288 lines
11 KiB
Rust
288 lines
11 KiB
Rust
use super::utils::make_iterator_snippet;
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use super::NEVER_LOOP;
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use clippy_utils::consts::{constant, Constant};
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use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::higher::ForLoop;
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use clippy_utils::source::snippet;
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use rustc_errors::Applicability;
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use rustc_hir::{Block, Destination, Expr, ExprKind, HirId, InlineAsmOperand, Pat, Stmt, StmtKind};
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use rustc_lint::LateContext;
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use rustc_span::Span;
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use std::iter::{once, Iterator};
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pub(super) fn check<'tcx>(
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cx: &LateContext<'tcx>,
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block: &Block<'tcx>,
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loop_id: HirId,
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span: Span,
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for_loop: Option<&ForLoop<'_>>,
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) {
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match never_loop_block(cx, block, &mut Vec::new(), loop_id) {
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NeverLoopResult::AlwaysBreak => {
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span_lint_and_then(cx, NEVER_LOOP, span, "this loop never actually loops", |diag| {
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if let Some(ForLoop {
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arg: iterator,
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pat,
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span: for_span,
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..
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}) = for_loop
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{
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// Suggests using an `if let` instead. This is `Unspecified` because the
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// loop may (probably) contain `break` statements which would be invalid
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// in an `if let`.
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diag.span_suggestion_verbose(
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for_span.with_hi(iterator.span.hi()),
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"if you need the first element of the iterator, try writing",
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for_to_if_let_sugg(cx, iterator, pat),
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Applicability::Unspecified,
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);
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}
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});
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},
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NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
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NeverLoopResult::IgnoreUntilEnd(_) => unreachable!(),
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}
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}
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#[derive(Copy, Clone)]
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enum NeverLoopResult {
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// A break/return always get triggered but not necessarily for the main loop.
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AlwaysBreak,
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// A continue may occur for the main loop.
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MayContinueMainLoop,
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// Ignore everything until the end of the block with this id
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IgnoreUntilEnd(HirId),
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Otherwise,
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}
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#[must_use]
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fn absorb_break(arg: NeverLoopResult) -> NeverLoopResult {
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match arg {
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NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
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NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
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NeverLoopResult::IgnoreUntilEnd(id) => NeverLoopResult::IgnoreUntilEnd(id),
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}
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}
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// Combine two results for parts that are called in order.
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#[must_use]
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fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
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match first {
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NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop | NeverLoopResult::IgnoreUntilEnd(_) => {
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first
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},
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NeverLoopResult::Otherwise => second,
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}
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}
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// Combine two results where only one of the part may have been executed.
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#[must_use]
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fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult, ignore_ids: &[HirId]) -> NeverLoopResult {
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match (b1, b2) {
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(NeverLoopResult::IgnoreUntilEnd(a), NeverLoopResult::IgnoreUntilEnd(b)) => {
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if ignore_ids.iter().find(|&e| e == &a || e == &b).unwrap() == &a {
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NeverLoopResult::IgnoreUntilEnd(b)
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} else {
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NeverLoopResult::IgnoreUntilEnd(a)
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}
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},
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(i @ NeverLoopResult::IgnoreUntilEnd(_), NeverLoopResult::AlwaysBreak)
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| (NeverLoopResult::AlwaysBreak, i @ NeverLoopResult::IgnoreUntilEnd(_)) => i,
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(NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
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(NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
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NeverLoopResult::MayContinueMainLoop
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},
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(NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
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}
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}
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fn never_loop_block<'tcx>(
