| use rustc::hir::*; |
| use rustc::lint::*; |
| use rustc::middle::const_val::ConstVal; |
| use rustc::ty::{self, Ty}; |
| use rustc::ty::subst::Substs; |
| use rustc_const_eval::ConstContext; |
| use rustc_const_math::ConstInt; |
| use std::cmp::Ordering; |
| use std::collections::Bound; |
| use syntax::ast::LitKind; |
| use syntax::ast::NodeId; |
| use syntax::codemap::Span; |
| use utils::paths; |
| use utils::{expr_block, in_external_macro, is_allowed, is_expn_of, match_type, remove_blocks, snippet, |
| span_lint_and_sugg, span_lint_and_then, span_note_and_lint, walk_ptrs_ty}; |
| use utils::sugg::Sugg; |
| |
| /// **What it does:** Checks for matches with a single arm where an `if let` |
| /// will usually suffice. |
| /// |
| /// **Why is this bad?** Just readability – `if let` nests less than a `match`. |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// match x { |
| /// Some(ref foo) => bar(foo), |
| /// _ => () |
| /// } |
| /// ``` |
| declare_lint! { |
| pub SINGLE_MATCH, |
| Warn, |
| "a match statement with a single nontrivial arm (i.e. where the other arm \ |
| is `_ => {}`) instead of `if let`" |
| } |
| |
| /// **What it does:** Checks for matches with a two arms where an `if let` will |
| /// usually suffice. |
| /// |
| /// **Why is this bad?** Just readability – `if let` nests less than a `match`. |
| /// |
| /// **Known problems:** Personal style preferences may differ. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// match x { |
| /// Some(ref foo) => bar(foo), |
| /// _ => bar(other_ref), |
| /// } |
| /// ``` |
| declare_lint! { |
| pub SINGLE_MATCH_ELSE, |
| Allow, |
| "a match statement with a two arms where the second arm's pattern is a wildcard \ |
| instead of `if let`" |
| } |
| |
| /// **What it does:** Checks for matches where all arms match a reference, |
| /// suggesting to remove the reference and deref the matched expression |
| /// instead. It also checks for `if let &foo = bar` blocks. |
| /// |
| /// **Why is this bad?** It just makes the code less readable. That reference |
| /// destructuring adds nothing to the code. |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// match x { |
| /// &A(ref y) => foo(y), |
| /// &B => bar(), |
| /// _ => frob(&x), |
| /// } |
| /// ``` |
| declare_lint! { |
| pub MATCH_REF_PATS, |
| Warn, |
| "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression" |
| } |
| |
| /// **What it does:** Checks for matches where match expression is a `bool`. It |
| /// suggests to replace the expression with an `if...else` block. |
| /// |
| /// **Why is this bad?** It makes the code less readable. |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// let condition: bool = true; |
| /// match condition { |
| /// true => foo(), |
| /// false => bar(), |
| /// } |
| /// ``` |
| declare_lint! { |
| pub MATCH_BOOL, |
| Warn, |
| "a match on a boolean expression instead of an `if..else` block" |
| } |
| |
| /// **What it does:** Checks for overlapping match arms. |
| /// |
| /// **Why is this bad?** It is likely to be an error and if not, makes the code |
| /// less obvious. |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// let x = 5; |
| /// match x { |
| /// 1 ... 10 => println!("1 ... 10"), |
| /// 5 ... 15 => println!("5 ... 15"), |
| /// _ => (), |
| /// } |
| /// ``` |
| declare_lint! { |
| pub MATCH_OVERLAPPING_ARM, |
| Warn, |
| "a match with overlapping arms" |
| } |
| |
| /// **What it does:** Checks for arm which matches all errors with `Err(_)` |
| /// and take drastic actions like `panic!`. |
| /// |
| /// **Why is this bad?** It is generally a bad practice, just like |
| /// catching all exceptions in java with `catch(Exception)` |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// let x : Result(i32, &str) = Ok(3); |
| /// match x { |
| /// Ok(_) => println!("ok"), |
| /// Err(_) => panic!("err"), |
| /// } |
| /// ``` |
| declare_lint! { |
| pub MATCH_WILD_ERR_ARM, |
| Warn, |
| "a match with `Err(_)` arm and take drastic actions" |
| } |
| |
| #[allow(missing_copy_implementations)] |
| pub struct MatchPass; |
| |
| impl LintPass for MatchPass { |
| fn get_lints(&self) -> LintArray { |
| lint_array!( |
| SINGLE_MATCH, |
| MATCH_REF_PATS, |
| MATCH_BOOL, |
| SINGLE_MATCH_ELSE, |
| MATCH_OVERLAPPING_ARM, |
| MATCH_WILD_ERR_ARM |
| ) |
