Move implicit_hasher to its own module

clippy_lints/src/implicit_hasher.rs

@@ -0,0 +1,377 @@
+#![allow(rustc::default_hash_types)]
+
+use std::borrow::Cow;
+use std::collections::BTreeMap;
+
+use rustc_errors::DiagnosticBuilder;
+use rustc_hir as hir;
+use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, NestedVisitorMap, Visitor};
+use rustc_hir::{Body, Expr, ExprKind, GenericArg, Item, ItemKind, QPath, TyKind};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::hir::map::Map;
+use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::{Ty, TyS, TypeckResults};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::source_map::Span;
+use rustc_span::symbol::sym;
+use rustc_typeck::hir_ty_to_ty;
+
+use if_chain::if_chain;
+
+use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
+use clippy_utils::paths;
+use clippy_utils::source::{snippet, snippet_opt};
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::{differing_macro_contexts, match_path};
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for public `impl` or `fn` missing generalization
+    /// over different hashers and implicitly defaulting to the default hashing
+    /// algorithm (`SipHash`).
+    ///
+    /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
+    /// used with them.
+    ///
+    /// **Known problems:** Suggestions for replacing constructors can contain
+    /// false-positives. Also applying suggestions can require modification of other
+    /// pieces of code, possibly including external crates.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// # use std::collections::HashMap;
+    /// # use std::hash::{Hash, BuildHasher};
+    /// # trait Serialize {};
+    /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
+    ///
+    /// pub fn foo(map: &mut HashMap<i32, i32>) { }
+    /// ```
+    /// could be rewritten as
+    /// ```rust
+    /// # use std::collections::HashMap;
+    /// # use std::hash::{Hash, BuildHasher};
+    /// # trait Serialize {};
+    /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
+    ///
+    /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
+    /// ```
+    pub IMPLICIT_HASHER,
+    pedantic,
+    "missing generalization over different hashers"
+}
+
+declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
+
+impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
+    #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
+        use rustc_span::BytePos;
+
+        fn suggestion<'tcx>(
+            cx: &LateContext<'tcx>,
+            diag: &mut DiagnosticBuilder<'_>,
+            generics_span: Span,
+            generics_suggestion_span: Span,
+            target: &ImplicitHasherType<'_>,
+            vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
+        ) {
+            let generics_snip = snippet(cx, generics_span, "");
+            // trim `<` `>`
+            let generics_snip = if generics_snip.is_empty() {
+                ""
+            } else {
+                &generics_snip[1..generics_snip.len() - 1]
+            };
+
+            multispan_sugg(
+                diag,
+                "consider adding a type parameter",
+                vec![
+                    (
+                        generics_suggestion_span,
+                        format!(
+                            "<{}{}S: ::std::hash::BuildHasher{}>",
+                            generics_snip,
+                            if generics_snip.is_empty() { "" } else { ", " },
+                            if vis.suggestions.is_empty() {
+                                ""
+                            } else {
+                                // request users to add `Default` bound so that generic constructors can be used
+                                " + Default"
+                            },
+                        ),
+                    ),
+                    (
+                        target.span(),
+                        format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
+                    ),
+                ],
+            );
+
+            if !vis.suggestions.is_empty() {
+                multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
+            }
+        }
+
+        if !cx.access_levels.is_exported(item.hir_id()) {
+            return;
+        }
+
+        match item.kind {
+            ItemKind::Impl(ref impl_) => {
+                let mut vis = ImplicitHasherTypeVisitor::new(cx);
+                vis.visit_ty(impl_.self_ty);
+
+                for target in &vis.found {
+                    if differing_macro_contexts(item.span, target.span()) {
+                        return;
+                    }
+
+                    let generics_suggestion_span = impl_.generics.span.substitute_dummy({
+                        let pos = snippet_opt(cx, item.span.until(target.span()))
+                            .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
+                        if let Some(pos) = pos {
+                            Span::new(pos, pos, item.span.data().ctxt)
+                        } else {
+                            return;
+                        }
+                    });
+
+                    let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
+                    for item in impl_.items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
+                        ctr_vis.visit_impl_item(item);
+                    }
+
+                    span_lint_and_then(
