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|
use super::utils::make_iterator_snippet;
use super::NEVER_LOOP;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::higher::ForLoop;
use clippy_utils::source::snippet;
use rustc_errors::Applicability;
use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, Pat, Stmt, StmtKind};
use rustc_lint::LateContext;
use rustc_span::Span;
use std::iter::{once, Iterator};
pub(super) fn check(
cx: &LateContext<'_>,
block: &Block<'_>,
loop_id: HirId,
span: Span,
for_loop: Option<&ForLoop<'_>>,
) {
match never_loop_block(block, loop_id) {
NeverLoopResult::AlwaysBreak => {
span_lint_and_then(cx, NEVER_LOOP, span, "this loop never actually loops", |diag| {
if let Some(ForLoop {
arg: iterator,
pat,
span: for_span,
..
}) = for_loop
{
// Suggests using an `if let` instead. This is `Unspecified` because the
// loop may (probably) contain `break` statements which would be invalid
// in an `if let`.
diag.span_suggestion_verbose(
for_span.with_hi(iterator.span.hi()),
"if you need the first element of the iterator, try writing",
for_to_if_let_sugg(cx, iterator, pat),
Applicability::Unspecified,
);
}
});
},
NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
}
}
enum NeverLoopResult {
// A break/return always get triggered but not necessarily for the main loop.
AlwaysBreak,
// A continue may occur for the main loop.
MayContinueMainLoop,
Otherwise,
}
#[must_use]
fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
match *arg {
NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
}
}
// Combine two results for parts that are called in order.
#[must_use]
fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
match first {
NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
NeverLoopResult::Otherwise => second,
}
}
// Combine two results where both parts are called but not necessarily in order.
#[must_use]
fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
match (left, right) {
(NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
NeverLoopResult::MayContinueMainLoop
},
(NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
(NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
}
}
// Combine two results where only one of the part may have been executed.
#[must_use]
fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
match (b1, b2) {
(NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
(NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
NeverLoopResult::MayContinueMainLoop
},
(NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
}
}
fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
let mut iter = block.stmts.iter().filter_map(stmt_to_expr).chain(block.expr);
never_loop_expr_seq(&mut iter, main_loop_id)
}
fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
es.map(|e| never_loop_expr(e, main_loop_id))
.fold(NeverLoopResult::Otherwise, combine_seq)
}
fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
match stmt.kind {
StmtKind::Semi(e, ..) | StmtKind::Expr(e, ..) => Some(e),
StmtKind::Local(local) => local.init,
StmtKind::Item(..) => None,
}
}
fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
match expr.kind {
ExprKind::Box(e)
| ExprKind::Unary(_, e)
| ExprKind::Cast(e, _)
| ExprKind::Type(e, _)
| ExprKind::Field(e, _)
| ExprKind::AddrOf(_, _, e)
| ExprKind::Repeat(e, _)
| ExprKind::DropTemps(e) => never_loop_expr(e, main_loop_id),
ExprKind::Let(let_expr) => never_loop_expr(let_expr.init, main_loop_id),
ExprKind::Array(es) | ExprKind::MethodCall(_, es, _) | ExprKind::Tup(es) => {
never_loop_expr_all(&mut es.iter(), main_loop_id)
},
ExprKind::Struct(_, fields, base) => {
let fields = never_loop_expr_all(&mut fields.iter().map(|f| f.expr), main_loop_id);
if let Some(base) = base {
combine_both(fields, never_loop_expr(base, main_loop_id))
} else {
fields
}
},
ExprKind::Call(e, es) => never_loop_expr_all(&mut once(e).chain(es.iter()), main_loop_id),
ExprKind::Binary(_, e1, e2)
| ExprKind::Assign(e1, e2, _)
| ExprKind::AssignOp(_, e1, e2)
| ExprKind::Index(e1, e2) => never_loop_expr_all(&mut [e1, e2].iter().copied(), main_loop_id),
ExprKind::Loop(b, _, _, _) => {
// Break can come from the inner loop so remove them.
absorb_break(&never_loop_block(b, main_loop_id))
},
ExprKind::If(e, e2, e3) => {
let e1 = never_loop_expr(e, main_loop_id);
let e2 = never_loop_expr(e2, main_loop_id);
let e3 = e3
.as_ref()
.map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
combine_seq(e1, combine_branches(e2, e3))
},
ExprKind::Match(e, arms, _) => {
let e = never_loop_expr(e, main_loop_id);
if arms.is_empty() {
e
} else {
let arms = never_loop_expr_branch(&mut arms.iter().map(|a| a.body), main_loop_id);
combine_seq(e, arms)
}
},
ExprKind::Block(b, _) => never_loop_block(b, main_loop_id),
ExprKind::Continue(d) => {
let id = d
.target_id
.expect("target ID can only be missing in the presence of compilation errors");
if id == main_loop_id {
NeverLoopResult::MayContinueMainLoop
} else {
NeverLoopResult::AlwaysBreak
}
},
ExprKind::Break(_, e) | ExprKind::Ret(e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
}),
ExprKind::InlineAsm(asm) => asm
.operands
.iter()
.map(|(o, _)| match o {
InlineAsmOperand::In { expr, .. } | InlineAsmOperand::InOut { expr, .. } => {
never_loop_expr(expr, main_loop_id)
},
InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
},
InlineAsmOperand::Const { .. }
| InlineAsmOperand::SymFn { .. }
| InlineAsmOperand::SymStatic { .. } => NeverLoopResult::Otherwise,
})
.fold(NeverLoopResult::Otherwise, combine_both),
ExprKind::Yield(_, _)
| ExprKind::Closure { .. }
| ExprKind::Path(_)
| ExprKind::ConstBlock(_)
| ExprKind::Lit(_)
| ExprKind::Err => NeverLoopResult::Otherwise,
}
}
fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
es.map(|e| never_loop_expr(e, main_loop_id))
.fold(NeverLoopResult::Otherwise, combine_both)
}
fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
e.map(|e| never_loop_expr(e, main_loop_id))
.fold(NeverLoopResult::AlwaysBreak, combine_branches)
}
fn for_to_if_let_sugg(cx: &LateContext<'_>, iterator: &Expr<'_>, pat: &Pat<'_>) -> String {
let pat_snippet = snippet(cx, pat.span, "_");
let iter_snippet = make_iterator_snippet(cx, iterator, &mut Applicability::Unspecified);
format!(
"if let Some({pat}) = {iter}.next()",
pat = pat_snippet,
iter = iter_snippet
)
}
|
