collapsible_if: split collapsible_else_if into its own lint so we can enable/disable it particularly

This splits up clippy::collapsible_if into collapsible_if for
if x {
  if y { }
}
=>
if x && y { }

and collapsible_else_if for

if x {
} else {
 if y { }
}

=>
if x {

} else if y {

}

so that we can lint for only the latter but not the first if we desire.

changelog: collapsible_if: split up linting for if x {} else { if y {} } into collapsible_else_if lint

8 files changed, 59 insertions, 34 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ec424068a54..b643627c2e9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1896,6 +1896,7 @@ Released 2018-09-13
 [`cmp_null`]: https://rust-lang.github.io/rust-clippy/master/index.html#cmp_null
 [`cmp_owned`]: https://rust-lang.github.io/rust-clippy/master/index.html#cmp_owned
 [`cognitive_complexity`]: https://rust-lang.github.io/rust-clippy/master/index.html#cognitive_complexity
+[`collapsible_else_if`]: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_else_if
 [`collapsible_if`]: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_if
 [`collapsible_match`]: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match
 [`comparison_chain`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_chain
diff --git a/clippy_lints/src/collapsible_if.rs b/clippy_lints/src/collapsible_if.rs
index 42bff564de0..93ccc76d0c9 100644
--- a/clippy_lints/src/collapsible_if.rs
+++ b/clippy_lints/src/collapsible_if.rs
@@ -23,9 +23,7 @@ use rustc_errors::Applicability;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for nested `if` statements which can be collapsed
-    /// by `&&`-combining their conditions and for `else { if ... }` expressions
-    /// that
-    /// can be collapsed to `else if ...`.
+    /// by `&&`-combining their conditions.
     ///
     /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
     /// makes code look more complex than it really is.
@@ -40,7 +38,31 @@ declare_clippy_lint! {
     ///     }
     /// }
     ///
-    /// // or
+    /// ```
+    ///
+    /// Should be written:
+    ///
+    /// ```rust.ignore
+    /// if x && y {
+    ///     …
+    /// }
+    /// ```
+    pub COLLAPSIBLE_IF,
+    style,
+    "nested `if`s that can be collapsed (e.g., `if x { if y { ... } }`"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for collapsible `else { if ... }` expressions
+    /// that can be collapsed to `else if ...`.
+    ///
+    /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
+    /// makes code look more complex than it really is.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust,ignore
     ///
     /// if x {
     ///     …
@@ -54,24 +76,18 @@ declare_clippy_lint! {
     /// Should be written:
     ///
     /// ```rust.ignore
-    /// if x && y {
-    ///     …
-    /// }
-    ///
-    /// // or
-    ///
     /// if x {
     ///     …
     /// } else if y {
     ///     …
     /// }
     /// ```
-    pub COLLAPSIBLE_IF,
+    pub COLLAPSIBLE_ELSE_IF,
     style,
-    "`if`s that can be collapsed (e.g., `if x { if y { ... } }` and `else { if x { ... } }`)"
+    "nested `else`-`if` expressions that can be collapsed (e.g., `else { if x { ... } }`)"
 }
 
-declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF]);
+declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]);
 
 impl EarlyLintPass for CollapsibleIf {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
@@ -112,7 +128,7 @@ fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
             let mut applicability = Applicability::MachineApplicable;
             span_lint_and_sugg(
                 cx,
-                COLLAPSIBLE_IF,
+                COLLAPSIBLE_ELSE_IF,
                 block.span,
                 "this `else { if .. }` block can be collapsed",
                 "collapse nested if block",
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 35b057d7b6a..4f41b6c77e2 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -556,6 +556,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &cargo_common_metadata::CARGO_COMMON_METADATA,
         &checked_conversions::CHECKED_CONVERSIONS,
         &cognitive_complexity::COGNITIVE_COMPLEXITY,
+        &collapsible_if::COLLAPSIBLE_ELSE_IF,
         &collapsible_if::COLLAPSIBLE_IF,
         &collapsible_match::COLLAPSIBLE_MATCH,
         &comparison_chain::COMPARISON_CHAIN,
@@ -1384,6 +1385,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&booleans::LOGIC_BUG),
         LintId::of(&booleans::NONMINIMAL_BOOL),
         LintId::of(&bytecount::NAIVE_BYTECOUNT),
+        LintId::of(&collapsible_if::COLLAPSIBLE_ELSE_IF),
         LintId::of(&collapsible_if::COLLAPSIBLE_IF),
         LintId::of(&collapsible_match::COLLAPSIBLE_MATCH),
         LintId::of(&comparison_chain::COMPARISON_CHAIN),
@@ -1653,6 +1655,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&attrs::UNKNOWN_CLIPPY_LINTS),
         LintId::of(&blacklisted_name::BLACKLISTED_NAME),
         LintId::of(&blocks_in_if_conditions::BLOCKS_IN_IF_CONDITIONS),
+        LintId::of(&collapsible_if::COLLAPSIBLE_ELSE_IF),
         LintId::of(&collapsible_if::COLLAPSIBLE_IF),
         LintId::of(&collapsible_match::COLLAPSIBLE_MATCH),
         LintId::of(&comparison_chain::COMPARISON_CHAIN),
diff --git a/tests/ui/collapsible_else_if.fixed b/tests/ui/collapsible_else_if.fixed
index ce2a1c28c8a..fa4bc30e933 100644
--- a/tests/ui/collapsible_else_if.fixed
+++ b/tests/ui/collapsible_else_if.fixed
@@ -3,6 +3,8 @@
 