| } |
| } |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass { |
| fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { |
| if in_external_macro(cx, expr.span) { |
| return; |
| } |
| if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node { |
| check_single_match(cx, ex, arms, expr); |
| check_match_bool(cx, ex, arms, expr); |
| check_overlapping_arms(cx, ex, arms); |
| check_wild_err_arm(cx, ex, arms); |
| } |
| if let ExprMatch(ref ex, ref arms, source) = expr.node { |
| check_match_ref_pats(cx, ex, arms, source, expr); |
| } |
| } |
| } |
| |
| #[cfg_attr(rustfmt, rustfmt_skip)] |
| fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) { |
| if arms.len() == 2 && |
| arms[0].pats.len() == 1 && arms[0].guard.is_none() && |
| arms[1].pats.len() == 1 && arms[1].guard.is_none() { |
| let els = remove_blocks(&arms[1].body); |
| let els = if is_unit_expr(els) { |
| None |
| } else if let ExprBlock(_) = els.node { |
| // matches with blocks that contain statements are prettier as `if let + else` |
| Some(els) |
| } else { |
| // allow match arms with just expressions |
| return; |
| }; |
| let ty = cx.tables.expr_ty(ex); |
| if ty.sty != ty::TyBool || is_allowed(cx, MATCH_BOOL, ex.id) { |
| check_single_match_single_pattern(cx, ex, arms, expr, els); |
| check_single_match_opt_like(cx, ex, arms, expr, ty, els); |
| } |
| } |
| } |
| |
| fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) { |
| if arms[1].pats[0].node == PatKind::Wild { |
| report_single_match_single_pattern(cx, ex, arms, expr, els); |
| } |
| } |
| |
| fn report_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) { |
| let lint = if els.is_some() { |
| SINGLE_MATCH_ELSE |
| } else { |
| SINGLE_MATCH |
| }; |
| let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, ".."))); |
| span_lint_and_sugg( |
| cx, |
| lint, |
| expr.span, |
| "you seem to be trying to use match for destructuring a single pattern. Consider using `if \ |
| let`", |
| "try this", |
| format!( |
| "if let {} = {} {}{}", |
| snippet(cx, arms[0].pats[0].span, ".."), |
| snippet(cx, ex.span, ".."), |
| expr_block(cx, &arms[0].body, None, ".."), |
| els_str |
| ), |
| ); |
| } |
| |
| fn check_single_match_opt_like(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, ty: Ty, els: Option<&Expr>) { |
| // list of candidate Enums we know will never get any more members |
| let candidates = &[ |
| (&paths::COW, "Borrowed"), |
| (&paths::COW, "Cow::Borrowed"), |
| (&paths::COW, "Cow::Owned"), |
| (&paths::COW, "Owned"), |
| (&paths::OPTION, "None"), |
| (&paths::RESULT, "Err"), |
| (&paths::RESULT, "Ok"), |
| ]; |
| |
| let path = match arms[1].pats[0].node { |
| PatKind::TupleStruct(ref path, ref inner, _) => { |
| // contains any non wildcard patterns? e.g. Err(err) |
| if inner.iter().any(|pat| pat.node != PatKind::Wild) { |
| return; |
| } |
| print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)) |
| }, |
| PatKind::Binding(BindingAnnotation::Unannotated, _, ident, None) => ident.node.to_string(), |
| PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)), |
| _ => return, |
| }; |
| |
| for &(ty_path, pat_path) in candidates { |
| if path == *pat_path && match_type(cx, ty, ty_path) { |
| report_single_match_single_pattern(cx, ex, arms, expr, els); |
| } |
| } |
| } |
| |
| fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) { |
| // type of expression == bool |
| if cx.tables.expr_ty(ex).sty == ty::TyBool { |
| span_lint_and_then( |
| cx, |
| MATCH_BOOL, |
| expr.span, |
| "you seem to be trying to match on a boolean expression", |
| move |db| { |
| if arms.len() == 2 && arms[0].pats.len() == 1 { |
| // no guards |
| let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node { |
| if let ExprLit(ref lit) = arm_bool.node { |
| match lit.node { |
| LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)), |
| LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)), |
| _ => None, |
| } |
| } else { |
| None |
| } |
| } else { |
| None |
| }; |
| |
| if let Some((true_expr, false_expr)) = exprs { |
| let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) { |
| (false, false) => Some(format!( |
| "if {} {} else {}", |
| snippet(cx, ex.span, "b"), |
| expr_block(cx, true_expr, None, ".."), |
| expr_block(cx, false_expr, None, "..") |
| )), |
| (false, true) => Some(format!( |
