src/tools/clippy/tests/ui/while_let_on_iterator.rs

   1 // run-rustfix
   2
   3 #![warn(clippy::while_let_on_iterator)]
   4 #![allow(
   5     clippy::never_loop,
   6     unreachable_code,
   7     unused_mut,
   8     dead_code,
   9     clippy::equatable_if_let
  10 )]
  11
  12 fn base() {
  13     let mut iter = 1..20;
  14     while let Option::Some(x) = iter.next() {
  15         println!("{}", x);
  16     }
  17
  18     let mut iter = 1..20;
  19     while let Some(x) = iter.next() {
  20         println!("{}", x);
  21     }
  22
  23     let mut iter = 1..20;
  24     while let Some(_) = iter.next() {}
  25
  26     let mut iter = 1..20;
  27     while let None = iter.next() {} // this is fine (if nonsensical)
  28
  29     let mut iter = 1..20;
  30     if let Some(x) = iter.next() {
  31         // also fine
  32         println!("{}", x)
  33     }
  34
  35     // the following shouldn't warn because it can't be written with a for loop
  36     let mut iter = 1u32..20;
  37     while let Some(_) = iter.next() {
  38         println!("next: {:?}", iter.next())
  39     }
  40
  41     // neither can this
  42     let mut iter = 1u32..20;
  43     while let Some(_) = iter.next() {
  44         println!("next: {:?}", iter.next());
  45     }
  46
  47     // or this
  48     let mut iter = 1u32..20;
  49     while let Some(_) = iter.next() {
  50         iter = 1..20;
  51     }
  52 }
  53
  54 // Issue #1188
  55 fn refutable() {
  56     let a = [42, 1337];
  57     let mut b = a.iter();
  58
  59     // consume all the 42s
  60     while let Some(&42) = b.next() {}
  61
  62     let a = [(1, 2, 3)];
  63     let mut b = a.iter();
  64
  65     while let Some(&(1, 2, 3)) = b.next() {}
  66
  67     let a = [Some(42)];
  68     let mut b = a.iter();
  69
  70     while let Some(&None) = b.next() {}
  71
  72     /* This gives “refutable pattern in `for` loop binding: `&_` not covered”
  73     for &42 in b {}
  74     for &(1, 2, 3) in b {}
  75     for &Option::None in b.next() {}
  76     // */
  77 }
  78
  79 fn refutable2() {
  80     // Issue 3780
  81     {
  82         let v = vec![1, 2, 3];
  83         let mut it = v.windows(2);
  84         while let Some([x, y]) = it.next() {
  85             println!("x: {}", x);
  86             println!("y: {}", y);
  87         }
  88
  89         let mut it = v.windows(2);
  90         while let Some([x, ..]) = it.next() {
  91             println!("x: {}", x);
  92         }
  93
  94         let mut it = v.windows(2);
  95         while let Some([.., y]) = it.next() {
  96             println!("y: {}", y);
  97         }
  98
  99         let mut it = v.windows(2);
 100         while let Some([..]) = it.next() {}
 101
 102         let v = vec![[1], [2], [3]];
 103         let mut it = v.iter();
 104         while let Some([1]) = it.next() {}
 105
 106         let mut it = v.iter();
 107         while let Some([_x]) = it.next() {}
 108     }
 109
 110     // binding
 111     {
 112         let v = vec![1, 2, 3];
 113         let mut it = v.iter();
 114         while let Some(x @ 1) = it.next() {
 115             println!("{}", x);
 116         }
 117
 118         let v = vec![[1], [2], [3]];
 119         let mut it = v.iter();
 120         while let Some(x @ [_]) = it.next() {
 121             println!("{:?}", x);
 122         }
 123     }
 124
 125     // false negative
 126     {
 127         let v = vec![1, 2, 3];
 128         let mut it = v.iter().map(Some);
 129         while let Some(Some(_) | None) = it.next() {
 130             println!("1");
 131         }
 132     }
 133 }
 134
 135 fn nested_loops() {
 136     let a = [42, 1337];
 137
 138     loop {
 139         let mut y = a.iter();
 140         while let Some(_) = y.next() {
 141             // use a for loop here
 142         }
 143     }
 144 }
 145
 146 fn issue1121() {
 147     use std::collections::HashSet;
 148     let mut values = HashSet::new();
 149     values.insert(1);
 150
 151     while let Some(&value) = values.iter().next() {
 152         values.remove(&value);
 153     }
 154 }
 155
 156 fn issue2965() {
 157     // This should not cause an ICE
 158
 159     use std::collections::HashSet;
 160     let mut values = HashSet::new();
 161     values.insert(1);
 162
 163     while let Some(..) = values.iter().next() {}
 164 }
 165
 166 fn issue3670() {
 167     let array = [Some(0), None, Some(1)];
 168     let mut iter = array.iter();
 169
 170     while let Some(elem) = iter.next() {
 171         let _ = elem.or_else(|| *iter.next()?);
 172     }
 173 }
 174
 175 fn issue1654() {
 176     // should not lint if the iterator is generated on every iteration
 177     use std::collections::HashSet;
 178     let mut values = HashSet::new();
 179     values.insert(1);
 180
 181     while let Some(..) = values.iter().next() {
 182         values.remove(&1);
 183     }
 184
 185     while let Some(..) = values.iter().map(|x| x + 1).next() {}
 186
 187     let chars = "Hello, World!".char_indices();
 188     while let Some((i, ch)) = chars.clone().next() {
 189         println!("{}: {}", i, ch);
 190     }
 191 }
 192
 193 fn issue6491() {
 194     // Used in outer loop, needs &mut
 195     let mut it = 1..40;
 196     while let Some(n) = it.next() {
 197         while let Some(m) = it.next() {
 198             if m % 10 == 0 {
 199                 break;
 200             }
 201             println!("doing something with m: {}", m);
 202         }
 203         println!("n still is {}", n);
 204     }
 205
 206     // This is fine, inner loop uses a new iterator.