 #[rustfmt::skip]
 #[warn(clippy::collapsible_if)]
+#[warn(clippy::collapsible_else_if)]
+
 fn main() {
     let x = "hello";
     let y = "world";
diff --git a/tests/ui/collapsible_else_if.rs b/tests/ui/collapsible_else_if.rs
index 99c40b8d38e..bf6c1d1f894 100644
--- a/tests/ui/collapsible_else_if.rs
+++ b/tests/ui/collapsible_else_if.rs
@@ -3,6 +3,8 @@
 
 #[rustfmt::skip]
 #[warn(clippy::collapsible_if)]
+#[warn(clippy::collapsible_else_if)]
+
 fn main() {
     let x = "hello";
     let y = "world";
diff --git a/tests/ui/collapsible_else_if.stderr b/tests/ui/collapsible_else_if.stderr
index 3d1c458879e..ee3e11ae565 100644
--- a/tests/ui/collapsible_else_if.stderr
+++ b/tests/ui/collapsible_else_if.stderr
@@ -1,5 +1,5 @@
 error: this `else { if .. }` block can be collapsed
-  --> $DIR/collapsible_else_if.rs:12:12
+  --> $DIR/collapsible_else_if.rs:14:12
    |
 LL |       } else {
    |  ____________^
@@ -9,7 +9,7 @@ LL | |         }
 LL | |     }
    | |_____^
    |
-   = note: `-D clippy::collapsible-if` implied by `-D warnings`
+   = note: `-D clippy::collapsible-else-if` implied by `-D warnings`
 help: collapse nested if block
    |
 LL |     } else if y == "world" {
@@ -18,7 +18,7 @@ LL |     }
    |
 
 error: this `else { if .. }` block can be collapsed
-  --> $DIR/collapsible_else_if.rs:20:12
+  --> $DIR/collapsible_else_if.rs:22:12
    |
 LL |       } else {
    |  ____________^
@@ -36,7 +36,7 @@ LL |     }
    |
 
 error: this `else { if .. }` block can be collapsed
-  --> $DIR/collapsible_else_if.rs:28:12
+  --> $DIR/collapsible_else_if.rs:30:12
    |
 LL |       } else {
    |  ____________^
@@ -59,7 +59,7 @@ LL |     }
    |
 
 error: this `else { if .. }` block can be collapsed
-  --> $DIR/collapsible_else_if.rs:39:12
+  --> $DIR/collapsible_else_if.rs:41:12
    |
 LL |       } else {
    |  ____________^
@@ -82,7 +82,7 @@ LL |     }
    |
 
 error: this `else { if .. }` block can be collapsed
-  --> $DIR/collapsible_else_if.rs:50:12
+  --> $DIR/collapsible_else_if.rs:52:12
    |
 LL |       } else {
    |  ____________^
@@ -105,7 +105,7 @@ LL |     }
    |
 
 error: this `else { if .. }` block can be collapsed
-  --> $DIR/collapsible_else_if.rs:61:12
+  --> $DIR/collapsible_else_if.rs:63:12
    |
 LL |       } else {
    |  ____________^
@@ -128,7 +128,7 @@ LL |     }
    |
 
