[`cmp_owned`]: https://rust-lang.github.io/rust-clippy/master/index.html#cmp_owned
[`cognitive_complexity`]: https://rust-lang.github.io/rust-clippy/master/index.html#cognitive_complexity
[`collapsible_if`]: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_if
+[`collapsible_match`]: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match
[`comparison_chain`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_chain
[`comparison_to_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_to_empty
[`copy_iterator`]: https://rust-lang.github.io/rust-clippy/master/index.html#copy_iterator
--- /dev/null
+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
+}
mod checked_conversions;
mod cognitive_complexity;
mod collapsible_if;
+mod collapsible_match;
mod comparison_chain;
mod copies;
mod copy_iterator;
&checked_conversions::CHECKED_CONVERSIONS,
&cognitive_complexity::COGNITIVE_COMPLEXITY,
&collapsible_if::COLLAPSIBLE_IF,
+ &collapsible_match::COLLAPSIBLE_MATCH,
&comparison_chain::COMPARISON_CHAIN,
&copies::IFS_SAME_COND,
&copies::IF_SAME_THEN_ELSE,
store.register_late_pass(|| box len_zero::LenZero);
store.register_late_pass(|| box attrs::Attributes);
store.register_late_pass(|| box blocks_in_if_conditions::BlocksInIfConditions);
+ store.register_late_pass(|| box collapsible_match::CollapsibleMatch);
store.register_late_pass(|| box unicode::Unicode);
store.register_late_pass(|| box unit_return_expecting_ord::UnitReturnExpectingOrd);
store.register_late_pass(|| box strings::StringAdd);
LintId::of(&booleans::NONMINIMAL_BOOL),
LintId::of(&bytecount::NAIVE_BYTECOUNT),
LintId::of(&collapsible_if::COLLAPSIBLE_IF),
+ LintId::of(&collapsible_match::COLLAPSIBLE_MATCH),
LintId::of(&comparison_chain::COMPARISON_CHAIN),
LintId::of(&copies::IFS_SAME_COND),
LintId::of(&copies::IF_SAME_THEN_ELSE),
LintId::of(&blacklisted_name::BLACKLISTED_NAME),
LintId::of(&blocks_in_if_conditions::BLOCKS_IN_IF_CONDITIONS),
LintId::of(&collapsible_if::COLLAPSIBLE_IF),
+ LintId::of(&collapsible_match::COLLAPSIBLE_MATCH),
LintId::of(&comparison_chain::COMPARISON_CHAIN),
LintId::of(&default::FIELD_REASSIGN_WITH_DEFAULT),
LintId::of(&doc::MISSING_SAFETY_DOC),
--- /dev/null
+#![warn(clippy::collapsible_match)]
+#![allow(clippy::needless_return, clippy::no_effect, clippy::single_match)]
+
+fn lint_cases(opt_opt: Option<Option<u32>>, res_opt: Result<Option<u32>, String>) {
+ // match without block
+ match res_opt {
+ Ok(val) => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ _ => return,
+ }
+
+ // match with block
+ match res_opt {
+ Ok(val) => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ _ => return,
+ }
+
+ // if let, if let
+ if let Ok(val) = res_opt {
+ if let Some(n) = val {
+ take(n);
+ }
+ }
+
+ // if let else, if let else
+ if let Ok(val) = res_opt {
+ if let Some(n) = val {
+ take(n);
+ } else {
+ return;
+ }
+ } else {
+ return;
+ }
+
+ // if let, match
+ if let Ok(val) = res_opt {
+ match val {
+ Some(n) => foo(n),
+ _ => (),
+ }
+ }
+
+ // match, if let
+ match res_opt {
+ Ok(val) => {
+ if let Some(n) = val {
+ take(n);
+ }
+ },
+ _ => {},
+ }
+
+ // if let else, match
+ if let Ok(val) = res_opt {
+ match val {
+ Some(n) => foo(n),
+ _ => return,
+ }
+ } else {
+ return;
+ }
+
+ // match, if let else
+ match res_opt {
+ Ok(val) => {
+ if let Some(n) = val {
+ take(n);
+ } else {
+ return;
+ }
+ },
+ _ => return,
+ }
+
+ // None in inner match same as outer wild branch
+ match res_opt {
+ Ok(val) => match val {
+ Some(n) => foo(n),
+ None => return,
+ },
+ _ => return,
+ }
+
+ // None in outer match same as inner wild branch
+ match opt_opt {
+ Some(val) => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ None => return,
+ }
+
+ // if guards on outer match
+ {
+ match res_opt {
+ Ok(val) if make() => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ _ => return,
+ }
+ match res_opt {
+ Ok(val) => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ _ if make() => return,
+ _ => return,
+ }
+ }
+
+ // macro
+ {
+ macro_rules! mac {
+ ($outer:expr => $pat:pat, $e:expr => $inner_pat:pat, $then:expr) => {
+ match $outer {
+ $pat => match $e {
+ $inner_pat => $then,
+ _ => return,
+ },
+ _ => return,
+ }
+ };
+ }
+ // Lint this since the patterns are not defined by the macro.