+                        cx,
+                        IMPLICIT_HASHER,
+                        target.span(),
+                        &format!(
+                            "impl for `{}` should be generalized over different hashers",
+                            target.type_name()
+                        ),
+                        move |diag| {
+                            suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
+                        },
+                    );
+                }
+            },
+            ItemKind::Fn(ref sig, ref generics, body_id) => {
+                let body = cx.tcx.hir().body(body_id);
+
+                for ty in sig.decl.inputs {
+                    let mut vis = ImplicitHasherTypeVisitor::new(cx);
+                    vis.visit_ty(ty);
+
+                    for target in &vis.found {
+                        if in_external_macro(cx.sess(), generics.span) {
+                            continue;
+                        }
+                        let generics_suggestion_span = generics.span.substitute_dummy({
+                            let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
+                                .and_then(|snip| {
+                                    let i = snip.find("fn")?;
+                                    Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
+                                })
+                                .expect("failed to create span for type parameters");
+                            Span::new(pos, pos, item.span.data().ctxt)
+                        });
+
+                        let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
+                        ctr_vis.visit_body(body);
+
+                        span_lint_and_then(
+                            cx,
+                            IMPLICIT_HASHER,
+                            target.span(),
+                            &format!(
+                                "parameter of type `{}` should be generalized over different hashers",
+                                target.type_name()
+                            ),
+                            move |diag| {
+                                suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
+                            },
+                        );
+                    }
+                }
+            },
+            _ => {},
+        }
+    }
+}
+
+enum ImplicitHasherType<'tcx> {
+    HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
+    HashSet(Span, Ty<'tcx>, Cow<'static, str>),
+}
+
+impl<'tcx> ImplicitHasherType<'tcx> {
+    /// Checks that `ty` is a target type without a `BuildHasher`.
+    fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
+        if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
+            let params: Vec<_> = path
+                .segments
+                .last()
+                .as_ref()?
+                .args
+                .as_ref()?
+                .args
+                .iter()
+                .filter_map(|arg| match arg {
+                    GenericArg::Type(ty) => Some(ty),
+                    _ => None,
+                })
+                .collect();
+            let params_len = params.len();
+
+            let ty = hir_ty_to_ty(cx.tcx, hir_ty);
+
+            if is_type_diagnostic_item(cx, ty, sym::hashmap_type) && params_len == 2 {
+                Some(ImplicitHasherType::HashMap(
+                    hir_ty.span,
+                    ty,
+                    snippet(cx, params[0].span, "K"),
+                    snippet(cx, params[1].span, "V"),
+                ))
+            } else if is_type_diagnostic_item(cx, ty, sym::hashset_type) && params_len == 1 {
+                Some(ImplicitHasherType::HashSet(
+                    hir_ty.span,
+                    ty,
+                    snippet(cx, params[0].span, "T"),
+                ))
+            } else {
+                None
+            }
+        } else {
+            None
+        }
+    }
+
+    fn type_name(&self) -> &'static str {
+        match *self {
+            ImplicitHasherType::HashMap(..) => "HashMap",
+            ImplicitHasherType::HashSet(..) => "HashSet",
+        }
+    }
+
+    fn type_arguments(&self) -> String {
+        match *self {
+            ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
+            ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
+        }
+    }
+
+    fn ty(&self) -> Ty<'tcx> {
+        match *self {
+            ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
+        }
+    }
+
+    fn span(&self) -> Span {
+        match *self {
+            ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
+        }
+    }
+}
+
+struct ImplicitHasherTypeVisitor<'a, 'tcx> {
+    cx: &'a LateContext<'tcx>,
+    found: Vec<ImplicitHasherType<'tcx>>,
+}
+
+impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
+    fn new(cx: &'a LateContext<'tcx>) -> Self {
+        Self { cx, found: vec![] }
+    }
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
+    type Map = Map<'tcx>;
+
+    fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
+        if let Some(target) = ImplicitHasherType::new(self.cx, t) {
+            self.found.push(target);
+        }
+
+        walk_ty(self, t);
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}
+
+/// Looks for default-hasher-dependent constructors like `HashMap::new`.
+struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
+    cx: &'a LateContext<'tcx>,
+    maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
+    target: &'b ImplicitHasherType<'tcx>,
+    suggestions: BTreeMap<Span, String>,
+}
+
+impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
+    fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
+        Self {
+            cx,
+            maybe_typeck_results: cx.maybe_typeck_results(),
+            target,
+            suggestions: BTreeMap::new(),
+        }
+    }
+}
+
+impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
+    type Map = Map<'tcx>;
+
+    fn visit_body(&mut self, body: &'tcx Body<'_>) {
+        let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
+        walk_body(self, body);
+        self.maybe_typeck_results = old_maybe_typeck_results;
+    }
+
+    fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
+        if_chain! {
+            if let ExprKind::Call(ref fun, ref args) = e.kind;
+            if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
+            if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
+            then {
+                if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
+                    return;
+                }
+
+                if match_path(ty_path, &paths::HASHMAP) {
+                    if method.ident.name == sym::new {
+                        self.suggestions
+                            .insert(e.span, "HashMap::default()".to_string());
+                    } else if method.ident.name == sym!(with_capacity) {
+                        self.suggestions.insert(
+                            e.span,
+                            format!(
+                                "HashMap::with_capacity_and_hasher({}, Default::default())",
+                                snippet(self.cx, args[0].span, "capacity"),
+                            ),
+                        );
+                    }
+                } else if match_path(ty_path, &paths::HASHSET) {
+                    if method.ident.name == sym::new {
+                        self.suggestions
+                            .insert(e.span, "HashSet::default()".to_string());
+                    } else if method.ident.name == sym!(with_capacity) {
+                        self.suggestions.insert(
+                            e.span,
+                            format!(
+                                "HashSet::with_capacity_and_hasher({}, Default::default())",
+                                snippet(self.cx, args[0].span, "capacity"),
+                            ),
+                        );
+                    }
+                }
+            }
+        }
+
+        walk_expr(self, e);
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
+    }
+}

clippy_lints/src/lib.rs

@@ -232,6 +232,7 @@ mod if_let_mutex;
 mod if_let_some_result;
 mod if_not_else;
 mod if_then_some_else_none;
+mod implicit_hasher;
 mod implicit_return;
 mod implicit_saturating_sub;
 mod inconsistent_struct_constructor;
@@ -685,6 +686,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &if_let_some_result::IF_LET_SOME_RESULT,
         &if_not_else::IF_NOT_ELSE,
         &if_then_some_else_none::IF_THEN_SOME_ELSE_NONE,
+        &implicit_hasher::IMPLICIT_HASHER,
         &implicit_return::IMPLICIT_RETURN,
         &implicit_saturating_sub::IMPLICIT_SATURATING_SUB,
         &inconsistent_struct_constructor::INCONSISTENT_STRUCT_CONSTRUCTOR,
@@ -961,7 +963,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &try_err::TRY_ERR,
         &types::BORROWED_BOX,
         &types::BOX_VEC,
-        &types::IMPLICIT_HASHER,
         &types::LINKEDLIST,
         &types::OPTION_OPTION,
         &types::RC_BUFFER,
@@ -1159,7 +1160,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| box infinite_iter::InfiniteIter);
