New lint truncate_with_drain #13603

Kither12 · 2024-10-25T08:12:07Z

I add new lint that replace vec.drain(x..) with vec.truncate(x). See #13580
changelog: new lint: [truncate_with_drain]

rustbot · 2024-10-25T08:12:13Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @blyxyas (or someone else) some time within the next two weeks.

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samueltardieu · 2024-10-25T13:19:46Z

tests/ui/truncate_with_drain.rs

+    let mut v = vec![1, 2, 3];
+    let n = v.drain(1..v.len()).count();
+
+    // Do not lint because iterator is assigned and used


Isn't that already fully covered by the "Do not lint because iterator is assigned" test?

I think used and assigned is different in this case and both need to have a test? Maybe I will remove the assigned_and_used test.

samueltardieu · 2024-10-25T13:21:22Z

tests/ui/truncate_with_drain.rs

+    let mut deque = VecDeque::from([1, 2, 3]);
+    let n = deque.drain(1..deque.len()).count();
+
+    // Do not lint because iterator is assigned and used


Ditto, looks already covered by the first test in this function.

samueltardieu · 2024-10-25T13:22:15Z

tests/ui/truncate_with_drain.rs

+    let mut s = String::from("Hello, world!");
+    let n = s.drain(1..s.len()).count();
+
+    // Do not lint because iterator is assigned and used


samueltardieu · 2024-10-25T13:22:40Z

tests/ui/truncate_with_drain.rs

+    let mut s = String::from("Hello, world!");
+    let iter = s.drain(1..);
+
+    // Do not lint because iterator is assigned and used


samueltardieu · 2024-10-25T13:24:05Z

clippy_lints/src/methods/mod.rs

@@ -4634,6 +4661,7 @@ impl Methods {
                        && matches!(kind, StmtKind::Semi(_))
                        && args.len() <= 1
                    {
+                        truncate_with_drain::check(cx, expr, recv, span, args.first());


Shouldn't clear_with_drain get a chance to run first?

I think the order is not important because truncate_with_drain don't lint on fully-opened range?

I thought it would check a 0.. as well but it doesn't. Agreed, the order is unimportant in this case.

samueltardieu · 2024-10-25T13:27:01Z

clippy_lints/src/methods/truncate_with_drain.rs

+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, span: Span, arg: Option<&Expr<'_>>) {
+    if let Some(arg) = arg {
+        if match_acceptable_type(cx, recv, &ACCEPTABLE_TYPES_WITH_ARG)


It feels unbalanced to pass ACCEPTABLE_TYPES_WITH_ARG while having String builtin into the function. Why not remove this third argument and have ACCEPTABLE_TYPES_WITH_ARG built inside match_acceptable_type() as well?

samueltardieu · 2024-10-25T13:28:14Z

clippy_lints/src/methods/truncate_with_drain.rs

+    }
+}
+
+fn match_acceptable_type(cx: &LateContext<'_>, expr: &Expr<'_>, types: &[rustc_span::Symbol]) -> bool {


Maybe a less "general" name would be better. is_handled_collection_type() maybe?

samueltardieu · 2024-10-25T13:30:24Z

tests/ui/truncate_with_drain.fixed

+
+    // Do lint
+    let mut v = vec![1, 2, 3];
+    v.truncate(1);


Wouldn't be better to include error markers to ensure a regression can be identified automatically?

I'm not sure I know what are error markers, did you mean adding new tests or something?

They explain what error should be raised, and where. See e.g. https://github.com/rust-lang/rust-clippy/blob/master/tests/ui/into_iter_without_iter.rs#L10

Thank you, I'll look into that

samueltardieu · 2024-10-25T13:33:13Z

clippy_lints/src/methods/truncate_with_drain.rs

+                false
+            }
+        });
+        let end_is_none_or_max = end.map_or(true, |end| match limits {


Maybe use end.is_none_or(|end| …), as a new lint will probably flag this hand-made construct.

samueltardieu · 2024-10-25T13:35:53Z

clippy_lints/src/methods/truncate_with_drain.rs

+                TRUNCATE_WITH_DRAIN,
+                span.with_hi(expr.span.hi()),
+                format!("`drain` used to truncate a `{ty_name}`"),
+                "try",


Since this is supposed to be machine-applicable, you could probably use "use" here instead of "try".

Jarcho · 2024-10-26T13:10:38Z

This is basically the same as an existing lint clear_with_drain except it allows a lower bound. The two lints should share an implementation.

Kither12 · 2024-10-26T16:44:19Z

This is basically the same as an existing lint clear_with_drain except it allows a lower bound. The two lints should share an implementation.

So do you think that we should merge two lints into one? I think we can possibly add a lint that replace vec.truncate(0) to vec.clear() as well.

