[rustc.git] / src / tools / clippy / clippy_lints / src / implicit_hasher.rs

#![cfg_attr(bootstrap, 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_def_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, 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(fun, args) = e.kind;
            if let ExprKind::Path(QPath::TypeRelative(ty, method)) = fun.kind;
            if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
            if let Some(ty_did) = ty_path.res.opt_def_id();
            then {
                if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
                    return;
                }

                if match_def_path(self.cx, ty_did, &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_def_path(self.cx, ty_did, &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())
    }
}
Commit	Line	Data
136023e0	1	#![cfg_attr(bootstrap, allow(rustc::default_hash_types))]
cdc7bbd5 XL	2
	3	use std::borrow::Cow;
	4	use std::collections::BTreeMap;
	5
	6	use rustc_errors::DiagnosticBuilder;
	7	use rustc_hir as hir;
	8	use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, NestedVisitorMap, Visitor};
	9	use rustc_hir::{Body, Expr, ExprKind, GenericArg, Item, ItemKind, QPath, TyKind};
	10	use rustc_lint::{LateContext, LateLintPass, LintContext};
	11	use rustc_middle::hir::map::Map;
	12	use rustc_middle::lint::in_external_macro;
	13	use rustc_middle::ty::{Ty, TyS, TypeckResults};
	14	use rustc_session::{declare_lint_pass, declare_tool_lint};
	15	use rustc_span::source_map::Span;
	16	use rustc_span::symbol::sym;
	17	use rustc_typeck::hir_ty_to_ty;
	18
	19	use if_chain::if_chain;
	20
	21	use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
	22	use clippy_utils::paths;
	23	use clippy_utils::source::{snippet, snippet_opt};
	24	use clippy_utils::ty::is_type_diagnostic_item;
	25	use clippy_utils::{differing_macro_contexts, match_def_path};
	26
	27	declare_clippy_lint! {
	28	/// What it does: Checks for public `impl` or `fn` missing generalization
	29	/// over different hashers and implicitly defaulting to the default hashing
	30	/// algorithm (`SipHash`).
	31	///
	32	/// Why is this bad? `HashMap` or `HashSet` with custom hashers cannot be
	33	/// used with them.
	34	///
	35	/// Known problems: Suggestions for replacing constructors can contain
	36	/// false-positives. Also applying suggestions can require modification of other
	37	/// pieces of code, possibly including external crates.
	38	///
	39	/// Example:
	40	/// ```rust
	41	/// # use std::collections::HashMap;
	42	/// # use std::hash::{Hash, BuildHasher};
	43	/// # trait Serialize {};
	44	/// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
	45	///
	46	/// pub fn foo(map: &mut HashMap<i32, i32>) { }
	47	/// ```
	48	/// could be rewritten as
	49	/// ```rust
	50	/// # use std::collections::HashMap;
	51	/// # use std::hash::{Hash, BuildHasher};
	52	/// # trait Serialize {};
	53	/// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
	54	///
	55	/// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
	56	/// ```
	57	pub IMPLICIT_HASHER,
	58	pedantic,
	59	"missing generalization over different hashers"
	60	}
	61
	62	declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
	63
	64	impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
	65	#[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
66	fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
67	use rustc_span::BytePos;
68
69	fn suggestion<'tcx>(
70	cx: &LateContext<'tcx>,
71	diag: &mut DiagnosticBuilder<'_>,
72	generics_span: Span,
73	generics_suggestion_span: Span,
74	target: &ImplicitHasherType<'_>,
