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unnecessary sort by: avoid dereferencing closure param
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@ebroto
ebroto committed Sep 23, 2020
1 parent e636b88 commit 9365660
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Showing 4 changed files with 81 additions and 69 deletions.
58 changes: 20 additions & 38 deletions clippy_lints/src/unnecessary_sort_by.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -170,22 +170,12 @@ fn mirrored_exprs(
}

fn detect_lint(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintTrigger> {
// NOTE: Vectors of references are not supported. In order to avoid hitting https://github.com/rust-lang/rust/issues/34162,
// (different unnamed lifetimes for closure arg and return type) we need to make sure the suggested
// closure parameter is not a reference in case we suggest `Reverse`. Trying to destructure more
// than one level of references would add some extra complexity as we would have to compensate
// in the closure body.

if_chain! {
if let ExprKind::MethodCall(name_ident, _, args, _) = &expr.kind;
if let name = name_ident.ident.name.to_ident_string();
if name == "sort_by" || name == "sort_unstable_by";
if let [vec, Expr { kind: ExprKind::Closure(_, _, closure_body_id, _, _), .. }] = args;
let vec_ty = cx.typeck_results().expr_ty(vec);
if utils::is_type_diagnostic_item(cx, vec_ty, sym!(vec_type));
let ty = vec_ty.walk().nth(1).unwrap().expect_ty(); // T in Vec<T>
if !matches!(&ty.kind(), ty::Ref(..));
if utils::is_copy(cx, ty);
if utils::is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(vec), sym!(vec_type));
if let closure_body = cx.tcx.hir().body(*closure_body_id);
if let &[
Param { pat: Pat { kind: PatKind::Binding(_, _, left_ident, _), .. }, ..},
Expand All @@ -210,40 +200,32 @@ fn detect_lint(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintTrigger> {
let vec_name = Sugg::hir(cx, &args[0], "..").to_string();
let unstable = name == "sort_unstable_by";

if_chain! {
if let ExprKind::Path(QPath::Resolved(_, Path {
segments: [PathSegment { ident: left_name, .. }], ..
})) = &left_expr.kind;
if left_name == left_ident;
then {
return Some(LintTrigger::Sort(SortDetection { vec_name, unstable }))
} else {
if !key_returns_borrow(cx, left_expr) {
return Some(LintTrigger::SortByKey(SortByKeyDetection {
vec_name,
unstable,
closure_arg,
closure_body,
reverse
}))
}
if let ExprKind::Path(QPath::Resolved(_, Path {
segments: [PathSegment { ident: left_name, .. }], ..
})) = &left_expr.kind {
if left_name == left_ident {
return Some(LintTrigger::Sort(SortDetection { vec_name, unstable }));
}
}

if !expr_borrows(cx, left_expr) {
return Some(LintTrigger::SortByKey(SortByKeyDetection {
vec_name,
unstable,
closure_arg,
closure_body,
reverse
}));
}
}
}

None
}

fn key_returns_borrow(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
if let Some(def_id) = utils::fn_def_id(cx, expr) {
let output = cx.tcx.fn_sig(def_id).output();
let ty = output.skip_binder();
return matches!(ty.kind(), ty::Ref(..))
|| ty.walk().any(|arg| matches!(arg.unpack(), GenericArgKind::Lifetime(_)));
}

false
fn expr_borrows(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
let ty = cx.typeck_results().expr_ty(expr);
matches!(ty.kind(), ty::Ref(..)) || ty.walk().any(|arg| matches!(arg.unpack(), GenericArgKind::Lifetime(_)))
}

impl LateLintPass<'_> for UnnecessarySortBy {
Expand All @@ -256,7 +238,7 @@ impl LateLintPass<'_> for UnnecessarySortBy {
"use Vec::sort_by_key here instead",
"try",
format!(
"{}.sort{}_by_key(|&{}| {})",
"{}.sort{}_by_key(|{}| {})",
trigger.vec_name,
if trigger.unstable { "_unstable" } else { "" },
trigger.closure_arg,
Expand Down
30 changes: 15 additions & 15 deletions tests/ui/unnecessary_sort_by.fixed
View file
Original file line number Diff line number Diff line change
Expand Up @@ -13,23 +13,24 @@ fn unnecessary_sort_by() {
// Forward examples
vec.sort();
vec.sort_unstable();
vec.sort_by_key(|&a| (a + 5).abs());
vec.sort_unstable_by_key(|&a| id(-a));
vec.sort_by_key(|a| (a + 5).abs());
vec.sort_unstable_by_key(|a| id(-a));
// Reverse examples
vec.sort_by_key(|&b| Reverse(b));
vec.sort_by_key(|&b| Reverse((b + 5).abs()));
vec.sort_unstable_by_key(|&b| Reverse(id(-b)));
vec.sort_by(|a, b| b.cmp(a)); // not linted to avoid suggesting `Reverse(b)` which would borrow
vec.sort_by_key(|b| Reverse((b + 5).abs()));
vec.sort_unstable_by_key(|b| Reverse(id(-b)));
// Negative examples (shouldn't be changed)
let c = &7;
vec.sort_by(|a, b| (b - a).cmp(&(a - b)));
vec.sort_by(|_, b| b.cmp(&5));
vec.sort_by(|_, b| b.cmp(c));
vec.sort_unstable_by(|a, _| a.cmp(c));