     store.register_late_pass(|| box inline_fn_without_body::InlineFnWithoutBody);
     store.register_late_pass(|| box useless_conversion::UselessConversion::default());
-    store.register_late_pass(|| box types::ImplicitHasher);
+    store.register_late_pass(|| box implicit_hasher::ImplicitHasher);
     store.register_late_pass(|| box fallible_impl_from::FallibleImplFrom);
     store.register_late_pass(|| box double_comparison::DoubleComparisons);
     store.register_late_pass(|| box question_mark::QuestionMark);
@@ -1373,6 +1374,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&functions::MUST_USE_CANDIDATE),
         LintId::of(&functions::TOO_MANY_LINES),
         LintId::of(&if_not_else::IF_NOT_ELSE),
+        LintId::of(&implicit_hasher::IMPLICIT_HASHER),
         LintId::of(&implicit_saturating_sub::IMPLICIT_SATURATING_SUB),
         LintId::of(&infinite_iter::MAYBE_INFINITE_ITER),
         LintId::of(&invalid_upcast_comparisons::INVALID_UPCAST_COMPARISONS),
@@ -1414,7 +1416,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&strings::STRING_ADD_ASSIGN),
         LintId::of(&trait_bounds::TRAIT_DUPLICATION_IN_BOUNDS),
         LintId::of(&trait_bounds::TYPE_REPETITION_IN_BOUNDS),
-        LintId::of(&types::IMPLICIT_HASHER),
         LintId::of(&types::LINKEDLIST),
         LintId::of(&types::OPTION_OPTION),
         LintId::of(&unicode::NON_ASCII_LITERAL),

clippy_lints/src/types/mod.rs

@@ -1,5 +1,3 @@
-#![allow(rustc::default_hash_types)]
-
 mod borrowed_box;
 mod box_vec;
 mod linked_list;
@@ -9,32 +7,18 @@ mod redundant_allocation;
 mod utils;
 mod vec_box;
 
-use std::borrow::Cow;
+use clippy_utils::diagnostics::span_lint;
-use std::collections::BTreeMap;
-
-use clippy_utils::diagnostics::{multispan_sugg, span_lint, span_lint_and_then};
-use clippy_utils::source::{snippet, snippet_opt};
-use clippy_utils::ty::is_type_diagnostic_item;
-use if_chain::if_chain;
-use rustc_errors::DiagnosticBuilder;
 use rustc_hir as hir;
-use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
+use rustc_hir::intravisit::{walk_ty, FnKind, NestedVisitorMap, Visitor};
 use rustc_hir::{
-    Body, Expr, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericParamKind, HirId, ImplItem, ImplItemKind, Item,
+    Body, FnDecl, FnRetTy, FnSig, GenericArg, GenericParamKind, HirId, ImplItem, ImplItemKind, Item, ItemKind, Local,
-    ItemKind, Local, MutTy, QPath, TraitFn, TraitItem, TraitItemKind, TyKind,
+    MutTy, QPath, TraitFn, TraitItem, TraitItemKind, TyKind,
 };
-use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::map::Map;
-use rustc_middle::lint::in_external_macro;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
-use rustc_middle::ty::{Ty, TyS, TypeckResults};
-use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
 use rustc_span::source_map::Span;
-use rustc_span::symbol::sym;
 use rustc_target::spec::abi::Abi;
-use rustc_typeck::hir_ty_to_ty;
-
-use clippy_utils::paths;
-use clippy_utils::{differing_macro_contexts, match_path};
 
 declare_clippy_lint! {
     /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
@@ -548,355 +532,3 @@ impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
         NestedVisitorMap::None
     }
 }
-
-declare_clippy_lint! {
-    /// **What it does:** Checks for public `impl` or `fn` missing generalization
-    /// over different hashers and implicitly defaulting to the default hashing
-    /// algorithm (`SipHash`).
-    ///
-    /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
-    /// used with them.
-    ///
-    /// **Known problems:** Suggestions for replacing constructors can contain
-    /// false-positives. Also applying suggestions can require modification of other
-    /// pieces of code, possibly including external crates.
