213 lines
8.4 KiB
Rust
213 lines
8.4 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::higher;
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use clippy_utils::sugg::Sugg;
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use clippy_utils::ty::is_type_diagnostic_item;
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use clippy_utils::{
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can_move_expr_to_closure, eager_or_lazy, in_constant, in_macro, is_else_clause, is_lang_ctor, peel_hir_expr_while,
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CaptureKind,
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};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::LangItem::OptionSome;
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use rustc_hir::{def::Res, BindingAnnotation, Block, Expr, ExprKind, Mutability, PatKind, Path, QPath, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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/// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
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/// idiomatically done with `Option::map_or` (if the else bit is a pure
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/// expression) or `Option::map_or_else` (if the else bit is an impure
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/// expression).
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///
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/// ### Why is this bad?
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/// Using the dedicated functions of the Option type is clearer and
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/// more concise than an `if let` expression.
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///
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/// ### Known problems
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/// This lint uses a deliberately conservative metric for checking
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/// if the inside of either body contains breaks or continues which will
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/// cause it to not suggest a fix if either block contains a loop with
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/// continues or breaks contained within the loop.
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///
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/// ### Example
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/// ```rust
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/// # let optional: Option<u32> = Some(0);
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/// # fn do_complicated_function() -> u32 { 5 };
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/// let _ = if let Some(foo) = optional {
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/// foo
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/// } else {
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/// 5
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/// };
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/// let _ = if let Some(foo) = optional {
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/// foo
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/// } else {
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/// let y = do_complicated_function();
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/// y*y
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/// };
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/// ```
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///
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/// should be
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///
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/// ```rust
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/// # let optional: Option<u32> = Some(0);
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/// # fn do_complicated_function() -> u32 { 5 };
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/// let _ = optional.map_or(5, |foo| foo);
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/// let _ = optional.map_or_else(||{
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/// let y = do_complicated_function();
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/// y*y
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/// }, |foo| foo);
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/// ```
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pub OPTION_IF_LET_ELSE,
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nursery,
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"reimplementation of Option::map_or"
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}
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declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
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/// Returns true iff the given expression is the result of calling `Result::ok`
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fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
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if let ExprKind::MethodCall(path, _, &[ref receiver], _) = &expr.kind {
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path.ident.name.as_str() == "ok"
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&& is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::Result)
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} else {
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false
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}
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}
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/// A struct containing information about occurrences of the
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/// `if let Some(..) = .. else` construct that this lint detects.
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struct OptionIfLetElseOccurence {
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option: String,
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method_sugg: String,
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some_expr: String,
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none_expr: String,
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}
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/// Extracts the body of a given arm. If the arm contains only an expression,
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/// then it returns the expression. Otherwise, it returns the entire block
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fn extract_body_from_expr<'a>(expr: &'a Expr<'a>) -> Option<&'a Expr<'a>> {
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if let ExprKind::Block(
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Block {
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stmts: block_stmts,
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expr: Some(block_expr),
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..
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},
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_,
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) = expr.kind
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{
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if let [] = block_stmts {
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Some(block_expr)
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} else {
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Some(expr)
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}
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} else {
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None
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}
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}
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fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
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format!(
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"{}{}",
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Sugg::hir(cx, cond_expr, "..").maybe_par(),
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if as_mut {
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".as_mut()"
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} else if as_ref {
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".as_ref()"
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} else {
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""
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}
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)
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}
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/// If this expression is the option if let/else construct we're detecting, then
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/// this function returns an `OptionIfLetElseOccurence` struct with details if
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/// this construct is found, or None if this construct is not found.
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fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionIfLetElseOccurence> {
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if_chain! {
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if !in_macro(expr.span); // Don't lint macros, because it behaves weirdly
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if !in_constant(cx, expr.hir_id);
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if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
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= higher::IfLet::hir(cx, expr);
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if !is_else_clause(cx.tcx, expr);
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if !is_result_ok(cx, let_expr); // Don't lint on Result::ok because a different lint does it already
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if let PatKind::TupleStruct(struct_qpath, [inner_pat], _) = &let_pat.kind;
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if is_lang_ctor(cx, struct_qpath, OptionSome);
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if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
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if let Some(some_captures) = can_move_expr_to_closure(cx, if_then);
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if let Some(none_captures) = can_move_expr_to_closure(cx, if_else);
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if some_captures
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.iter()
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.filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
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.all(|(x, y)| x.is_imm_ref() && y.is_imm_ref());
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then {
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let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
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let some_body = extract_body_from_expr(if_then)?;
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let none_body = extract_body_from_expr(if_else)?;
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let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) {
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"map_or"
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} else {
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"map_or_else"
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};
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let capture_name = id.name.to_ident_string();
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let (as_ref, as_mut) = match &let_expr.kind {
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ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
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ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
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_ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
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};
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let cond_expr = match let_expr.kind {
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// Pointer dereferencing happens automatically, so we can omit it in the suggestion
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ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
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_ => let_expr,
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};
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// Check if captures the closure will need conflict with borrows made in the scrutinee.
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// TODO: check all the references made in the scrutinee expression. This will require interacting
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// with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
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if as_ref || as_mut {
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let e = peel_hir_expr_while(cond_expr, |e| match e.kind {
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ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
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_ => None,
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});
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if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(local_id), .. })) = e.kind {
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match some_captures.get(local_id)
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.or_else(|| (method_sugg == "map_or_else").then(|| ()).and_then(|_| none_captures.get(local_id)))
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{
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Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None,
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Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None,
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Some(CaptureKind::Ref(Mutability::Not)) | None => (),
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}
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}
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}
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Some(OptionIfLetElseOccurence {
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option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
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method_sugg: method_sugg.to_string(),
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some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
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none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
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})
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} else {
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None
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}
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}
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}
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impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
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if let Some(detection) = detect_option_if_let_else(cx, expr) {
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span_lint_and_sugg(
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cx,
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OPTION_IF_LET_ELSE,
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expr.span,
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format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
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"try",
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format!(
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"{}.{}({}, {})",
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detection.option, detection.method_sugg, detection.none_expr, detection.some_expr,
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),
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Applicability::MaybeIncorrect,
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);
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}
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}
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}
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