+ // Allows the lint to work on if_chain! for example.
+ // Fixing the lint requires knowledge of the specific macro, but we optimistically assume that
+ // there is still a better way to write this.
+ mac!(res_opt => Ok(val), val => Some(n), foo(n));
+ }
+}
+
+fn negative_cases(res_opt: Result<Option<u32>, String>, res_res: Result<Result<u32, String>, String>) {
+ // no wild pattern in outer match
+ match res_opt {
+ Ok(val) => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ Err(_) => return,
+ }
+
+ // inner branch is not wild or None
+ match res_res {
+ Ok(val) => match val {
+ Ok(n) => foo(n),
+ Err(_) => return,
+ },
+ _ => return,
+ }
+
+ // statement before inner match
+ match res_opt {
+ Ok(val) => {
+ "hi buddy";
+ match val {
+ Some(n) => foo(n),
+ _ => return,
+ }
+ },
+ _ => return,
+ }
+
+ // statement after inner match
+ match res_opt {
+ Ok(val) => {
+ match val {
+ Some(n) => foo(n),
+ _ => return,
+ }
+ "hi buddy";
+ },
+ _ => return,
+ }
+
+ // wild branches do not match
+ match res_opt {
+ Ok(val) => match val {
+ Some(n) => foo(n),
+ _ => {
+ "sup";
+ return;
+ },
+ },
+ _ => return,
+ }
+
+ // binding used in if guard
+ match res_opt {
+ Ok(val) if val.is_some() => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ _ => return,
+ }
+
+ // binding used in inner match body
+ match res_opt {
+ Ok(val) => match val {
+ Some(_) => take(val),
+ _ => return,
+ },
+ _ => return,
+ }
+
+ // if guard on inner match
+ {
+ match res_opt {
+ Ok(val) => match val {
+ Some(n) if make() => foo(n),
+ _ => return,
+ },
+ _ => return,
+ }
+ match res_opt {
+ Ok(val) => match val {
+ _ => make(),
+ _ if make() => return,
+ },
+ _ => return,
+ }
+ }
+
+ // differing macro contexts
+ {
+ macro_rules! mac {
+ ($val:ident) => {
+ match $val {
+ Some(n) => foo(n),
+ _ => return,
+ }
+ };
+ }
+ match res_opt {
+ Ok(val) => mac!(val),
+ _ => return,
+ }
+ }
+
+ // OR pattern
+ enum E<T> {
+ A(T),
+ B(T),
+ C(T),
+ };
+ match make::<E<Option<u32>>>() {
+ E::A(val) | E::B(val) => match val {
+ Some(n) => foo(n),
+ _ => return,
+ },
+ _ => return,
+ }
+ match make::<Option<E<u32>>>() {
+ Some(val) => match val {
+ E::A(val) | E::B(val) => foo(val),
+ _ => return,
+ },
+ _ => return,
+ }
+}
+
+fn make<T>() -> T {
+ unimplemented!()
+}
+
+fn foo<T, U>(t: T) -> U {
+ unimplemented!()
+}
+
+fn take<T>(t: T) {}
+
+fn main() {}
--- /dev/null
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:7:20
+ |
+LL | Ok(val) => match val {
+ | ____________________^
+LL | | Some(n) => foo(n),
+LL | | _ => return,
+LL | | },
+ | |_________^
+ |
+ = note: `-D clippy::collapsible-match` implied by `-D warnings`
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:7:12
+ |
+LL | Ok(val) => match val {
+ | ^^^ Replace this binding
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:16:20
+ |
+LL | Ok(val) => match val {
+ | ____________________^
+LL | | Some(n) => foo(n),
+LL | | _ => return,
+LL | | },
+ | |_________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:16:12
+ |
+LL | Ok(val) => match val {
+ | ^^^ Replace this binding
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:25:9
+ |
+LL | / if let Some(n) = val {
+LL | | take(n);
+LL | | }
+ | |_________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:24:15
+ |
+LL | if let Ok(val) = res_opt {
+ | ^^^ Replace this binding
+LL | if let Some(n) = val {
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:32:9
+ |
+LL | / if let Some(n) = val {
+LL | | take(n);
