatively, one can add some text to the
     /// attribute to improve the lint message.
     ///
     /// **Known problems:** None.
     ///
     /// **Examples:**
     /// ```rust
     /// #[must_use]
     /// fn double_must_use() -> Result<(), ()> {
     ///     unimplemented!();
     /// }
     /// ```
     pub DOUBLE_MUST_USE,
     style,
     "`#[must_use]` attribute on a `#[must_use]`-returning function / method"
 }

 declare_clippy_lint! {
     /// **What it does:** Checks for public functions that have no
     /// [`#[must_use]`] attribute, but return something not already marked
     /// must-use, have no mutable arg and mutate no statics.
     ///
     /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
     ///
     /// **Why is this bad?** Not bad at all, this lint just shows places where
     /// you could add the attribute.
     ///
     /// **Known problems:** The lint only checks the arguments for mutable
     /// types without looking if they are actually changed. On the other hand,
     /// it also ignores a broad range of potentially interesting side effects,
     /// because we cannot decide whether the programmer intends the function to
     /// be called for the side effect or the result. Expect many false
     /// positives. At least we don't lint if the result type is unit or already
     /// `#[must_use]`.
     ///
     /// **Examples:**
     /// ```rust
     /// // this could be annotated with `#[must_use]`.
     /// fn id<T>(t: T) -> T { t }
     /// ```
     pub MUST_USE_CANDIDATE,
     pedantic,
     "function or method that could take a `#[must_use]` attribute"
 }

 #[derive(Copy, Clone)]
 pub struct Functions {
     threshold: u64,
     max_lines: u64,
 }

 impl Functions {
     pub fn new(threshold: u64, max_lines: u64) -> Self {
         Self { threshold, max_lines }
     }
 }

 impl_lint_pass!(Functions => [
     TOO_MANY_ARGUMENTS,
     TOO_MANY_LINES,
     NOT_UNSAFE_PTR_ARG_DEREF,
     MUST_USE_UNIT,
     DOUBLE_MUST_USE,
     MUST_USE_CANDIDATE,
 ]);

 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Functions {
     fn check_fn(
         &mut self,
         cx: &LateContext<'a, 'tcx>,
         kind: intravisit::FnKind<'tcx>,
         decl: &'tcx hir::FnDecl,
         body: &'tcx hir::Body,
         span: Span,
         hir_id: hir::HirId,
     ) {
         let is_impl = if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
             matches!(item.kind, hir::ItemKind::Impl(_, _, _, _, Some(_), _, _))
         } else {
             false
         };

         let unsafety = match kind {
             hir::intravisit::FnKind::ItemFn(_, _, hir::FnHeader { unsafety, .. }, _, _) => unsafety,
             hir::intravisit::FnKind::Method(_, sig, _, _) => sig.header.unsafety,
             hir::intravisit::FnKind::Closure(_) => return,
         };

         // don't warn for implementations, it's not their fault
         if !is_impl {
             // don't lint extern functions decls, it's not their fault either
             match kind {
                 hir::intravisit::FnKind::Method(
                     _,
                     &hir::MethodSig {
                         header: hir::FnHeader { abi: Abi::Rust, .. },
                         ..
                     },
                     _,
                     _,
                 )
                 | hir::intravisit::FnKind::ItemFn(_, _, hir::FnHeader { abi: Abi::Rust, .. }, _, _) => {
                     self.check_arg_number(cx, decl, span.with_hi(decl.output.span().hi()))
                 },
                 _ => {},
             }
         }

         Self::check_raw_ptr(cx, unsafety, decl, body, hir_id);
         self.check_line_number(cx, span, body);
     }

     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
         let attr = must_use_attr(&item.attrs);
         if let hir::ItemKind::Fn(ref decl, ref _header, ref _generics, ref body_id) = item.kind {
             if let Some(attr) = attr {
                 let fn_header_span = item.span.with_hi(decl.output.span().hi());
                 check_needless_must_use(cx, decl, item.hir_id, item.span, fn_header_span, attr);
                 return;
             }
             if cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
                 check_must_use_candidate(
                     cx,
                     decl,
                     cx.tcx.hir().body(*body_id),
                     item.span,
                     item.hir_id,
                     item.span.with_hi(decl.output.span().hi()),
                     "this function could have a `#[must_use]` attribute",
                 );
             }
         }
     }

     fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::ImplItem) {
         if let hir::ImplItemKind::Method(ref sig, ref body_id) = item.kind {
             let attr = must_use_attr(&item.attrs);
             if let Some(attr) = attr {
                 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
                 check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
             } else if cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
                 check_must_use_candidate(
                     cx,
                     &sig.decl,
                     cx.tcx.hir().body(*body_id),
                     item.span,
                     item.hir_id,
                     item.span.with_hi(sig.decl.output.span().hi()),
                     "this method could have a `#[must_use]` attribute",
                 );
             }
         }
     }

     fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::TraitItem) {
         if let hir::TraitItemKind::Method(ref sig, ref eid) = item.kind {
             // don't lint extern functions decls, it's not their fault
             if sig.header.abi == Abi::Rust {
                 self.check_arg_number(cx, &sig.decl, item.span.with_hi(sig.decl.output.span().hi()));
             }

