Implement unnecesary_filter_map lint
This commit is contained in:
Michael Wright
parent
cdde22c2cc
commit
f5ffac4fce
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@ -864,6 +864,7 @@ All notable changes to this project will be documented in this file.
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[`unit_arg`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unit_arg
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[`unit_cmp`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unit_cmp
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[`unnecessary_cast`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unnecessary_cast
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[`unnecessary_filter_map`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unnecessary_filter_map
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[`unnecessary_fold`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unnecessary_fold
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[`unnecessary_mut_passed`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unnecessary_mut_passed
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[`unnecessary_operation`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unnecessary_operation
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@ -9,7 +9,7 @@ We are currently in the process of discussing Clippy 1.0 via the RFC process in
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A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
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[There are 278 lints included in this crate!](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
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[There are 279 lints included in this crate!](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
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We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
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@ -614,6 +614,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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methods::SINGLE_CHAR_PATTERN,
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methods::STRING_EXTEND_CHARS,
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methods::TEMPORARY_CSTRING_AS_PTR,
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methods::UNNECESSARY_FILTER_MAP,
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methods::UNNECESSARY_FOLD,
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methods::USELESS_ASREF,
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methods::WRONG_SELF_CONVENTION,
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@ -829,6 +830,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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methods::CLONE_ON_COPY,
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methods::FILTER_NEXT,
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methods::SEARCH_IS_SOME,
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methods::UNNECESSARY_FILTER_MAP,
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methods::USELESS_ASREF,
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misc::SHORT_CIRCUIT_STATEMENT,
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misc_early::REDUNDANT_CLOSURE_CALL,
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@ -1,5 +1,6 @@
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use crate::rustc::hir;
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use crate::rustc::hir::def::Def;
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use crate::rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
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use crate::rustc::lint::{in_external_macro, LateContext, LateLintPass, Lint, LintArray, LintContext, LintPass};
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use crate::rustc::ty::{self, Ty};
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use crate::rustc::{declare_tool_lint, lint_array};
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@ -8,6 +9,7 @@ use crate::syntax::ast;
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use crate::syntax::source_map::{BytePos, Span};
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use crate::utils::paths;
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use crate::utils::sugg;
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use crate::utils::usage::mutated_variables;
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use crate::utils::{
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get_arg_name, get_trait_def_id, implements_trait, in_macro, is_copy, is_expn_of, is_self, is_self_ty,
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iter_input_pats, last_path_segment, match_def_path, match_path, match_qpath, match_trait_method, match_type,
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@ -692,6 +694,27 @@ declare_clippy_lint! {
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"using `fold` when a more succinct alternative exists"
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}
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/// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
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///
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/// **Why is this bad?** Complexity
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///
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/// **Known problems:** None
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///
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/// **Example:**
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/// ```rust
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/// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
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/// ```
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/// This could be written as:
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/// ```rust
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/// let _ = (0..3).filter(|&x| x > 2);
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/// ```
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declare_clippy_lint! {
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pub UNNECESSARY_FILTER_MAP,
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complexity,
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"using `filter_map` when a more succinct alternative exists"
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}
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(
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@ -725,7 +748,8 @@ impl LintPass for Pass {
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STRING_EXTEND_CHARS,
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ITER_CLONED_COLLECT,
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USELESS_ASREF,
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UNNECESSARY_FOLD
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UNNECESSARY_FOLD,
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UNNECESSARY_FILTER_MAP
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)
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}
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}
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@ -791,6 +815,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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lint_asref(cx, expr, "as_mut", arglists[0]);
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} else if let Some(arglists) = method_chain_args(expr, &["fold"]) {
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lint_unnecessary_fold(cx, expr, arglists[0]);
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} else if let Some(arglists) = method_chain_args(expr, &["filter_map"]) {
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unnecessary_filter_map::lint(cx, expr, arglists[0]);
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}
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lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
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@ -1398,6 +1424,144 @@ fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args:
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};
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}
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mod unnecessary_filter_map {
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use super::*;
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pub(super) fn lint(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
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if !match_trait_method(cx, expr, &paths::ITERATOR) {
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return;
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}
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if let hir::ExprKind::Closure(_, _, body_id, ..) = args[1].node {
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let body = cx.tcx.hir.body(body_id);
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let arg_id = body.arguments[0].pat.id;
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let mutates_arg = match mutated_variables(&body.value, cx) {
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Some(used_mutably) => used_mutably.contains(&arg_id),
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None => true,
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};
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let (mut found_mapping, mut found_filtering) = check_expression(&cx, arg_id, &body.value);
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let mut return_visitor = ReturnVisitor::new(&cx, arg_id);
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return_visitor.visit_expr(&body.value);
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found_mapping |= return_visitor.found_mapping;
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found_filtering |= return_visitor.found_filtering;
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if !found_filtering {
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span_lint(
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cx,
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UNNECESSARY_FILTER_MAP,
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expr.span,
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"this `.filter_map` can be written more simply using `.map`",
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);
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return;
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}
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if !found_mapping && !mutates_arg {
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span_lint(
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cx,
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UNNECESSARY_FILTER_MAP,
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expr.span,
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"this `.filter_map` can be written more simply using `.filter`",
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);
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return;
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}
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}
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}
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// returns (found_mapping, found_filtering)
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fn check_expression<'a, 'tcx: 'a>(cx: &'a LateContext<'a, 'tcx>, arg_id: ast::NodeId, expr: &'tcx hir::Expr) -> (bool, bool) {
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match &expr.node {
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hir::ExprKind::Call(ref func, ref args) => {
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if_chain! {
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if let hir::ExprKind::Path(ref path) = func.node;
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then {
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if match_qpath(path, &paths::OPTION_SOME) {
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if_chain! {
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if let hir::ExprKind::Path(path) = &args[0].node;
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if let Def::Local(ref local) = cx.tables.qpath_def(path, args[0].hir_id);
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then {
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if arg_id == *local {
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return (false, false)
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}
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}
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}
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return (true, false);
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} else {
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// We don't know. It might do anything.