Jarcho · 2024-10-27T13:06:05Z

If you can come up with a good name I have no objection. I would have personally named these something like manual_collection_clear just to open up the possibility of detecting more cases.

Kither12 · 2024-10-27T15:08:39Z

If you can come up with a good name I have no objection. I would have personally named these something like manual_collection_clear just to open up the possibility of detecting more cases.

How about manual_collection_truncate, and then check for truncate(0) and replace to clear()? With that I think we can lint more cases like split_off(x) too.

blyxyas

Good first patch, some changes to be made =^w^=
Thanks for the contribution! ❤️

blyxyas · 2024-10-28T10:49:33Z

tests/ui/truncate_with_drain.rs

Could you add error anotations?
While not enforced by CI yet, we'd like to have them enforced, at least manually.

let mut v = vec![1, 2, 3]; //~^ ERROR: <error msg>

blyxyas · 2024-10-28T10:55:15Z

clippy_lints/src/methods/truncate_with_drain.rs

+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, span: Span, arg: Option<&Expr<'_>>) {
+    if let Some(arg) = arg {
+        if is_handled_collection_type(cx, recv)


In these all the three functions you call expr_ty on the typecheck results. While this is cached, it's still not ideal. Could you refactor it so that it's only called once in the main check function?

blyxyas · 2024-10-28T14:39:08Z

clippy_lints/src/methods/truncate_with_drain.rs

+    // Use `opt_item_name` while `String` is not a diagnostic item
+        && let Some(ty_name) = cx.tcx.opt_item_name(adt.did())
+    {
+        if let Some(higher::Range { start: Some(start), .. }) = higher::Range::hir(arg) {


Instead of re-parsing the Range, could you pass it from is_range_open_ended or refactor it so that the higher::Range comes from the main check function?

blyxyas · 2024-10-28T14:42:33Z

clippy_lints/src/methods/mod.rs

@@ -4166,6 +4167,31 @@ declare_clippy_lint! {
    "calling `.first().is_some()` or `.first().is_none()` instead of `.is_empty()`"
 }

+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of `.drain(x..)` for the sole purpose of truncate a container.


Suggested change

/// Checks for usage of `.drain(x..)` for the sole purpose of truncate a container.

/// Checks for usage of `.drain(x..)` for the sole purpose of truncating a container.

blyxyas · 2024-10-28T14:42:56Z

clippy_lints/src/methods/mod.rs

+    #[clippy::version = "1.84.0"]
+    pub TRUNCATE_WITH_DRAIN,
+    nursery,
+    "calling `drain` in order to `truncate` a `Vec`"


The use of truncate here is as a verb, not as a function name, unless I misunderstood something 👀

Suggested change

"calling `drain` in order to `truncate` a `Vec`"

"calling `drain` in order to truncate a `Vec`"

blyxyas · 2024-10-28T14:58:20Z

clippy_lints/src/methods/truncate_with_drain.rs

+use rustc_hir::{Expr, ExprKind, LangItem, Path, QPath};
+use rustc_lint::LateContext;
+use rustc_middle::mir::Const;
+use rustc_middle::ty::{self as rustc_ty};


Is there are reason you alias this? I just spent 3 minutes looking for any reference of it in the documentation and the IDE wasn't helping 😅

I think just importing as ty (the default) would be less confusing

blyxyas · 2024-10-28T15:27:44Z

clippy_lints/src/methods/truncate_with_drain.rs

+            if let rustc_ty::Adt(_, subst) = ty.kind()
+                && let bnd_ty = subst.type_at(0)
+                && let Some(min_val) = bnd_ty.numeric_min_val(cx.tcx)
+                && let Some(min_const) = mir_to_const(cx.tcx, Const::from_ty_const(min_val, bnd_ty, cx.tcx))
+                && let Some(start_const) = ConstEvalCtxt::new(cx).eval(start)


Why is this block needed?

AFAIK there isn't any equivalence on ..n = i64::MIN..n, in fact, for signed integers the second one will give a syntax error.

It checks for usize::MIN..n if I'm not wrong

blyxyas · 2024-10-28T15:27:54Z

clippy_lints/src/methods/truncate_with_drain.rs

+        });
+        let end_is_none_or_max = end.is_none_or(|end| match limits {
+            RangeLimits::Closed => {
+                if let rustc_ty::Adt(_, subst) = ty.kind()


The same question here.

bors · 2024-10-29T08:18:55Z

☔ The latest upstream changes (presumably #13437) made this pull request unmergeable. Please resolve the merge conflicts.

