rust/clippy_lints/src/entry.rs

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use rustc::hir::*;
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use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
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use rustc::lint::*;
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use syntax::codemap::Span;
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use utils::SpanlessEq;
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use utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty};
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/// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
/// or `BTreeMap`.
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///
/// **Why is this bad?** Using `entry` is more efficient.
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///
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/// **Known problems:** Some false negatives, eg.:
/// ```rust
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/// let k = &key;
/// if !m.contains_key(k) { m.insert(k.clone(), v); }
/// ```
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///
/// **Example:**
/// ```rust
/// if !m.contains_key(&k) { m.insert(k, v) }
/// ```
/// can be rewritten as:
/// ```rust
/// m.entry(k).or_insert(v);
/// ```
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declare_clippy_lint! {
pub MAP_ENTRY,
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perf,
"use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
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}
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#[derive(Copy, Clone)]
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pub struct HashMapLint;
impl LintPass for HashMapLint {
fn get_lints(&self) -> LintArray {
lint_array!(MAP_ENTRY)
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}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapLint {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let ExprIf(ref check, ref then_block, ref else_block) = expr.node {
if let ExprUnary(UnOp::UnNot, ref check) = check.node {
if let Some((ty, map, key)) = check_cond(cx, check) {
// in case of `if !m.contains_key(&k) { m.insert(k, v); }`
// we can give a better error message
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let sole_expr = {
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else_block.is_none() && if let ExprBlock(ref then_block, _) = then_block.node {
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(then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
} else {
true
}
};
let mut visitor = InsertVisitor {
cx,
span: expr.span,
ty,
map,
key,
sole_expr,
};
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walk_expr(&mut visitor, &**then_block);
}
} else if let Some(ref else_block) = *else_block {
if let Some((ty, map, key)) = check_cond(cx, check) {
let mut visitor = InsertVisitor {
cx,
span: expr.span,
ty,
map,
key,
sole_expr: false,
};
walk_expr(&mut visitor, else_block);
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}
}
}
}
}
fn check_cond<'a, 'tcx, 'b>(
cx: &'a LateContext<'a, 'tcx>,
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check: &'b Expr,
) -> Option<(&'static str, &'b Expr, &'b Expr)> {
if_chain! {
if let ExprMethodCall(ref path, _, ref params) = check.node;
if params.len() >= 2;
if path.name == "contains_key";
if let ExprAddrOf(_, ref key) = params[1].node;
then {
let map = &params[0];
let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));
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return if match_type(cx, obj_ty, &paths::BTREEMAP) {
Some(("BTreeMap", map, key))
}
else if match_type(cx, obj_ty, &paths::HASHMAP) {
Some(("HashMap", map, key))
}
else {
None
};
}
}
None
}
struct InsertVisitor<'a, 'tcx: 'a, 'b> {
cx: &'a LateContext<'a, 'tcx>,
span: Span,
ty: &'static str,
map: &'b Expr,
key: &'b Expr,
sole_expr: bool,
}
impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if_chain! {
if let ExprMethodCall(ref path, _, ref params) = expr.node;
if params.len() == 3;
if path.name == "insert";
if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
then {
span_lint_and_then(self.cx, MAP_ENTRY, self.span,
&format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
if self.sole_expr {
let help = format!("{}.entry({}).or_insert({})",
snippet(self.cx, self.map.span, "map"),
snippet(self.cx, params[1].span, ".."),
snippet(self.cx, params[2].span, ".."));
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db.span_suggestion(self.span, "consider using", help);
}
else {
let help = format!("{}.entry({})",
snippet(self.cx, self.map.span, "map"),
snippet(self.cx, params[1].span, ".."));
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db.span_suggestion(self.span, "consider using", help);
}
});
}
}
if !self.sole_expr {
walk_expr(self, expr);
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}
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
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}