From 32fde0b5116b3a1115d11c49a9bf2af2ebdd5773 Mon Sep 17 00:00:00 2001 From: Ericko Samudera Date: Mon, 25 May 2020 23:22:01 +0700 Subject: [PATCH] New lint: iter_next_slice --- CHANGELOG.md | 1 + clippy_lints/src/lib.rs | 3 + clippy_lints/src/loops.rs | 26 ++++----- clippy_lints/src/methods/mod.rs | 84 ++++++++++++++++++++++++++- clippy_lints/src/needless_continue.rs | 2 +- src/lintlist/mod.rs | 7 +++ tests/ui/into_iter_on_ref.fixed | 2 + tests/ui/into_iter_on_ref.rs | 2 + tests/ui/into_iter_on_ref.stderr | 8 ++- tests/ui/iter_next_slice.fixed | 24 ++++++++ tests/ui/iter_next_slice.rs | 24 ++++++++ tests/ui/iter_next_slice.stderr | 28 +++++++++ tests/ui/needless_collect.fixed | 2 +- tests/ui/needless_collect.stderr | 16 ++--- 14 files changed, 204 insertions(+), 25 deletions(-) create mode 100644 tests/ui/iter_next_slice.fixed create mode 100644 tests/ui/iter_next_slice.rs create mode 100644 tests/ui/iter_next_slice.stderr diff --git a/CHANGELOG.md b/CHANGELOG.md index 2ac9057199ff..714e25a32ea6 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1401,6 +1401,7 @@ Released 2018-09-13 [`items_after_statements`]: https://rust-lang.github.io/rust-clippy/master/index.html#items_after_statements [`iter_cloned_collect`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_cloned_collect [`iter_next_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_next_loop +[`iter_next_slice`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_next_slice [`iter_nth`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_nth [`iter_nth_zero`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_nth_zero [`iter_skip_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_skip_next diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 057d39d4c825..7c16dbd8f267 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -669,6 +669,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &methods::INTO_ITER_ON_REF, &methods::ITERATOR_STEP_BY_ZERO, &methods::ITER_CLONED_COLLECT, + &methods::ITER_NEXT_SLICE, &methods::ITER_NTH, &methods::ITER_NTH_ZERO, &methods::ITER_SKIP_NEXT, @@ -1303,6 +1304,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&methods::INTO_ITER_ON_REF), LintId::of(&methods::ITERATOR_STEP_BY_ZERO), LintId::of(&methods::ITER_CLONED_COLLECT), + LintId::of(&methods::ITER_NEXT_SLICE), LintId::of(&methods::ITER_NTH), LintId::of(&methods::ITER_NTH_ZERO), LintId::of(&methods::ITER_SKIP_NEXT), @@ -1483,6 +1485,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&methods::CHARS_NEXT_CMP), LintId::of(&methods::INTO_ITER_ON_REF), LintId::of(&methods::ITER_CLONED_COLLECT), + LintId::of(&methods::ITER_NEXT_SLICE), LintId::of(&methods::ITER_NTH_ZERO), LintId::of(&methods::ITER_SKIP_NEXT), LintId::of(&methods::MANUAL_SATURATING_ARITHMETIC), diff --git a/clippy_lints/src/loops.rs b/clippy_lints/src/loops.rs index 38a5829b3f74..dbe41823a9cf 100644 --- a/clippy_lints/src/loops.rs +++ b/clippy_lints/src/loops.rs @@ -27,7 +27,7 @@ use rustc_middle::middle::region; use rustc_middle::ty::{self, Ty}; use rustc_session::{declare_lint_pass, declare_tool_lint}; use rustc_span::source_map::Span; -use rustc_span::BytePos; +use rustc_span::symbol::Symbol; use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase}; use std::iter::{once, Iterator}; use std::mem; @@ -2381,32 +2381,32 @@ fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'a, ' match_type(cx, ty, &paths::BTREEMAP) || is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) { if method.ident.name == sym!(len) { - let span = shorten_needless_collect_span(expr); + let span = shorten_span(expr, sym!(collect)); span_lint_and_sugg( cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, "replace with", - ".count()".to_string(), + "count()".to_string(), Applicability::MachineApplicable, ); } if method.ident.name == sym!(is_empty) { - let span = shorten_needless_collect_span(expr); + let span = shorten_span(expr, sym!(iter)); span_lint_and_sugg( cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, "replace with", - ".next().is_none()".to_string(), + "get(0).is_none()".to_string(), Applicability::MachineApplicable, ); } if method.ident.name == sym!