             let attr = must_use_attr(&item.attrs);
             if let Some(attr) = attr {
                 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
                 check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
             }
             if let hir::TraitMethod::Provided(eid) = *eid {
                 let body = cx.tcx.hir().body(eid);
                 Self::check_raw_ptr(cx, sig.header.unsafety, &sig.decl, body, item.hir_id);

                 if attr.is_none() && cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
                     check_must_use_candidate(
                         cx,
                         &sig.decl,
                         body,
                         item.span,
                         item.hir_id,
                         item.span.with_hi(sig.decl.output.span().hi()),
                         "this method could have a `#[must_use]` attribute",
                     );
                 }
             }
         }
     }
 }

 impl<'a, 'tcx> Functions {
     fn check_arg_number(self, cx: &LateContext<'_, '_>, decl: &hir::FnDecl, fn_span: Span) {
         let args = decl.inputs.len() as u64;
         if args > self.threshold {
             span_lint(
                 cx,
                 TOO_MANY_ARGUMENTS,
                 fn_span,
                 &format!("this function has too many arguments ({}/{})", args, self.threshold),
             );
         }
     }

     fn check_line_number(self, cx: &LateContext<'_, '_>, span: Span, body: &'tcx hir::Body) {
         if in_external_macro(cx.sess(), span) {
             return;
         }

         let code_snippet = snippet(cx, body.value.span, "..");
         let mut line_count: u64 = 0;
         let mut in_comment = false;
         let mut code_in_line;

         // Skip the surrounding function decl.
         let start_brace_idx = code_snippet.find('{').map_or(0, |i| i + 1);
         let end_brace_idx = code_snippet.rfind('}').unwrap_or_else(|| code_snippet.len());
         let function_lines = code_snippet[start_brace_idx..end_brace_idx].lines();

         for mut line in function_lines {
             code_in_line = false;
             loop {
                 line = line.trim_start();
                 if line.is_empty() {
                     break;
                 }
                 if in_comment {
                     match line.find("*/") {
                         Some(i) => {
                             line = &line[i + 2..];
                             in_comment = false;
                             continue;
                         },
                         None => break,
                     }
                 } else {
                     let multi_idx = line.find("/*").unwrap_or_else(|| line.len());
                     let single_idx = line.find("//").unwrap_or_else(|| line.len());
                     code_in_line |= multi_idx > 0 && single_idx > 0;
                     // Implies multi_idx is below line.len()
                     if multi_idx < single_idx {
                         line = &line[multi_idx + 2..];
                         in_comment = true;
                         continue;
                     }
                     break;
                 }
             }
             if code_in_line {
                 line_count += 1;
             }
         }

         if line_count > self.max_lines {
             span_lint(cx, TOO_MANY_LINES, span, "This function has a large number of lines.")
         }
     }

     fn check_raw_ptr(
         cx: &LateContext<'a, 'tcx>,
         unsafety: hir::Unsafety,
         decl: &'tcx hir::FnDecl,
         body: &'tcx hir::Body,
         hir_id: hir::HirId,
     ) {
         let expr = &body.value;
         if unsafety == hir::Unsafety::Normal && cx.access_levels.is_exported(hir_id) {
             let raw_ptrs = iter_input_pats(decl, body)
                 .zip(decl.inputs.iter())
                 .filter_map(|(arg, ty)| raw_ptr_arg(arg, ty))
                 .collect::<FxHashSet<_>>();

             if !raw_ptrs.is_empty() {
                 let tables = cx.tcx.body_tables(body.id());
                 let mut v = DerefVisitor {
                     cx,
                     ptrs: raw_ptrs,
                     tables,
                 };

                 hir::intravisit::walk_expr(&mut v, expr);
             }
         }
     }
 }

 fn check_needless_must_use(
     cx: &LateContext<'_, '_>,
     decl: &hir::FnDecl,
     item_id: hir::HirId,
     item_span: Span,
     fn_header_span: Span,
     attr: &Attribute,
 ) {
     if in_external_macro(cx.sess(), item_span) {
         return;
     }
     if returns_unit(decl) {
         span_lint_and_then(
             cx,
             MUST_USE_UNIT,
             fn_header_span,
             "this unit-returning function has a `#[must_use]` attribute",
             |db| {
                 db.span_suggestion(
                     attr.span,
                     "remove the attribute",
                     "".into(),
                     Applicability::MachineApplicable,
                 );
             },
         );
     } else if !attr.is_value_str() && is_must_use_ty(cx, return_ty(cx, item_id)) {
         span_help_and_lint(
             cx,
             DOUBLE_MUST_USE,
             fn_header_span,
             "this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]`",
             "either add some descriptive text or remove the attribute",
         );
     }
 }

 fn check_must_use_candidate<'a, 'tcx>(
     cx: &LateContext<'a, 'tcx>,
     decl: &'tcx hir::FnDecl,
     body: &'tcx hir::Body,
     item_span: Span,
     item_id: hir::HirId,
     fn_span: Span,
     msg: &str,
 ) {
     if has_mutable_arg(cx, body)
         || mutates_static(cx, body)
         || in_external_macro(cx.sess(), item_span)
         || returns_unit(decl)
         || is_must_use_ty(cx, return_ty(cx, item_id))
     {
         return;
     }
     span_lint_and_then(cx, MUST_USE_CANDIDATE, fn_span, msg, |db| {
         if let Some(snippet) = snippet_opt(cx, fn_span) {
             db.span_suggestion(
                 fn_span,
                 "add the attribute",
                 format!("#[must_use] {}", snippet),
                 Applicability::MachineApplicable,
             );
         }
     });
 }

