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rust-clippy/clippy_lints/src/option_if_let_else.rs

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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::sugg::Sugg;
use clippy_utils::{
can_move_expr_to_closure, eager_or_lazy, higher, in_constant, is_else_clause, is_lang_ctor, peel_blocks,
peel_hir_expr_while, CaptureKind,
};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
use rustc_hir::{
def::Res, Arm, BindingAnnotation, Expr, ExprKind, MatchSource, Mutability, Pat, PatKind, Path, QPath, UnOp,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Lints usage of `if let Some(v) = ... { y } else { x }` and
/// `match .. { Some(v) => y, None/_ => x }` which are more
/// idiomatically done with `Option::map_or` (if the else bit is a pure
/// expression) or `Option::map_or_else` (if the else bit is an impure
/// expression).
///
/// ### Why is this bad?
/// Using the dedicated functions of the `Option` type is clearer and
/// more concise than an `if let` expression.
///
/// ### Known problems
/// This lint uses a deliberately conservative metric for checking
/// if the inside of either body contains breaks or continues which will
/// cause it to not suggest a fix if either block contains a loop with
/// continues or breaks contained within the loop.
///
/// ### Example
/// ```rust
/// # let optional: Option<u32> = Some(0);
/// # fn do_complicated_function() -> u32 { 5 };
/// let _ = if let Some(foo) = optional {
/// foo
/// } else {
/// 5
/// };
/// let _ = match optional {
/// Some(val) => val + 1,
/// None => 5
/// };
/// let _ = if let Some(foo) = optional {
/// foo
/// } else {
/// let y = do_complicated_function();
/// y*y
/// };
/// ```
///
/// should be
///
/// ```rust
/// # let optional: Option<u32> = Some(0);
/// # fn do_complicated_function() -> u32 { 5 };
/// let _ = optional.map_or(5, |foo| foo);
/// let _ = optional.map_or(5, |val| val + 1);
/// let _ = optional.map_or_else(||{
/// let y = do_complicated_function();
/// y*y
/// }, |foo| foo);
/// ```
// FIXME: Before moving this lint out of nursery, the lint name needs to be updated. It now also
// covers matches and `Result`.
#[clippy::version = "1.47.0"]
pub OPTION_IF_LET_ELSE,
nursery,
"reimplementation of Option::map_or"
}
declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
/// A struct containing information about occurrences of construct that this lint detects
///
/// Such as:
///
/// ```ignore
/// if let Some(..) = {..} else {..}
/// ```
/// or
/// ```ignore
/// match x {
/// Some(..) => {..},
/// None/_ => {..}
/// }
/// ```
struct OptionOccurence {
option: String,
method_sugg: String,
some_expr: String,
none_expr: String,
}
fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
format!(
"{}{}",
Sugg::hir_with_macro_callsite(cx, cond_expr, "..").maybe_par(),
if as_mut {
".as_mut()"
} else if as_ref {
".as_ref()"
} else {
""
}
)
}
fn try_get_option_occurence<'tcx>(
cx: &LateContext<'tcx>,
pat: &Pat<'tcx>,
expr: &Expr<'_>,
if_then: &'tcx Expr<'_>,
if_else: &'tcx Expr<'_>,
) -> Option<OptionOccurence> {
let cond_expr = match expr.kind {
ExprKind::Unary(UnOp::Deref, inner_expr) | ExprKind::AddrOf(_, _, inner_expr) => inner_expr,
_ => expr,
};
let inner_pat = try_get_inner_pat(cx, pat)?;
if_chain! {
if let PatKind::Binding(bind_annotation, _, id, None) = inner_pat.kind;
if let Some(some_captures) = can_move_expr_to_closure(cx, if_then);
if let Some(none_captures) = can_move_expr_to_closure(cx, if_else);
if some_captures
.iter()
.filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
.all(|(x, y)| x.is_imm_ref() && y.is_imm_ref());
then {
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let capture_mut = if bind_annotation == BindingAnnotation::MUT { "mut " } else { "" };
let some_body = peel_blocks(if_then);
let none_body = peel_blocks(if_else);
let method_sugg = if eager_or_lazy::switch_to_eager_eval(cx, none_body) { "map_or" } else { "map_or_else" };
let capture_name = id.name.to_ident_string();
let (as_ref, as_mut) = match &expr.kind {
ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
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_ => (bind_annotation == BindingAnnotation::REF, bind_annotation == BindingAnnotation::REF_MUT),
};
// Check if captures the closure will need conflict with borrows made in the scrutinee.
