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use rustc::hir::*;
use rustc::lint::*;
use rustc::ty;
use syntax::ast::{Name, UintTy};
use utils::{contains_name, get_pat_name, match_type, paths, single_segment_path, snippet, span_lint_and_sugg,
walk_ptrs_ty};
declare_lint! {
pub NAIVE_BYTECOUNT,
Warn,
"use of naive `<slice>.filter(|&x| x == y).count()` to count byte values"
}
#[derive(Copy, Clone)]
pub struct ByteCount;
impl LintPass for ByteCount {
fn get_lints(&self) -> LintArray {
lint_array!(NAIVE_BYTECOUNT)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ByteCount {
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
if_chain! {
if let ExprMethodCall(ref count, _, ref count_args) = expr.node;
if count.name == "count";
if count_args.len() == 1;
if let ExprMethodCall(ref filter, _, ref filter_args) = count_args[0].node;
if filter.name == "filter";
if filter_args.len() == 2;
if let ExprClosure(_, _, body_id, _, _) = filter_args[1].node;
then {
let body = cx.tcx.hir.body(body_id);
if_chain! {
if body.arguments.len() == 1;
if let Some(argname) = get_pat_name(&body.arguments[0].pat);
if let ExprBinary(ref op, ref l, ref r) = body.value.node;
if op.node == BiEq;
if match_type(cx,
walk_ptrs_ty(cx.tables.expr_ty(&filter_args[0])),
&paths::SLICE_ITER);
then {
let needle = match get_path_name(l) {
Some(name) if check_arg(name, argname, r) => r,
_ => match get_path_name(r) {
Some(name) if check_arg(name, argname, l) => l,
_ => { return; }
}
};
if ty::TyUint(UintTy::U8) != walk_ptrs_ty(cx.tables.expr_ty(needle)).sty {
return;
}
let haystack = if let ExprMethodCall(ref path, _, ref args) =
filter_args[0].node {
let p = path.name;
if (p == "iter" || p == "iter_mut") && args.len() == 1 {
&args[0]
} else {
&filter_args[0]
}
} else {
&filter_args[0]
};
span_lint_and_sugg(cx,
NAIVE_BYTECOUNT,
expr.span,
"You appear to be counting bytes the naive way",
"Consider using the bytecount crate",
format!("bytecount::count({}, {})",
snippet(cx, haystack.span, ".."),
snippet(cx, needle.span, "..")));
}
};
}
};
}
}
fn check_arg(name: Name, arg: Name, needle: &Expr) -> bool {
name == arg && !contains_name(name, needle)
}
fn get_path_name(expr: &Expr) -> Option<Name> {
match expr.node {
ExprBox(ref e) | ExprAddrOf(_, ref e) | ExprUnary(UnOp::UnDeref, ref e) => get_path_name(e),
ExprBlock(ref b) => if b.stmts.is_empty() {
b.expr.as_ref().and_then(|p| get_path_name(p))
} else {
None
},
ExprPath(ref qpath) => single_segment_path(qpath).map(|ps| ps.name),
_ => None,
}
}