263 lines
9.5 KiB
Rust
263 lines
9.5 KiB
Rust
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use crate::utils::{
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is_type_diagnostic_item, match_def_path, paths, peel_hir_expr_refs, peel_mid_ty_refs_is_mutable,
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snippet_with_applicability, span_lint_and_sugg,
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};
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use rustc_ast::util::parser::PREC_POSTFIX;
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use rustc_errors::Applicability;
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use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, Mutability, Pat, PatKind, Path, QPath};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_middle::lint::in_external_macro;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::symbol::{sym, Ident};
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declare_clippy_lint! {
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/// **What it does:** Checks for usages of `match` which could be implemented using `map`
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///
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/// **Why is this bad?** Using the `map` method is clearer and more concise.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// match Some(0) {
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/// Some(x) => Some(x + 1),
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/// None => None,
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/// };
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/// ```
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/// Use instead:
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/// ```rust
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/// Some(0).map(|x| x + 1);
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/// ```
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pub MANUAL_MAP,
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style,
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"reimplementation of `map`"
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}
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declare_lint_pass!(ManualMap => [MANUAL_MAP]);
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impl LateLintPass<'_> for ManualMap {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if in_external_macro(cx.sess(), expr.span) {
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return;
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}
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if let ExprKind::Match(scrutinee, [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }], _) =
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expr.kind
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{
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let (scrutinee_ty, ty_ref_count, ty_mutability) =
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peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee));
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if !is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type)
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|| !is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type)
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{
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return;
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}
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let (some_expr, some_pat, pat_ref_count, is_wild_none) =
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match (try_parse_pattern(cx, arm1.pat), try_parse_pattern(cx, arm2.pat)) {
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(Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count }))
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if is_none_expr(cx, arm1.body) =>
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{
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(arm2.body, pattern, ref_count, true)
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},
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(Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count }))
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if is_none_expr(cx, arm1.body) =>
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{
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(arm2.body, pattern, ref_count, false)
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},
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(Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild))
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if is_none_expr(cx, arm2.body) =>
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{
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(arm1.body, pattern, ref_count, true)
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},
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(Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None))
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if is_none_expr(cx, arm2.body) =>
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{
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(arm1.body, pattern, ref_count, false)
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},
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_ => return,
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};
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// Top level or patterns aren't allowed in closures.
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if matches!(some_pat.kind, PatKind::Or(_)) {
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return;
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}
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let some_expr = match get_some_expr(cx, some_expr) {
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Some(expr) => expr,
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None => return,
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};
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// Determine which binding mode to use.
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let explicit_ref = some_pat.contains_explicit_ref_binding();
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let binding_mutability = explicit_ref.or(if ty_ref_count != pat_ref_count {
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Some(ty_mutability)
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} else {
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None
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});
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let as_ref_str = match binding_mutability {
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Some(Mutability::Mut) => ".as_mut()",
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Some(Mutability::Not) => ".as_ref()",
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None => "",
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};
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let mut app = Applicability::MachineApplicable;
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// Remove address-of expressions from the scrutinee. `as_ref` will be called,
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// the type is copyable, or the option is being passed by value.
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let scrutinee = peel_hir_expr_refs(scrutinee).0;
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let scrutinee_str = snippet_with_applicability(cx, scrutinee.span, "_", &mut app);
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let scrutinee_str = if expr.precedence().order() < PREC_POSTFIX {
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// Parens are needed to chain method calls.
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format!("({})", scrutinee_str)
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} else {
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scrutinee_str.into()
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};
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let body_str = if let PatKind::Binding(annotation, _, some_binding, None) = some_pat.kind {
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if let Some(func) = can_pass_as_func(cx, some_binding, some_expr) {
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snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
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} else {
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// `ref` and `ref mut` annotations were handled earlier.
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let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
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"mut "
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} else {
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""
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};
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format!(
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"|{}{}| {}",
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annotation,
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some_binding,
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snippet_with_applicability(cx, some_expr.span, "..", &mut app)
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)
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}
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} else if !is_wild_none && explicit_ref.is_none() {
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// TODO: handle explicit reference annotations.
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format!(
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"|{}| {}",
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snippet_with_applicability(cx, some_pat.span, "..", &mut app),
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snippet_with_applicability(cx, some_expr.span, "..", &mut app)
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)
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} else {
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// Refutable bindings and mixed reference annotations can't be handled by `map`.
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return;
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};
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span_lint_and_sugg(
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cx,
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MANUAL_MAP,
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expr.span,
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"manual implementation of `Option::map`",
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"try this",
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format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str),
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app,
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);
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}
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}
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}
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// Checks whether the expression could be passed as a function, or whether a closure is needed.
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// Returns the function to be passed to `map` if it exists.
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fn can_pass_as_func(cx: &LateContext<'tcx>, binding: Ident, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
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match expr.kind {
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ExprKind::Call(func, [arg])
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if matches!(arg.kind,
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ExprKind::Path(QPath::Resolved(None, Path { segments: [path], ..}))
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if path.ident == binding
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) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
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{
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Some(func)
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},
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_ => None,
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}
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}
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enum OptionPat<'a> {
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Wild,
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None,
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Some {
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// The pattern contained in the `Some` tuple.
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pattern: &'a Pat<'a>,
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// The number of references before the `Some` tuple.
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// e.g. `&&Some(_)` has a ref count of 2.
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ref_count: usize,
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},
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}
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// Try to parse into a recognized `Option` pattern.
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// i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
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fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) -> Option<OptionPat<'tcx>> {
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fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize) -> Option<OptionPat<'tcx>> {
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match pat.kind {
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PatKind::Wild => Some(OptionPat::Wild),
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PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1),
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PatKind::Path(QPath::Resolved(None, path))
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if path
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.res
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.opt_def_id()
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.map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)) =>
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{
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Some(OptionPat::None)
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},
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PatKind::TupleStruct(QPath::Resolved(None, path), [pattern], _)
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if path
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.res
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.opt_def_id()
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.map_or(false, |id| match_def_path(cx, id, &paths::OPTION_SOME)) =>
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{
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Some(OptionPat::Some { pattern, ref_count })
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},
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_ => None,
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}
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}
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f(cx, pat, 0)
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}
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// Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
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fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
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// TODO: Allow more complex expressions.
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match expr.kind {
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ExprKind::Call(
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Expr {
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kind: ExprKind::Path(QPath::Resolved(None, path)),
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..
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},
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[arg],
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) => {
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if match_def_path(cx, path.res.opt_def_id()?, &paths::OPTION_SOME) {
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Some(arg)
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} else {
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None
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}
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},
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ExprKind::Block(
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Block {
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stmts: [],
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expr: Some(expr),
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..
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},
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_,
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) => get_some_expr(cx, expr),
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_ => None,
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}
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}
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// Checks for the `None` value.
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fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
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match expr.kind {
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ExprKind::Path(QPath::Resolved(None, path)) => path
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.res
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.opt_def_id()
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.map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)),
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ExprKind::Block(
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Block {
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stmts: [],
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expr: Some(expr),
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..
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},
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_,
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) => is_none_expr(cx, expr),
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_ => false,
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}
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}
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