+LL | | } else {
+LL | | return;
+LL | | }
+ | |_________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:31:15
+ |
+LL | if let Ok(val) = res_opt {
+ | ^^^ Replace this binding
+LL | if let Some(n) = val {
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:43:9
+ |
+LL | / match val {
+LL | | Some(n) => foo(n),
+LL | | _ => (),
+LL | | }
+ | |_________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:42:15
+ |
+LL | if let Ok(val) = res_opt {
+ | ^^^ Replace this binding
+LL | match val {
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:52:13
+ |
+LL | / if let Some(n) = val {
+LL | | take(n);
+LL | | }
+ | |_____________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:51:12
+ |
+LL | Ok(val) => {
+ | ^^^ Replace this binding
+LL | if let Some(n) = val {
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:61:9
+ |
+LL | / match val {
+LL | | Some(n) => foo(n),
+LL | | _ => return,
+LL | | }
+ | |_________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:60:15
+ |
+LL | if let Ok(val) = res_opt {
+ | ^^^ Replace this binding
+LL | match val {
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:72:13
+ |
+LL | / if let Some(n) = val {
+LL | | take(n);
+LL | | } else {
+LL | | return;
+LL | | }
+ | |_____________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:71:12
+ |
+LL | Ok(val) => {
+ | ^^^ Replace this binding
+LL | if let Some(n) = val {
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:83:20
+ |
+LL | Ok(val) => match val {
+ | ____________________^
+LL | | Some(n) => foo(n),
+LL | | None => return,
+LL | | },
+ | |_________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:83:12
+ |
+LL | Ok(val) => match val {
+ | ^^^ Replace this binding
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:92:22
+ |
+LL | Some(val) => match val {
+ | ______________________^
+LL | | Some(n) => foo(n),
+LL | | _ => return,
+LL | | },
+ | |_________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:92:14
+ |
+LL | Some(val) => match val {
+ | ^^^ Replace this binding
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:102:34
+ |
+LL | Ok(val) if make() => match val {
+ | __________________________________^
+LL | | Some(n) => foo(n),
+LL | | _ => return,
+LL | | },
+ | |_____________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:102:16
+ |
+LL | Ok(val) if make() => match val {
+ | ^^^ Replace this binding
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:109:24
+ |
+LL | Ok(val) => match val {
+ | ________________________^
+LL | | Some(n) => foo(n),
+LL | | _ => return,
+LL | | },
+ | |_____________^
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:109:16
+ |
+LL | Ok(val) => match val {
+ | ^^^ Replace this binding
+LL | Some(n) => foo(n),
+ | ^^^^^^^ with this pattern
+
+error: Unnecessary nested match
+ --> $DIR/collapsible_match.rs:123:29
+ |
+LL | $pat => match $e {
+ | _____________________________^
+LL | | $inner_pat => $then,
+LL | | _ => return,
+LL | | },
+ | |_____________________^
+...
+LL | mac!(res_opt => Ok(val), val => Some(n), foo(n));
+ | ------------------------------------------------- in this macro invocation
+ |
+help: The outer pattern can be modified to include the inner pattern.
+ --> $DIR/collapsible_match.rs:135:28
+ |
+LL | mac!(res_opt => Ok(val), val => Some(n), foo(n));
+ | ^^^ ^^^^^^^ with this pattern
+ | |
+ | Replace this binding
+ = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 13 previous errors
+
projects / rust.git / commitdiff