Auto merge of #3978 - phansch:rustfix_len_zero, r=flip1995

Add run-rustfix for len_zero lint

* Extracts len_without_is_empty into separate file
* Adds `// run-rustfix` to `tests/ui/len_zero.rs`

cc #3630

tests/ui/len_without_is_empty.rs

@@ -0,0 +1,145 @@
+#![warn(clippy::len_without_is_empty)]
+#![allow(dead_code, unused)]
+
+pub struct PubOne;
+
+impl PubOne {
+    pub fn len(self: &Self) -> isize {
+        1
+    }
+}
+
+impl PubOne {
+    // A second impl for this struct -- the error span shouldn't mention this.
+    pub fn irrelevant(self: &Self) -> bool {
+        false
+    }
+}
+
+// Identical to `PubOne`, but with an `allow` attribute on the impl complaining `len`.
+pub struct PubAllowed;
+
+#[allow(clippy::len_without_is_empty)]
+impl PubAllowed {
+    pub fn len(self: &Self) -> isize {
+        1
+    }
+}
+
+// No `allow` attribute on this impl block, but that doesn't matter -- we only require one on the
+// impl containing `len`.
+impl PubAllowed {
+    pub fn irrelevant(self: &Self) -> bool {
+        false
+    }
+}
+
+pub trait PubTraitsToo {
+    fn len(self: &Self) -> isize;
+}
+
+impl PubTraitsToo for One {
+    fn len(self: &Self) -> isize {
+        0
+    }
+}
+
+pub struct HasIsEmpty;
+
+impl HasIsEmpty {
+    pub fn len(self: &Self) -> isize {
+        1
+    }
+
+    fn is_empty(self: &Self) -> bool {
+        false
+    }
+}
+
+pub struct HasWrongIsEmpty;
+
+impl HasWrongIsEmpty {
+    pub fn len(self: &Self) -> isize {
+        1
+    }
+
+    pub fn is_empty(self: &Self, x: u32) -> bool {
+        false
+    }
+}
+
+struct NotPubOne;
+
+impl NotPubOne {
+    pub fn len(self: &Self) -> isize {
+        // No error; `len` is pub but `NotPubOne` is not exported anyway.
+        1
+    }
+}
+
+struct One;
+
+impl One {
+    fn len(self: &Self) -> isize {
+        // No error; `len` is private; see issue #1085.
+        1
+    }
+}
+
+trait TraitsToo {
+    fn len(self: &Self) -> isize;
+    // No error; `len` is private; see issue #1085.
+}
+
+impl TraitsToo for One {
+    fn len(self: &Self) -> isize {
+        0
+    }
+}
+
+struct HasPrivateIsEmpty;
+
+impl HasPrivateIsEmpty {
+    pub fn len(self: &Self) -> isize {
+        1
+    }
+
+    fn is_empty(self: &Self) -> bool {
+        false
+    }
+}
+
+struct Wither;
+
+pub trait WithIsEmpty {
+    fn len(self: &Self) -> isize;
+    fn is_empty(self: &Self) -> bool;
+}
+
+impl WithIsEmpty for Wither {
+    fn len(self: &Self) -> isize {
+        1
+    }
+
+    fn is_empty(self: &Self) -> bool {
+        false
+    }
+}
+
+pub trait Empty {
+    fn is_empty(&self) -> bool;
+}
+
+pub trait InheritingEmpty: Empty {
+    // Must not trigger `LEN_WITHOUT_IS_EMPTY`.
+    fn len(&self) -> isize;
+}
+
+// This used to ICE.
+pub trait Foo: Sized {}
+
+pub trait DependsOnFoo: Foo {
+    fn len(&mut self) -> usize;
+}
+
+fn main() {}

