clean up a few lint docs

clippy_lints/src/approx_const.rs

@@ -23,11 +23,11 @@ declare_clippy_lint! {
     ///
     /// **Example:**
     /// ```rust
-    /// // Bad
     /// let x = 3.14;
     /// let y = 1_f64 / x;
-    ///
+    /// ```
-    /// // Good
+    /// Use predefined constants instead:
+    /// ```rust
     /// let x = std::f32::consts::PI;
     /// let y = std::f64::consts::FRAC_1_PI;
     /// ```

clippy_lints/src/assertions_on_constants.rs

@@ -11,16 +11,14 @@ declare_clippy_lint! {
     /// **What it does:** Checks for `assert!(true)` and `assert!(false)` calls.
     ///
     /// **Why is this bad?** Will be optimized out by the compiler or should probably be replaced by a
-    /// panic!() or unreachable!()
+    /// `panic!()` or `unreachable!()`
     ///
     /// **Known problems:** None
     ///
     /// **Example:**
     /// ```rust,ignore
     /// assert!(false)
-    /// // or
     /// assert!(true)
-    /// // or
     /// const B: bool = false;
     /// assert!(B)
     /// ```

clippy_lints/src/block_in_if_condition.rs

@@ -35,7 +35,7 @@ declare_clippy_lint! {
     /// **Known problems:** None.
     ///
     /// **Example:**
-    /// ```ignore
+    /// ```rust,ignore
     /// if { let x = somefunc(); x } {}
     /// // or
     /// if somefunc(|x| { x == 47 }) {}

clippy_lints/src/needless_bool.rs

@@ -51,7 +51,13 @@ declare_clippy_lint! {
     ///
     /// **Example:**
     /// ```rust,ignore
-    /// if x == true {} // could be `if x { }`
+    /// if x == true {}
+    /// if y == false {}
+    /// ```
+    /// use `x` directly:
+    /// ```rust,ignore
+    /// if x {}
+    /// if !y {}
     /// ```
     pub BOOL_COMPARISON,
     complexity,

clippy_lints/src/swap.rs

@@ -54,7 +54,7 @@ declare_clippy_lint! {
     /// a = b;
     /// b = a;
     /// ```
-    /// Could be written as:
+    /// If swapping is intended, use `swap()` instead:
     /// ```rust
     /// # let mut a = 1;
     /// # let mut b = 2;

clippy_lints/src/types.rs

@@ -1642,7 +1642,7 @@ declare_clippy_lint! {
     /// **Example:**
     ///
     /// ```rust
-    /// let vec: Vec<isize> = vec![];
+    /// let vec: Vec<isize> = Vec::new();
     /// if vec.len() <= 0 {}
     /// if 100 > std::i32::MAX {}
     /// ```