-    ///
-    /// **Example:**
-    /// ```rust
-    /// # use std::collections::HashMap;
-    /// # use std::hash::{Hash, BuildHasher};
-    /// # trait Serialize {};
-    /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
-    ///
-    /// pub fn foo(map: &mut HashMap<i32, i32>) { }
-    /// ```
-    /// could be rewritten as
-    /// ```rust
-    /// # use std::collections::HashMap;
-    /// # use std::hash::{Hash, BuildHasher};
-    /// # trait Serialize {};
-    /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
-    ///
-    /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
-    /// ```
-    pub IMPLICIT_HASHER,
-    pedantic,
-    "missing generalization over different hashers"
-}
-
-declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
-
-impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
-    #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
-    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
-        use rustc_span::BytePos;
-
-        fn suggestion<'tcx>(
-            cx: &LateContext<'tcx>,
-            diag: &mut DiagnosticBuilder<'_>,
-            generics_span: Span,
-            generics_suggestion_span: Span,
-            target: &ImplicitHasherType<'_>,
-            vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
-        ) {
-            let generics_snip = snippet(cx, generics_span, "");
-            // trim `<` `>`
-            let generics_snip = if generics_snip.is_empty() {
-                ""
-            } else {
-                &generics_snip[1..generics_snip.len() - 1]
-            };
-
-            multispan_sugg(
-                diag,
-                "consider adding a type parameter",
-                vec![
-                    (
-                        generics_suggestion_span,
-                        format!(
-                            "<{}{}S: ::std::hash::BuildHasher{}>",
-                            generics_snip,
-                            if generics_snip.is_empty() { "" } else { ", " },
-                            if vis.suggestions.is_empty() {
-                                ""
-                            } else {
-                                // request users to add `Default` bound so that generic constructors can be used
-                                " + Default"
-                            },
-                        ),
-                    ),
-                    (
-                        target.span(),
-                        format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
-                    ),
-                ],
-            );
-
-            if !vis.suggestions.is_empty() {
-                multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
-            }
-        }
-
-        if !cx.access_levels.is_exported(item.hir_id()) {
-            return;
-        }
-
-        match item.kind {
-            ItemKind::Impl(ref impl_) => {
-                let mut vis = ImplicitHasherTypeVisitor::new(cx);
-                vis.visit_ty(impl_.self_ty);
-
-                for target in &vis.found {
-                    if differing_macro_contexts(item.span, target.span()) {
-                        return;
-                    }
-
-                    let generics_suggestion_span = impl_.generics.span.substitute_dummy({
-                        let pos = snippet_opt(cx, item.span.until(target.span()))
-                            .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
-                        if let Some(pos) = pos {
-                            Span::new(pos, pos, item.span.data().ctxt)
-                        } else {
-                            return;
-                        }
-                    });
-
-                    let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
-                    for item in impl_.items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
-                        ctr_vis.visit_impl_item(item);
-                    }
-
-                    span_lint_and_then(
-                        cx,
-                        IMPLICIT_HASHER,
-                        target.span(),
-                        &format!(
-                            "impl for `{}` should be generalized over different hashers",
-                            target.type_name()
-                        ),
-                        move |diag| {
-                            suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
-                        },
-                    );
-                }
-            },
-            ItemKind::Fn(ref sig, ref generics, body_id) => {
-                let body = cx.tcx.hir().body(body_id);
-
-                for ty in sig.decl.inputs {
-                    let mut vis = ImplicitHasherTypeVisitor::new(cx);
-                    vis.visit_ty(ty);
-
-                    for target in &vis.found {
-                        if in_external_macro(cx.sess(), generics.span) {
-                            continue;
-                        }
-                        let generics_suggestion_span = generics.span.substitute_dummy({
-                            let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
-                                .and_then(|snip| {
-                                    let i = snip.find("fn")?;
-                                    Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
-                                })
-                                .expect("failed to create span for type parameters");
-                            Span::new(pos, pos, item.span.data().ctxt)
-                        });
-
-                        let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
-                        ctr_vis.visit_body(body);
-
-                        span_lint_and_then(
-                            cx,
-                            IMPLICIT_HASHER,
-                            target.span(),
-                            &format!(
-                                "parameter of type `{}` should be generalized over different hashers",
-                                target.type_name()
-                            ),
-                            move |diag| {
-                                suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
-                            },
-                        );
-                    }
-                }
-            },
-            _ => {},
-        }
-    }
-}
-
-enum ImplicitHasherType<'tcx> {
-    HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
-    HashSet(Span, Ty<'tcx>, Cow<'static, str>),
-}
-
-impl<'tcx> ImplicitHasherType<'tcx> {
-    /// Checks that `ty` is a target type without a `BuildHasher`.
-    fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
-        if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
-            let params: Vec<_> = path
-                .segments
-                .last()
-                .as_ref()?
-                .args
-                .as_ref()?
