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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,172 @@ | ||
| use crate::utils::visitors::LocalUsedVisitor; | ||
| use crate::utils::{span_lint_and_then, SpanlessEq}; | ||
| use if_chain::if_chain; | ||
| use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res}; | ||
| use rustc_hir::{Arm, Expr, ExprKind, Guard, HirId, Pat, PatKind, QPath, StmtKind}; | ||
| use rustc_lint::{LateContext, LateLintPass}; | ||
| use rustc_middle::ty::{DefIdTree, TyCtxt}; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
| use rustc_span::{MultiSpan, Span}; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// **What it does:** Finds nested `match` or `if let` expressions where the patterns may be "collapsed" together | ||
| /// without adding any branches. | ||
| /// | ||
| /// Note that this lint is not intended to find _all_ cases where nested match patterns can be merged, but only | ||
| /// cases where merging would most likely make the code more readable. | ||
| /// | ||
| /// **Why is this bad?** It is unnecessarily verbose and complex. | ||
| /// | ||
| /// **Known problems:** None. | ||
| /// | ||
| /// **Example:** | ||
| /// | ||
| /// ```rust | ||
| /// fn func(opt: Option<Result<u64, String>>) { | ||
| /// let n = match opt { | ||
| /// Some(n) => match n { | ||
| /// Ok(n) => n, | ||
| /// _ => return, | ||
| /// } | ||
| /// None => return, | ||
| /// }; | ||
| /// } | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```rust | ||
| /// fn func(opt: Option<Result<u64, String>>) { | ||
| /// let n = match opt { | ||
| /// Some(Ok(n)) => n, | ||
| /// _ => return, | ||
| /// }; | ||
| /// } | ||
| /// ``` | ||
| pub COLLAPSIBLE_MATCH, | ||
| style, | ||
| "Nested `match` or `if let` expressions where the patterns may be \"collapsed\" together." | ||
| } | ||
|
|
||
| declare_lint_pass!(CollapsibleMatch => [COLLAPSIBLE_MATCH]); | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for CollapsibleMatch { | ||
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) { | ||
| if let ExprKind::Match(_expr, arms, _source) = expr.kind { | ||
| if let Some(wild_arm) = arms.iter().rfind(|arm| arm_is_wild_like(arm, cx.tcx)) { | ||
| for arm in arms { | ||
| check_arm(arm, wild_arm, cx); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn check_arm(arm: &Arm<'_>, wild_outer_arm: &Arm<'_>, cx: &LateContext<'_>) { | ||
| if_chain! { | ||
| let expr = strip_singleton_blocks(arm.body); | ||
| if let ExprKind::Match(expr_in, arms_inner, _) = expr.kind; | ||
| // the outer arm pattern and the inner match | ||
| if expr_in.span.ctxt() == arm.pat.span.ctxt(); | ||
| // there must be no more than two arms in the inner match for this lint | ||
| if arms_inner.len() == 2; | ||
| // no if guards on the inner match | ||
| if arms_inner.iter().all(|arm| arm.guard.is_none()); | ||
| // match expression must be a local binding | ||
| // match <local> { .. } | ||
| if let ExprKind::Path(QPath::Resolved(None, path)) = expr_in.kind; | ||
| if let Res::Local(binding_id) = path.res; | ||
| // one of the branches must be "wild-like" | ||
| if let Some(wild_inner_arm_idx) = arms_inner.iter().rposition(|arm_inner| arm_is_wild_like(arm_inner, cx.tcx)); | ||
| let (wild_inner_arm, non_wild_inner_arm) = | ||
| (&arms_inner[wild_inner_arm_idx], &arms_inner[1 - wild_inner_arm_idx]); | ||
| if !pat_contains_or(non_wild_inner_arm.pat); | ||
| // the binding must come from the pattern of the containing match arm | ||
| // ..<local>.. => match <local> { .. } | ||
| if let Some(binding_span) = find_pat_binding(arm.pat, binding_id); | ||
| // the "wild-like" branches must be equal | ||
| if SpanlessEq::new(cx).eq_expr(wild_inner_arm.body, wild_outer_arm.body); | ||
| // the binding must not be used in the if guard | ||
| if !matches!(arm.guard, Some(Guard::If(guard)) if LocalUsedVisitor::new(binding_id).check_expr(guard)); | ||
| // ...or anywhere in the inner match | ||
| if !arms_inner.iter().any(|arm| LocalUsedVisitor::new(binding_id).check_arm(arm)); | ||
| then { | ||
| span_lint_and_then( | ||
| cx, | ||
| COLLAPSIBLE_MATCH, | ||
| expr.span, | ||
| "Unnecessary nested match", | ||
| |diag| { | ||
| let mut help_span = MultiSpan::from_spans(vec![binding_span, non_wild_inner_arm.pat.span]); | ||
| help_span.push_span_label(binding_span, "Replace this binding".into()); | ||
| help_span.push_span_label(non_wild_inner_arm.pat.span, "with this pattern".into()); | ||
| diag.span_help(help_span, "The outer pattern can be modified to include the inner pattern."); | ||
| }, | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn strip_singleton_blocks<'hir>(mut expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> { | ||
| while let ExprKind::Block(block, _) = expr.kind { | ||
| match (block.stmts, block.expr) { | ||
| ([stmt], None) => match stmt.kind { | ||
| StmtKind::Expr(e) | StmtKind::Semi(e) => expr = e, | ||
| _ => break, | ||
| }, | ||
| ([], Some(e)) => expr = e, | ||
| _ => break, | ||
| } | ||
| } | ||
| expr | ||
| } | ||
|
|
||
| /// A "wild-like" pattern is wild ("_") or `None`. | ||
| /// For this lint to apply, both the outer and inner match expressions | ||
| /// must have "wild-like" branches that can be combined. | ||
| fn arm_is_wild_like(arm: &Arm<'_>, tcx: TyCtxt<'_>) -> bool { | ||
| if arm.guard.is_some() { | ||
| return false; | ||
| } | ||
| match arm.pat.kind { | ||
| PatKind::Binding(..) | PatKind::Wild => true, | ||
| PatKind::Path(QPath::Resolved(None, path)) if is_none_ctor(path.res, tcx) => true, | ||
| _ => false, | ||
| } | ||
| } | ||
|
|
||
| fn find_pat_binding(pat: &Pat<'_>, hir_id: HirId) -> Option<Span> { | ||
| let mut span = None; | ||
| 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 | ||
| }, | ||
| _ => true, | ||
| }); | ||
| span | ||
| } | ||
|
|
||
| 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 | ||
| } | ||
|
|
||
| fn is_none_ctor(res: Res, tcx: TyCtxt<'_>) -> bool { | ||
| if let Some(none_id) = tcx.lang_items().option_none_variant() { | ||
| if let Res::Def(DefKind::Ctor(CtorOf::Variant, CtorKind::Const), id) = res { | ||
| if let Some(variant_id) = tcx.parent(id) { | ||
| return variant_id == none_id; | ||
| } | ||
| } | ||
| } | ||
| false | ||
| } |
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