Changed Cognitive Complexity as per issue 3793

* CoC is now a pre-expansion Early pass.
* The full draft of issue 3793 has been implemented.
* Affected tests have been updated.
  ** In particular, ui/eta.rs has been reordered s.t. it's easier to read.
     Its cognitive complexity doesn't seem high at the time of writing,
     so it was tagged as `allow(clippy::cognitive_complexity)` after being
     reordered.
* Tests for CoC have been updated.

Author: felix91gr

Diff for: clippy_lints/src/cognitive_complexity.rs

@@ -306,6 +306,13 @@ pub fn register_pre_expansion_lints(
     );
     store.register_pre_expansion_pass(Some(session), true, false, box attrs::CfgAttrPass);
     store.register_pre_expansion_pass(Some(session), true, false, box dbg_macro::Pass);
+
+    store.register_pre_expansion_pass(
+        Some(session),
+        true,
+        false,
+        box cognitive_complexity::CognitiveComplexity::new(conf.cognitive_complexity_threshold),
+    )
 }
 
 #[doc(hidden)]
@@ -370,6 +377,7 @@ pub fn read_conf(reg: &rustc_plugin::Registry<'_>) -> Conf {
 ///
 /// Used in `./src/driver.rs`.
 #[allow(clippy::too_many_lines)]
+#[allow(clippy::cognitive_complexity)]
 #[rustfmt::skip]
 pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
     let mut store = reg.sess.lint_store.borrow_mut();
@@ -478,9 +486,6 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
     reg.register_late_lint_pass(box no_effect::Pass);
     reg.register_late_lint_pass(box temporary_assignment::Pass);
     reg.register_late_lint_pass(box transmute::Transmute);
-    reg.register_late_lint_pass(
-        box cognitive_complexity::CognitiveComplexity::new(conf.cognitive_complexity_threshold)
-    );
     reg.register_late_lint_pass(box escape::Pass{too_large_for_stack: conf.too_large_for_stack});
     reg.register_early_lint_pass(box misc_early::MiscEarly);
     reg.register_late_lint_pass(box panic_unimplemented::Pass);

Diff for: clippy_lints/src/lib.rs

@@ -109,7 +109,7 @@ define_Conf! {
     /// Lint: BLACKLISTED_NAME. The list of blacklisted names to lint about
     (blacklisted_names, "blacklisted_names", ["foo", "bar", "baz", "quux"] => Vec<String>),
     /// Lint: COGNITIVE_COMPLEXITY. The maximum cognitive complexity a function can have
-    (cognitive_complexity_threshold, "cognitive_complexity_threshold", 25 => u64),
+    (cognitive_complexity_threshold, "cognitive_complexity_threshold", 50 => u64),
     /// DEPRECATED LINT: CYCLOMATIC_COMPLEXITY. Use the Cognitive Complexity lint instead.
     (cyclomatic_complexity_threshold, "cyclomatic_complexity_threshold", None => Option<u64>),
     /// Lint: DOC_MARKDOWN. The list of words this lint should not consider as identifiers needing ticks

Diff for: clippy_lints/src/utils/conf.rs

@@ -153,6 +153,7 @@ fn has_attr(sess: &Session, attrs: &[Attribute]) -> bool {
     get_attr(sess, attrs, "dump").count() > 0
 }
 
+#[allow(clippy::cognitive_complexity)]
 #[allow(clippy::similar_names)]
 fn print_expr(cx: &LateContext<'_, '_>, expr: &hir::Expr, indent: usize) {
     let ind = "  ".repeat(indent);
@@ -415,6 +416,7 @@ fn print_item(cx: &LateContext<'_, '_>, item: &hir::Item) {
     }
 }
 
+#[allow(clippy::cognitive_complexity)]
 #[allow(clippy::similar_names)]
 fn print_pat(cx: &LateContext<'_, '_>, pat: &hir::Pat, indent: usize) {
     let ind = "  ".repeat(indent);