 error: this `else { if .. }` block can be collapsed
-  --> $DIR/collapsible_else_if.rs:72:12
+  --> $DIR/collapsible_else_if.rs:74:12
    |
 LL |       } else {
    |  ____________^
diff --git a/tests/ui/if_same_then_else2.rs b/tests/ui/if_same_then_else2.rs
index 8d54f75b5d1..e83ce47e563 100644
--- a/tests/ui/if_same_then_else2.rs
+++ b/tests/ui/if_same_then_else2.rs
@@ -1,6 +1,7 @@
 #![warn(clippy::if_same_then_else)]
 #![allow(
     clippy::blacklisted_name,
+    clippy::collapsible_else_if,
     clippy::collapsible_if,
     clippy::ifs_same_cond,
     clippy::needless_return,
diff --git a/tests/ui/if_same_then_else2.stderr b/tests/ui/if_same_then_else2.stderr
index da2be6c8aa5..f98e30fa376 100644
--- a/tests/ui/if_same_then_else2.stderr
+++ b/tests/ui/if_same_then_else2.stderr
@@ -1,5 +1,5 @@
 error: this `if` has identical blocks
-  --> $DIR/if_same_then_else2.rs:20:12
+  --> $DIR/if_same_then_else2.rs:21:12
    |
 LL |       } else {
    |  ____________^
@@ -13,7 +13,7 @@ LL | |     }
    |
    = note: `-D clippy::if-same-then-else` implied by `-D warnings`
 note: same as this
-  --> $DIR/if_same_then_else2.rs:11:13
+  --> $DIR/if_same_then_else2.rs:12:13
    |
 LL |       if true {
    |  _____________^
@@ -26,7 +26,7 @@ LL | |     } else {
    | |_____^
 
 error: this `if` has identical blocks
-  --> $DIR/if_same_then_else2.rs:34:12
+  --> $DIR/if_same_then_else2.rs:35:12
    |
 LL |       } else {
    |  ____________^
@@ -36,7 +36,7 @@ LL | |     }
    | |_____^
    |
 note: same as this
-  --> $DIR/if_same_then_else2.rs:32:13
+  --> $DIR/if_same_then_else2.rs:33:13
    |
 LL |       if true {
    |  _____________^
@@ -45,7 +45,7 @@ LL | |     } else {
    | |_____^
 
 error: this `if` has identical blocks
-  --> $DIR/if_same_then_else2.rs:41:12
+  --> $DIR/if_same_then_else2.rs:42:12
    |
 LL |       } else {
    |  ____________^
@@ -55,7 +55,7 @@ LL | |     }
    | |_____^
    |
 note: same as this
-  --> $DIR/if_same_then_else2.rs:39:13
+  --> $DIR/if_same_then_else2.rs:40:13
    |
 LL |       if true {
    |  _____________^
@@ -64,7 +64,7 @@ LL | |     } else {
    | |_____^
 
 error: this `if` has identical blocks
-  --> $DIR/if_same_then_else2.rs:91:12
+  --> $DIR/if_same_then_else2.rs:92:12
    |
 LL |       } else {
    |  ____________^
@@ -74,7 +74,7 @@ LL | |     };
    | |_____^
    |
 note: same as this
-  --> $DIR/if_same_then_else2.rs:89:21
+  --> $DIR/if_same_then_else2.rs:90:21
    |
 LL |       let _ = if true {
    |  _____________________^
@@ -83,7 +83,7 @@ LL | |     } else {
    | |_____^
 
 error: this `if` has identical blocks
-  --> $DIR/if_same_then_else2.rs:98:12
+  --> $DIR/if_same_then_else2.rs:99:12
    |
 LL |       } else {
    |  ____________^
@@ -93,7 +93,7 @@ LL | |     }
    | |_____^
    |
 note: same as this
-  --> $DIR/if_same_then_else2.rs:96:13
+  --> $DIR/if_same_then_else2.rs:97:13
    |
 LL |       if true {
    |  _____________^
@@ -102,7 +102,7 @@ LL | |     } else {
    | |_____^
 
 error: this `if` has identical blocks
-  --> $DIR/if_same_then_else2.rs:123:12
+  --> $DIR/if_same_then_else2.rs:124:12
    |
 LL |       } else {
    |  ____________^
@@ -112,7 +112,7 @@ LL | |     }
    | |_____^
    |
 note: same as this
-  --> $DIR/if_same_then_else2.rs:120:20
+  --> $DIR/if_same_then_else2.rs:121:20
    |
 LL |       } else if true {
    |  ____________________^