diff --git a/clippy_lints/src/methods/unnecessary_fold.rs b/clippy_lints/src/methods/unnecessary_fold.rs index 5a3d12fd790..de29d99cf8d 100644 --- a/clippy_lints/src/methods/unnecessary_fold.rs +++ b/clippy_lints/src/methods/unnecessary_fold.rs @@ -7,10 +7,74 @@ use rustc_hir as hir; use rustc_hir::PatKind; use rustc_lint::LateContext; +use rustc_middle::ty; use rustc_span::{source_map::Span, sym}; use super::UNNECESSARY_FOLD; +/// No turbofish needed in any case. +fn no_turbofish(_: &LateContext<'_>, _: &hir::Expr<'_>) -> bool { + false +} + +/// Turbofish (`::`) may be needed, but can be omitted if we are certain +/// that the type can be inferred from usage. +fn turbofish_if_not_inferred(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool { + let parent = cx.tcx.hir().get_parent(expr.hir_id); + + // some common cases where turbofish isn't needed: + // - assigned to a local variable with a type annotation + if let hir::Node::Local(local) = parent + && local.ty.is_some() + { + return false; + } + + // - part of a function call argument, can be inferred from the function signature (provided that + // the parameter is not a generic type parameter) + if let hir::Node::Expr(parent_expr) = parent + && let hir::ExprKind::Call(recv, args) = parent_expr.kind + && let hir::ExprKind::Path(ref qpath) = recv.kind + && let Some(fn_def_id) = cx.qpath_res(qpath, recv.hir_id).opt_def_id() + && let fn_sig = cx.tcx.fn_sig(fn_def_id).skip_binder().skip_binder() + && let Some(arg_pos) = args.iter().position(|arg| arg.hir_id == expr.hir_id) + && let Some(ty) = fn_sig.inputs().get(arg_pos) + && !matches!(ty.kind(), ty::Param(_)) + { + return false; + } + + // if it's neither of those, stay on the safe side and suggest turbofish, + // even if it could work! + true +} + +#[derive(Copy, Clone)] +struct Replacement { + method_name: &'static str, + has_args: bool, + requires_turbofish: fn(&LateContext<'_>, &hir::Expr<'_>) -> bool, +} +impl Replacement { + /// `any(f)`, `all(f)` + pub fn non_generic(method_name: &'static str) -> Self { + Self { + method_name, + has_args: true, + requires_turbofish: no_turbofish, + } + } + + /// `sum::()`, `product::()` + pub fn generic(method_name: &'static str) -> Self { + Self { + method_name, + has_args: false, + requires_turbofish: turbofish_if_not_inferred, + } + } +} + pub(super) fn check( cx: &LateContext<'_>, expr: &hir::Expr<'_>, @@ -24,8 +88,7 @@ fn check_fold_with_op( acc: &hir::Expr<'_>, fold_span: Span, op: hir::BinOpKind, - replacement_method_name: &str, - replacement_has_args: bool, + replacement: Replacement, ) { if_chain! { // Extract the body of the closure passed to fold @@ -43,18 +106,27 @@ fn check_fold_with_op( if let PatKind::Binding(_, second_arg_id, second_arg_ident, _) = strip_pat_refs(param_b.pat).kind; if path_to_local_id(left_expr, first_arg_id); - if replacement_has_args || path_to_local_id(right_expr, second_arg_id); + if replacement.has_args || path_to_local_id(right_expr, second_arg_id); then { let mut applicability = Applicability::MachineApplicable; - let sugg = if replacement_has_args { + + let turbofish = if (replacement.requires_turbofish)(cx, expr) { + format!("::<{}>", cx.typeck_results().expr_ty_adjusted(right_expr).peel_refs()) + } else { + String::new() + }; + + let sugg = if replacement.has_args { format!( - "{replacement_method_name}(|{second_arg_ident}| {r})", + "{method}{turbofish}(|{second_arg_ident}| {r})", + method = replacement.method_name, r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability), ) } else { format!( - "{replacement_method_name}()", + "{method}{turbofish}()", + method = replacement.method_name, ) }; @@ -80,11 +152,43 @@ fn check_fold_with_op( // Check if the first argument to .fold is a suitable literal if let hir::ExprKind::Lit(lit) = init.kind { match lit.node { - ast::LitKind::Bool(false) => check_fold_with_op(cx, expr, acc, fold_span, hir::BinOpKind::Or, "any", true), - ast::LitKind::Bool(true) => check_fold_with_op(cx, expr, acc, fold_span, hir::BinOpKind::And, "all", true), - ast::LitKind::Int(0, _) => check_fold_with_op(cx, expr, acc, fold_span, hir::BinOpKind::Add, "sum", false), + ast::LitKind::Bool(false) => { + check_fold_with_op( + cx, + expr, + acc, + fold_span, + hir::BinOpKind::Or, + Replacement::non_generic("any"), + ); + }, + ast::LitKind::Bool(true) => { + check_fold_with_op( + cx, + expr, + acc, + fold_span, + hir::BinOpKind::And, + Replacement::non_generic("all"), + ); + }, + ast::LitKind::Int(0, _) => check_fold_with_op( + cx, + expr, + acc, + fold_span, + hir::BinOpKind::Add, + Replacement::generic("sum"), + ), ast::LitKind::Int(1, _) => { - check_fold_with_op(cx, expr, acc, fold_span, hir::BinOpKind::Mul, "product", false); + check_fold_with_op( + cx, + expr, + acc, + fold_span, + hir::BinOpKind::Mul, + Replacement::generic("product"), + ); }, _ => (), } diff --git a/tests/ui/unnecessary_fold.fixed b/tests/ui/unnecessary_fold.fixed index 2bed14973ca..bd1d4a152ae 100644 --- a/tests/ui/unnecessary_fold.fixed +++ b/tests/ui/unnecessary_fold.fixed @@ -49,4 +49,28 @@ fn unnecessary_fold_over_multiple_lines() { .any(|x| x > 2); } +fn issue10000() { + use std::collections::HashMap; + use std::hash::BuildHasher; + + fn anything(_: T) {} + fn num(_: i32) {} + fn smoketest_map(mut map: HashMap) { + map.insert(0, 0); + assert_eq!(map.values().sum::(), 0); + + // more cases: + let _ = map.values().sum::(); + let _ = map.values().product::(); + let _: i32 = map.values().sum(); + let _: i32 = map.values().product(); + anything(map.values().sum::()); + anything(map.values().product::()); + num(map.values().sum()); + num(map.values().product()); + } + + smoketest_map(HashMap::new()); +} + fn main() {} diff --git a/tests/ui/unnecessary_fold.rs b/tests/ui/unnecessary_fold.rs index a3cec8ea3d5..d27cc460c44 100644 --- a/tests/ui/unnecessary_fold.rs +++ b/tests/ui/unnecessary_fold.rs @@ -49,4 +49,28 @@ fn unnecessary_fold_over_multiple_lines() { .fold(false, |acc, x| acc || x > 2); } +fn issue10000() { + use std::collections::HashMap; + use std::hash::BuildHasher; + + fn anything(_: T) {} + fn num(_: i32) {} + fn smoketest_map(mut map: HashMap) { + map.insert(0, 0); + assert_eq!(map.values().fold(0, |x, y| x + y), 0); + + // more cases: + let _ = map.values().fold(0, |x, y| x + y); + let _ = map.values().fold(1, |x, y| x * y); + let _: i32 = map.values().fold(0, |x, y| x + y); + let _: i32 = map.values().fold(1, |x, y| x * y); + anything(map.values().fold(0, |x, y| x + y)); + anything(map.values().fold(1, |x, y| x * y)); + num(map.values().fold(0, |x, y| x + y)); + num(map.values().fold(1, |x, y| x * y)); + } + + smoketest_map(HashMap::new()); +} + fn main() {} diff --git a/tests/ui/unnecessary_fold.stderr b/tests/ui/unnecessary_fold.stderr index 22c44588ab7..98979f7477f 100644 --- a/tests/ui/unnecessary_fold.stderr +++ b/tests/ui/unnecessary_fold.stderr @@ -36,5 +36,59 @@ error: this `.fold` can be written more succinctly using another method LL | .fold(false, |acc, x| acc || x > 2); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `any(|x| x > 2)` -error: aborting due to 6 previous errors +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:60:33 + | +LL | assert_eq!(map.values().fold(0, |x, y| x + y), 0); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `sum::()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:63:30 + | +LL | let _ = map.values().fold(0, |x, y| x + y); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `sum::()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:64:30 + | +LL | let _ = map.values().fold(1, |x, y| x * y); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `product::()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:65:35 + | +LL | let _: i32 = map.values().fold(0, |x, y| x + y); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `sum()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:66:35 + | +LL | let _: i32 = map.values().fold(1, |x, y| x * y); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `product()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:67:31 + | +LL | anything(map.values().fold(0, |x, y| x + y)); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `sum::()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:68:31 + | +LL | anything(map.values().fold(1, |x, y| x * y)); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `product::()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:69:26 + | +LL | num(map.values().fold(0, |x, y| x + y)); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `sum()` + +error: this `.fold` can be written more succinctly using another method + --> $DIR/unnecessary_fold.rs:70:26 + | +LL | num(map.values().fold(1, |x, y| x * y)); + | ^^^^^^^^^^^^^^^^^^^^^ help: try: `product()` + +error: aborting due to 15 previous errors