Diff for: clippy_lints/src/utils/inspector.rs

@@ -133,16 +133,6 @@ fn bloo() {
     }
 }
 
-#[clippy::cognitive_complexity = "0"]
-fn lots_of_short_circuits() -> bool {
-    true && false && true && false && true && false && true
-}
-
-#[clippy::cognitive_complexity = "0"]
-fn lots_of_short_circuits2() -> bool {
-    true || false || true || false || true || false || true
-}
-
 #[clippy::cognitive_complexity = "0"]
 fn baa() {
     let x = || match 99 {
@@ -369,3 +359,32 @@ fn early_ret() -> i32 {
         _ => return 6,
     }
 }
+
+#[clippy::cognitive_complexity = "0"]
+fn osscilating_logical_chain_1() -> bool {
+    true && false || true && false
+}
+
+// This tests that the only thing that matters 
+// is the change in operator
+#[clippy::cognitive_complexity = "0"]
+fn osscilating_logical_chain_2() -> bool {
+    true && false && true && false || true && false && true && false
+}
+
+#[clippy::cognitive_complexity = "0"]
+fn osscilating_logical_chain_3() -> bool {
+    (true && false) || (true && false)
+}
+
+#[clippy::cognitive_complexity = "1"]
+fn nested_functions_are_counted(n: usize) -> usize {
+    fn lucas_number(n: usize) -> usize {
+        match n {
+            0 => 2,
+            1 => 1,
+            _ => lucas_number(n - 1) + lucas_number(n - 2),
+        }
+    }
+    lucas_number(n)
+}

