diff --git a/README.md b/README.md index 55976104058..72ce27392a7 100644 --- a/README.md +++ b/README.md @@ -29,6 +29,7 @@ len_zero | warn | checking `.len() == 0` or `.len() > 0` (or let_and_return | warn | creating a let-binding and then immediately returning it like `let x = expr; x` at the end of a function let_unit_value | warn | creating a let binding to a value of unit type, which usually can't be used afterwards linkedlist | warn | usage of LinkedList, usually a vector is faster, or a more specialized data structure like a RingBuf +match_ref_pats | warn | a match has all arms prefixed with `&`; the match expression can be dereferenced instead modulo_one | warn | taking a number modulo 1, which always returns 0 mut_mut | warn | usage of double-mut refs, e.g. `&mut &mut ...` (either copy'n'paste error, or shows a fundamental misunderstanding of references) needless_bool | warn | if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }` diff --git a/src/lib.rs b/src/lib.rs index fbeebb210fe..26af063c9a5 100755 --- a/src/lib.rs +++ b/src/lib.rs @@ -88,6 +88,7 @@ pub fn plugin_registrar(reg: &mut Registry) { loops::EXPLICIT_ITER_LOOP, loops::ITER_NEXT_LOOP, loops::NEEDLESS_RANGE_LOOP, + matches::MATCH_REF_PATS, matches::SINGLE_MATCH, methods::OPTION_UNWRAP_USED, methods::RESULT_UNWRAP_USED, diff --git a/src/matches.rs b/src/matches.rs index b9f6cbc4326..b704a2b47bb 100644 --- a/src/matches.rs +++ b/src/matches.rs @@ -3,23 +3,27 @@ use syntax::ast; use syntax::ast::*; use std::borrow::Cow; -use utils::{snippet, snippet_block, span_help_and_lint}; +use utils::{snippet, snippet_block, span_lint, span_help_and_lint}; declare_lint!(pub SINGLE_MATCH, Warn, "a match statement with a single nontrivial arm (i.e, where the other arm \ is `_ => {}`) is used; recommends `if let` instead"); +declare_lint!(pub MATCH_REF_PATS, Warn, + "a match has all arms prefixed with `&`; the match expression can be \ + dereferenced instead"); #[allow(missing_copy_implementations)] pub struct MatchPass; impl LintPass for MatchPass { fn get_lints(&self) -> LintArray { - lint_array!(SINGLE_MATCH) + lint_array!(SINGLE_MATCH, MATCH_REF_PATS) } fn check_expr(&mut self, cx: &Context, expr: &Expr) { if let ExprMatch(ref ex, ref arms, ast::MatchSource::Normal) = expr.node { - // check preconditions: only two arms + // check preconditions for SINGLE_MATCH + // only two arms if arms.len() == 2 && // both of the arms have a single pattern and no guard arms[0].pats.len() == 1 && arms[0].guard.is_none() && @@ -48,6 +52,13 @@ impl LintPass for MatchPass { body_code) ); } + + // check preconditions for MATCH_REF_PATS + if has_only_ref_pats(arms) { + span_lint(cx, MATCH_REF_PATS, expr.span, &format!( + "instead of prefixing all patterns with `&`, you can dereference the \ + expression to match: `match *{} {{ ...`", snippet(cx, ex.span, ".."))); + } } } } @@ -59,3 +70,16 @@ fn is_unit_expr(expr: &Expr) -> bool { _ => false, } } + +fn has_only_ref_pats(arms: &[Arm]) -> bool { + for arm in arms { + for pat in &arm.pats { + match pat.node { + PatRegion(..) => (), // &-patterns + PatWild(..) => (), // an "anything" wildcard is also fine + _ => return false, + } + } + } + true +} diff --git a/tests/compile-fail/match_if_let.rs b/tests/compile-fail/matches.rs similarity index 58% rename from tests/compile-fail/match_if_let.rs rename to tests/compile-fail/matches.rs index bf2e7e43a52..43cf43b68df 100755 --- a/tests/compile-fail/match_if_let.rs +++ b/tests/compile-fail/matches.rs @@ -2,8 +2,9 @@ #![plugin(clippy)] #![deny(clippy)] +#![allow(unused)] -fn main(){ +fn single_match(){ let x = Some(1u8); match x { //~ ERROR you seem to be trying to use match //~^ HELP try @@ -36,3 +37,23 @@ fn main(){ _ => println!("nope"), } } + +fn ref_pats() { + let ref v = Some(0); + match v { //~ERROR instead of prefixing all patterns with `&` + &Some(v) => println!("{:?}", v), + &None => println!("none"), + } + match v { // this doesn't trigger, we have a different pattern + &Some(v) => println!("some"), + other => println!("other"), + } + let ref tup = (1, 2); + match tup { //~ERROR instead of prefixing all patterns with `&` + &(v, 1) => println!("{}", v), + _ => println!("none"), + } +} + +fn main() { +}