 fn must_use_attr(attrs: &[Attribute]) -> Option<&Attribute> {
     attrs.iter().find(|attr| {
         attr.ident().map_or(false, |ident| {
             let ident: &str = &ident.as_str();
             "must_use" == ident
         })
     })
 }

 fn returns_unit(decl: &hir::FnDecl) -> bool {
     match decl.output {
         hir::FunctionRetTy::DefaultReturn(_) => true,
         hir::FunctionRetTy::Return(ref ty) => match ty.kind {
             hir::TyKind::Tup(ref tys) => tys.is_empty(),
             hir::TyKind::Never => true,
             _ => false,
         },
     }
 }

 fn is_must_use_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>) -> bool {
     use ty::TyKind::*;
     match ty.kind {
         Adt(ref adt, _) => must_use_attr(&cx.tcx.get_attrs(adt.did)).is_some(),
         Foreign(ref did) => must_use_attr(&cx.tcx.get_attrs(*did)).is_some(),
         Slice(ref ty) | Array(ref ty, _) | RawPtr(ty::TypeAndMut { ref ty, .. }) | Ref(_, ref ty, _) => {
             // for the Array case we don't need to care for the len == 0 case
             // because we don't want to lint functions returning empty arrays
             is_must_use_ty(cx, *ty)
         },
         Tuple(ref substs) => substs.types().any(|ty| is_must_use_ty(cx, ty)),
         Opaque(ref def_id, _) => {
             for (predicate, _) in cx.tcx.predicates_of(*def_id).predicates {
                 if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
                     if must_use_attr(&cx.tcx.get_attrs(poly_trait_predicate.skip_binder().trait_ref.def_id)).is_some() {
                         return true;
                     }
                 }
             }
             false
         },
         Dynamic(binder, _) => {
             for predicate in binder.skip_binder().iter() {
                 if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
                     if must_use_attr(&cx.tcx.get_attrs(trait_ref.def_id)).is_some() {
                         return true;
                     }
                 }
             }
             false
         },
         _ => false,
     }
 }

 fn has_mutable_arg(cx: &LateContext<'_, '_>, body: &hir::Body) -> bool {
     let mut tys = FxHashSet::default();
     body.params.iter().any(|param| is_mutable_pat(cx, &param.pat, &mut tys))
 }

 fn is_mutable_pat(cx: &LateContext<'_, '_>, pat: &hir::Pat, tys: &mut FxHashSet<DefId>) -> bool {
     if let hir::PatKind::Wild = pat.kind {
         return false; // ignore `_` patterns
     }
     let def_id = pat.hir_id.owner_def_id();
     if cx.tcx.has_typeck_tables(def_id) {
         is_mutable_ty(cx, &cx.tcx.typeck_tables_of(def_id).pat_ty(pat), pat.span, tys)
     } else {
         false
     }
 }

 static KNOWN_WRAPPER_TYS: &[&[&str]] = &[&["alloc", "rc", "Rc"], &["std", "sync", "Arc"]];

 fn is_mutable_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>, span: Span, tys: &mut FxHashSet<DefId>) -> bool {
     use ty::TyKind::*;
     match ty.kind {
         // primitive types are never mutable
         Bool | Char | Int(_) | Uint(_) | Float(_) | Str => false,
         Adt(ref adt, ref substs) => {
             tys.insert(adt.did) && !ty.is_freeze(cx.tcx, cx.param_env, span)
                 || KNOWN_WRAPPER_TYS.iter().any(|path| match_def_path(cx, adt.did, path))
                     && substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys))
         },
         Tuple(ref substs) => substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys)),
         Array(ty, _) | Slice(ty) => is_mutable_ty(cx, ty, span, tys),
         RawPtr(ty::TypeAndMut { ty, mutbl }) | Ref(_, ty, mutbl) => {
             mutbl == hir::Mutability::MutMutable || is_mutable_ty(cx, ty, span, tys)
         },
         // calling something constitutes a side effect, so return true on all callables
         // also never calls need not be used, so return true for them, too
         _ => true,
     }
 }

 fn raw_ptr_arg(arg: &hir::Param, ty: &hir::Ty) -> Option<hir::HirId> {
     if let (&hir::PatKind::Binding(_, id, _, _), &hir::TyKind::Ptr(_)) = (&arg.pat.kind, &ty.kind) {
         Some(id)
     } else {
         None
     }
 }

 struct DerefVisitor<'a, 'tcx> {
     cx: &'a LateContext<'a, 'tcx>,
     ptrs: FxHashSet<hir::HirId>,
     tables: &'a ty::TypeckTables<'tcx>,
 }

 impl<'a, 'tcx> intravisit::Visitor<'tcx> for DerefVisitor<'a, 'tcx> {
     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
         match expr.kind {
             hir::ExprKind::Call(ref f, ref args) => {
                 let ty = self.tables.expr_ty(f);