75	vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
76	) {
77	let generics_snip = snippet(cx, generics_span, "");
78	// trim `<` `>`
79	let generics_snip = if generics_snip.is_empty() {
80	""
81	} else {
82	&generics_snip[1..generics_snip.len() - 1]
83	};
84
85	multispan_sugg(
86	diag,
87	"consider adding a type parameter",
88	vec![
89	(
90	generics_suggestion_span,
91	format!(
92	"<{}{}S: ::std::hash::BuildHasher{}>",
93	generics_snip,
94	if generics_snip.is_empty() { "" } else { ", " },
95	if vis.suggestions.is_empty() {
96	""
97	} else {
98	// request users to add `Default` bound so that generic constructors can be used
99	" + Default"
100	},
101	),
102	),
103	(
104	target.span(),
105	format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
106	),
107	],
108	);
109
110	if !vis.suggestions.is_empty() {
111	multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
112	}
113	}
114
115	if !cx.access_levels.is_exported(item.hir_id()) {
116	return;
117	}
118
119	match item.kind {
120	ItemKind::Impl(ref impl_) => {
121	let mut vis = ImplicitHasherTypeVisitor::new(cx);
122	vis.visit_ty(impl_.self_ty);
123
124	for target in &vis.found {
125	if differing_macro_contexts(item.span, target.span()) {
126	return;
127	}
128
129	let generics_suggestion_span = impl_.generics.span.substitute_dummy({
130	let pos = snippet_opt(cx, item.span.until(target.span()))
131	.and_then(\|snip\| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
132	if let Some(pos) = pos {
133	Span::new(pos, pos, item.span.data().ctxt)
134	} else {
135	return;
136	}
137	});
138
139	let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
140	for item in impl_.items.iter().map(\|item\| cx.tcx.hir().impl_item(item.id)) {
141	ctr_vis.visit_impl_item(item);
142	}
143
144	span_lint_and_then(
145	cx,
146	IMPLICIT_HASHER,
147	target.span(),
148	&format!(
149	"impl for `{}` should be generalized over different hashers",
150	target.type_name()
151	),
152	move \|diag\| {
153	suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
154	},
155	);
156	}
157	},
158	ItemKind::Fn(ref sig, ref generics, body_id) => {
159	let body = cx.tcx.hir().body(body_id);
160
161	for ty in sig.decl.inputs {
162	let mut vis = ImplicitHasherTypeVisitor::new(cx);
163	vis.visit_ty(ty);
164
165	for target in &vis.found {
166	if in_external_macro(cx.sess(), generics.span) {
167	continue;
168	}
169	let generics_suggestion_span = generics.span.substitute_dummy({
170	let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
171	.and_then(\|snip\| {
172	let i = snip.find("fn")?;
173	Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
174	})
175	.expect("failed to create span for type parameters");
176	Span::new(pos, pos, item.span.data().ctxt)
177	});
178
179	let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
180	ctr_vis.visit_body(body);
181
182	span_lint_and_then(
183	cx,
184	IMPLICIT_HASHER,
185	target.span(),
186	&format!(
187	"parameter of type `{}` should be generalized over different hashers",
188	target.type_name()
189	),
190	move \|diag\| {
191	suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
192	},
193	);
194	}
195	}
196	},
197	_ => {},
198	}
199	}
200	}
201
202	enum ImplicitHasherType<'tcx> {
203	HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
204	HashSet(Span, Ty<'tcx>, Cow<'static, str>),
205	}
206
207	impl<'tcx> ImplicitHasherType<'tcx> {
208	/// Checks that `ty` is a target type without a `BuildHasher`.
209	fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
210	if let TyKind::Path(QPath::Resolved(None, path)) = hir_ty.kind {
211	let params: Vec<_> = path
212	.segments
213	.last()
214	.as_ref()?
215	.args
216	.as_ref()?