// TODO: check all the references made in the scrutinee expression. This will require interacting
// with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
if as_ref || as_mut {
let e = peel_hir_expr_while(cond_expr, |e| match e.kind {
ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
_ => None,
});
if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(local_id), .. })) = e.kind {
match some_captures.get(local_id)
.or_else(|| (method_sugg == "map_or_else").then_some(()).and_then(|_| none_captures.get(local_id)))
{
Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None,
Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None,
Some(CaptureKind::Ref(Mutability::Not)) | None => (),
}
}
}
return Some(OptionOccurence {
option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
method_sugg: method_sugg.to_string(),
some_expr: format!("|{capture_mut}{capture_name}| {}", Sugg::hir_with_macro_callsite(cx, some_body, "..")),
none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir_with_macro_callsite(cx, none_body, "..")),
});
}
}
None
}
fn try_get_inner_pat<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'tcx>) -> Option<&'tcx Pat<'tcx>> {
if let PatKind::TupleStruct(ref qpath, [inner_pat], ..) = pat.kind {
if is_lang_ctor(cx, qpath, OptionSome) || is_lang_ctor(cx, qpath, ResultOk) {
return Some(inner_pat);
}
}
None
}
/// If this expression is the option if let/else construct we're detecting, then
/// this function returns an `OptionOccurence` struct with details if
/// this construct is found, or None if this construct is not found.
fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurence> {
if let Some(higher::IfLet {
let_pat,
let_expr,
if_then,
if_else: Some(if_else),
}) = higher::IfLet::hir(cx, expr)
{
if !is_else_clause(cx.tcx, expr) {
return try_get_option_occurence(cx, let_pat, let_expr, if_then, if_else);
}
}
None
}
fn detect_option_match<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurence> {
if let ExprKind::Match(ex, arms, MatchSource::Normal) = expr.kind {
if let Some((let_pat, if_then, if_else)) = try_convert_match(cx, arms) {
return try_get_option_occurence(cx, let_pat, ex, if_then, if_else);
}
}
None
}
fn try_convert_match<'tcx>(
cx: &LateContext<'tcx>,
arms: &[Arm<'tcx>],
) -> Option<(&'tcx Pat<'tcx>, &'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
if arms.len() == 2 {
return if is_none_or_err_arm(cx, &arms[1]) {
Some((arms[0].pat, arms[0].body, arms[1].body))
} else if is_none_or_err_arm(cx, &arms[0]) {
Some((arms[1].pat, arms[1].body, arms[0].body))
} else {
None
};
}
None
}
fn is_none_or_err_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
match arm.pat.kind {
PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
PatKind::TupleStruct(ref qpath, [first_pat], _) => {
is_lang_ctor(cx, qpath, ResultErr) && matches!(first_pat.kind, PatKind::Wild)
},
PatKind::Wild => true,
_ => false,
}
}
impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
// Don't lint macros and constants
if expr.span.from_expansion() || in_constant(cx, expr.hir_id) {
return;
}
let detection = detect_option_if_let_else(cx, expr).or_else(|| detect_option_match(cx, expr));
if let Some(det) = detection {
span_lint_and_sugg(
cx,
OPTION_IF_LET_ELSE,
expr.span,
format!("use Option::{} instead of an if let/else", det.method_sugg).as_str(),
"try",
format!(
"{}.{}({}, {})",
det.option, det.method_sugg, det.none_expr, det.some_expr
),
Applicability::MaybeIncorrect,
);
}
}
}