[FP] identity_op in front of if #8730

tamaroning · 2022-04-22T03:40:45Z

changelog: FP: [identity_op]: is now allowed in front of if statements, blocks and other expressions where the suggestion would be invalid.

Resolved simular problems with blocks, mathces, and loops.
identity_op always does NOT suggest reducing 0 + if b { 1 } else { 2 } + 3 into if b { 1 } else { 2 } + 3 even in the case that the expression is in f(expr) or let x = expr; for now.

rust-highfive · 2022-04-22T03:40:48Z

r? @Manishearth

(rust-highfive has picked a reviewer for you, use r? to override)

hellow554 · 2022-04-22T06:04:29Z

tests/ui/identity_op.rs

+    // See #8724
+    let a = 0;
+    let b = true;
+    0 + if b { 1 } else { 2 };


I would like to see a testcase like let _c = 0 + if b { 1 } else { 2 };
Maybe also a function like I wrote in #8724:

pub fn decide(a: bool, b: bool) -> u32 { 0 + if a { 1 } else { 2 } + if b { 3 } else { 5 } }

tamaroning · 2022-04-22T16:17:15Z

Hmm, uitest somehow fails.
~~Despite of attribute #[allow(clippy::identity_op)], the warning of identity_op occurs.~~

...
---- compile_test stdout ----
diff of stderr:

+error: the operation is ineffective. Consider reducing it to `i`
error: test failed, to rerun pass '--test compile-test'
+  --> $DIR/without_loop_counters.rs:104:13
+   |
+LL |         dst[i - 0] = src[i];
+   |             ^^^^^
+   |
+   = note: `-D clippy::identity-op` implied by `-D warnings`
+
...

rust-clippy/tests/ui/manual_memcpy/without_loop_counters.rs

Lines 102 to 105 in ed22428

    
           #[allow(clippy::identity_op)] 
        
           for i in 0..5 { 
        
               dst[i - 0] = src[i]; 
        
           }

4/23
Updated without_loop_counters test

clippy_lints/src/identity_op.rs

+    fn reducible_to_right(&mut self, right: &'tcx Expr<'_>) -> bool {
+        if self.top_level_binop {
+            true
+        } else {
+            !if let ExprKind::If(..) | ExprKind::Match(..) = right.kind {
+                self.leftmost
+            } else {
+                false
            }
-            match cmp.node {
-                BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
-                    check(cx, left, 0, e.span, right.span);
-                    check(cx, right, 0, e.span, left.span);
-                },
-                BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span),
-                BinOpKind::Mul => {
-                    check(cx, left, 1, e.span, right.span);
-                    check(cx, right, 1, e.span, left.span);
-                },
-                BinOpKind::Div => check(cx, right, 1, e.span, left.span),
-                BinOpKind::BitAnd => {
-                    check(cx, left, -1, e.span, right.span);
-                    check(cx, right, -1, e.span, left.span);
-                },
-                BinOpKind::Rem => check_remainder(cx, left, right, e.span, left.span),
-                _ => (),
+        }
+    }


Manishearth · 2022-04-25T07:39:20Z

r? @Alexendoo

(I'm travelling rn and might not be able to do full reviews, can rubber-stamp after you've had a look at it)

Alexendoo

👋

Alexendoo · 2022-04-25T12:54:11Z

clippy_lints/src/identity_op.rs

+struct ExprVisitor<'a, 'tcx> {
+    cx: &'a LateContext<'tcx>,
+    leftmost: bool,
+    top_level_binop: bool,
+}


I think a visitor is too confusing here, e.g. leftmost is always true by the time it reaches the self.reducible_to_right calls

A simpler alternative would be to go back to using check_expr in the lint pass and checking if e's parent expr is an ExprKind::Binary to determine if it's top level or not

Thanks for your review. I fixed it.

I think the visitor can be removed entirely, at least for all the test cases leftmost is still always true in self.reducible_to_right because the order statements are visited in are

a + b + c + d; // 1 LLLLLLLLL R // 2 LLLLL R // 3 L R

I believe just checking the ExprKind of right as you do in reducible_to_right + is_toplevel_binary is enough

Ohh I misunderstood what you meant. And it seems to work for test cases.

Alexendoo · 2022-04-28T16:01:10Z

clippy_lints/src/identity_op.rs

+// Checks if `left op ..right` can be actually reduced to `right`
+// e.g. `0 + if b { 1 } + else { 2 } +  if b { 3 } + else { 4 }`
+// cannot be reduced to `if b { 1 } + else { 2 } +  if b { 3 } + else { 4 }`
+// See #8724


nit

Suggested change

// Checks if `left op ..right` can be actually reduced to `right`

// e.g. `0 + if b { 1 } + else { 2 } + if b { 3 } + else { 4 }`

// cannot be reduced to `if b { 1 } + else { 2 } + if b { 3 } + else { 4 }`

// See #8724

/// Checks if `left op ..right` can be actually reduced to `right`

/// e.g. `0 + if b { 1 } else { 2 } + if b { 3 } else { 4 }`

/// cannot be reduced to `if b { 1 } else { 2 } + if b { 3 } else { 4 }`

/// See #8724

Thanks. Fixed it.

