222 lines
7.8 KiB
Rust
222 lines
7.8 KiB
Rust
use super::NEEDLESS_MATCH;
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use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::source::snippet_with_applicability;
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use clippy_utils::ty::{is_type_diagnostic_item, same_type_and_consts};
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use clippy_utils::{
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eq_expr_value, get_parent_expr_for_hir, get_parent_node, higher, is_else_clause, is_res_lang_ctor, over, path_res,
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peel_blocks_with_stmt,
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};
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use rustc_errors::Applicability;
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use rustc_hir::LangItem::OptionNone;
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use rustc_hir::{Arm, BindingAnnotation, ByRef, Expr, ExprKind, FnRetTy, Guard, Node, Pat, PatKind, Path, QPath};
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use rustc_hir_analysis::hir_ty_to_ty;
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use rustc_lint::LateContext;
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use rustc_span::sym;
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pub(crate) fn check_match(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
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if arms.len() > 1 && expr_ty_matches_p_ty(cx, ex, expr) && check_all_arms(cx, ex, arms) {
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let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
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cx,
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NEEDLESS_MATCH,
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expr.span,
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"this match expression is unnecessary",
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"replace it with",
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snippet_with_applicability(cx, ex.span, "..", &mut applicability).to_string(),
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applicability,
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);
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}
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}
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/// Check for nop `if let` expression that assembled as unnecessary match
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///
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/// ```rust,ignore
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/// if let Some(a) = option {
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/// Some(a)
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/// } else {
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/// None
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/// }
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/// ```
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/// OR
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/// ```rust,ignore
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/// if let SomeEnum::A = some_enum {
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/// SomeEnum::A
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/// } else if let SomeEnum::B = some_enum {
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/// SomeEnum::B
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/// } else {
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/// some_enum
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/// }
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/// ```
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pub(crate) fn check_if_let<'tcx>(cx: &LateContext<'tcx>, ex: &Expr<'_>, if_let: &higher::IfLet<'tcx>) {
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if !is_else_clause(cx.tcx, ex) && expr_ty_matches_p_ty(cx, if_let.let_expr, ex) && check_if_let_inner(cx, if_let) {
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let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
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cx,
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NEEDLESS_MATCH,
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ex.span,
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"this if-let expression is unnecessary",
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"replace it with",
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snippet_with_applicability(cx, if_let.let_expr.span, "..", &mut applicability).to_string(),
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applicability,
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);
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}
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}
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fn check_all_arms(cx: &LateContext<'_>, match_expr: &Expr<'_>, arms: &[Arm<'_>]) -> bool {
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for arm in arms {
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let arm_expr = peel_blocks_with_stmt(arm.body);
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if let Some(guard_expr) = &arm.guard {
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match guard_expr {
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// gives up if `pat if expr` can have side effects
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Guard::If(if_cond) => {
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if if_cond.can_have_side_effects() {
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return false;
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}
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},
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// gives up `pat if let ...` arm
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Guard::IfLet(_) => {
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return false;
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},
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};
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}
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if let PatKind::Wild = arm.pat.kind {
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if !eq_expr_value(cx, match_expr, strip_return(arm_expr)) {
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return false;
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}
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} else if !pat_same_as_expr(arm.pat, arm_expr) {
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return false;
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}
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}
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true
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}
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fn check_if_let_inner(cx: &LateContext<'_>, if_let: &higher::IfLet<'_>) -> bool {
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if let Some(if_else) = if_let.if_else {
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if !pat_same_as_expr(if_let.let_pat, peel_blocks_with_stmt(if_let.if_then)) {
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return false;
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}
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// Recursively check for each `else if let` phrase,
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if let Some(ref nested_if_let) = higher::IfLet::hir(cx, if_else) {
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return check_if_let_inner(cx, nested_if_let);
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}
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if matches!(if_else.kind, ExprKind::Block(..)) {
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let else_expr = peel_blocks_with_stmt(if_else);
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if matches!(else_expr.kind, ExprKind::Block(..)) {
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return false;
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}
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let ret = strip_return(else_expr);
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let let_expr_ty = cx.typeck_results().expr_ty(if_let.let_expr);
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if is_type_diagnostic_item(cx, let_expr_ty, sym::Option) {
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return is_res_lang_ctor(cx, path_res(cx, ret), OptionNone) || eq_expr_value(cx, if_let.let_expr, ret);
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}
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return eq_expr_value(cx, if_let.let_expr, ret);
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}
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}
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false
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}
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/// Strip `return` keyword if the expression type is `ExprKind::Ret`.
