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|
use super::WHILE_LET_LOOP;
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::{snippet, snippet_indent, snippet_opt};
use clippy_utils::ty::needs_ordered_drop;
use clippy_utils::visitors::any_temporaries_need_ordered_drop;
use clippy_utils::{higher, peel_blocks};
use rustc_ast::BindingMode;
use rustc_errors::Applicability;
use rustc_hir::{Block, Expr, ExprKind, LetStmt, MatchSource, Pat, PatKind, Path, QPath, StmtKind, Ty};
use rustc_lint::LateContext;
pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) {
let (init, let_info) = match (loop_block.stmts, loop_block.expr) {
([stmt, ..], _) => match stmt.kind {
StmtKind::Let(LetStmt {
init: Some(e),
els: None,
pat,
ty,
..
}) => (*e, Some((*pat, *ty))),
StmtKind::Semi(e) | StmtKind::Expr(e) => (e, None),
_ => return,
},
([], Some(e)) => (e, None),
_ => return,
};
let has_trailing_exprs = loop_block.stmts.len() + usize::from(loop_block.expr.is_some()) > 1;
if let Some(if_let) = higher::IfLet::hir(cx, init)
&& let Some(else_expr) = if_let.if_else
&& is_simple_break_expr(else_expr)
{
could_be_while_let(
cx,
expr,
if_let.let_pat,
if_let.let_expr,
has_trailing_exprs,
let_info,
if_let.if_then,
);
} else if let ExprKind::Match(scrutinee, [arm1, arm2], MatchSource::Normal) = init.kind
&& arm1.guard.is_none()
&& arm2.guard.is_none()
&& is_simple_break_expr(arm2.body)
{
could_be_while_let(cx, expr, arm1.pat, scrutinee, has_trailing_exprs, let_info, arm1.body);
}
}
/// Returns `true` if expr contains a single break expression without a label or sub-expression,
/// possibly embedded in blocks.
fn is_simple_break_expr(e: &Expr<'_>) -> bool {
if let ExprKind::Block(b, _) = e.kind {
match (b.stmts, b.expr) {
([s], None) => matches!(s.kind, StmtKind::Expr(e) | StmtKind::Semi(e) if is_simple_break_expr(e)),
([], Some(e)) => is_simple_break_expr(e),
_ => false,
}
} else {
matches!(e.kind, ExprKind::Break(dest, None) if dest.label.is_none())
}
}
fn could_be_while_let<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'_>,
let_pat: &'tcx Pat<'_>,
let_expr: &'tcx Expr<'_>,
has_trailing_exprs: bool,
let_info: Option<(&Pat<'_>, Option<&Ty<'_>>)>,
inner_expr: &Expr<'_>,
) {
if has_trailing_exprs
&& (needs_ordered_drop(cx, cx.typeck_results().expr_ty(let_expr))
|| any_temporaries_need_ordered_drop(cx, let_expr))
{
// Switching to a `while let` loop will extend the lifetime of some values.
return;
}
// NOTE: we used to build a body here instead of using
// ellipsis, this was removed because:
// 1) it was ugly with big bodies;
// 2) it was not indented properly;
// 3) it wasn’t very smart (see #675).
let inner_content = if let Some((pat, ty)) = let_info
// Prevent trivial reassignments such as `let x = x;` or `let _ = …;`, but
// keep them if the type has been explicitly specified.
&& (!is_trivial_assignment(pat, peel_blocks(inner_expr)) || ty.is_some())
&& let Some(pat_str) = snippet_opt(cx, pat.span)
&& let Some(init_str) = snippet_opt(cx, peel_blocks(inner_expr).span)
{
let ty_str = ty
.map(|ty| format!(": {}", snippet(cx, ty.span, "_")))
.unwrap_or_default();
format!(
"\n{indent} let {pat_str}{ty_str} = {init_str};\n{indent} ..\n{indent}",
indent = snippet_indent(cx, expr.span).unwrap_or_default(),
)
} else {
" .. ".into()
};
span_lint_and_sugg(
cx,
WHILE_LET_LOOP,
expr.span,
"this loop could be written as a `while let` loop",
"try",
format!(
"while let {} = {} {{{inner_content}}}",
snippet(cx, let_pat.span, ".."),
snippet(cx, let_expr.span, ".."),
),
Applicability::HasPlaceholders,
);
}
fn is_trivial_assignment(pat: &Pat<'_>, init: &Expr<'_>) -> bool {
match (pat.kind, init.kind) {
(PatKind::Wild, _) => true,
(
PatKind::Binding(BindingMode::NONE, _, pat_ident, None),
ExprKind::Path(QPath::Resolved(None, Path { segments: [init], .. })),
) => pat_ident.name == init.ident.name,
_ => false,
}
}
|