217	.args
218	.iter()
219	.filter_map(\|arg\| match arg {
220	GenericArg::Type(ty) => Some(ty),
221	_ => None,
222	})
223	.collect();
224	let params_len = params.len();
225
226	let ty = hir_ty_to_ty(cx.tcx, hir_ty);
227
228	if is_type_diagnostic_item(cx, ty, sym::hashmap_type) && params_len == 2 {
229	Some(ImplicitHasherType::HashMap(
230	hir_ty.span,
231	ty,
232	snippet(cx, params[0].span, "K"),
233	snippet(cx, params[1].span, "V"),
234	))
235	} else if is_type_diagnostic_item(cx, ty, sym::hashset_type) && params_len == 1 {
236	Some(ImplicitHasherType::HashSet(
237	hir_ty.span,
238	ty,
239	snippet(cx, params[0].span, "T"),
240	))
241	} else {
242	None
243	}
244	} else {
245	None
246	}
247	}
248
249	fn type_name(&self) -> &'static str {
250	match *self {
251	ImplicitHasherType::HashMap(..) => "HashMap",
252	ImplicitHasherType::HashSet(..) => "HashSet",
253	}
254	}
255
256	fn type_arguments(&self) -> String {
257	match *self {
258	ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
259	ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
260	}
261	}
262
263	fn ty(&self) -> Ty<'tcx> {
264	match *self {
265	ImplicitHasherType::HashMap(_, ty, ..) \| ImplicitHasherType::HashSet(_, ty, ..) => ty,
266	}
267	}
268
269	fn span(&self) -> Span {
270	match *self {
271	ImplicitHasherType::HashMap(span, ..) \| ImplicitHasherType::HashSet(span, ..) => span,
272	}
273	}
274	}
275
276	struct ImplicitHasherTypeVisitor<'a, 'tcx> {
277	cx: &'a LateContext<'tcx>,
278	found: Vec<ImplicitHasherType<'tcx>>,
279	}
280
281	impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
282	fn new(cx: &'a LateContext<'tcx>) -> Self {
283	Self { cx, found: vec![] }
284	}
285	}
286
287	impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
288	type Map = Map<'tcx>;
289
290	fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
291	if let Some(target) = ImplicitHasherType::new(self.cx, t) {
292	self.found.push(target);
293	}
294
295	walk_ty(self, t);
296	}
297
298	fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
299	NestedVisitorMap::None
300	}
301	}
302
303	/// Looks for default-hasher-dependent constructors like `HashMap::new`.
304	struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
305	cx: &'a LateContext<'tcx>,
306	maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
307	target: &'b ImplicitHasherType<'tcx>,
308	suggestions: BTreeMap<Span, String>,
309	}
310
311	impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
312	fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
313	Self {
314	cx,
315	maybe_typeck_results: cx.maybe_typeck_results(),
316	target,
317	suggestions: BTreeMap::new(),
318	}
319	}
320	}
321
322	impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
323	type Map = Map<'tcx>;
324
325	fn visit_body(&mut self, body: &'tcx Body<'_>) {
326	let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
327	walk_body(self, body);
328	self.maybe_typeck_results = old_maybe_typeck_results;
329	}
330
331	fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
332	if_chain! {
333	if let ExprKind::Call(fun, args) = e.kind;
334	if let ExprKind::Path(QPath::TypeRelative(ty, method)) = fun.kind;
335	if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
336	if let Some(ty_did) = ty_path.res.opt_def_id();
337	then {
338	if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
339	return;
340	}
341
342	if match_def_path(self.cx, ty_did, &paths::HASHMAP) {
343	if method.ident.name == sym::new {
344	self.suggestions
345	.insert(e.span, "HashMap::default()".to_string());
346	} else if method.ident.name == sym!(with_capacity) {
347	self.suggestions.insert(
348	e.span,
349	format!(
350	"HashMap::with_capacity_and_hasher({}, Default::default())",
351	snippet(self.cx, args[0].span, "capacity"),
352	),
353	);
354	}
355	} else if match_def_path(self.cx, ty_did, &paths::HASHSET) {
356	if method.ident.name == sym::new {
357	self.suggestions
358	.insert(e.span, "HashSet::default()".to_string());
359	} else if method.ident.name == sym!(with_capacity) {
360	self.suggestions.insert(
361	e.span,
362	format!(
363	"HashSet::with_capacity_and_hasher({}, Default::default())",
364	snippet(self.cx, args[0].span, "capacity"),
365	),
366	);
367	}
368	}
369	}
370	}
371
372	walk_expr(self, e);
373	}
374
375	fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
376	NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
377	}
378	}