Implement flat_map lint #4231

jeremystucki · 2019-06-24T13:12:45Z

Fixes #4224

changelog: New Lint flat_map_identity to detect unnecessary calls to flat_map

Manishearth · 2019-06-24T14:42:46Z

PR body needs a changelog entry

Also, not sure if this lint name is appropriate

flip1995 · 2019-06-24T16:21:31Z

Maybe FLAT_MAP_IDENTITY?

lopopolo · 2019-06-27T12:37:44Z

Does this handle .flat_map(std::convert::identity) too? 😄

bors · 2019-07-17T08:09:30Z

☔ The latest upstream changes (presumably #4259) made this pull request unmergeable. Please resolve the merge conflicts.

flip1995 · 2019-08-01T16:25:33Z

Ping from triage @jeremystucki. Do you want to continue working on this?

jeremystucki · 2019-08-05T07:21:42Z

Ah sorry totally forgot about that one, I've been really busy.
I only got time in a week or so. Would you like to continue working on this in the meantime?

flip1995 · 2019-08-05T07:25:41Z

No worries. Just return to this once you have more time. I labeled it with help-wanted, in case someone wants to take over in the mean time.

flip1995 · 2019-08-11T18:40:44Z

clippy_lints/src/methods/mod.rs

+        if match_trait_method(cx, expr, &paths::ITERATOR);
+
+        if flat_map_args.len() == 2;
+        if let hir::ExprKind::Closure(_, _, body_id, _, _) = flat_map_args[1].node;


You could insert the then of the if_chain! here and then split up the two if chains for |x| x and convert::identity, like this:

Suggested change

if let hir::ExprKind::Closure(_, _, body_id, _, _) = flat_map_args[1].node;

then {

let arg = flat_map_args[1];

if_chain! {

if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg.node;

// check for `|x| x`

}

if_chain! {

if let hir::ExprKind::Path(ref qpath) = arg.node;

// check for `convert::identity`

}

}

Co-authored-by: Philipp Krones <hello@philkrones.com>

jeremystucki · 2019-08-12T06:36:07Z

r? @flip1995

flip1995 · 2019-08-12T07:49:08Z

clippy_lints/src/methods/mod.rs

+    /// iter.flatten();
+    /// ```
+    pub FLAT_MAP_IDENTITY,
+    pedantic,


This should be a style or complexity lint IMO.

Everything else LGTM

flip1995

You have to run update_lints

Also both lints can be easily implemented as MachineApplicable lints. Steps to do this:

swap the span_lint function with the span_lint_and_sugg function
As the span, only use the span of the call to flat_map(..)
Add the sugg-message: "try" (or something similar)
Add as the sugg: "flatten()"
In the second if_chain!: don't shadow expr, but name it arg or something else. (This binding can also be shared between both inner if_chain!s)
Remove "This can be simplified by calling flatten()" from the lint message.
Add // run-rustfix to the top of the test file
Update the .stderr file.

jeremystucki · 2019-08-12T19:45:49Z

I can't quite figure out how to get the correct span. Can anyone help me?

This is the current diff:

 error: called `flat_map(|x| x)` on an `Iterator`
   --> $DIR/unnecessary_flat_map.rs:9:14
    |
 LL |     iterator.flat_map(|x| x);
-   |              ^^^^^^^^^^^^^^^ help: try: `flatten()`
+   |              ^^^^^^^^ help: try: `flatten()`
    |
    = note: `-D clippy::flat-map-identity` implied by `-D warnings`
 
 error: called `flat_map(std::convert::identity)` on an `Iterator`
   --> $DIR/unnecessary_flat_map.rs:12:14
    |
 LL |     iterator.flat_map(convert::identity);
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
+   |              ^^^^^^^^ help: try: `flatten()`
 
 error: aborting due to 2 previous errors

flip1995 · 2019-08-13T07:19:47Z

The refactor looks really good!

It seems, that you have to construct the span (In the apply_lints closure):

span.with_hi(expr.span.hi())

This should give you the correct span.

flip1995 · 2019-08-14T08:00:34Z

@bors r+

Thanks!

bors · 2019-08-14T08:00:35Z

📌 Commit 2bfcf89 has been approved by flip1995

bors · 2019-08-14T08:41:34Z

⌛ Testing commit 2bfcf89 with merge 2cf7ee5...