| "if {} {}", |
| snippet(cx, ex.span, "b"), |
| expr_block(cx, true_expr, None, "..") |
| )), |
| (true, false) => { |
| let test = Sugg::hir(cx, ex, ".."); |
| Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, ".."))) |
| }, |
| (true, true) => None, |
| }; |
| |
| if let Some(sugg) = sugg { |
| db.span_suggestion(expr.span, "consider using an if/else expression", sugg); |
| } |
| } |
| } |
| }, |
| ); |
| } |
| } |
| |
| fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr, arms: &'tcx [Arm]) { |
| if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() { |
| let ranges = all_ranges(cx, arms, ex.id); |
| let type_ranges = type_ranges(&ranges); |
| if !type_ranges.is_empty() { |
| if let Some((start, end)) = overlapping(&type_ranges) { |
| span_note_and_lint( |
| cx, |
| MATCH_OVERLAPPING_ARM, |
| start.span, |
| "some ranges overlap", |
| end.span, |
| "overlaps with this", |
| ); |
| } |
| } |
| } |
| } |
| |
| fn check_wild_err_arm(cx: &LateContext, ex: &Expr, arms: &[Arm]) { |
| let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex)); |
| if match_type(cx, ex_ty, &paths::RESULT) { |
| for arm in arms { |
| if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node { |
| let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)); |
| if_chain! { |
| if path_str == "Err"; |
| if inner.iter().any(|pat| pat.node == PatKind::Wild); |
| if let ExprBlock(ref block) = arm.body.node; |
| if is_panic_block(block); |
| then { |
| // `Err(_)` arm with `panic!` found |
| span_note_and_lint(cx, |
| MATCH_WILD_ERR_ARM, |
| arm.pats[0].span, |
| "Err(_) will match all errors, maybe not a good idea", |
| arm.pats[0].span, |
| "to remove this warning, match each error seperately \ |
| or use unreachable macro"); |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| // If the block contains only a `panic!` macro (as expression or statement) |
| fn is_panic_block(block: &Block) -> bool { |
| match (&block.expr, block.stmts.len(), block.stmts.first()) { |
| (&Some(ref exp), 0, _) => { |
| is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none() |
| }, |
| (&None, 1, Some(stmt)) => { |
| is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none() |
| }, |
| _ => false, |
| } |
| } |
| |
| fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) { |
| if has_only_ref_pats(arms) { |
| if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node { |
| span_lint_and_then( |
| cx, |
| MATCH_REF_PATS, |
| expr.span, |
| "you don't need to add `&` to both the expression and the patterns", |
| |db| { |
| let inner = Sugg::hir(cx, inner, ".."); |
| let template = match_template(expr.span, source, &inner); |
| db.span_suggestion(expr.span, "try", template); |
| }, |
| ); |
| } else { |
| span_lint_and_then( |
| cx, |
| MATCH_REF_PATS, |
| expr.span, |
| "you don't need to add `&` to all patterns", |
| |db| { |
| let ex = Sugg::hir(cx, ex, ".."); |
| let template = match_template(expr.span, source, &ex.deref()); |
| db.span_suggestion( |
| expr.span, |
| "instead of prefixing all patterns with `&`, you can dereference the expression", |
| template, |
| ); |
| }, |
| ); |
| } |
| } |
| } |
| |
| /// Get all arms that are unbounded `PatRange`s. |
| fn all_ranges<'a, 'tcx>( |
| cx: &LateContext<'a, 'tcx>, |
| arms: &'tcx [Arm], |
| id: NodeId, |
| ) -> Vec<SpannedRange<&'tcx ty::Const<'tcx>>> { |
| let parent_item = cx.tcx.hir.get_parent(id); |
| let parent_def_id = cx.tcx.hir.local_def_id(parent_item); |
| let substs = Substs::identity_for_item(cx.tcx, parent_def_id); |
| let constcx = ConstContext::new(cx.tcx, cx.param_env.and(substs), cx.tables); |
| arms.iter() |
| .flat_map(|arm| { |
| if let Arm { |
| ref pats, |
| guard: None, |
| .. |
| } = *arm |
| { |
| pats.iter() |
| } else { |
| [].iter() |
| }.filter_map(|pat| { |
| if_chain! { |
| if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node; |
| if let Ok(lhs) = constcx.eval(lhs); |
| if let Ok(rhs) = constcx.eval(rhs); |
| then { |
| let rhs = match *range_end { |
| RangeEnd::Included => Bound::Included(rhs), |
| RangeEnd::Excluded => Bound::Excluded(rhs), |
| }; |
| return Some(SpannedRange { span: pat.span, node: (lhs, rhs) }); |
| } |
| } |
| |
| if_chain! { |
| if let PatKind::Lit(ref value) = pat.node; |
| if let Ok(value) = constcx.eval(value); |
| then { |
