Add examples to some complexity lints

Author: BO41

clippy_lints/src/loops.rs

@@ -312,6 +312,14 @@ declare_clippy_lint! {
     /// for i in 0..v.len() { foo(v[i]); }
     /// for i in 0..v.len() { bar(i, v[i]); }
     /// ```
+    /// Could be written as
+    /// ```rust
+    /// # let v = vec![1];
+    /// # fn foo(bar: usize) {}
+    /// # fn bar(bar: usize, baz: usize) {}
+    /// for item in &v { foo(*item); }
+    /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
+    /// ```
     pub EXPLICIT_COUNTER_LOOP,
     complexity,
     "for-looping with an explicit counter when `_.enumerate()` would do"

clippy_lints/src/methods/mod.rs

@@ -302,6 +302,11 @@ declare_clippy_lint! {
     /// # let vec = vec![1];
     /// vec.iter().filter(|x| **x == 0).next();
     /// ```
+    /// Could be written as
+    /// ```rust
+    /// # let vec = vec![1];
+    /// vec.iter().find(|x| **x == 0);
+    /// ```
     pub FILTER_NEXT,
     complexity,
     "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
@@ -425,6 +430,11 @@ declare_clippy_lint! {
     /// # let vec = vec![1];
     /// vec.iter().find(|x| **x == 0).is_some();
     /// ```
+    /// Could be written as
+    /// ```rust
+    /// # let vec = vec![1];
+    /// vec.iter().any(|x| **x == 0);
+    /// ```
     pub SEARCH_IS_SOME,
     complexity,
     "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
@@ -442,7 +452,12 @@ declare_clippy_lint! {
     /// **Example:**
     /// ```rust
     /// let name = "foo";
-    /// name.chars().next() == Some('_');
+    /// if name.chars().next() == Some('_') {};
+    /// ```
+    /// Could be written as
+    /// ```rust
+    /// let name = "foo";
+    /// if name.starts_with('_') {};
     /// ```
     pub CHARS_NEXT_CMP,
     complexity,

clippy_lints/src/needless_bool.rs

@@ -31,6 +31,10 @@ declare_clippy_lint! {
     ///     true
     /// }
     /// ```
+    /// Could be written as
+    /// ```rust,ignore
+    /// !x
+    /// ```
     pub NEEDLESS_BOOL,
     complexity,
     "if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"

clippy_lints/src/ranges.rs

@@ -43,6 +43,11 @@ declare_clippy_lint! {
     /// # let x = vec![1];
     /// x.iter().zip(0..x.len());
     /// ```
+    /// Could be written as
+    /// ```rust
+    /// # let x = vec![1];
+    /// x.iter().enumerate();
+    /// ```
     pub RANGE_ZIP_WITH_LEN,
     complexity,
     "zipping iterator with a range when `enumerate()` would do"
@@ -64,6 +69,10 @@ declare_clippy_lint! {
     /// ```rust,ignore
     /// for x..(y+1) { .. }
     /// ```
+    /// Could be written as
+    /// ```rust,ignore
+    /// for x..=y { .. }
+    /// ```
     pub RANGE_PLUS_ONE,
     complexity,
     "`x..(y+1)` reads better as `x..=y`"
@@ -82,6 +91,10 @@ declare_clippy_lint! {
     /// ```rust,ignore
     /// for x..=(y-1) { .. }
     /// ```
+    /// Could be written as
+    /// ```rust,ignore
+    /// for x..y { .. }
+    /// ```
     pub RANGE_MINUS_ONE,
     complexity,
     "`x..=(y-1)` reads better as `x..y`"