                 if type_is_unsafe_function(self.cx, ty) {
                     for arg in args {
                         self.check_arg(arg);
                     }
                 }
             },
             hir::ExprKind::MethodCall(_, _, ref args) => {
                 let def_id = self.tables.type_dependent_def_id(expr.hir_id).unwrap();
                 let base_type = self.cx.tcx.type_of(def_id);

                 if type_is_unsafe_function(self.cx, base_type) {
                     for arg in args {
                         self.check_arg(arg);
                     }
                 }
             },
             hir::ExprKind::Unary(hir::UnDeref, ref ptr) => self.check_arg(ptr),
             _ => (),
         }

         intravisit::walk_expr(self, expr);
     }

     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
         intravisit::NestedVisitorMap::None
     }
 }

 impl<'a, 'tcx> DerefVisitor<'a, 'tcx> {
     fn check_arg(&self, ptr: &hir::Expr) {
         if let hir::ExprKind::Path(ref qpath) = ptr.kind {
             if let Res::Local(id) = qpath_res(self.cx, qpath, ptr.hir_id) {
                 if self.ptrs.contains(&id) {
                     span_lint(
                         self.cx,
                         NOT_UNSAFE_PTR_ARG_DEREF,
                         ptr.span,
                         "this public function dereferences a raw pointer but is not marked `unsafe`",
                     );
                 }
             }
         }
     }
 }

 struct StaticMutVisitor<'a, 'tcx> {
     cx: &'a LateContext<'a, 'tcx>,
     mutates_static: bool,
 }

 impl<'a, 'tcx> intravisit::Visitor<'tcx> for StaticMutVisitor<'a, 'tcx> {
     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
         use hir::ExprKind::*;

         if self.mutates_static {
             return;
         }
         match expr.kind {
             Call(_, ref args) | MethodCall(_, _, ref args) => {
                 let mut tys = FxHashSet::default();
                 for arg in args {
                     let def_id = arg.hir_id.owner_def_id();
                     if self.cx.tcx.has_typeck_tables(def_id)
                         && is_mutable_ty(
                             self.cx,
                             self.cx.tcx.typeck_tables_of(def_id).expr_ty(arg),
                             arg.span,
                             &mut tys,
                         )
                         && is_mutated_static(self.cx, arg)
                     {
                         self.mutates_static = true;
                         return;
                     }
                     tys.clear();
                 }
             },
             Assign(ref target, _) | AssignOp(_, ref target, _) | AddrOf(hir::Mutability::MutMutable, ref target) => {
                 self.mutates_static |= is_mutated_static(self.cx, target)
             },
             _ => {},
         }
     }

     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
         intravisit::NestedVisitorMap::None
     }
 }

 fn is_mutated_static(cx: &LateContext<'_, '_>, e: &hir::Expr) -> bool {
     use hir::ExprKind::*;

     match e.kind {
         Path(ref qpath) => {
             if let Res::Local(_) = qpath_res(cx, qpath, e.hir_id) {
                 false
             } else {
                 true
             }
         },
         Field(ref inner, _) | Index(ref inner, _) => is_mutated_static(cx, inner),
         _ => false,
     }
 }

 fn mutates_static<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, body: &'tcx hir::Body) -> bool {
     let mut v = StaticMutVisitor {
         cx,
         mutates_static: false,
     };
     intravisit::walk_expr(&mut v, &body.value);
     v.mutates_static
 }
	use crate::utils::{
	attrs::is_proc_macro, iter_input_pats, match_def_path, qpath_res, return_ty, snippet, snippet_opt,
	span_help_and_lint, span_lint, span_lint_and_then, type_is_unsafe_function,
	};
	use matches::matches;
	use rustc::hir::{self, def::Res, def_id::DefId, intravisit};
	use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
	use rustc::ty::{self, Ty};
	use rustc::{declare_tool_lint, impl_lint_pass};
	use rustc_data_structures::fx::FxHashSet;
	use rustc_errors::Applicability;
	use rustc_target::spec::abi::Abi;
	use syntax::ast::Attribute;
	use syntax::source_map::Span;

	declare_clippy_lint! {
	/// What it does: Checks for functions with too many parameters.
	///
	/// Why is this bad? Functions with lots of parameters are considered bad
	/// style and reduce readability (“what does the 5th parameter mean?”). Consider
	/// grouping some parameters into a new type.
	///
	/// Known problems: None.
	///
	/// Example:
	/// ```rust
	/// # struct Color;
	/// fn foo(x: u32, y: u32, name: &str, c: Color, w: f32, h: f32, a: f32, b: f32) {
	/// // ..
	/// }
	/// ```
	pub TOO_MANY_ARGUMENTS,
	complexity,
	"functions with too many arguments"
	}

	declare_clippy_lint! {
	/// What it does: Checks for functions with a large amount of lines.
	///
	/// Why is this bad? Functions with a lot of lines are harder to understand
	/// due to having to look at a larger amount of code to understand what the
	/// function is doing. Consider splitting the body of the function into
	/// multiple functions.
	///
	/// Known problems: None.
	///
	/// Example:
	/// ``` rust
	/// fn im_too_long() {
	/// println!("");
	/// // ... 100 more LoC
	/// println!("");
	/// }
	/// ```
	pub TOO_MANY_LINES,
	pedantic,
	"functions with too many lines"
	}