(contains) { let contains_arg = snippet(cx, args[1].span, "??"); - let span = shorten_needless_collect_span(expr); + let span = shorten_span(expr, sym!(collect)); span_lint_and_then( cx, NEEDLESS_COLLECT, @@ -2422,7 +2422,7 @@ fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'a, ' span, "replace with", format!( - ".any(|{}| x == {})", + "any(|{}| x == {})", arg, pred ), Applicability::MachineApplicable, @@ -2435,13 +2435,13 @@ fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'a, ' } } -fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span { - if_chain! { - if let ExprKind::MethodCall(_, _, ref args) = expr.kind; - if let ExprKind::MethodCall(_, ref span, _) = args[0].kind; - then { - return expr.span.with_lo(span.lo() - BytePos(1)); +fn shorten_span(expr: &Expr<'_>, target_fn_name: Symbol) -> Span { + let mut current_expr = expr; + while let ExprKind::MethodCall(ref path, ref span, ref args) = current_expr.kind { + if path.ident.name == target_fn_name { + return expr.span.with_lo(span.lo()); } + current_expr = &args[0]; } unreachable!() } diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs index 32b3b7f7947f..7cb04d4d81c4 100644 --- a/clippy_lints/src/methods/mod.rs +++ b/clippy_lints/src/methods/mod.rs @@ -26,7 +26,7 @@ use rustc_span::symbol::{sym, SymbolStr}; use crate::consts::{constant, Constant}; use crate::utils::usage::mutated_variables; use crate::utils::{ - get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, in_macro, is_copy, + get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait, in_macro, is_copy, is_ctor_or_promotable_const_function, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment, match_def_path, match_qpath, match_trait_method, match_type, match_var, method_calls, method_chain_args, paths, remove_blocks, return_ty, same_tys, single_segment_path, snippet, snippet_with_applicability, @@ -1242,6 +1242,32 @@ declare_clippy_lint! { "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`" } +declare_clippy_lint! { + /// **What it does:** Checks for usage of `iter().next()` on a Slice or an Array + /// + /// **Why is this bad?** These can be shortened into `.get()` + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```rust + /// # let a = [1, 2, 3]; + /// # let b = vec![1, 2, 3]; + /// a[2..].iter().next(); + /// b.iter().next(); + /// ``` + /// should be written as: + /// ```rust + /// # let a = [1, 2, 3]; + /// # let b = vec![1, 2, 3]; + /// a.get(2); + /// b.get(0); + /// ``` + pub ITER_NEXT_SLICE, + style, + "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`" +} + declare_lint_pass!(Methods => [ UNWRAP_USED, EXPECT_USED, @@ -1273,6 +1299,7 @@ declare_lint_pass!(Methods => [ FIND_MAP, MAP_FLATTEN, ITERATOR_STEP_BY_ZERO, + ITER_NEXT_SLICE, ITER_NTH, ITER_NTH_ZERO, ITER_SKIP_NEXT, @@ -1320,6 +1347,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods { }, ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]), ["next", "skip_while"] => lint_skip_while_next(cx, expr, arg_lists[1]), + ["next", "iter"] => lint_iter_next(cx, expr, arg_lists[1]), ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]), ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]), ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]), @@ -2184,6 +2212,60 @@ fn lint_step_by<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr<'_>, args } } +fn lint_iter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<'_>, iter_args: &'tcx [hir::Expr<'_>]) { + let caller_expr = &iter_args[0]; + + // Skip lint if the `iter().next()` expression is a for loop argument, + // since it is already covered by `&loops::ITER_NEXT_LOOP` + let mut parent_expr_opt = get_parent_expr(cx, expr); + while let Some(parent_expr) = parent_expr_opt { + if higher::for_loop(parent_expr).is_some() { + return; + } + parent_expr_opt = get_parent_expr(cx, parent_expr); + } + + if derefs_to_slice(cx, caller_expr, cx.tables.expr_ty(caller_expr)).is_some() { + // caller is a Slice + if_chain! { + if let hir::ExprKind::Index(ref caller_var, ref index_expr) = &caller_expr.kind; + if let Some(higher::Range { start: Some(start_expr), end: None, limits: ast::RangeLimits::HalfOpen }) + = higher::range(cx, index_expr); + if let hir::ExprKind::Lit(ref start_lit) = &start_expr.kind; + if let ast::LitKind::Int(start_idx, _) = start_lit.node; + then { + let mut applicability = Applicability::MachineApplicable; + span_lint_and_sugg( + cx, + ITER_NEXT_SLICE, + expr.span, + "Using `.iter().next()` on a Slice without end index.", + "try calling", + format!