…te-items = true

This lint checks for code that looks like ```rust let something : Vec<_> = (0..100).map(|_| { 1 + 2 + 3 }).collect(); ``` which is more clear as ```rust let something : Vec<_> = std::iter::repeat_with(|| { 1 + 2 + 3 }).take(100).collect(); ``` or ```rust let something : Vec<_> = std::iter::repeat_n(1 + 2 + 3, 100) .collect(); ``` That is, a map over a range which does nothing with the parameter passed to it is simply a function (or closure) being called `n` times and could be more semantically expressed using `take`.

`gen` will be a reserved word in Rust 2024.

Reorder the suggested code for the `IntoIterator` to match the ordering of the trait declaration: ```rust impl IntoIterator for ... { type Item = ...; type IntoIter = ...; ```

…issing_docs_in_private_items`

In Rust 2024, by default lifetimes will be captured which does not reflect the reality since we return an iterator of `DefId` which do not capture the input parameters.

samueltardieu · 2024-11-05T08:37:18Z

Btw, the list of commits brought in this PR doesn't look right.

blyxyas · 2024-11-13T18:55:37Z

@Kither12 if you're having troubles with removing those commits from this PR, you can close it and re-open one. (In the worst case scenario, copy pasting the changes)
Remember to assign me using r? @blyxyas at the end of the PR description if you're going that route.

new lint truncate_with_drain

9458180

rustbot assigned blyxyas Oct 25, 2024

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Oct 25, 2024

samueltardieu reviewed Oct 25, 2024

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Kither12 added 3 commits October 26, 2024 00:00

update tests

cbe2c17

fix test

46872ff

update lint

a9cf5db

blyxyas requested changes Oct 28, 2024

View reviewed changes

Kither12 and others added 16 commits November 4, 2024 13:58

refactor implementation

b8566a2

add error anotations

51b6e6b

Fix indentation of website code snippets

5baa69c

Stop linting unused_io_amount in io traits

336dbdc

borrow_deref_ref: do not trigger on &raw references

7ad6ee6

Add test case for missing_errors_doc at tests with option check-priva…

4779156

…te-items = true

Unvacation giraffate and remove gh-pages -> xFrednet assignment

aa459f3

fix: remove unnecessary unfilter_map usages

91a735f

fix: simplify suggestion

220907d

fix: linter

65597e2

Swap Msrv from Vec to SmallVec

a593379

check if we need a parenthesis

13b6db5

fix: usage of a deprecated Node.js version

3cf33b0

Fire large_const_arrays for computed array lengths

127f647

New lint needless_as_bytes

8af2c6f

Replace .map(…).any(identity) by .any(…)

5308aba

samueltardieu and others added 24 commits November 4, 2024 17:05

Add new lint: map_all_any_identity

613fb2c

Fix is_from_proc_macro attr

2d9ef63

Add 'CoAP' to doc-valid-idents

3b7c7a9

Extend large_include_file lint to also work on attributes

3fa97fb

Do not use gen as a variable name

e909052

`gen` will be a reserved word in Rust 2024.

Cleanup code suggestion for into_iter_without_iter

46efc39

Reorder the suggested code for the `IntoIterator` to match the ordering of the trait declaration: ```rust impl IntoIterator for ... { type Item = ...; type IntoIter = ...; ```

Explain why clippy's HIR const eval exists

9823466

[infinite_loops]: fix suggestion error on async functions/closures

f82b856

Watch tests/compile-test.rs in cargo dev serve

3832b84

Use match ergonomics compatible with editions 2021 and 2024

f4fffd4

new lint: source_item_ordering

2254a98

Improve display of clippy lints page when JS is disabled

ed2e336

Improve theme handling when JS is disabled

31c13e6

Handle noscript style with "js" class on <html>.

82874ef

don't lint unnamed constants in missing_docs_in_private_items

4b4f004

don't lint nested items that don't have generated documentation in `m…

c7ad6d5

…issing_docs_in_private_items`

Return iterator must not capture lifetimes in Rust 2024

d123731

In Rust 2024, by default lifetimes will be captured which does not reflect the reality since we return an iterator of `DefId` which do not capture the input parameters.

no_mangle attribute requires unsafe in Rust 2024

50f8753

needless_continue: check labels consistency before warning

ee0b9b9

new lint truncate_with_drain

448c448

add error anotations

6bee700

small fix

f8f9ed7

fix clippy error

13af889

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New lint truncate_with_drain #13603

New lint truncate_with_drain #13603

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	/// Checks for usage of `.drain(x..)` for the sole purpose of truncate a container.
	/// Checks for usage of `.drain(x..)` for the sole purpose of truncating a container.

	"calling `drain` in order to `truncate` a `Vec`"
	"calling `drain` in order to truncate a `Vec`"

New lint truncate_with_drain #13603

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New lint truncate_with_drain #13603

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