-                .args
-                .iter()
-                .filter_map(|arg| match arg {
-                    GenericArg::Type(ty) => Some(ty),
-                    _ => None,
-                })
-                .collect();
-            let params_len = params.len();
-
-            let ty = hir_ty_to_ty(cx.tcx, hir_ty);
-
-            if is_type_diagnostic_item(cx, ty, sym::hashmap_type) && params_len == 2 {
-                Some(ImplicitHasherType::HashMap(
-                    hir_ty.span,
-                    ty,
-                    snippet(cx, params[0].span, "K"),
-                    snippet(cx, params[1].span, "V"),
-                ))
-            } else if is_type_diagnostic_item(cx, ty, sym::hashset_type) && params_len == 1 {
-                Some(ImplicitHasherType::HashSet(
-                    hir_ty.span,
-                    ty,
-                    snippet(cx, params[0].span, "T"),
-                ))
-            } else {
-                None
-            }
-        } else {
-            None
-        }
-    }
-
-    fn type_name(&self) -> &'static str {
-        match *self {
-            ImplicitHasherType::HashMap(..) => "HashMap",
-            ImplicitHasherType::HashSet(..) => "HashSet",
-        }
-    }
-
-    fn type_arguments(&self) -> String {
-        match *self {
-            ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
-            ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
-        }
-    }
-
-    fn ty(&self) -> Ty<'tcx> {
-        match *self {
-            ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
-        }
-    }
-
-    fn span(&self) -> Span {
-        match *self {
-            ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
-        }
-    }
-}
-
-struct ImplicitHasherTypeVisitor<'a, 'tcx> {
-    cx: &'a LateContext<'tcx>,
-    found: Vec<ImplicitHasherType<'tcx>>,
-}
-
-impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
-    fn new(cx: &'a LateContext<'tcx>) -> Self {
-        Self { cx, found: vec![] }
-    }
-}
-
-impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
-    type Map = Map<'tcx>;
-
-    fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
-        if let Some(target) = ImplicitHasherType::new(self.cx, t) {
-            self.found.push(target);
-        }
-
-        walk_ty(self, t);
-    }
-
-    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
-        NestedVisitorMap::None
-    }
-}
-
-/// Looks for default-hasher-dependent constructors like `HashMap::new`.
-struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
-    cx: &'a LateContext<'tcx>,
-    maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
-    target: &'b ImplicitHasherType<'tcx>,
-    suggestions: BTreeMap<Span, String>,
-}
-
-impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
-    fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
-        Self {
-            cx,
-            maybe_typeck_results: cx.maybe_typeck_results(),
-            target,
-            suggestions: BTreeMap::new(),
-        }
-    }
-}
-
-impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
-    type Map = Map<'tcx>;
-
-    fn visit_body(&mut self, body: &'tcx Body<'_>) {
-        let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
-        walk_body(self, body);
-        self.maybe_typeck_results = old_maybe_typeck_results;
-    }
-
-    fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
-        if_chain! {
-            if let ExprKind::Call(ref fun, ref args) = e.kind;
-            if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
-            if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
-            then {
-                if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
-                    return;
-                }
-
-                if match_path(ty_path, &paths::HASHMAP) {
-                    if method.ident.name == sym::new {
-                        self.suggestions
-                            .insert(e.span, "HashMap::default()".to_string());
-                    } else if method.ident.name == sym!(with_capacity) {
-                        self.suggestions.insert(
-                            e.span,
-                            format!(
-                                "HashMap::with_capacity_and_hasher({}, Default::default())",
-                                snippet(self.cx, args[0].span, "capacity"),
-                            ),
-                        );
-                    }
-                } else if match_path(ty_path, &paths::HASHSET) {
-                    if method.ident.name == sym::new {
-                        self.suggestions
-                            .insert(e.span, "HashSet::default()".to_string());
-                    } else if method.ident.name == sym!(with_capacity) {
-                        self.suggestions.insert(
-                            e.span,
-                            format!(
-                                "HashSet::with_capacity_and_hasher({}, Default::default())",
-                                snippet(self.cx, args[0].span, "capacity"),
-                            ),
-                        );
-                    }
-                }
-            }
-        }
-
-        walk_expr(self, e);
-    }
-
-    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
-        NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
-    }
-}