Alexendoo · 2022-04-28T16:58:52Z

tests/ui/identity_op.rs

+    let _ = 0 + if 0 + 1 > 0 { 1 } else { 2 } + if 0 + 1 > 0 { 3 } else { 4 };
+    let _ = 0 + match 0 + 1 { 0 => 10, _ => 20 } + match 0 + 1  { 0 => 30, _ => 40 };


There's a false negative in here, in contexts where it's unambiguously an expression it is fine to reduce these, e.g.

let b = true; f(0 + if b { 1 } else { 2 } + 3); let _ = 0 + if b { 1 } else { 2 } + 3; const _: i32 = 0 + if b { 1 } else { 2 } + 3;

Perhaps instead of get_parent_expr it should be a get_parent_node, checking the node's variant

Thanks.
But I think it seems to be enough to use get_parent_expr.
Is there need to check node variants, using get_parent_node?

Those cases don't lint currently but they could do is what I mean, as in

// doesn't trigger the lint f(0 + if b { 1 } else { 2 } + 3); // but it could, as the following is valid f(if b { 1 } else { 2 } + 3);

It'd be also fine to leave it as is and make a note of that under a Known problems section in the lint description

I didn't aware of this case. I will leave it as it is and add documents.

Added documents

Alexendoo · 2022-04-28T16:59:20Z

tests/ui/manual_memcpy/without_loop_counters.rs

@@ -99,7 +100,6 @@ pub fn manual_copy(src: &[i32], dst: &mut [i32], dst2: &mut [i32]) {
        dst[i] = src[i - from];
    }

-    #[allow(clippy::identity_op)]


nit: can move this back now

Alexendoo · 2022-04-28T17:00:01Z

clippy_lints/src/identity_op.rs

+// cannot be reduced to `if b { 1 } + else { 2 } +  if b { 3 } + else { 4 }`
+// See #8724
+fn reducible_to_right(cx: &LateContext<'_>, binary: &Expr<'_>, right: &Expr<'_>) -> bool {
+    if let ExprKind::If(..) | ExprKind::Match(..) = right.kind {


Can also include ExprKind::Block and ExprKind::Loop

Manishearth · 2022-04-29T11:19:01Z

@bors deletage=Alexendoo

Manishearth · 2022-04-29T12:21:00Z

@bors delegate=Alexendoo

bors · 2022-04-29T12:21:02Z

✌️ @Alexendoo can now approve this pull request

Alexendoo · 2022-04-30T22:12:06Z

Thanks @tamaroning!

Changes look good, please could you squash your commits into one with a descriptive message and then it'll be good to go

fix Update identity_op.rs ok update without_loop_counters test chore fix chore remove visitor and leftmost fix add document

Alexendoo · 2022-05-02T18:21:28Z

Thanks!

@bors r+

bors · 2022-05-02T18:21:30Z

📌 Commit 6ad810f has been approved by Alexendoo

[FP] identity_op in front of if fix #8724 changelog:

bors · 2022-05-02T18:21:36Z

⌛ Testing commit 6ad810f with merge 59d7a90...

bors · 2022-05-02T18:22:11Z

💔 Test failed - checks-action_test

xFrednet · 2022-05-02T19:35:18Z

Hey, the changelog entry from the PR description is still missing. Could you add one? Then all tests should pass 🙃

tamaroning · 2022-05-03T03:50:34Z

@xFrednet Sorry, could you rerun the test?

xFrednet · 2022-05-03T07:05:47Z

No problem @tamaroning, usually I would edit the changelog entry myself if it's the last thing, but here I wasn't sure anymore how it was exactly fixed. 🙃 Thank you for the changes 👍

@bors retry

bors · 2022-05-03T07:05:53Z

⌛ Testing commit 6ad810f with merge 0ceacbe...

bors · 2022-05-03T07:21:10Z

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Alexendoo
Pushing 0ceacbe to master...

…dnet `identity_op`: add parenthesis to suggestions where required changelog: [`identity_op`]: add parenthesis to suggestions where required Follow up to #8730, wraps the cases we can't lint as-is in parenthesis rather than ignoring them Catches a couple new FPs with mixed operator precedences and `as` casts ```rust // such as 0 + { a } * 2; 0 + a as usize; ``` The suggestions are now applied using `span_lint_and_sugg` rather than appearing in just the message and have a `run-rustfix` test

rust-highfive assigned Manishearth Apr 22, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Apr 22, 2022

hellow554 reviewed Apr 22, 2022

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tamaroning marked this pull request as ready for review April 22, 2022 16:17

tamaroning commented Apr 23, 2022

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Alexendoo reviewed Apr 25, 2022

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giraffate assigned giraffate and unassigned Manishearth Apr 27, 2022

Alexendoo reviewed Apr 28, 2022

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improve identity_op

6ad810f

fix Update identity_op.rs ok update without_loop_counters test chore fix chore remove visitor and leftmost fix add document

tamaroning force-pushed the fix8724 branch from ec16773 to 6ad810f Compare May 1, 2022 02:04

Alexendoo approved these changes May 2, 2022

View reviewed changes

bors added a commit that referenced this pull request May 2, 2022

Auto merge of #8730 - tamaroning:fix8724, r=Alexendoo

59d7a90

[FP] identity_op in front of if fix #8724 changelog:

bors merged commit 0ceacbe into rust-lang:master May 3, 2022

Alexendoo mentioned this pull request May 4, 2022

identity_op: add parenthesis to suggestions where required #8786

Merged

		let _ = 0 + if 0 + 1 > 0 { 1 } else { 2 } + if 0 + 1 > 0 { 3 } else { 4 };
		let _ = 0 + match 0 + 1 { 0 => 10, _ => 20 } + match 0 + 1 { 0 => 30, _ => 40 };

[FP] identity_op in front of if #8730

[FP] identity_op in front of if #8730

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