	declare_clippy_lint! {
	/// What it does: Checks for public functions that dereference raw pointer
	/// arguments but are not marked unsafe.
	///
	/// Why is this bad? The function should probably be marked `unsafe`, since
	/// for an arbitrary raw pointer, there is no way of telling for sure if it is
	/// valid.
	///
	/// Known problems:
	///
	/// * It does not check functions recursively so if the pointer is passed to a
	/// private non-`unsafe` function which does the dereferencing, the lint won't
	/// trigger.
	/// * It only checks for arguments whose type are raw pointers, not raw pointers
	/// got from an argument in some other way (`fn foo(bar: &[*const u8])` or
	/// `some_argument.get_raw_ptr()`).
	///
	/// Example:
	/// ```rust
	/// pub fn foo(x: *const u8) {
	/// println!("{}", unsafe { *x });
	/// }
	/// ```
	pub NOT_UNSAFE_PTR_ARG_DEREF,
	correctness,
	"public functions dereferencing raw pointer arguments but not marked `unsafe`"
	}

	declare_clippy_lint! {
	/// What it does: Checks for a [`#[must_use]`] attribute on
	/// unit-returning functions and methods.
	///
	/// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
	///
	/// Why is this bad? Unit values are useless. The attribute is likely
	/// a remnant of a refactoring that removed the return type.
	///
	/// Known problems: None.
	///
	/// Examples:
	/// ```rust
	/// #[must_use]
	/// fn useless() { }
	/// ```
	pub MUST_USE_UNIT,
	style,
	"`#[must_use]` attribute on a unit-returning function / method"
	}

	declare_clippy_lint! {
	/// What it does: Checks for a [`#[must_use]`] attribute without
	/// further information on functions and methods that return a type already
	/// marked as `#[must_use]`.
	///
	/// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
	///
	/// Why is this bad? The attribute isn't needed. Not using the result
	/// will already be reported. Alternatively, one can add some text to the
	/// attribute to improve the lint message.
	///
	/// Known problems: None.
	///
	/// Examples:
	/// ```rust
	/// #[must_use]
	/// fn double_must_use() -> Result<(), ()> {
	/// unimplemented!();
	/// }
	/// ```
	pub DOUBLE_MUST_USE,
	style,
	"`#[must_use]` attribute on a `#[must_use]`-returning function / method"
	}

	declare_clippy_lint! {
	/// What it does: Checks for public functions that have no
	/// [`#[must_use]`] attribute, but return something not already marked
	/// must-use, have no mutable arg and mutate no statics.
	///
	/// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
	///
	/// Why is this bad? Not bad at all, this lint just shows places where
	/// you could add the attribute.
	///
	/// Known problems: The lint only checks the arguments for mutable
	/// types without looking if they are actually changed. On the other hand,
	/// it also ignores a broad range of potentially interesting side effects,
	/// because we cannot decide whether the programmer intends the function to
	/// be called for the side effect or the result. Expect many false
	/// positives. At least we don't lint if the result type is unit or already
	/// `#[must_use]`.
	///
	/// Examples:
	/// ```rust
	/// // this could be annotated with `#[must_use]`.
	/// fn id<T>(t: T) -> T { t }
	/// ```
	pub MUST_USE_CANDIDATE,
	pedantic,
	"function or method that could take a `#[must_use]` attribute"
	}

	#[derive(Copy, Clone)]
	pub struct Functions {
	threshold: u64,
	max_lines: u64,
	}

	impl Functions {
	pub fn new(threshold: u64, max_lines: u64) -> Self {
	Self { threshold, max_lines }
	}
	}

	impl_lint_pass!(Functions => [
	TOO_MANY_ARGUMENTS,
	TOO_MANY_LINES,
	NOT_UNSAFE_PTR_ARG_DEREF,
	MUST_USE_UNIT,
	DOUBLE_MUST_USE,
	MUST_USE_CANDIDATE,
	]);

	impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Functions {
	fn check_fn(
	&mut self,
	cx: &LateContext<'a, 'tcx>,
	kind: intravisit::FnKind<'tcx>,
	decl: &'tcx hir::FnDecl,
	body: &'tcx hir::Body,
	span: Span,
	hir_id: hir::HirId,
	) {
	let is_impl = if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
	matches!(item.kind, hir::ItemKind::Impl(_, _, _, _, Some(_), _, _))
	} else {
	false
	};

	let unsafety = match kind {
	hir::intravisit::FnKind::ItemFn(_, _, hir::FnHeader { unsafety, .. }, _, _) => unsafety,
	hir::intravisit::FnKind::Method(_, sig, _, _) => sig.header.unsafety,
	hir::intravisit::FnKind::Closure(_) => return,
	};

	// don't warn for implementations, it's not their fault
	if !is_impl {
	// don't lint extern functions decls, it's not their fault either
	match kind {
	hir::intravisit::FnKind::Method(
	_,
	&hir::MethodSig {
	header: hir::FnHeader { abi: Abi::Rust, .. },
	..
	},
	_,
	_,
	)
	\| hir::intravisit::FnKind::ItemFn(_, _, hir::FnHeader { abi: Abi::Rust, .. }, _, _) => {
	self.check_arg_number(cx, decl, span.with_hi(decl.output.span().hi()))
	},
	_ => {},
	}
	}

