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|
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::higher::IfLetOrMatch;
use clippy_utils::source::snippet;
use clippy_utils::visitors::is_local_used;
use clippy_utils::{
is_res_lang_ctor, is_unit_expr, path_to_local, peel_blocks_with_stmt, peel_ref_operators, SpanlessEq,
};
use if_chain::if_chain;
use rustc_errors::MultiSpan;
use rustc_hir::LangItem::OptionNone;
use rustc_hir::{Arm, Expr, Guard, HirId, Let, Pat, PatKind};
use rustc_lint::LateContext;
use rustc_span::Span;
use super::COLLAPSIBLE_MATCH;
pub(super) fn check_match<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'_>]) {
if let Some(els_arm) = arms.iter().rfind(|arm| arm_is_wild_like(cx, arm)) {
for arm in arms {
check_arm(cx, true, arm.pat, arm.body, arm.guard.as_ref(), Some(els_arm.body));
}
}
}
pub(super) fn check_if_let<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
body: &'tcx Expr<'_>,
else_expr: Option<&'tcx Expr<'_>>,
) {
check_arm(cx, false, pat, body, None, else_expr);
}
fn check_arm<'tcx>(
cx: &LateContext<'tcx>,
outer_is_match: bool,
outer_pat: &'tcx Pat<'tcx>,
outer_then_body: &'tcx Expr<'tcx>,
outer_guard: Option<&'tcx Guard<'tcx>>,
outer_else_body: Option<&'tcx Expr<'tcx>>,
) {
let inner_expr = peel_blocks_with_stmt(outer_then_body);
if_chain! {
if let Some(inner) = IfLetOrMatch::parse(cx, inner_expr);
if let Some((inner_scrutinee, inner_then_pat, inner_else_body)) = match inner {
IfLetOrMatch::IfLet(scrutinee, pat, _, els) => Some((scrutinee, pat, els)),
IfLetOrMatch::Match(scrutinee, arms, ..) => if_chain! {
// if there are more than two arms, collapsing would be non-trivial
if arms.len() == 2 && arms.iter().all(|a| a.guard.is_none());
// one of the arms must be "wild-like"
if let Some(wild_idx) = arms.iter().rposition(|a| arm_is_wild_like(cx, a));
then {
let (then, els) = (&arms[1 - wild_idx], &arms[wild_idx]);
Some((scrutinee, then.pat, Some(els.body)))
} else {
None
}
},
};
if outer_pat.span.ctxt() == inner_scrutinee.span.ctxt();
// match expression must be a local binding
// match <local> { .. }
if let Some(binding_id) = path_to_local(peel_ref_operators(cx, inner_scrutinee));
if !pat_contains_or(inner_then_pat);
// the binding must come from the pattern of the containing match arm
// ..<local>.. => match <local> { .. }
if let (Some(binding_span), is_innermost_parent_pat_struct)
= find_pat_binding_and_is_innermost_parent_pat_struct(outer_pat, binding_id);
// the "else" branches must be equal
if match (outer_else_body, inner_else_body) {
(None, None) => true,
(None, Some(e)) | (Some(e), None) => is_unit_expr(e),
(Some(a), Some(b)) => SpanlessEq::new(cx).eq_expr(a, b),
};
// the binding must not be used in the if guard
if outer_guard.map_or(
true,
|(Guard::If(e) | Guard::IfLet(Let { init: e, .. }))| !is_local_used(cx, *e, binding_id)
);
// ...or anywhere in the inner expression
if match inner {
IfLetOrMatch::IfLet(_, _, body, els) => {
!is_local_used(cx, body, binding_id) && els.map_or(true, |e| !is_local_used(cx, e, binding_id))
},
IfLetOrMatch::Match(_, arms, ..) => !arms.iter().any(|arm| is_local_used(cx, arm, binding_id)),
};
then {
let msg = format!(
"this `{}` can be collapsed into the outer `{}`",
if matches!(inner, IfLetOrMatch::Match(..)) { "match" } else { "if let" },
if outer_is_match { "match" } else { "if let" },
);
// collapsing patterns need an explicit field name in struct pattern matching
// ex: Struct {x: Some(1)}
let replace_msg = if is_innermost_parent_pat_struct {
format!(", prefixed by {}:", snippet(cx, binding_span, "their field name"))
} else {
String::new()
};
span_lint_and_then(
cx,
COLLAPSIBLE_MATCH,
inner_expr.span,
&msg,
|diag| {
let mut help_span = MultiSpan::from_spans(vec![binding_span, inner_then_pat.span]);
help_span.push_span_label(binding_span, "replace this binding");
help_span.push_span_label(inner_then_pat.span, format!("with this pattern{replace_msg}"));
diag.span_help(help_span, "the outer pattern can be modified to include the inner pattern");
},
);
}
}
}
/// A "wild-like" arm has a wild (`_`) or `None` pattern and no guard. Such arms can be "collapsed"
/// into a single wild arm without any significant loss in semantics or readability.
fn arm_is_wild_like(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
if arm.guard.is_some() {
return false;
}
match arm.pat.kind {
PatKind::Binding(..) | PatKind::Wild => true,
PatKind::Path(ref qpath) => is_res_lang_ctor(cx, cx.qpath_res(qpath, arm.pat.hir_id), OptionNone),
_ => false,
}
}
fn find_pat_binding_and_is_innermost_parent_pat_struct(pat: &Pat<'_>, hir_id: HirId) -> (Option<Span>, bool) {
let mut span = None;
let mut is_innermost_parent_pat_struct = false;
pat.walk_short(|p| match &p.kind {
// ignore OR patterns
PatKind::Or(_) => false,
PatKind::Binding(_bm, _, _ident, _) => {
let found = p.hir_id == hir_id;
if found {
span = Some(p.span);
}
!found
},
_ => {
is_innermost_parent_pat_struct = matches!(p.kind, PatKind::Struct(..));
true
},
});
(span, is_innermost_parent_pat_struct)
}
fn pat_contains_or(pat: &Pat<'_>) -> bool {
let mut result = false;
pat.walk(|p| {
let is_or = matches!(p.kind, PatKind::Or(_));
result |= is_or;
!is_or
});
result
}
|
