Move implicit_hasher to its own module

Author: Y-Nak

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())
+    }
+}