212 lines
8.4 KiB
Rust
212 lines
8.4 KiB
Rust
use super::utils::make_iterator_snippet;
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use super::NEVER_LOOP;
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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, 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(
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cx: &LateContext<'tcx>,
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block: &'tcx Block<'_>,
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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(block, 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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}
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}
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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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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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}
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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 => first,
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NeverLoopResult::Otherwise => second,
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}
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}
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// Combine two results where both parts are called but not necessarily in order.
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#[must_use]
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fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
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match (left, right) {
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(NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
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NeverLoopResult::MayContinueMainLoop
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},
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(NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
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(NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
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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) -> NeverLoopResult {
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match (b1, b2) {
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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(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
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let mut iter = block.stmts.iter().filter_map(stmt_to_expr).chain(block.expr);
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never_loop_expr_seq(&mut iter, main_loop_id)
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}
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fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
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es.map(|e| never_loop_expr(e, main_loop_id))
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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>> {
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match stmt.kind {
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StmtKind::Semi(e, ..) | StmtKind::Expr(e, ..) => Some(e),
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StmtKind::Local(local) => local.init,
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StmtKind::Item(..) => None,
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}
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}
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fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
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match expr.kind {
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ExprKind::Box(e)
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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::Let(_, e, _)
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| ExprKind::Field(e, _)
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| ExprKind::AddrOf(_, _, e)
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| ExprKind::Struct(_, _, Some(e))
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| ExprKind::Repeat(e, _)
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| ExprKind::DropTemps(e) => never_loop_expr(e, main_loop_id),
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ExprKind::Array(es) | ExprKind::MethodCall(_, _, es, _) | ExprKind::Tup(es) => {
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never_loop_expr_all(&mut es.iter(), main_loop_id)
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},
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ExprKind::Call(e, es) => never_loop_expr_all(&mut once(e).chain(es.iter()), 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(&mut [e1, e2].iter().copied(), 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(b, 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(e, main_loop_id);
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let e2 = never_loop_expr(e2, main_loop_id);
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let e3 = e3
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.as_ref()
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.map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
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combine_seq(e1, combine_branches(e2, e3))
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},
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ExprKind::Match(e, arms, _) => {
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let e = never_loop_expr(e, 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(&mut arms.iter().map(|a| &*a.body), 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, _) => never_loop_block(b, main_loop_id),
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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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ExprKind::Break(_, e) | ExprKind::Ret(e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
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combine_seq(never_loop_expr(e, main_loop_id), 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, .. }
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| InlineAsmOperand::InOut { expr, .. }
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| InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
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InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
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InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
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never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
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},
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InlineAsmOperand::Const { .. } => NeverLoopResult::Otherwise,
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})
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.fold(NeverLoopResult::Otherwise, combine_both),
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ExprKind::Struct(_, _, None)
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| ExprKind::Yield(_, _)
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| ExprKind::Closure(_, _, _, _, _)
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| ExprKind::LlvmInlineAsm(_)
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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<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
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es.map(|e| never_loop_expr(e, main_loop_id))
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.fold(NeverLoopResult::Otherwise, combine_both)
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}
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fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
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e.map(|e| never_loop_expr(e, main_loop_id))
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.fold(NeverLoopResult::AlwaysBreak, combine_branches)
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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!(
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"if let Some({pat}) = {iter}.next()",
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pat = pat_snippet,
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iter = iter_snippet
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)
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}
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