tests/ui/len_without_is_empty.stderr

@@ -0,0 +1,54 @@
+error: item `PubOne` has a public `len` method but no corresponding `is_empty` method
+  --> $DIR/len_without_is_empty.rs:6:1
+   |
+LL | / impl PubOne {
+LL | |     pub fn len(self: &Self) -> isize {
+LL | |         1
+LL | |     }
+LL | | }
+   | |_^
+   |
+   = note: `-D clippy::len-without-is-empty` implied by `-D warnings`
+
+error: trait `PubTraitsToo` has a `len` method but no (possibly inherited) `is_empty` method
+  --> $DIR/len_without_is_empty.rs:37:1
+   |
+LL | / pub trait PubTraitsToo {
+LL | |     fn len(self: &Self) -> isize;
+LL | | }
+   | |_^
+
+error: item `HasIsEmpty` has a public `len` method but a private `is_empty` method
+  --> $DIR/len_without_is_empty.rs:49:1
+   |
+LL | / impl HasIsEmpty {
+LL | |     pub fn len(self: &Self) -> isize {
+LL | |         1
+LL | |     }
+...  |
+LL | |     }
+LL | | }
+   | |_^
+
+error: item `HasWrongIsEmpty` has a public `len` method but no corresponding `is_empty` method
+  --> $DIR/len_without_is_empty.rs:61:1
+   |
+LL | / impl HasWrongIsEmpty {
+LL | |     pub fn len(self: &Self) -> isize {
+LL | |         1
+LL | |     }
+...  |
+LL | |     }
+LL | | }
+   | |_^
+
+error: trait `DependsOnFoo` has a `len` method but no (possibly inherited) `is_empty` method
+  --> $DIR/len_without_is_empty.rs:141:1
+   |
+LL | / pub trait DependsOnFoo: Foo {
+LL | |     fn len(&mut self) -> usize;
+LL | | }
+   | |_^
+
+error: aborting due to 5 previous errors
+

tests/ui/len_zero.fixed

@@ -0,0 +1,143 @@
+// run-rustfix
+
+#![warn(clippy::len_zero)]
+#![allow(dead_code, unused, clippy::len_without_is_empty)]
+
+pub struct One;
+struct Wither;
+
+trait TraitsToo {
+    fn len(self: &Self) -> isize;
+    // No error; `len` is private; see issue #1085.
+}
+
+impl TraitsToo for One {
+    fn len(self: &Self) -> isize {
+        0
+    }
+}
+
+pub struct HasIsEmpty;
+
+impl HasIsEmpty {
+    pub fn len(self: &Self) -> isize {
+        1
+    }
+
+    fn is_empty(self: &Self) -> bool {
+        false
+    }
+}
+
+pub struct HasWrongIsEmpty;
+
+impl HasWrongIsEmpty {
+    pub fn len(self: &Self) -> isize {
+        1
+    }
+
+    pub fn is_empty(self: &Self, x: u32) -> bool {
+        false
+    }
+}
+
+pub trait WithIsEmpty {
+    fn len(self: &Self) -> isize;
+    fn is_empty(self: &Self) -> bool;
+}
+
+impl WithIsEmpty for Wither {
+    fn len(self: &Self) -> isize {
+        1
+    }
+
+    fn is_empty(self: &Self) -> bool {
+        false
+    }
+}
+
+fn main() {
+    let x = [1, 2];
+    if x.is_empty() {
+        println!("This should not happen!");
+    }
+
+    if "".is_empty() {}
+
+    let y = One;
+    if y.len() == 0 {
+        // No error; `One` does not have `.is_empty()`.
+        println!("This should not happen either!");
+    }
+
+    let z: &TraitsToo = &y;
+    if z.len() > 0 {
+        // No error; `TraitsToo` has no `.is_empty()` method.
+        println!("Nor should this!");
+    }
+
+    let has_is_empty = HasIsEmpty;
+    if has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if !has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if !has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if !has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if has_is_empty.len() > 1 {
+        // No error.
+        println!("This can happen.");
+    }
+    if has_is_empty.len() <= 1 {
+        // No error.
+        println!("This can happen.");
+    }
+    if has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if !has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if !has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if !has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if has_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    if 1 < has_is_empty.len() {
+        // No error.
+        println!("This can happen.");
+    }
+    if 1 >= has_is_empty.len() {
+        // No error.
+        println!("This can happen.");
+    }
+    assert!(!has_is_empty.is_empty());
+
+    let with_is_empty: &WithIsEmpty = &Wither;
+    if with_is_empty.is_empty() {
+        println!("Or this!");
+    }
+    assert!(!with_is_empty.is_empty());
+
+    let has_wrong_is_empty = HasWrongIsEmpty;
+    if has_wrong_is_empty.len() == 0 {
+        // No error; `HasWrongIsEmpty` does not have `.is_empty()`.
+        println!("Or this!");
+    }
+}
+
+fn test_slice(b: &[u8]) {
+    if !b.is_empty() {}
+}

tests/ui/len_zero.rs

@@ -1,66 +1,10 @@
-#![warn(clippy::len_without_is_empty, clippy::len_zero)]
-#![allow(dead_code, unused)]
+// run-rustfix
 