	Self::check_raw_ptr(cx, unsafety, decl, body, hir_id);
	self.check_line_number(cx, span, body);
	}

	fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
	let attr = must_use_attr(&item.attrs);
	if let hir::ItemKind::Fn(ref decl, ref _header, ref _generics, ref body_id) = item.kind {
	if let Some(attr) = attr {
	let fn_header_span = item.span.with_hi(decl.output.span().hi());
	check_needless_must_use(cx, decl, item.hir_id, item.span, fn_header_span, attr);
	return;
	}
	if cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
	check_must_use_candidate(
	cx,
	decl,
	cx.tcx.hir().body(*body_id),
	item.span,
	item.hir_id,
	item.span.with_hi(decl.output.span().hi()),
	"this function could have a `#[must_use]` attribute",
	);
	}
	}
	}

	fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::ImplItem) {
	if let hir::ImplItemKind::Method(ref sig, ref body_id) = item.kind {
	let attr = must_use_attr(&item.attrs);
	if let Some(attr) = attr {
	let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
	check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
	} else if cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
	check_must_use_candidate(
	cx,
	&sig.decl,
	cx.tcx.hir().body(*body_id),
	item.span,
	item.hir_id,
	item.span.with_hi(sig.decl.output.span().hi()),
	"this method could have a `#[must_use]` attribute",
	);
	}
	}
	}

	fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::TraitItem) {
	if let hir::TraitItemKind::Method(ref sig, ref eid) = item.kind {
	// don't lint extern functions decls, it's not their fault
	if sig.header.abi == Abi::Rust {
	self.check_arg_number(cx, &sig.decl, item.span.with_hi(sig.decl.output.span().hi()));
	}

	let attr = must_use_attr(&item.attrs);
	if let Some(attr) = attr {
	let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
	check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
	}
	if let hir::TraitMethod::Provided(eid) = *eid {
	let body = cx.tcx.hir().body(eid);
	Self::check_raw_ptr(cx, sig.header.unsafety, &sig.decl, body, item.hir_id);

	if attr.is_none() && cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
	check_must_use_candidate(
	cx,
	&sig.decl,
	body,
	item.span,
	item.hir_id,
	item.span.with_hi(sig.decl.output.span().hi()),
	"this method could have a `#[must_use]` attribute",
	);
	}
	}
	}
	}
	}

	impl<'a, 'tcx> Functions {
	fn check_arg_number(self, cx: &LateContext<'_, '_>, decl: &hir::FnDecl, fn_span: Span) {
	let args = decl.inputs.len() as u64;
	if args > self.threshold {
	span_lint(
	cx,
	TOO_MANY_ARGUMENTS,
	fn_span,
	&format!("this function has too many arguments ({}/{})", args, self.threshold),
	);
	}
	}

	fn check_line_number(self, cx: &LateContext<'_, '_>, span: Span, body: &'tcx hir::Body) {
	if in_external_macro(cx.sess(), span) {
	return;
	}

	let code_snippet = snippet(cx, body.value.span, "..");
	let mut line_count: u64 = 0;
	let mut in_comment = false;
	let mut code_in_line;

	// Skip the surrounding function decl.
	let start_brace_idx = code_snippet.find('{').map_or(0, \|i\| i + 1);
	let end_brace_idx = code_snippet.rfind('}').unwrap_or_else(\|\| code_snippet.len());
	let function_lines = code_snippet[start_brace_idx..end_brace_idx].lines();

	for mut line in function_lines {
	code_in_line = false;
	loop {
	line = line.trim_start();
	if line.is_empty() {
	break;
	}
	if in_comment {
	match line.find("*/") {
	Some(i) => {
	line = &line[i + 2..];
	in_comment = false;
	continue;
	},
	None => break,
	}
	} else {
	let multi_idx = line.find("/*").unwrap_or_else(\|\| line.len());
	let single_idx = line.find("//").unwrap_or_else(\|\| line.len());
	code_in_line \|= multi_idx > 0 && single_idx > 0;
	// Implies multi_idx is below line.len()
	if multi_idx < single_idx {
	line = &line[multi_idx + 2..];
	in_comment = true;
	continue;
	}
	break;
	}
	}
	if code_in_line {
	line_count += 1;
	}
	}

	if line_count > self.max_lines {
	span_lint(cx, TOO_MANY_LINES, span, "This function has a large number of lines.")
	}
	}

	fn check_raw_ptr(
	cx: &LateContext<'a, 'tcx>,
	unsafety: hir::Unsafety,
	decl: &'tcx hir::FnDecl,
	body: &'tcx hir::Body,
	hir_id: hir::HirId,
	) {
	let expr = &body.value;
	if unsafety == hir::Unsafety::Normal && cx.access_levels.is_exported(hir_id) {
	let raw_ptrs = iter_input_pats(decl, body)
	.zip(decl.inputs.iter())
	.filter_map(\|(arg, ty)\| raw_ptr_arg(arg, ty))
	.collect::<FxHashSet<_>>();