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cx: &LateContext<'tcx>,
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block: &Block<'tcx>,
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ignore_ids: &mut Vec<HirId>,
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main_loop_id: HirId,
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) -> NeverLoopResult {
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let iter = block
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.stmts
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.iter()
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.filter_map(stmt_to_expr)
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.chain(block.expr.map(|expr| (expr, None)));
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iter.map(|(e, els)| {
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let e = never_loop_expr(cx, e, ignore_ids, main_loop_id);
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// els is an else block in a let...else binding
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els.map_or(e, |els| {
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combine_branches(e, never_loop_block(cx, els, ignore_ids, main_loop_id), ignore_ids)
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})
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})
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.fold(NeverLoopResult::Otherwise, combine_seq)
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}
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fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<(&'tcx Expr<'tcx>, Option<&'tcx Block<'tcx>>)> {
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match stmt.kind {
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StmtKind::Semi(e) | StmtKind::Expr(e) => Some((e, None)),
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// add the let...else expression (if present)
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StmtKind::Local(local) => local.init.map(|init| (init, local.els)),
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StmtKind::Item(..) => None,
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}
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}
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#[allow(clippy::too_many_lines)]
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fn never_loop_expr<'tcx>(
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cx: &LateContext<'tcx>,
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expr: &Expr<'tcx>,
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ignore_ids: &mut Vec<HirId>,
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main_loop_id: HirId,
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) -> NeverLoopResult {
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match expr.kind {
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ExprKind::Unary(_, e)
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| ExprKind::Cast(e, _)
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| ExprKind::Type(e, _)
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| ExprKind::Field(e, _)
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| ExprKind::AddrOf(_, _, e)
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| ExprKind::Repeat(e, _)
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| ExprKind::DropTemps(e) => never_loop_expr(cx, e, ignore_ids, main_loop_id),
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ExprKind::Let(let_expr) => never_loop_expr(cx, let_expr.init, ignore_ids, main_loop_id),
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ExprKind::Array(es) | ExprKind::Tup(es) => never_loop_expr_all(cx, &mut es.iter(), ignore_ids, main_loop_id),
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ExprKind::MethodCall(_, receiver, es, _) => never_loop_expr_all(
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cx,
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&mut std::iter::once(receiver).chain(es.iter()),
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ignore_ids,
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main_loop_id,
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),
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ExprKind::Struct(_, fields, base) => {
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let fields = never_loop_expr_all(cx, &mut fields.iter().map(|f| f.expr), ignore_ids, main_loop_id);
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if let Some(base) = base {
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combine_seq(fields, never_loop_expr(cx, base, ignore_ids, main_loop_id))
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} else {
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fields
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}
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},
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ExprKind::Call(e, es) => never_loop_expr_all(cx, &mut once(e).chain(es.iter()), ignore_ids, main_loop_id),
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ExprKind::Binary(_, e1, e2)
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| ExprKind::Assign(e1, e2, _)
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| ExprKind::AssignOp(_, e1, e2)
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| ExprKind::Index(e1, e2) => never_loop_expr_all(cx, &mut [e1, e2].iter().copied(), ignore_ids, main_loop_id),
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ExprKind::Loop(b, _, _, _) => {
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// Break can come from the inner loop so remove them.
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absorb_break(never_loop_block(cx, b, ignore_ids, main_loop_id))
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},
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ExprKind::If(e, e2, e3) => {
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let e1 = never_loop_expr(cx, e, ignore_ids, main_loop_id);
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let e2 = never_loop_expr(cx, e2, ignore_ids, main_loop_id);
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// If we know the `if` condition evaluates to `true`, don't check everything past it; it
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// should just return whatever's evaluated for `e1` and `e2` since `e3` is unreachable
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if let Some(Constant::Bool(true)) = constant(cx, cx.typeck_results(), e) {
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return combine_seq(e1, e2);
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}
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let e3 = e3.as_ref().map_or(NeverLoopResult::Otherwise, |e| {
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never_loop_expr(cx, e, ignore_ids, main_loop_id)
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});
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combine_seq(e1, combine_branches(e2, e3, ignore_ids))
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},
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ExprKind::Match(e, arms, _) => {
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let e = never_loop_expr(cx, e, ignore_ids, main_loop_id);
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if arms.is_empty() {
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e
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} else {
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let arms = never_loop_expr_branch(cx, &mut arms.iter().map(|a| a.body), ignore_ids, main_loop_id);
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combine_seq(e, arms)
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}
