375 lines
15 KiB
Rust
375 lines
15 KiB
Rust
use super::NEEDLESS_RANGE_LOOP;
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use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
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use clippy_utils::source::snippet;
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use clippy_utils::ty::has_iter_method;
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use clippy_utils::visitors::is_local_used;
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use clippy_utils::{contains_name, higher, is_integer_const, match_trait_method, paths, sugg, SpanlessEq};
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use if_chain::if_chain;
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use rustc_ast::ast;
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use rustc_data_structures::fx::{FxHashMap, FxHashSet};
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use rustc_hir::def::{DefKind, Res};
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use rustc_hir::intravisit::{walk_expr, Visitor};
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use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, QPath};
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use rustc_lint::LateContext;
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use rustc_middle::middle::region;
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use rustc_middle::ty::{self, Ty};
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use rustc_span::symbol::{sym, Symbol};
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use std::iter::{self, Iterator};
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use std::mem;
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/// Checks for looping over a range and then indexing a sequence with it.
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/// The iteratee must be a range literal.
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#[allow(clippy::too_many_lines)]
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pub(super) fn check<'tcx>(
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cx: &LateContext<'tcx>,
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pat: &'tcx Pat<'_>,
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arg: &'tcx Expr<'_>,
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body: &'tcx Expr<'_>,
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expr: &'tcx Expr<'_>,
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) {
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if let Some(higher::Range {
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start: Some(start),
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ref end,
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limits,
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}) = higher::Range::hir(arg)
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{
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// the var must be a single name
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if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
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let mut visitor = VarVisitor {
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cx,
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var: canonical_id,
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indexed_mut: FxHashSet::default(),
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indexed_indirectly: FxHashMap::default(),
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indexed_directly: FxHashMap::default(),
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referenced: FxHashSet::default(),
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nonindex: false,
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prefer_mutable: false,
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};
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walk_expr(&mut visitor, body);
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// linting condition: we only indexed one variable, and indexed it directly
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if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
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let (indexed, (indexed_extent, indexed_ty)) = visitor
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.indexed_directly
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.into_iter()
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.next()
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.expect("already checked that we have exactly 1 element");
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// ensure that the indexed variable was declared before the loop, see #601
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if let Some(indexed_extent) = indexed_extent {
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let parent_def_id = cx.tcx.hir().get_parent_item(expr.hir_id);
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let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
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let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
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if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
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return;
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}
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}
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// don't lint if the container that is indexed does not have .iter() method
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let has_iter = has_iter_method(cx, indexed_ty);
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if has_iter.is_none() {
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return;
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}
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// don't lint if the container that is indexed into is also used without
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// indexing
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if visitor.referenced.contains(&indexed) {
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return;
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}
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let starts_at_zero = is_integer_const(cx, start, 0);
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let skip = if starts_at_zero {
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String::new()
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} else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
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return;
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} else {
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format!(".skip({})", snippet(cx, start.span, ".."))
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};
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let mut end_is_start_plus_val = false;
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let take = if let Some(end) = *end {
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let mut take_expr = end;
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if let ExprKind::Binary(ref op, left, right) = end.kind {
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if op.node == BinOpKind::Add {
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let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
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let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
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if start_equal_left {
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take_expr = right;
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} else if start_equal_right {
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take_expr = left;
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}
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end_is_start_plus_val = start_equal_left | start_equal_right;
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}
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}
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if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
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String::new()
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} else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
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return;
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} else {
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match limits {
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ast::RangeLimits::Closed => {
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let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
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format!(".take({})", take_expr + sugg::ONE)
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},
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ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
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}
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}
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} else {
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String::new()
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};
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let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
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("mut ", "iter_mut")
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} else {
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("", "iter")
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};
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let take_is_empty = take.is_empty();
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let mut method_1 = take;
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let mut method_2 = skip;
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if end_is_start_plus_val {
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mem::swap(&mut method_1, &mut method_2);
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}
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if visitor.nonindex {
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span_lint_and_then(
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cx,
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NEEDLESS_RANGE_LOOP,
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arg.span,
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&format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
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|diag| {
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multispan_sugg(
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diag,
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"consider using an iterator",
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vec![
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(pat.span, format!("({}, <item>)", ident.name)),
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(
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arg.span,
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format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
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),
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],
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);
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},
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);
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} else {
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let repl = if starts_at_zero && take_is_empty {
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format!("&{}{}", ref_mut, indexed)
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} else {
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format!("{}.{}(){}{}", indexed, method, method_1, method_2)
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};
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span_lint_and_then(
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cx,
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NEEDLESS_RANGE_LOOP,
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arg.span,
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&format!("the loop variable `{}` is only used to index `{}`", ident.name, indexed),
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|diag| {
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multispan_sugg(
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diag,
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"consider using an iterator",
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vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
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);
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},
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);
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}
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}
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}
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}
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}
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fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
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if_chain! {
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if let ExprKind::MethodCall(method, len_args, _) = expr.kind;
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if len_args.len() == 1;
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if method.ident.name == sym::len;
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if let ExprKind::Path(QPath::Resolved(_, path)) = len_args[0].kind;
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if path.segments.len() == 1;
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if path.segments[0].ident.name == var;
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then {
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return true;
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}
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}
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false
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}
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fn is_end_eq_array_len<'tcx>(
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cx: &LateContext<'tcx>,
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end: &Expr<'_>,
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limits: ast::RangeLimits,
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indexed_ty: Ty<'tcx>,
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) -> bool {
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if_chain! {
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if let ExprKind::Lit(ref lit) = end.kind;
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if let ast::LitKind::Int(end_int, _) = lit.node;
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if let ty::Array(_, arr_len_const) = indexed_ty.kind();
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if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
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then {
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return match limits {
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ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
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ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
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};
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}
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}
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false
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}
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struct VarVisitor<'a, 'tcx> {
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/// context reference
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cx: &'a LateContext<'tcx>,
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/// var name to look for as index
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var: HirId,
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/// indexed variables that are used mutably
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indexed_mut: FxHashSet<Symbol>,
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/// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
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indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
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/// subset of `indexed` of vars that are indexed directly: `v[i]`
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/// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
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indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
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/// Any names that are used outside an index operation.