-pub struct PubOne;
+#![warn(clippy::len_zero)]
+#![allow(dead_code, unused, clippy::len_without_is_empty)]
 
-impl PubOne {
-    pub fn len(self: &Self) -> isize {
-        1
-    }
-}
-
-impl PubOne {
-    // A second impl for this struct -- the error span shouldn't mention this.
-    pub fn irrelevant(self: &Self) -> bool {
-        false
-    }
-}
-
-// Identical to `PubOne`, but with an `allow` attribute on the impl complaining `len`.
-pub struct PubAllowed;
-
-#[allow(clippy::len_without_is_empty)]
-impl PubAllowed {
-    pub fn len(self: &Self) -> isize {
-        1
-    }
-}
-
-// No `allow` attribute on this impl block, but that doesn't matter -- we only require one on the
-// impl containing `len`.
-impl PubAllowed {
-    pub fn irrelevant(self: &Self) -> bool {
-        false
-    }
-}
-
-struct NotPubOne;
-
-impl NotPubOne {
-    pub fn len(self: &Self) -> isize {
-        // No error; `len` is pub but `NotPubOne` is not exported anyway.
-        1
-    }
-}
-
-struct One;
-
-impl One {
-    fn len(self: &Self) -> isize {
-        // No error; `len` is private; see issue #1085.
-        1
-    }
-}
-
-pub trait PubTraitsToo {
-    fn len(self: &Self) -> isize;
-}
-
-impl PubTraitsToo for One {
-    fn len(self: &Self) -> isize {
-        0
-    }
-}
+pub struct One;
+struct Wither;
 
 trait TraitsToo {
     fn len(self: &Self) -> isize;
@@ -73,18 +17,6 @@ impl TraitsToo for One {
     }
 }
 
-struct HasPrivateIsEmpty;
-
-impl HasPrivateIsEmpty {
-    pub fn len(self: &Self) -> isize {
-        1
-    }
-
-    fn is_empty(self: &Self) -> bool {
-        false
-    }
-}
-
 pub struct HasIsEmpty;
 
 impl HasIsEmpty {
@@ -97,23 +29,6 @@ impl HasIsEmpty {
     }
 }
 
-struct Wither;
-
-pub trait WithIsEmpty {
-    fn len(self: &Self) -> isize;
-    fn is_empty(self: &Self) -> bool;
-}
-
-impl WithIsEmpty for Wither {
-    fn len(self: &Self) -> isize {
-        1
-    }
-
-    fn is_empty(self: &Self) -> bool {
-        false
-    }
-}
-
 pub struct HasWrongIsEmpty;
 
 impl HasWrongIsEmpty {
@@ -126,13 +41,19 @@ impl HasWrongIsEmpty {
     }
 }
 
-pub trait Empty {
-    fn is_empty(&self) -> bool;
+pub trait WithIsEmpty {
+    fn len(self: &Self) -> isize;
+    fn is_empty(self: &Self) -> bool;
 }
 
-pub trait InheritingEmpty: Empty {
-    // Must not trigger `LEN_WITHOUT_IS_EMPTY`.
-    fn len(&self) -> isize;
+impl WithIsEmpty for Wither {
+    fn len(self: &Self) -> isize {
+        1
+    }
+
+    fn is_empty(self: &Self) -> bool {
+        false
+    }
 }
 
 fn main() {
@@ -220,10 +141,3 @@ fn main() {
 fn test_slice(b: &[u8]) {
     if b.len() != 0 {}
 }
-
-// This used to ICE.
-pub trait Foo: Sized {}
-
-pub trait DependsOnFoo: Foo {
-    fn len(&mut self) -> usize;
-}

