Only suggest .iter() when chunks_exact is not in a for loop

Author: rommeld

clippy_lints/src/methods/chunks_exact_with_const_size.rs

@@ -1,9 +1,10 @@
 use super::CHUNKS_EXACT_WITH_CONST_SIZE;
 use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::higher::ForLoop;
 use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::snippet_with_applicability;
-use clippy_utils::sym;
 use clippy_utils::visitors::is_const_evaluatable;
+use clippy_utils::{get_parent_expr, sym};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, Node, PatKind};
 use rustc_lint::LateContext;
@@ -75,10 +76,27 @@ pub(super) fn check<'tcx>(
                         ));
                     }
                 } else {
+                    let in_for_loop = {
+                        let mut cur_expr = expr;
+                        loop {
+                            if let Some(parent_expr) = get_parent_expr(cx, cur_expr) {
+                                if let Some(for_loop) = ForLoop::hir(parent_expr)
+                                    && for_loop.arg.hir_id == expr.hir_id
+                                {
+                                    break true;
+                                }
+                                cur_expr = parent_expr;
+                            } else {
+                                break false;
+                            }
+                        }
+                    };
+
+                    let suffix = if in_for_loop { ".0" } else { ".0.iter()" };
                     diag.span_suggestion(
                         call_span,
                         "consider using `as_chunks` instead",
-                        format!("{as_chunks}.0.iter()"),
+                        format!("{as_chunks}{suffix}"),
                         applicability,
                     );
                 }

tests/ui/chunks_exact_with_const_size.fixed

@@ -10,23 +10,26 @@ fn main() {
     for chunk in it {}
 
     // Should trigger - direct iteration without binding (gets suggestion)
-    for chunk in slice.as_chunks::<4>().0.iter() {
+    for chunk in slice.as_chunks::<4>().0 {
         //~^ chunks_exact_with_const_size
         let _ = chunk;
     }
 
     // Should trigger - direct iteration with const
     const CHUNK_SIZE: usize = 4;
-    for chunk in slice.as_chunks::<CHUNK_SIZE>().0.iter() {
+    for chunk in slice.as_chunks::<CHUNK_SIZE>().0 {
         //~^ chunks_exact_with_const_size
         let _ = chunk;
     }
 
-    // Should trigger - chunks_exact_mut with direct iteration (gets suggestion)
-    // Note: The suggestion uses .iter() but should use .iter_mut() - this is a known limitation
+    // Should trigger - chunks_exact_mut with direct iteration (gets suggestion without .iter())
     let mut arr = [1, 2, 3, 4, 5, 6, 7, 8];
-    for chunk in arr.as_chunks_mut::<4>().0.iter() {
+    for chunk in arr.as_chunks_mut::<4>().0 {
         //~^ chunks_exact_with_const_size
         let _ = chunk;
     }
+
+    // Should trigger - used with iterator method (not for loop, so needs .iter())
+    let _: Vec<_> = slice.as_chunks::<4>().0.iter().collect();
+    //~^ chunks_exact_with_const_size
 }

tests/ui/chunks_exact_with_const_size.rs

@@ -22,11 +22,14 @@ fn main() {
         let _ = chunk;
     }
 
-    // Should trigger - chunks_exact_mut with direct iteration (gets suggestion)
-    // Note: The suggestion uses .iter() but should use .iter_mut() - this is a known limitation
+    // Should trigger - chunks_exact_mut with direct iteration (gets suggestion without .iter())
     let mut arr = [1, 2, 3, 4, 5, 6, 7, 8];
     for chunk in arr.chunks_exact_mut(4) {
         //~^ chunks_exact_with_const_size
         let _ = chunk;
     }
+
+    // Should trigger - used with iterator method (not for loop, so needs .iter())
+    let _: Vec<_> = slice.chunks_exact(4).collect();
+    //~^ chunks_exact_with_const_size
 }

tests/ui/chunks_exact_with_const_size.stderr

@@ -2,7 +2,7 @@ error: using `chunks_exact` with a constant chunk size
   --> tests/ui/chunks_exact_with_const_size.rs:13:24
    |
 LL |     for chunk in slice.chunks_exact(4) {
-   |                        ^^^^^^^^^^^^^^^ help: consider using `as_chunks` instead: `as_chunks::<4>().0.iter()`
+   |                        ^^^^^^^^^^^^^^^ help: consider using `as_chunks` instead: `as_chunks::<4>().0`
    |
    = note: `-D clippy::chunks-exact-with-const-size` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::chunks_exact_with_const_size)]`
@@ -11,13 +11,19 @@ error: using `chunks_exact` with a constant chunk size
   --> tests/ui/chunks_exact_with_const_size.rs:20:24
    |
 LL |     for chunk in slice.chunks_exact(CHUNK_SIZE) {
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `as_chunks` instead: `as_chunks::<CHUNK_SIZE>().0.iter()`
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `as_chunks` instead: `as_chunks::<CHUNK_SIZE>().0`
 
 error: using `chunks_exact_mut` with a constant chunk size
-  --> tests/ui/chunks_exact_with_const_size.rs:28:22
+  --> tests/ui/chunks_exact_with_const_size.rs:27:22
    |
 LL |     for chunk in arr.chunks_exact_mut(4) {
-   |                      ^^^^^^^^^^^^^^^^^^^ help: consider using `as_chunks` instead: `as_chunks_mut::<4>().0.iter()`
+   |                      ^^^^^^^^^^^^^^^^^^^ help: consider using `as_chunks` instead: `as_chunks_mut::<4>().0`
 
-error: aborting due to 3 previous errors
+error: using `chunks_exact` with a constant chunk size
+  --> tests/ui/chunks_exact_with_const_size.rs:33:27
+   |
+LL |     let _: Vec<_> = slice.chunks_exact(4).collect();
+   |                           ^^^^^^^^^^^^^^^ help: consider using `as_chunks` instead: `as_chunks::<4>().0.iter()`
+
+error: aborting due to 4 previous errors