("{}.get({})", snippet_with_applicability(cx, caller_var.span, "..", &mut applicability), start_idx), + applicability, + ); + } + } + } else if is_type_diagnostic_item(cx, cx.tables.expr_ty(caller_expr), sym!(vec_type)) + || matches!(&walk_ptrs_ty(cx.tables.expr_ty(caller_expr)).kind, ty::Array(_, _)) + { + // caller is a Vec or an Array + let mut applicability = Applicability::MachineApplicable; + span_lint_and_sugg( + cx, + ITER_NEXT_SLICE, + expr.span, + "Using `.iter().next()` on an array", + "try calling", + format!( + "{}.get(0)", + snippet_with_applicability(cx, caller_expr.span, "..", &mut applicability) + ), + applicability, + ); + } +} + fn lint_iter_nth<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, expr: &hir::Expr<'_>, diff --git a/clippy_lints/src/needless_continue.rs b/clippy_lints/src/needless_continue.rs index 28183810df48..a971d041ca66 100644 --- a/clippy_lints/src/needless_continue.rs +++ b/clippy_lints/src/needless_continue.rs @@ -424,7 +424,7 @@ fn erode_from_back(s: &str) -> String { } fn span_of_first_expr_in_block(block: &ast::Block) -> Option { - block.stmts.iter().next().map(|stmt| stmt.span) + block.stmts.get(0).map(|stmt| stmt.span) } #[cfg(test)] diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs index 8211a57b5643..79da1f3702e3 100644 --- a/src/lintlist/mod.rs +++ b/src/lintlist/mod.rs @@ -934,6 +934,13 @@ pub static ref ALL_LINTS: Vec = vec![ deprecation: None, module: "loops", }, + Lint { + name: "iter_next_slice", + group: "style", + desc: "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`", + deprecation: None, + module: "methods", + }, Lint { name: "iter_nth", group: "perf", diff --git a/tests/ui/into_iter_on_ref.fixed b/tests/ui/into_iter_on_ref.fixed index c30d23de3f86..7f92d0dbdc97 100644 --- a/tests/ui/into_iter_on_ref.fixed +++ b/tests/ui/into_iter_on_ref.fixed @@ -40,4 +40,6 @@ fn main() { let _ = (&HashSet::::new()).iter(); //~ WARN equivalent to .iter() let _ = std::path::Path::new("12/34").iter(); //~ WARN equivalent to .iter() let _ = std::path::PathBuf::from("12/34").iter(); //~ ERROR equivalent to .iter() + + let _ = (&[1, 2, 3]).iter().next(); //~ WARN equivalent to .iter() } diff --git a/tests/ui/into_iter_on_ref.rs b/tests/ui/into_iter_on_ref.rs index 94bc1689619a..416056d3fdb9 100644 --- a/tests/ui/into_iter_on_ref.rs +++ b/tests/ui/into_iter_on_ref.rs @@ -40,4 +40,6 @@ fn main() { let _ = (&HashSet::::new()).into_iter(); //~ WARN equivalent to .iter() let _ = std::path::Path::new("12/34").into_iter(); //~ WARN equivalent to .iter() let _ = std::path::PathBuf::from("12/34").into_iter(); //~ ERROR equivalent to .iter() + + let _ = (&[1, 2, 3]).into_iter().next(); //~ WARN equivalent to .iter() } diff --git a/tests/ui/into_iter_on_ref.stderr b/tests/ui/into_iter_on_ref.stderr index 80e2d104f824..1cd6400b0195 100644 --- a/tests/ui/into_iter_on_ref.stderr +++ b/tests/ui/into_iter_on_ref.stderr @@ -156,5 +156,11 @@ error: this `.into_iter()` call is equivalent to `.iter()` and will not move the LL | let _ = std::path::PathBuf::from("12/34").into_iter(); //~ ERROR equivalent to .iter() | ^^^^^^^^^ help: call directly: `iter` -error: aborting due to 26 previous errors +error: this `.into_iter()` call is equivalent to `.iter()` and will not move the `array` + --> $DIR/into_iter_on_ref.rs:44:26 + | +LL | let _ = (&[1, 2, 3]).into_iter().next(); //~ WARN equivalent to .iter() + | ^^^^^^^^^ help: call directly: `iter` + +error: aborting due to 27 previous errors diff --git a/tests/ui/iter_next_slice.fixed b/tests/ui/iter_next_slice.fixed new file mode 100644 index 000000000000..79c1db87ac3c --- /dev/null +++ b/tests/ui/iter_next_slice.fixed @@ -0,0 +1,24 @@ +// run-rustfix +#![warn(clippy::iter_next_slice)] + +fn main() { + // test code goes here + let s = [1, 2, 3]; + let v = vec![1, 2, 3]; + + s.get(0); + // Should be replaced by s.get(0) + + s.get(2); + // Should be replaced by s.get(2) + + v.get(5); + // Should be replaced by v.get(5) + + v.get(0); + // Should be replaced by v.get(0) + + let o = Some(5); + o.iter().next(); + // Shouldn't be linted since this is not a Slice or an Array +} diff --git a/tests/ui/iter_next_slice.rs b/tests/ui/iter_next_slice.rs new file mode 100644 index 000000000000..ef9a55f3d997 --- /dev/null +++ b/tests/ui/iter_next_slice.rs @@ -0,0 +1,24 @@ +// run-rustfix +#![warn(clippy::iter_next_slice)] + +fn main() { + // test code goes here + let s = [1, 2, 3]; + let v = vec![1, 2, 3]; + + s.iter().next(); + // Should be replaced by s.get(0) + + s[2..].iter().next(); + // Should be replaced by s.get(2) + + v[5..].iter().next(); + // Should be replaced by v.get(5) + + v.iter().next(); + // Should be replaced by v.get(0) + + let o = Some(5); + o.iter().next(); + // Shouldn't be linted since this is not a Slice or an Array +} diff --git a/tests/ui/iter_next_slice.stderr b/tests/ui/iter_next_slice.stderr new file mode 100644 index 000000000000..bbf61df0cda6 --- /dev/null +++ b/tests/ui/iter_next_slice.stderr @@ -0,0 +1,28 @@ +error: Using `.iter().next()` on an array + --> $DIR/iter_next_slice.rs:9:5 + | +LL | s.iter().next(); + | ^^^^^^^^^^^^^^^ help: try calling: `s.get(0)` + | + = note: `-D clippy::iter-next-slice` implied by `-D warnings` + +error: Using `.iter().next()` on a Slice without end index. + --> $DIR/iter_next_slice.rs:12:5 + | +LL | s[2..].iter().next(); + | ^^^^^^^^^^^^^^^^^^^^ help: try calling: `s.get(2)` + +error: Using `.iter().next()` on a Slice without end index. + --> $DIR/iter_next_slice.rs:15:5 + | +LL | v[5..].iter().next(); + | ^^^^^^^^^^^^^^^^^^^^ help: try calling: `v.get(5)` + +error: Using `.iter().next()` on an array + --> $DIR/iter_next_slice.rs:18:5 + | +LL | v.iter().next(); + | ^^^^^^^^^^^^^^^ help: try calling: `v.get(0)` + +error: aborting due to 4 previous errors + diff --git a/tests/ui/needless_collect.fixed b/tests/ui/needless_collect.fixed index b4227eaf2f8b..be37dc16b9a3 100644 --- a/tests/ui/needless_collect.fixed +++ b/tests/ui/needless_collect.fixed @@ -9,7 +9,7 @@ use std::collections::{BTreeSet, HashMap, HashSet}; fn main() { let sample = [1; 5]; let len = sample.iter().count(); - if sample.iter().next().is_none() { + if sample.get(0).is_none() { // Empty } sample.iter().cloned().any(|x| x == 1); diff --git a/tests/ui/needless_collect.stderr b/tests/ui/needless_collect.stderr index 8884c8e16129..9113aad90dd7 100644 --- a/tests/ui/needless_collect.stderr +++ b/tests/ui/needless_collect.stderr @@ -1,28 +1,28 @@ error: avoid using `collect()` when not needed - --> $DIR/needless_collect.rs:11:28 + --> $DIR/needless_collect.rs:11:29 | LL | let len = sample.iter().collect::>().len(); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `.count()` + | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `count()` | = note: `-D clippy::needless-collect` implied by `-D warnings` error: avoid using `collect()` when not needed - --> $DIR/needless_collect.rs:12:21 + --> $DIR/needless_collect.rs:12:15 | LL | if sample.iter().collect::>().is_empty() { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `.next().is_none()` + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `get(0).is_none()` error: avoid using `collect()` when not needed - --> $DIR/needless_collect.rs:15:27 + --> $DIR/needless_collect.rs:15:28 | LL | sample.iter().cloned().collect::>().contains(&1); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `.any(|x| x == 1)` + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `any(|x| x == 1)` error: avoid using `collect()` when not needed - --> $DIR/needless_collect.rs:16:34 + --> $DIR/needless_collect.rs:16:35 | LL | sample.iter().map(|x| (x, x)).collect::>().len(); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `.count()` + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `count()` error: aborting due to 4 previous errors