 207     let mut it = 1..40;
 208     while let Some(n) = it.next() {
 209         let mut it = 1..40;
 210         while let Some(m) = it.next() {
 211             if m % 10 == 0 {
 212                 break;
 213             }
 214             println!("doing something with m: {}", m);
 215         }
 216
 217         // Weird binding shouldn't change anything.
 218         let (mut it, _) = (1..40, 0);
 219         while let Some(m) = it.next() {
 220             if m % 10 == 0 {
 221                 break;
 222             }
 223             println!("doing something with m: {}", m);
 224         }
 225
 226         // Used after the loop, needs &mut.
 227         let mut it = 1..40;
 228         while let Some(m) = it.next() {
 229             if m % 10 == 0 {
 230                 break;
 231             }
 232             println!("doing something with m: {}", m);
 233         }
 234         println!("next item {}", it.next().unwrap());
 235
 236         println!("n still is {}", n);
 237     }
 238 }
 239
 240 fn issue6231() {
 241     // Closure in the outer loop, needs &mut
 242     let mut it = 1..40;
 243     let mut opt = Some(0);
 244     while let Some(n) = opt.take().or_else(|| it.next()) {
 245         while let Some(m) = it.next() {
 246             if n % 10 == 0 {
 247                 break;
 248             }
 249             println!("doing something with m: {}", m);
 250         }
 251         println!("n still is {}", n);
 252     }
 253 }
 254
 255 fn issue1924() {
 256     struct S<T>(T);
 257     impl<T: Iterator<Item = u32>> S<T> {
 258         fn f(&mut self) -> Option<u32> {
 259             // Used as a field.
 260             while let Some(i) = self.0.next() {
 261                 if i < 3 || i > 7 {
 262                     return Some(i);
 263                 }
 264             }
 265             None
 266         }
 267
 268         fn f2(&mut self) -> Option<u32> {
 269             // Don't lint, self borrowed inside the loop
 270             while let Some(i) = self.0.next() {
 271                 if i == 1 {
 272                     return self.f();
 273                 }
 274             }
 275             None
 276         }
 277     }
 278     impl<T: Iterator<Item = u32>> S<(S<T>, Option<u32>)> {
 279         fn f3(&mut self) -> Option<u32> {
 280             // Don't lint, self borrowed inside the loop
 281             while let Some(i) = self.0.0.0.next() {
 282                 if i == 1 {
 283                     return self.0.0.f();
 284                 }
 285             }
 286             while let Some(i) = self.0.0.0.next() {
 287                 if i == 1 {
 288                     return self.f3();
 289                 }
 290             }
 291             // This one is fine, a different field is borrowed
 292             while let Some(i) = self.0.0.0.next() {
 293                 if i == 1 {
 294                     return self.0.1.take();
 295                 } else {
 296                     self.0.1 = Some(i);
 297                 }
 298             }
 299             None
 300         }
 301     }
 302
 303     struct S2<T>(T, u32);
 304     impl<T: Iterator<Item = u32>> Iterator for S2<T> {
 305         type Item = u32;
 306         fn next(&mut self) -> Option<u32> {
 307             self.0.next()
 308         }
 309     }
 310
 311     // Don't lint, field of the iterator is accessed in the loop
 312     let mut it = S2(1..40, 0);
 313     while let Some(n) = it.next() {
 314         if n == it.1 {
 315             break;
 316         }
 317     }
 318
 319     // Needs &mut, field of the iterator is accessed after the loop
 320     let mut it = S2(1..40, 0);
 321     while let Some(n) = it.next() {
 322         if n == 0 {
 323             break;
 324         }
 325     }
 326     println!("iterator field {}", it.1);
 327 }
 328
 329 fn issue7249() {
 330     let mut it = 0..10;
 331     let mut x = || {
 332         // Needs &mut, the closure can be called multiple times
 333         while let Some(x) = it.next() {
 334             if x % 2 == 0 {
 335                 break;
 336             }
 337         }
 338     };
 339     x();
 340     x();
 341 }
 342
 343 fn issue7510() {
 344     let mut it = 0..10;
 345     let it = &mut it;
 346     // Needs to reborrow `it` as the binding isn't mutable
 347     while let Some(x) = it.next() {
 348         if x % 2 == 0 {
 349             break;
 350         }
 351     }
 352     println!("{}", it.next().unwrap());
 353
 354     struct S<T>(T);
 355     let mut it = 0..10;
 356     let it = S(&mut it);
 357     // Needs to reborrow `it.0` as the binding isn't mutable
 358     while let Some(x) = it.0.next() {
 359         if x % 2 == 0 {
 360             break;
 361         }
 362     }
 363     println!("{}", it.0.next().unwrap());
 364 }
 365
 366 fn exact_match_with_single_field() {
 367     struct S<T>(T);
 368     let mut s = S(0..10);
 369     // Don't lint. `s.0` is used inside the loop.
 370     while let Some(_) = s.0.next() {
 371         let _ = &mut s.0;
 372     }
 373 }
 374
 375 fn main() {
 376     let mut it = 0..20;
 377     while let Some(..) = it.next() {
 378         println!("test");
 379     }
 380 }