	if !raw_ptrs.is_empty() {
	let tables = cx.tcx.body_tables(body.id());
	let mut v = DerefVisitor {
	cx,
	ptrs: raw_ptrs,
	tables,
	};

	hir::intravisit::walk_expr(&mut v, expr);
	}
	}
	}
	}

	fn check_needless_must_use(
	cx: &LateContext<'_, '_>,
	decl: &hir::FnDecl,
	item_id: hir::HirId,
	item_span: Span,
	fn_header_span: Span,
	attr: &Attribute,
	) {
	if in_external_macro(cx.sess(), item_span) {
	return;
	}
	if returns_unit(decl) {
	span_lint_and_then(
	cx,
	MUST_USE_UNIT,
	fn_header_span,
	"this unit-returning function has a `#[must_use]` attribute",
	\|db\| {
	db.span_suggestion(
	attr.span,
	"remove the attribute",
	"".into(),
	Applicability::MachineApplicable,
	);
	},
	);
	} else if !attr.is_value_str() && is_must_use_ty(cx, return_ty(cx, item_id)) {
	span_help_and_lint(
	cx,
	DOUBLE_MUST_USE,
	fn_header_span,
	"this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]`",
	"either add some descriptive text or remove the attribute",
	);
	}
	}

	fn check_must_use_candidate<'a, 'tcx>(
	cx: &LateContext<'a, 'tcx>,
	decl: &'tcx hir::FnDecl,
	body: &'tcx hir::Body,
	item_span: Span,
	item_id: hir::HirId,
	fn_span: Span,
	msg: &str,
	) {
	if has_mutable_arg(cx, body)
	\|\| mutates_static(cx, body)
	\|\| in_external_macro(cx.sess(), item_span)
	\|\| returns_unit(decl)
	\|\| is_must_use_ty(cx, return_ty(cx, item_id))
	{
	return;
	}
	span_lint_and_then(cx, MUST_USE_CANDIDATE, fn_span, msg, \|db\| {
	if let Some(snippet) = snippet_opt(cx, fn_span) {
	db.span_suggestion(
	fn_span,
	"add the attribute",
	format!("#[must_use] {}", snippet),
	Applicability::MachineApplicable,
	);
	}
	});
	}

	fn must_use_attr(attrs: &[Attribute]) -> Option<&Attribute> {
	attrs.iter().find(\|attr\| {
	attr.ident().map_or(false, \|ident\| {
	let ident: &str = &ident.as_str();
	"must_use" == ident
	})
	})
	}

	fn returns_unit(decl: &hir::FnDecl) -> bool {
	match decl.output {
	hir::FunctionRetTy::DefaultReturn(_) => true,
	hir::FunctionRetTy::Return(ref ty) => match ty.kind {
	hir::TyKind::Tup(ref tys) => tys.is_empty(),
	hir::TyKind::Never => true,
	_ => false,
	},
	}
	}

	fn is_must_use_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>) -> bool {
	use ty::TyKind::*;
	match ty.kind {
	Adt(ref adt, _) => must_use_attr(&cx.tcx.get_attrs(adt.did)).is_some(),
	Foreign(ref did) => must_use_attr(&cx.tcx.get_attrs(*did)).is_some(),
	Slice(ref ty) \| Array(ref ty, _) \| RawPtr(ty::TypeAndMut { ref ty, .. }) \| Ref(_, ref ty, _) => {
	// for the Array case we don't need to care for the len == 0 case
	// because we don't want to lint functions returning empty arrays
	is_must_use_ty(cx, *ty)
	},
	Tuple(ref substs) => substs.types().any(\|ty\| is_must_use_ty(cx, ty)),
	Opaque(ref def_id, _) => {
	for (predicate, _) in cx.tcx.predicates_of(*def_id).predicates {
	if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
	if must_use_attr(&cx.tcx.get_attrs(poly_trait_predicate.skip_binder().trait_ref.def_id)).is_some() {
	return true;
	}
	}
	}
	false
	},
	Dynamic(binder, _) => {
	for predicate in binder.skip_binder().iter() {
	if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
	if must_use_attr(&cx.tcx.get_attrs(trait_ref.def_id)).is_some() {
	return true;
	}
	}
	}
	false
	},
	_ => false,
	}
	}

	fn has_mutable_arg(cx: &LateContext<'_, '_>, body: &hir::Body) -> bool {
	let mut tys = FxHashSet::default();
	body.params.iter().any(\|param\| is_mutable_pat(cx, &param.pat, &mut tys))
	}

	fn is_mutable_pat(cx: &LateContext<'_, '_>, pat: &hir::Pat, tys: &mut FxHashSet<DefId>) -> bool {
	if let hir::PatKind::Wild = pat.kind {
	return false; // ignore `_` patterns
	}
	let def_id = pat.hir_id.owner_def_id();
	if cx.tcx.has_typeck_tables(def_id) {
	is_mutable_ty(cx, &cx.tcx.typeck_tables_of(def_id).pat_ty(pat), pat.span, tys)
	} else {
	false
	}
	}

	static KNOWN_WRAPPER_TYS: &[&[&str]] = &[&["alloc", "rc", "Rc"], &["std", "sync", "Arc"]];