// Ignore vectors of references
// Vectors of references are fine as long as the resulting key does not borrow
let mut vec: Vec<&&&isize> = vec![&&&3, &&&6, &&&1, &&&2, &&&5];
vec.sort_by(|a, b| (***a).abs().cmp(&(***b).abs()));
vec.sort_unstable_by(|a, b| (***a).abs().cmp(&(***b).abs()));
vec.sort_by_key(|a| (***a).abs());
vec.sort_unstable_by_key(|a| (***a).abs());
// `Reverse(b)` would borrow in the following cases, don't lint
vec.sort_by(|a, b| b.cmp(a));
vec.sort_unstable_by(|a, b| b.cmp(a));
}
Expand Down Expand Up @@ -68,10 +69,9 @@ mod issue_5754 {
}
}

// `Vec::sort_by_key` closure parameter is `F: FnMut(&T) -> K`
// The suggestion is destructuring T and we know T is not a reference, so test that non-Copy T are
// not linted.
// The closure parameter is not dereferenced anymore, so non-Copy types can be linted
mod issue_6001 {
use super::*;
struct Test(String);

impl Test {
Expand All @@ -85,11 +85,11 @@ mod issue_6001 {
let mut args: Vec<Test> = vec![];

// Forward
args.sort_by(|a, b| a.name().cmp(&b.name()));
args.sort_unstable_by(|a, b| a.name().cmp(&b.name()));
args.sort_by_key(|a| a.name());
args.sort_unstable_by_key(|a| a.name());
// Reverse
args.sort_by(|a, b| b.name().cmp(&a.name()));
args.sort_unstable_by(|a, b| b.name().cmp(&a.name()));
args.sort_by_key(|b| Reverse(b.name()));
args.sort_unstable_by_key(|b| Reverse(b.name()));
}
}

Expand Down
10 changes: 5 additions & 5 deletions tests/ui/unnecessary_sort_by.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ fn unnecessary_sort_by() {
vec.sort_by(|a, b| (a + 5).abs().cmp(&(b + 5).abs()));
vec.sort_unstable_by(|a, b| id(-a).cmp(&id(-b)));
// Reverse examples
vec.sort_by(|a, b| b.cmp(a));
vec.sort_by(|a, b| b.cmp(a)); // not linted to avoid suggesting `Reverse(b)` which would borrow
vec.sort_by(|a, b| (b + 5).abs().cmp(&(a + 5).abs()));
vec.sort_unstable_by(|a, b| id(-b).cmp(&id(-a)));
// Negative examples (shouldn't be changed)
Expand All @@ -26,10 +26,11 @@ fn unnecessary_sort_by() {
vec.sort_by(|_, b| b.cmp(c));
vec.sort_unstable_by(|a, _| a.cmp(c));

// Ignore vectors of references
// Vectors of references are fine as long as the resulting key does not borrow
let mut vec: Vec<&&&isize> = vec![&&&3, &&&6, &&&1, &&&2, &&&5];
vec.sort_by(|a, b| (***a).abs().cmp(&(***b).abs()));
vec.sort_unstable_by(|a, b| (***a).abs().cmp(&(***b).abs()));
// `Reverse(b)` would borrow in the following cases, don't lint
vec.sort_by(|a, b| b.cmp(a));
vec.sort_unstable_by(|a, b| b.cmp(a));
}
Expand Down Expand Up @@ -68,10 +69,9 @@ mod issue_5754 {
}
}

// `Vec::sort_by_key` closure parameter is `F: FnMut(&T) -> K`
// The suggestion is destructuring T and we know T is not a reference, so test that non-Copy T are
// not linted.
// The closure parameter is not dereferenced anymore, so non-Copy types can be linted
mod issue_6001 {
use super::*;
struct Test(String);

impl Test {
Expand Down
52 changes: 41 additions & 11 deletions tests/ui/unnecessary_sort_by.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,31 +16,61 @@ error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:16:5
|
LL | vec.sort_by(|a, b| (a + 5).abs().cmp(&(b + 5).abs()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_by_key(|&a| (a + 5).abs())`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_by_key(|a| (a + 5).abs())`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:17:5
|
LL | vec.sort_unstable_by(|a, b| id(-a).cmp(&id(-b)));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_unstable_by_key(|&a| id(-a))`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:19:5
|
LL | vec.sort_by(|a, b| b.cmp(a));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_by_key(|&b| Reverse(b))`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_unstable_by_key(|a| id(-a))`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:20:5
|
LL | vec.sort_by(|a, b| (b + 5).abs().cmp(&(a + 5).abs()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_by_key(|&b| Reverse((b + 5).abs()))`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_by_key(|b| Reverse((b + 5).abs()))`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:21:5
|
LL | vec.sort_unstable_by(|a, b| id(-b).cmp(&id(-a)));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_unstable_by_key(|&b| Reverse(id(-b)))`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_unstable_by_key(|b| Reverse(id(-b)))`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:31:5
|
LL | vec.sort_by(|a, b| (***a).abs().cmp(&(***b).abs()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_by_key(|a| (***a).abs())`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:32:5
|
LL | vec.sort_unstable_by(|a, b| (***a).abs().cmp(&(***b).abs()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.sort_unstable_by_key(|a| (***a).abs())`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:88:9
|
LL | args.sort_by(|a, b| a.name().cmp(&b.name()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `args.sort_by_key(|a| a.name())`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:89:9
|
LL | args.sort_unstable_by(|a, b| a.name().cmp(&b.name()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `args.sort_unstable_by_key(|a| a.name())`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:91:9
|
LL | args.sort_by(|a, b| b.name().cmp(&a.name()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `args.sort_by_key(|b| Reverse(b.name()))`

error: use Vec::sort_by_key here instead
--> $DIR/unnecessary_sort_by.rs:92:9
|
LL | args.sort_unstable_by(|a, b| b.name().cmp(&a.name()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `args.sort_unstable_by_key(|b| Reverse(b.name()))`

error: aborting due to 7 previous errors
error: aborting due to 12 previous errors

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