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return (true, true);
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}
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}
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}
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(true, true)
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},
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hir::ExprKind::Block(ref block, _) => {
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if let Some(expr) = &block.expr {
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check_expression(cx, arg_id, &expr)
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} else {
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(false, false)
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}
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},
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// There must be an else_arm or there will be a type error
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hir::ExprKind::If(_, ref if_arm, Some(ref else_arm)) => {
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let if_check = check_expression(cx, arg_id, if_arm);
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let else_check = check_expression(cx, arg_id, else_arm);
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(if_check.0 | else_check.0, if_check.1 | else_check.1)
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},
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hir::ExprKind::Match(_, ref arms, _) => {
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let mut found_mapping = false;
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let mut found_filtering = false;
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for arm in arms {
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let (m, f) = check_expression(cx, arg_id, &arm.body);
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found_mapping |= m;
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found_filtering |= f;
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}
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(found_mapping, found_filtering)
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},
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hir::ExprKind::Path(path) if match_qpath(path, &paths::OPTION_NONE) => (false, true),
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_ => (true, true)
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}
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}
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struct ReturnVisitor<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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arg_id: ast::NodeId,
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// Found a non-None return that isn't Some(input)
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found_mapping: bool,
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// Found a return that isn't Some
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found_filtering: bool,
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}
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impl<'a, 'tcx: 'a> ReturnVisitor<'a, 'tcx> {
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fn new(cx: &'a LateContext<'a, 'tcx>, arg_id: ast::NodeId) -> ReturnVisitor<'a, 'tcx> {
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ReturnVisitor {
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cx,
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arg_id,
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found_mapping: false,
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found_filtering: false,
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}
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}
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}
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impl<'a, 'tcx> Visitor<'tcx> for ReturnVisitor<'a, 'tcx> {
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fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
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if let hir::ExprKind::Ret(Some(expr)) = &expr.node {
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let (found_mapping, found_filtering) = check_expression(self.cx, self.arg_id, expr);
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self.found_mapping |= found_mapping;
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self.found_filtering |= found_filtering;
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} else {
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walk_expr(self, expr);
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}
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}
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fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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NestedVisitorMap::None
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}
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}
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}
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fn lint_iter_nth(cx: &LateContext<'_, '_>, expr: &hir::Expr, iter_args: &[hir::Expr], is_mut: bool) {
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let mut_str = if is_mut { "_mut" } else { "" };
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let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
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@ -443,3 +443,17 @@ fn main() {
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let opt = Some(0);
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let _ = opt.unwrap();
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}
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/// Checks implementation of `UNNECESSARY_FILTER_MAP` lint
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fn unnecessary_filter_map() {
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let _ = (0..4).filter_map(|x| if x > 1 { Some(x) } else { None });
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let _ = (0..4).filter_map(|x| { if x > 1 { return Some(x); }; None });
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let _ = (0..4).filter_map(|x| match x {
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0 | 1 => None,
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_ => Some(x),
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});
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let _ = (0..4).filter_map(|x| Some(x + 1));
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let _ = (0..4).filter_map(i32::checked_abs);
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}
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@ -453,5 +453,35 @@ error: used unwrap() on an Option value. If you don't want to handle the None ca
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= note: `-D clippy::option-unwrap-used` implied by `-D warnings`
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error: aborting due to 56 previous errors
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error: this `.filter_map` can be written more simply using `.filter`
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--> $DIR/methods.rs:449:13
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449 | let _ = (0..4).filter_map(|x| if x > 1 { Some(x) } else { None });
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= note: `-D clippy::unnecessary-filter-map` implied by `-D warnings`
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error: this `.filter_map` can be written more simply using `.filter`
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--> $DIR/methods.rs:450:13
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450 | let _ = (0..4).filter_map(|x| { if x > 1 { return Some(x); }; None });
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: this `.filter_map` can be written more simply using `.filter`
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--> $DIR/methods.rs:451:13
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451 | let _ = (0..4).filter_map(|x| match x {
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| _____________^
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452 | | 0 | 1 => None,
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453 | | _ => Some(x),
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454 | | });
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| |______^
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error: this `.filter_map` can be written more simply using `.map`
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--> $DIR/methods.rs:456:13
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456 | let _ = (0..4).filter_map(|x| Some(x + 1));
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 60 previous errors
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