	fn is_mutable_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>, span: Span, tys: &mut FxHashSet<DefId>) -> bool {
	use ty::TyKind::*;
	match ty.kind {
	// primitive types are never mutable
	Bool \| Char \| Int(_) \| Uint(_) \| Float(_) \| Str => false,
	Adt(ref adt, ref substs) => {
	tys.insert(adt.did) && !ty.is_freeze(cx.tcx, cx.param_env, span)
	\|\| KNOWN_WRAPPER_TYS.iter().any(\|path\| match_def_path(cx, adt.did, path))
	&& substs.types().any(\|ty\| is_mutable_ty(cx, ty, span, tys))
	},
	Tuple(ref substs) => substs.types().any(\|ty\| is_mutable_ty(cx, ty, span, tys)),
	Array(ty, _) \| Slice(ty) => is_mutable_ty(cx, ty, span, tys),
	RawPtr(ty::TypeAndMut { ty, mutbl }) \| Ref(_, ty, mutbl) => {
	mutbl == hir::Mutability::MutMutable \|\| is_mutable_ty(cx, ty, span, tys)
	},
	// calling something constitutes a side effect, so return true on all callables
	// also never calls need not be used, so return true for them, too
	_ => true,
	}
	}

	fn raw_ptr_arg(arg: &hir::Param, ty: &hir::Ty) -> Option<hir::HirId> {
	if let (&hir::PatKind::Binding(_, id, _, _), &hir::TyKind::Ptr(_)) = (&arg.pat.kind, &ty.kind) {
	Some(id)
	} else {
	None
	}
	}

	struct DerefVisitor<'a, 'tcx> {
	cx: &'a LateContext<'a, 'tcx>,
	ptrs: FxHashSet<hir::HirId>,
	tables: &'a ty::TypeckTables<'tcx>,
	}

	impl<'a, 'tcx> intravisit::Visitor<'tcx> for DerefVisitor<'a, 'tcx> {
	fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
	match expr.kind {
	hir::ExprKind::Call(ref f, ref args) => {
	let ty = self.tables.expr_ty(f);

	if type_is_unsafe_function(self.cx, ty) {
	for arg in args {
	self.check_arg(arg);
	}
	}
	},
	hir::ExprKind::MethodCall(_, _, ref args) => {
	let def_id = self.tables.type_dependent_def_id(expr.hir_id).unwrap();
	let base_type = self.cx.tcx.type_of(def_id);

	if type_is_unsafe_function(self.cx, base_type) {
	for arg in args {
	self.check_arg(arg);
	}
	}
	},
	hir::ExprKind::Unary(hir::UnDeref, ref ptr) => self.check_arg(ptr),
	_ => (),
	}

	intravisit::walk_expr(self, expr);
	}

	fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
	intravisit::NestedVisitorMap::None
	}
	}

	impl<'a, 'tcx> DerefVisitor<'a, 'tcx> {
	fn check_arg(&self, ptr: &hir::Expr) {
	if let hir::ExprKind::Path(ref qpath) = ptr.kind {
	if let Res::Local(id) = qpath_res(self.cx, qpath, ptr.hir_id) {
	if self.ptrs.contains(&id) {
	span_lint(
	self.cx,
	NOT_UNSAFE_PTR_ARG_DEREF,
	ptr.span,
	"this public function dereferences a raw pointer but is not marked `unsafe`",
	);
	}
	}
	}
	}
	}

	struct StaticMutVisitor<'a, 'tcx> {
	cx: &'a LateContext<'a, 'tcx>,
	mutates_static: bool,
	}

	impl<'a, 'tcx> intravisit::Visitor<'tcx> for StaticMutVisitor<'a, 'tcx> {
	fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
	use hir::ExprKind::*;

	if self.mutates_static {
	return;
	}
	match expr.kind {
	Call(_, ref args) \| MethodCall(_, _, ref args) => {
	let mut tys = FxHashSet::default();
	for arg in args {
	let def_id = arg.hir_id.owner_def_id();
	if self.cx.tcx.has_typeck_tables(def_id)
	&& is_mutable_ty(
	self.cx,
	self.cx.tcx.typeck_tables_of(def_id).expr_ty(arg),
	arg.span,
	&mut tys,
	)
	&& is_mutated_static(self.cx, arg)
	{
	self.mutates_static = true;
	return;
	}
	tys.clear();
	}
	},
	Assign(ref target, _) \| AssignOp(_, ref target, _) \| AddrOf(hir::Mutability::MutMutable, ref target) => {
	self.mutates_static \|= is_mutated_static(self.cx, target)
	},
	_ => {},
	}
	}

	fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
	intravisit::NestedVisitorMap::None
	}
	}

	fn is_mutated_static(cx: &LateContext<'_, '_>, e: &hir::Expr) -> bool {
	use hir::ExprKind::*;

	match e.kind {
	Path(ref qpath) => {
	if let Res::Local(_) = qpath_res(cx, qpath, e.hir_id) {
	false
	} else {
	true
	}
	},
	Field(ref inner, _) \| Index(ref inner, _) => is_mutated_static(cx, inner),
	_ => false,
	}
	}

	fn mutates_static<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, body: &'tcx hir::Body) -> bool {
	let mut v = StaticMutVisitor {
	cx,
	mutates_static: false,
	};
	intravisit::walk_expr(&mut v, &body.value);
	v.mutates_static
	}