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fn strip_return<'hir>(expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> {
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if let ExprKind::Ret(Some(ret)) = expr.kind {
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ret
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} else {
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expr
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}
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}
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/// Manually check for coercion casting by checking if the type of the match operand or let expr
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/// differs with the assigned local variable or the function return type.
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fn expr_ty_matches_p_ty(cx: &LateContext<'_>, expr: &Expr<'_>, p_expr: &Expr<'_>) -> bool {
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if let Some(p_node) = get_parent_node(cx.tcx, p_expr.hir_id) {
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match p_node {
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// Compare match_expr ty with local in `let local = match match_expr {..}`
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Node::Local(local) => {
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let results = cx.typeck_results();
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return same_type_and_consts(results.node_type(local.hir_id), results.expr_ty(expr));
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},
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// compare match_expr ty with RetTy in `fn foo() -> RetTy`
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Node::Item(..) => {
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if let Some(fn_decl) = p_node.fn_decl() {
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if let FnRetTy::Return(ret_ty) = fn_decl.output {
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return same_type_and_consts(hir_ty_to_ty(cx.tcx, ret_ty), cx.typeck_results().expr_ty(expr));
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}
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}
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},
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// check the parent expr for this whole block `{ match match_expr {..} }`
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Node::Block(block) => {
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if let Some(block_parent_expr) = get_parent_expr_for_hir(cx, block.hir_id) {
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return expr_ty_matches_p_ty(cx, expr, block_parent_expr);
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}
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},
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// recursively call on `if xxx {..}` etc.
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Node::Expr(p_expr) => {
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return expr_ty_matches_p_ty(cx, expr, p_expr);
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},
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_ => {},
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}
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}
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false
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}
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fn pat_same_as_expr(pat: &Pat<'_>, expr: &Expr<'_>) -> bool {
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let expr = strip_return(expr);
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match (&pat.kind, &expr.kind) {
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// Example: `Some(val) => Some(val)`
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(PatKind::TupleStruct(QPath::Resolved(_, path), tuple_params, _), ExprKind::Call(call_expr, call_params)) => {
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if let ExprKind::Path(QPath::Resolved(_, call_path)) = call_expr.kind {
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return over(path.segments, call_path.segments, |pat_seg, call_seg| {
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pat_seg.ident.name == call_seg.ident.name
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}) && same_non_ref_symbols(tuple_params, call_params);
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}
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},
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// Example: `val => val`
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(
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PatKind::Binding(annot, _, pat_ident, _),
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ExprKind::Path(QPath::Resolved(
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_,
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Path {
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segments: [first_seg, ..],
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..
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},
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)),
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) => {
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return !matches!(annot, BindingAnnotation(ByRef::Yes, _)) && pat_ident.name == first_seg.ident.name;
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},
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// Example: `Custom::TypeA => Custom::TypeB`, or `None => None`
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(PatKind::Path(QPath::Resolved(_, p_path)), ExprKind::Path(QPath::Resolved(_, e_path))) => {
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return over(p_path.segments, e_path.segments, |p_seg, e_seg| {
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p_seg.ident.name == e_seg.ident.name
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});
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},
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// Example: `5 => 5`
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(PatKind::Lit(pat_lit_expr), ExprKind::Lit(expr_spanned)) => {
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if let ExprKind::Lit(pat_spanned) = &pat_lit_expr.kind {
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return pat_spanned.node == expr_spanned.node;
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}
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},
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_ => {},
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}
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false
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}
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fn same_non_ref_symbols(pats: &[Pat<'_>], exprs: &[Expr<'_>]) -> bool {
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if pats.len() != exprs.len() {
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return false;
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}
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for i in 0..pats.len() {
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if !pat_same_as_expr(&pats[i], &exprs[i]) {
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return false;
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}
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}
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true
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}
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