From 5753614152b4c6d9c0d20bc311a335c4746c3ed0 Mon Sep 17 00:00:00 2001 From: nahuakang Date: Wed, 27 Jan 2021 09:34:59 +0100 Subject: [PATCH] Draft skeleton for new lint --- CHANGELOG.md | 1 + clippy_lints/src/lib.rs | 3 ++ clippy_lints/src/loops.rs | 64 +++++++++++++++++++++++++++++++++++++++ 3 files changed, 68 insertions(+) diff --git a/CHANGELOG.md b/CHANGELOG.md index dadb6832d..e8e738313 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1969,6 +1969,7 @@ Released 2018-09-13 [`fn_to_numeric_cast_with_truncation`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_to_numeric_cast_with_truncation [`for_kv_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#for_kv_map [`for_loops_over_fallibles`]: https://rust-lang.github.io/rust-clippy/master/index.html#for_loops_over_fallibles +[`for_loops_over_options`]: https://rust-lang.github.io/rust-clippy/master/index.html#for_loops_over_options [`forget_copy`]: https://rust-lang.github.io/rust-clippy/master/index.html#forget_copy [`forget_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#forget_ref [`from_iter_instead_of_collect`]: https://rust-lang.github.io/rust-clippy/master/index.html#from_iter_instead_of_collect diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 54007c29c..379320873 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -685,6 +685,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &loops::EXPLICIT_ITER_LOOP, &loops::FOR_KV_MAP, &loops::FOR_LOOPS_OVER_FALLIBLES, + &loops::FOR_LOOPS_OVER_OPTIONS, &loops::ITER_NEXT_LOOP, &loops::MANUAL_MEMCPY, &loops::MUT_RANGE_BOUND, @@ -1488,6 +1489,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&loops::EXPLICIT_COUNTER_LOOP), LintId::of(&loops::FOR_KV_MAP), LintId::of(&loops::FOR_LOOPS_OVER_FALLIBLES), + LintId::of(&loops::FOR_LOOPS_OVER_OPTIONS), LintId::of(&loops::ITER_NEXT_LOOP), LintId::of(&loops::MANUAL_MEMCPY), LintId::of(&loops::MUT_RANGE_BOUND), @@ -1820,6 +1822,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&lifetimes::EXTRA_UNUSED_LIFETIMES), LintId::of(&lifetimes::NEEDLESS_LIFETIMES), LintId::of(&loops::EXPLICIT_COUNTER_LOOP), + LintId::of(&loops::FOR_LOOPS_OVER_OPTIONS), LintId::of(&loops::MUT_RANGE_BOUND), LintId::of(&loops::SINGLE_ELEMENT_LOOP), LintId::of(&loops::WHILE_LET_LOOP), diff --git a/clippy_lints/src/loops.rs b/clippy_lints/src/loops.rs index 5211ca7da..c1a59650c 100644 --- a/clippy_lints/src/loops.rs +++ b/clippy_lints/src/loops.rs @@ -494,6 +494,37 @@ declare_clippy_lint! { "there is no reason to have a single element loop" } +declare_clippy_lint! { + /// **What it does:** Checks for iteration of `Option`s with + /// a single `if let Some()` expression inside. + /// + /// **Why is this bad?** It is verbose and can be simplified + /// by first calling the `flatten` method on the `Iterator`. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// + /// ```rust + /// let x = vec![Some(1), Some(2), Some(3)]; + /// for n in x { + /// if let Some(n) = n { + /// println!("{}", n); + /// } + /// } + /// ``` + /// Use instead: + /// ```rust + /// let x = vec![Some(1), Some(2), Some(3)]; + /// for n in x.iter().flatten() { + /// println!("{}", n); + /// } + /// ``` + pub FOR_LOOPS_OVER_OPTIONS, + complexity, + "for loops over `Option`s or `Result`s with a single expression can be simplified" +} + declare_lint_pass!(Loops => [ MANUAL_MEMCPY, NEEDLESS_RANGE_LOOP, @@ -501,6 +532,7 @@ declare_lint_pass!(Loops => [ EXPLICIT_INTO_ITER_LOOP, ITER_NEXT_LOOP, FOR_LOOPS_OVER_FALLIBLES, + FOR_LOOPS_OVER_OPTIONS, WHILE_LET_LOOP, NEEDLESS_COLLECT, EXPLICIT_COUNTER_LOOP, @@ -830,6 +862,7 @@ fn check_for_loop<'tcx>( check_for_mut_range_bound(cx, arg, body); check_for_single_element_loop(cx, pat, arg, body, expr); detect_same_item_push(cx, pat, arg, body, expr); + check_for_loop_over_options_or_results(cx, pat, arg, body, expr); } // this function assumes the given expression is a `for` loop. @@ -1953,6 +1986,37 @@ fn check_for_single_element_loop<'tcx>( } } +/// Check if a for loop loops over `Option`s or `Result`s and contains only +/// a `if let Some` or `if let Ok` expression. +fn check_for_loop_over_options_or_results<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + expr: &'tcx Expr<'_>, +) { + if_chain! { + if let ExprKind::Block(ref block, _) = body.kind; + if block.stmts.is_empty(); + if let Some(inner_expr) = block.expr; + if let ExprKind::Match(ref _match_expr, ref _match_arms, MatchSource::IfLetDesugar{ contains_else_clause }) = inner_expr.kind; + if !contains_else_clause; + then { + // println!("if_let_expr:\n{:?}", snippet(cx, if_let_expr.span, "..")); + // println!("pat is:\n {:?}", snippet(cx, pat.span, "..")); + // println!("arg is:\n {:?}", snippet(cx, arg.span, "..")); + // println!("body is:\n {:?}", snippet(cx, body.span, "..")); + // println!("arg kind is: {:?}", arg.kind); + // println!("expr is:\n {:?}", snippet(cx, expr.span, "..")); + // todo!(); + let arg_snippet = snippet(cx, arg.span, ".."); + let msg = "looping over `Option`s or `Result`s with an `if let` expression."; + let hint = format!("try turn {} into an `Iterator` and use `flatten`: `{}.iter().flatten()`", arg_snippet, arg_snippet); + span_lint_and_help(cx, FOR_LOOPS_OVER_OPTIONS, expr.span, msg, None, &hint); + } + } +} + struct MutatePairDelegate<'a, 'tcx> { cx: &'a LateContext<'tcx>, hir_id_low: Option,