| return Some(SpannedRange { span: pat.span, node: (value, Bound::Included(value)) }); |
| } |
| } |
| |
| None |
| }) |
| }) |
| .collect() |
| } |
| |
| #[derive(Debug, Eq, PartialEq)] |
| pub struct SpannedRange<T> { |
| pub span: Span, |
| pub node: (T, Bound<T>), |
| } |
| |
| type TypedRanges = Vec<SpannedRange<ConstInt>>; |
| |
| /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway |
| /// and other types than |
| /// `Uint` and `Int` probably don't make sense. |
| fn type_ranges(ranges: &[SpannedRange<&ty::Const>]) -> TypedRanges { |
| ranges |
| .iter() |
| .filter_map(|range| match range.node { |
| ( |
| &ty::Const { |
| val: ConstVal::Integral(start), |
| .. |
| }, |
| Bound::Included(&ty::Const { |
| val: ConstVal::Integral(end), |
| .. |
| }), |
| ) => Some(SpannedRange { |
| span: range.span, |
| node: (start, Bound::Included(end)), |
| }), |
| ( |
| &ty::Const { |
| val: ConstVal::Integral(start), |
| .. |
| }, |
| Bound::Excluded(&ty::Const { |
| val: ConstVal::Integral(end), |
| .. |
| }), |
| ) => Some(SpannedRange { |
| span: range.span, |
| node: (start, Bound::Excluded(end)), |
| }), |
| ( |
| &ty::Const { |
| val: ConstVal::Integral(start), |
| .. |
| }, |
| Bound::Unbounded, |
| ) => Some(SpannedRange { |
| span: range.span, |
| node: (start, Bound::Unbounded), |
| }), |
| _ => None, |
| }) |
| .collect() |
| } |
| |
| fn is_unit_expr(expr: &Expr) -> bool { |
| match expr.node { |
| ExprTup(ref v) if v.is_empty() => true, |
| ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true, |
| _ => false, |
| } |
| } |
| |
| fn has_only_ref_pats(arms: &[Arm]) -> bool { |
| let mapped = arms.iter() |
| .flat_map(|a| &a.pats) |
| .map(|p| { |
| match p.node { |
| PatKind::Ref(..) => Some(true), // &-patterns |
| PatKind::Wild => Some(false), // an "anything" wildcard is also fine |
| _ => None, // any other pattern is not fine |
| } |
| }) |
| .collect::<Option<Vec<bool>>>(); |
| // look for Some(v) where there's at least one true element |
| mapped.map_or(false, |v| v.iter().any(|el| *el)) |
| } |
| |
| fn match_template(span: Span, source: MatchSource, expr: &Sugg) -> String { |
| match source { |
| MatchSource::Normal => format!("match {} {{ .. }}", expr), |
| MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr), |
| MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr), |
| MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"), |
| MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"), |
| } |
| } |
| |
| pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)> |
| where |
| T: Copy + Ord, |
| { |
| #[derive(Copy, Clone, Debug, Eq, PartialEq)] |
| enum Kind<'a, T: 'a> { |
| Start(T, &'a SpannedRange<T>), |
| End(Bound<T>, &'a SpannedRange<T>), |
| } |
| |
| impl<'a, T: Copy> Kind<'a, T> { |
| fn range(&self) -> &'a SpannedRange<T> { |
| match *self { |
| Kind::Start(_, r) | Kind::End(_, r) => r, |
| } |
| } |
| |
| fn value(self) -> Bound<T> { |
| match self { |
| Kind::Start(t, _) => Bound::Included(t), |
| Kind::End(t, _) => t, |
| } |
| } |
| } |
| |
| impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> { |
| fn partial_cmp(&self, other: &Self) -> Option<Ordering> { |
| Some(self.cmp(other)) |
| } |
| } |
| |
| impl<'a, T: Copy + Ord> Ord for Kind<'a, T> { |
| fn cmp(&self, other: &Self) -> Ordering { |
| match (self.value(), other.value()) { |
| (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b), |
| // Range patterns cannot be unbounded (yet) |
| (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(), |
| (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) { |
| Ordering::Equal => Ordering::Greater, |
| other => other, |
| }, |
| (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) { |
| Ordering::Equal => Ordering::Less, |
| other => other, |
| }, |
| } |
| } |
| } |
| |
| let mut values = Vec::with_capacity(2 * ranges.len()); |
| |
| for r in ranges { |
| values.push(Kind::Start(r.node.0, r)); |
| values.push(Kind::End(r.node.1, r)); |
| } |
| |
| values.sort(); |
| |
| for (a, b) in values.iter().zip(values.iter().skip(1)) { |
| match (a, b) { |
| (&Kind::Start(_, ra), &Kind::End(_, rb)) => if ra.node != rb.node { |
| return Some((ra, rb)); |
| }, |
| (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (), |
| _ => return Some((a.range(), b.range())), |
| } |
| } |
| |
| None |
| } |