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/// Used to detect things like `&mut vec` used together with `vec[i]`
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referenced: FxHashSet<Symbol>,
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/// has the loop variable been used in expressions other than the index of
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/// an index op?
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nonindex: bool,
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/// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
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/// takes `&mut self`
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prefer_mutable: bool,
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}
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impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
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fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
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if_chain! {
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// the indexed container is referenced by a name
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if let ExprKind::Path(ref seqpath) = seqexpr.kind;
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if let QPath::Resolved(None, seqvar) = *seqpath;
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if seqvar.segments.len() == 1;
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if is_local_used(self.cx, idx, self.var);
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then {
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if self.prefer_mutable {
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self.indexed_mut.insert(seqvar.segments[0].ident.name);
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}
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let index_used_directly = matches!(idx.kind, ExprKind::Path(_));
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let res = self.cx.qpath_res(seqpath, seqexpr.hir_id);
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match res {
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Res::Local(hir_id) => {
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let parent_def_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
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let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
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if index_used_directly {
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self.indexed_directly.insert(
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seqvar.segments[0].ident.name,
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(Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
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);
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} else {
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self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
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}
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return false; // no need to walk further *on the variable*
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}
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Res::Def(DefKind::Static | DefKind::Const, ..) => {
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if index_used_directly {
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self.indexed_directly.insert(
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seqvar.segments[0].ident.name,
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(None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
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);
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} else {
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self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
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}
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return false; // no need to walk further *on the variable*
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}
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_ => (),
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}
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}
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}
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true
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}
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}
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impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
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fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
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if_chain! {
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// a range index op
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if let ExprKind::MethodCall(meth, [args_0, args_1, ..], _) = &expr.kind;
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if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
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|| (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
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if !self.check(args_1, args_0, expr);
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then { return }
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}
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if_chain! {
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// an index op
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if let ExprKind::Index(seqexpr, idx) = expr.kind;
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if !self.check(idx, seqexpr, expr);
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then { return }
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}
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if_chain! {
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// directly using a variable
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if let ExprKind::Path(QPath::Resolved(None, path)) = expr.kind;
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if let Res::Local(local_id) = path.res;
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then {
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if local_id == self.var {
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self.nonindex = true;
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} else {
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// not the correct variable, but still a variable
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self.referenced.insert(path.segments[0].ident.name);
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}
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}
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}
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let old = self.prefer_mutable;
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match expr.kind {
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ExprKind::AssignOp(_, lhs, rhs) | ExprKind::Assign(lhs, rhs, _) => {
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self.prefer_mutable = true;
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self.visit_expr(lhs);
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self.prefer_mutable = false;
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self.visit_expr(rhs);
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},
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ExprKind::AddrOf(BorrowKind::Ref, mutbl, expr) => {
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if mutbl == Mutability::Mut {
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self.prefer_mutable = true;
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}
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self.visit_expr(expr);
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},
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ExprKind::Call(f, args) => {
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self.visit_expr(f);
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for expr in args {
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let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
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self.prefer_mutable = false;
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if let ty::Ref(_, _, mutbl) = *ty.kind() {
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if mutbl == Mutability::Mut {
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self.prefer_mutable = true;
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}
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}
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self.visit_expr(expr);
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}
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},
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ExprKind::MethodCall(_, args, _) => {
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let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
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for (ty, expr) in iter::zip(self.cx.tcx.fn_sig(def_id).inputs().skip_binder(), args) {
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self.prefer_mutable = false;
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if let ty::Ref(_, _, mutbl) = *ty.kind() {
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if mutbl == Mutability::Mut {
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self.prefer_mutable = true;
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}
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}
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self.visit_expr(expr);
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}
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},
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ExprKind::Closure(_, _, body_id, ..) => {
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let body = self.cx.tcx.hir().body(body_id);
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self.visit_expr(&body.value);
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},
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_ => walk_expr(self, expr),
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}
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self.prefer_mutable = old;
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}
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}
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