diff --git a/README.md b/README.md index 63ecbf11fcf9..04b0bd0e384a 100644 --- a/README.md +++ b/README.md @@ -6,7 +6,7 @@ A collection of lints to catch common mistakes and improve your Rust code. [Jump to usage instructions](#usage) ##Lints -There are 99 lints included in this crate: +There are 100 lints included in this crate: name | default | meaning ---------------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ @@ -34,6 +34,7 @@ name [expl_impl_clone_on_copy](https://github.com/Manishearth/rust-clippy/wiki#expl_impl_clone_on_copy) | warn | implementing `Clone` explicitly on `Copy` types [explicit_counter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_counter_loop) | warn | for-looping with an explicit counter when `_.enumerate()` would do [explicit_iter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_iter_loop) | warn | for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do +[extend_from_slice](https://github.com/Manishearth/rust-clippy/wiki#extend_from_slice) | warn | `.extend_from_slice(_)` is a faster way to extend a Vec by a slice [filter_next](https://github.com/Manishearth/rust-clippy/wiki#filter_next) | warn | using `filter(p).next()`, which is more succinctly expressed as `.find(p)` [float_cmp](https://github.com/Manishearth/rust-clippy/wiki#float_cmp) | warn | using `==` or `!=` on float values (as floating-point operations usually involve rounding errors, it is always better to check for approximate equality within small bounds) [identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op) | warn | using identity operations, e.g. `x + 0` or `y / 1` diff --git a/src/lib.rs b/src/lib.rs index b0cf4d469723..6d706888fc31 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -200,6 +200,7 @@ pub fn plugin_registrar(reg: &mut Registry) { matches::MATCH_REF_PATS, matches::SINGLE_MATCH, methods::CHARS_NEXT_CMP, + methods::EXTEND_FROM_SLICE, methods::FILTER_NEXT, methods::OK_EXPECT, methods::OPTION_MAP_UNWRAP_OR, diff --git a/src/methods.rs b/src/methods.rs index 6338961b56b3..a5f27440f941 100644 --- a/src/methods.rs +++ b/src/methods.rs @@ -14,7 +14,7 @@ }; use utils::{ BTREEMAP_ENTRY_PATH, DEFAULT_TRAIT_PATH, HASHMAP_ENTRY_PATH, OPTION_PATH, RESULT_PATH, - STRING_PATH + STRING_PATH, VEC_PATH, }; use utils::MethodArgs; use rustc::middle::cstore::CrateStore; @@ -212,9 +212,20 @@ declare_lint!(pub OR_FUN_CALL, Warn, "using any `*or` method when the `*or_else` would do"); +/// **What it does:** This lint `Warn`s on using `.extend(s)` on a `vec` to extend the vec by a slice. +/// +/// **Why is this bad?** Since Rust 1.6, the `extend_from_slice(_)` method is stable and at least for now faster. +/// +/// **Known problems:** None. +/// +/// **Example:** `my_vec.extend(&xs)` +declare_lint!(pub EXTEND_FROM_SLICE, Warn, + "`.extend_from_slice(_)` is a faster way to extend a Vec by a slice"); + impl LintPass for MethodsPass { fn get_lints(&self) -> LintArray { - lint_array!(OPTION_UNWRAP_USED, + lint_array!(EXTEND_FROM_SLICE, + OPTION_UNWRAP_USED, RESULT_UNWRAP_USED, STR_TO_STRING, STRING_TO_STRING, @@ -256,6 +267,8 @@ fn check_expr(&mut self, cx: &LateContext, expr: &Expr) { lint_search_is_some(cx, expr, "position", arglists[0], arglists[1]); } else if let Some(arglists) = method_chain_args(expr, &["rposition", "is_some"]) { lint_search_is_some(cx, expr, "rposition", arglists[0], arglists[1]); + } else if let Some(arglists) = method_chain_args(expr, &["extend"]) { + lint_extend(cx, expr, arglists[0]); } lint_or_fun_call(cx, expr, &name.node.as_str(), &args); @@ -427,6 +440,53 @@ fn check_general_case( } } +fn lint_extend(cx: &LateContext, expr: &Expr, args: &MethodArgs) { + let (obj_ty, _) = walk_ptrs_ty_depth(cx.tcx.expr_ty(&args[0])); + if !match_type(cx, obj_ty, &VEC_PATH) { + return; + } + let arg_ty = cx.tcx.expr_ty(&args[1]); + if let Some((span, r)) = derefs_to_slice(cx, &args[1], &arg_ty) { + span_lint(cx, EXTEND_FROM_SLICE, expr.span, + &format!("use of `extend` to extend a Vec by a slice")) + .span_suggestion(expr.span, "try this", + format!("{}.extend_from_slice({}{})", + snippet(cx, args[0].span, "_"), + r, snippet(cx, span, "_"))); + } +} + +fn derefs_to_slice(cx: &LateContext, expr: &Expr, ty: &ty::Ty) + -> Option<(Span, &'static str)> { + fn may_slice(cx: &LateContext, ty: &ty::Ty) -> bool { + match ty.sty { + ty::TySlice(_) => true, + ty::TyStruct(..) => match_type(cx, ty, &VEC_PATH), + ty::TyArray(_, size) => size < 32, + ty::TyRef(_, ty::TypeAndMut { ty: ref inner, .. }) | + ty::TyBox(ref inner) => may_slice(cx, inner), + _ => false + } + } + if let ExprMethodCall(name, _, ref args) = expr.node { + if &name.node.as_str() == &"iter" && + may_slice(cx, &cx.tcx.expr_ty(&args[0])) { + Some((args[0].span, "&")) + } else { + None + } + } else { + match ty.sty { + ty::TySlice(_) => Some((expr.span, "")), + ty::TyRef(_, ty::TypeAndMut { ty: ref inner, .. }) | + ty::TyBox(ref inner) => if may_slice(cx, inner) { + Some((expr.span, "")) + } else { None }, + _ => None + } + } +} + #[allow(ptr_arg)] // Type of MethodArgs is potentially a Vec /// lint use of `unwrap()` for `Option`s and `Result`s diff --git a/tests/compile-fail/methods.rs b/tests/compile-fail/methods.rs index 535e8cc4a26c..c72e602ac2bf 100644 --- a/tests/compile-fail/methods.rs +++ b/tests/compile-fail/methods.rs @@ -304,3 +304,22 @@ fn starts_with() { //~| HELP like this //~| SUGGESTION !"".starts_with(' ') } + +fn use_extend_from_slice() { + let mut v : Vec<&'static str> = vec![]; + v.extend(&["Hello", "World"]); //~ERROR use of `extend` + v.extend(&vec!["Some", "more"]); + //~^ERROR use of `extend` + //~| HELP try this + //~| SUGGESTION v.extend_from_slice(&vec!["Some", "more"]); + + v.extend(vec!["And", "even", "more"].iter()); //~ERROR use of `extend` + let o : Option<&'static str> = None; + v.extend(o); + v.extend(Some("Bye")); + v.extend(vec!["Not", "like", "this"]); + v.extend(["But", "this"].iter()); + //~^ERROR use of `extend + //~| HELP try this + //~| SUGGESTION v.extend_from_slice(&["But", "this"]); +}