tests/ui/len_zero.stderr

@@ -1,49 +1,5 @@
-error: item `PubOne` has a public `len` method but no corresponding `is_empty` method
-  --> $DIR/len_zero.rs:6:1
-   |
-LL | / impl PubOne {
-LL | |     pub fn len(self: &Self) -> isize {
-LL | |         1
-LL | |     }
-LL | | }
-   | |_^
-   |
-   = note: `-D clippy::len-without-is-empty` implied by `-D warnings`
-
-error: trait `PubTraitsToo` has a `len` method but no (possibly inherited) `is_empty` method
-  --> $DIR/len_zero.rs:55:1
-   |
-LL | / pub trait PubTraitsToo {
-LL | |     fn len(self: &Self) -> isize;
-LL | | }
-   | |_^
-
-error: item `HasIsEmpty` has a public `len` method but a private `is_empty` method
-  --> $DIR/len_zero.rs:90:1
-   |
-LL | / impl HasIsEmpty {
-LL | |     pub fn len(self: &Self) -> isize {
-LL | |         1
-LL | |     }
-...  |
-LL | |     }
-LL | | }
-   | |_^
-
-error: item `HasWrongIsEmpty` has a public `len` method but no corresponding `is_empty` method
-  --> $DIR/len_zero.rs:119:1
-   |
-LL | / impl HasWrongIsEmpty {
-LL | |     pub fn len(self: &Self) -> isize {
-LL | |         1
-LL | |     }
-...  |
-LL | |     }
-LL | | }
-   | |_^
-
 error: length comparison to zero
-  --> $DIR/len_zero.rs:140:8
+  --> $DIR/len_zero.rs:61:8
    |
 LL |     if x.len() == 0 {
    |        ^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `x.is_empty()`
@@ -51,90 +7,82 @@ LL |     if x.len() == 0 {
    = note: `-D clippy::len-zero` implied by `-D warnings`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:144:8
+  --> $DIR/len_zero.rs:65:8
    |
 LL |     if "".len() == 0 {}
    |        ^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `"".is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:159:8
+  --> $DIR/len_zero.rs:80:8
    |
 LL |     if has_is_empty.len() == 0 {
    |        ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:162:8
+  --> $DIR/len_zero.rs:83:8
    |
 LL |     if has_is_empty.len() != 0 {
    |        ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `!has_is_empty.is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:165:8
+  --> $DIR/len_zero.rs:86:8
    |
 LL |     if has_is_empty.len() > 0 {
    |        ^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `!has_is_empty.is_empty()`
 
 error: length comparison to one
-  --> $DIR/len_zero.rs:168:8
+  --> $DIR/len_zero.rs:89:8
    |
 LL |     if has_is_empty.len() < 1 {
    |        ^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()`
 
 error: length comparison to one
-  --> $DIR/len_zero.rs:171:8
+  --> $DIR/len_zero.rs:92:8
    |
 LL |     if has_is_empty.len() >= 1 {
    |        ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `!has_is_empty.is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:182:8
+  --> $DIR/len_zero.rs:103:8
    |
 LL |     if 0 == has_is_empty.len() {
    |        ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:185:8
+  --> $DIR/len_zero.rs:106:8
    |
 LL |     if 0 != has_is_empty.len() {
    |        ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `!has_is_empty.is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:188:8
+  --> $DIR/len_zero.rs:109:8
    |
 LL |     if 0 < has_is_empty.len() {
    |        ^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `!has_is_empty.is_empty()`
 
 error: length comparison to one
-  --> $DIR/len_zero.rs:191:8
+  --> $DIR/len_zero.rs:112:8
    |
 LL |     if 1 <= has_is_empty.len() {
    |        ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `!has_is_empty.is_empty()`
 
 error: length comparison to one
-  --> $DIR/len_zero.rs:194:8
+  --> $DIR/len_zero.rs:115:8
    |
 LL |     if 1 > has_is_empty.len() {
    |        ^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:208:8
+  --> $DIR/len_zero.rs:129:8
    |
 LL |     if with_is_empty.len() == 0 {
    |        ^^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `with_is_empty.is_empty()`
 
 error: length comparison to zero
-  --> $DIR/len_zero.rs:221:8
+  --> $DIR/len_zero.rs:142:8
    |
 LL |     if b.len() != 0 {}
    |        ^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `!b.is_empty()`
 
-error: trait `DependsOnFoo` has a `len` method but no (possibly inherited) `is_empty` method
-  --> $DIR/len_zero.rs:227:1
-   |
-LL | / pub trait DependsOnFoo: Foo {
-LL | |     fn len(&mut self) -> usize;
-LL | | }
-   | |_^
-
-error: aborting due to 19 previous errors
+error: aborting due to 14 previous errors