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},
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ExprKind::Block(b, l) => {
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if l.is_some() {
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ignore_ids.push(b.hir_id);
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}
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let ret = never_loop_block(cx, b, ignore_ids, main_loop_id);
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if l.is_some() {
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ignore_ids.pop();
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}
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match ret {
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NeverLoopResult::IgnoreUntilEnd(a) if a == b.hir_id => NeverLoopResult::Otherwise,
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_ => ret,
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}
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},
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ExprKind::Continue(d) => {
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let id = d
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.target_id
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.expect("target ID can only be missing in the presence of compilation errors");
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if id == main_loop_id {
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NeverLoopResult::MayContinueMainLoop
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} else {
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NeverLoopResult::AlwaysBreak
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}
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},
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// checks if break targets a block instead of a loop
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ExprKind::Break(Destination { target_id: Ok(t), .. }, e) if ignore_ids.contains(&t) => e
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.map_or(NeverLoopResult::IgnoreUntilEnd(t), |e| {
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never_loop_expr(cx, e, ignore_ids, main_loop_id)
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}),
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ExprKind::Break(_, e) | ExprKind::Ret(e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
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combine_seq(
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never_loop_expr(cx, e, ignore_ids, main_loop_id),
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NeverLoopResult::AlwaysBreak,
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)
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}),
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ExprKind::Become(e) => combine_seq(
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never_loop_expr(cx, e, ignore_ids, main_loop_id),
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NeverLoopResult::AlwaysBreak,
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),
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ExprKind::InlineAsm(asm) => asm
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.operands
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.iter()
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.map(|(o, _)| match o {
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InlineAsmOperand::In { expr, .. } | InlineAsmOperand::InOut { expr, .. } => {
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never_loop_expr(cx, expr, ignore_ids, main_loop_id)
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},
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InlineAsmOperand::Out { expr, .. } => {
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never_loop_expr_all(cx, &mut expr.iter().copied(), ignore_ids, main_loop_id)
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},
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InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => never_loop_expr_all(
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cx,
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&mut once(*in_expr).chain(out_expr.iter().copied()),
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ignore_ids,
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main_loop_id,
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),
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InlineAsmOperand::Const { .. }
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| InlineAsmOperand::SymFn { .. }
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| InlineAsmOperand::SymStatic { .. } => NeverLoopResult::Otherwise,
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})
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.fold(NeverLoopResult::Otherwise, combine_seq),
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ExprKind::OffsetOf(_, _)
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| ExprKind::Yield(_, _)
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| ExprKind::Closure { .. }
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| ExprKind::Path(_)
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| ExprKind::ConstBlock(_)
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| ExprKind::Lit(_)
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| ExprKind::Err(_) => NeverLoopResult::Otherwise,
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}
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}
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fn never_loop_expr_all<'tcx, T: Iterator<Item = &'tcx Expr<'tcx>>>(
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cx: &LateContext<'tcx>,
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es: &mut T,
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ignore_ids: &mut Vec<HirId>,
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main_loop_id: HirId,
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) -> NeverLoopResult {
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es.map(|e| never_loop_expr(cx, e, ignore_ids, main_loop_id))
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.fold(NeverLoopResult::Otherwise, combine_seq)
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}
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fn never_loop_expr_branch<'tcx, T: Iterator<Item = &'tcx Expr<'tcx>>>(
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cx: &LateContext<'tcx>,
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e: &mut T,
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ignore_ids: &mut Vec<HirId>,
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main_loop_id: HirId,
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) -> NeverLoopResult {
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e.fold(NeverLoopResult::AlwaysBreak, |a, b| {
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combine_branches(a, never_loop_expr(cx, b, ignore_ids, main_loop_id), ignore_ids)
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})
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}
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fn for_to_if_let_sugg(cx: &LateContext<'_>, iterator: &Expr<'_>, pat: &Pat<'_>) -> String {
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let pat_snippet = snippet(cx, pat.span, "_");
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let iter_snippet = make_iterator_snippet(cx, iterator, &mut Applicability::Unspecified);
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format!("if let Some({pat_snippet}) = {iter_snippet}.next()")
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}
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