Implement flat_map lint Fixes #4224 changelog: New Lint `flat_map_identity` to detect unnecessary calls to `flat_map`

bors · 2019-08-14T08:54:05Z

💔 Test failed - status-appveyor

phansch · 2019-08-14T09:28:17Z

@bors retry (should work after #4378)

bors · 2019-08-14T09:36:22Z

⌛ Testing commit 2bfcf89 with merge 4f8bdf3...

Implement flat_map lint Fixes #4224 changelog: New Lint `flat_map_identity` to detect unnecessary calls to `flat_map`

bors · 2019-08-14T10:17:51Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: flip1995
Pushing 4f8bdf3 to master...

This commit fixes the file names of the `flat_map_identity` test. Previously, their names were started with `unnecessary_flat_map` even though the lint rule name is `flat_map_identity`. This inconsistency happened probably because the rule name was changed during the discussion in the PR where this rule was introduced. ref: rust-lang#4231

Fix file names of flat_map_identity test This patch fixes the file names of the `flat_map_identity` test. Previously, their names were started with `unnecessary_flat_map` even though the lint rule name is `flat_map_identity`. This inconsistency happened probably because the rule name was changed during the discussion in the PR where this rule was introduced. ref: #4231 changelog: none

flip1995 added the S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) label Jul 3, 2019

jeremystucki added 2 commits July 8, 2019 17:11

Add test for unnecessary_flat_map

1fd617d

Implement flat_map lint

c7da4c2

flip1995 added the E-help-wanted Call for participation: Help is requested to fix this issue. label Aug 5, 2019

jeremystucki added 3 commits August 11, 2019 19:22

Merge branch 'origin/master' into flat-map

05d9f88

Handle calls with 'std::convert::identity'

f0ce04f

Rename 'flat_map' → 'flat_map_identity'

b651f19

flip1995 reviewed Aug 11, 2019

View reviewed changes

jeremystucki and others added 3 commits August 11, 2019 21:02

Refactor if_chain

5fd7d44

Co-authored-by: Philipp Krones <hello@philkrones.com>

Update rustdoc

df90630

Run 'update_lints'

6ddf8c3

flip1995 reviewed Aug 12, 2019

View reviewed changes

Change lint type from 'pedantic' → 'complexity'

09e9568

flip1995 requested changes Aug 12, 2019

View reviewed changes

jeremystucki added 2 commits August 12, 2019 21:29

Minor refactoring

3a65e4e

Use 'span_lint_and_sugg'

d51136d

jeremystucki and others added 2 commits August 12, 2019 21:47

Run 'update_lints'

4275d7b

Add 'unnecessary_flat_map.fixed'

6a263c0

flip1995 approved these changes Aug 13, 2019

View reviewed changes

Use correct span

d578c43

jeremystucki added 2 commits August 13, 2019 21:50

Update test

2fe5e2c

Merge branch 'origin/master' into flat-map

2bfcf89

bors added a commit that referenced this pull request Aug 14, 2019

Auto merge of #4231 - jeremystucki:flat-map, r=flip1995

2cf7ee5

Implement flat_map lint Fixes #4224 changelog: New Lint `flat_map_identity` to detect unnecessary calls to `flat_map`

bors added a commit that referenced this pull request Aug 14, 2019

Auto merge of #4231 - jeremystucki:flat-map, r=flip1995

4f8bdf3

Implement flat_map lint Fixes #4224 changelog: New Lint `flat_map_identity` to detect unnecessary calls to `flat_map`

bors merged commit 2bfcf89 into rust-lang:master Aug 14, 2019

jeremystucki deleted the flat-map branch August 14, 2019 11:42

magurotuna mentioned this pull request Feb 3, 2021

Fix file names of flat_map_identity test #6669

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Implement flat_map lint #4231

Implement flat_map lint #4231

jeremystucki commented Jun 24, 2019 •

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-        if let hir::ExprKind::Closure(_, _, body_id, _, _) = flat_map_args[1].node;
+        then {
+            let arg = flat_map_args[1];
+            if_chain! {
+                if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg.node;
+                // check for `|x| x`
+            }
+            if_chain! {
+                if let hir::ExprKind::Path(ref qpath) = arg.node;
+                // check for `convert::identity`
+            }
+        }

Implement flat_map lint #4231

Implement flat_map lint #4231

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