Diff for: tests/ui/cognitive_complexity.rs

@@ -1,4 +1,4 @@
-error: the function has a cognitive complexity of 28
+error: the function has a cognitive complexity of 54
   --> $DIR/cognitive_complexity.rs:6:1
    |
 LL | / fn main() {
@@ -13,7 +13,7 @@ LL | | }
    = note: `-D clippy::cognitive-complexity` implied by `-D warnings`
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 7
+error: the function has a cognitive complexity of 11
   --> $DIR/cognitive_complexity.rs:91:1
    |
 LL | / fn kaboom() {
@@ -27,29 +27,9 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 1
+error: the function has a cognitive complexity of 5
   --> $DIR/cognitive_complexity.rs:137:1
    |
-LL | / fn lots_of_short_circuits() -> bool {
-LL | |     true && false && true && false && true && false && true
-LL | | }
-   | |_^
-   |
-   = help: you could split it up into multiple smaller functions
-
-error: the function has a cognitive complexity of 1
-  --> $DIR/cognitive_complexity.rs:142:1
-   |
-LL | / fn lots_of_short_circuits2() -> bool {
-LL | |     true || false || true || false || true || false || true
-LL | | }
-   | |_^
-   |
-   = help: you could split it up into multiple smaller functions
-
-error: the function has a cognitive complexity of 2
-  --> $DIR/cognitive_complexity.rs:147:1
-   |
 LL | / fn baa() {
 LL | |     let x = || match 99 {
 LL | |         0 => 0,
@@ -61,23 +41,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 2
-  --> $DIR/cognitive_complexity.rs:148:13
-   |
-LL |       let x = || match 99 {
-   |  _____________^
-LL | |         0 => 0,
-LL | |         1 => 1,
-LL | |         2 => 2,
-...  |
-LL | |         _ => 42,
-LL | |     };
-   | |_____^
-   |
-   = help: you could split it up into multiple smaller functions
-
-error: the function has a cognitive complexity of 2
-  --> $DIR/cognitive_complexity.rs:165:1
+error: the function has a cognitive complexity of 3
+  --> $DIR/cognitive_complexity.rs:155:1
    |
 LL | / fn bar() {
 LL | |     match 99 {
@@ -89,8 +54,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 2
-  --> $DIR/cognitive_complexity.rs:184:1
+error: the function has a cognitive complexity of 5
+  --> $DIR/cognitive_complexity.rs:174:1
    |
 LL | / fn barr() {
 LL | |     match 99 {
@@ -103,8 +68,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 3
-  --> $DIR/cognitive_complexity.rs:194:1
+error: the function has a cognitive complexity of 10
+  --> $DIR/cognitive_complexity.rs:184:1
    |
 LL | / fn barr2() {
 LL | |     match 99 {
@@ -117,8 +82,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 2
-  --> $DIR/cognitive_complexity.rs:210:1
+error: the function has a cognitive complexity of 5
+  --> $DIR/cognitive_complexity.rs:200:1
    |
 LL | / fn barrr() {
 LL | |     match 99 {
@@ -131,8 +96,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 3
-  --> $DIR/cognitive_complexity.rs:220:1
+error: the function has a cognitive complexity of 10
+  --> $DIR/cognitive_complexity.rs:210:1
    |
 LL | / fn barrr2() {
 LL | |     match 99 {
@@ -145,8 +110,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 2
-  --> $DIR/cognitive_complexity.rs:236:1
+error: the function has a cognitive complexity of 5
+  --> $DIR/cognitive_complexity.rs:226:1
    |
 LL | / fn barrrr() {
 LL | |     match 99 {
@@ -159,8 +124,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 3
-  --> $DIR/cognitive_complexity.rs:246:1
+error: the function has a cognitive complexity of 10
+  --> $DIR/cognitive_complexity.rs:236:1
    |
 LL | / fn barrrr2() {
 LL | |     match 99 {
@@ -173,8 +138,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 2
-  --> $DIR/cognitive_complexity.rs:262:1
+error: the function has a cognitive complexity of 4
+  --> $DIR/cognitive_complexity.rs:252:1
    |
 LL | / fn cake() {
 LL | |     if 4 == 5 {
@@ -187,8 +152,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 4
-  --> $DIR/cognitive_complexity.rs:272:1
+error: the function has a cognitive complexity of 11
+  --> $DIR/cognitive_complexity.rs:262:1
    |
 LL | / pub fn read_file(input_path: &str) -> String {
 LL | |     use std::fs::File;
@@ -201,8 +166,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 1
-  --> $DIR/cognitive_complexity.rs:303:1
+error: the function has a cognitive complexity of 2
+  --> $DIR/cognitive_complexity.rs:293:1
    |
 LL | / fn void(void: Void) {
 LL | |     if true {
@@ -213,8 +178,19 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 1
-  --> $DIR/cognitive_complexity.rs:316:1
+error: the function has a cognitive complexity of 2
+  --> $DIR/cognitive_complexity.rs:300:1
+   |
+LL | / fn mcarton_sees_all() {
+LL | |     panic!("meh");
+LL | |     panic!("möh");
+LL | | }
+   | |_^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: the function has a cognitive complexity of 3
+  --> $DIR/cognitive_complexity.rs:306:1
    |
 LL | / fn try() -> Result<i32, &'static str> {
 LL | |     match 5 {
@@ -226,8 +202,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 1
-  --> $DIR/cognitive_complexity.rs:324:1
+error: the function has a cognitive complexity of 11
+  --> $DIR/cognitive_complexity.rs:314:1
    |
 LL | / fn try_again() -> Result<i32, &'static str> {
 LL | |     let _ = try!(Ok(42));
@@ -240,8 +216,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 1
-  --> $DIR/cognitive_complexity.rs:340:1
+error: the function has a cognitive complexity of 9
+  --> $DIR/cognitive_complexity.rs:330:1
    |
 LL | / fn early() -> Result<i32, &'static str> {
 LL | |     return Ok(5);
@@ -254,8 +230,8 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: the function has a cognitive complexity of 8
-  --> $DIR/cognitive_complexity.rs:354:1
+error: the function has a cognitive complexity of 13
+  --> $DIR/cognitive_complexity.rs:344:1
    |
 LL | / fn early_ret() -> i32 {
 LL | |     let a = if true { 42 } else { return 0; };
@@ -268,5 +244,63 @@ LL | | }
    |
    = help: you could split it up into multiple smaller functions
 
-error: aborting due to 20 previous errors
+error: the function has a cognitive complexity of 2
+  --> $DIR/cognitive_complexity.rs:364:1
+   |
+LL | / fn osscilating_logical_chain_1() -> bool {
+LL | |     true && false || true && false
+LL | | }
+   | |_^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: the function has a cognitive complexity of 2
+  --> $DIR/cognitive_complexity.rs:371:1
+   |
+LL | / fn osscilating_logical_chain_2() -> bool {
+LL | |     true && false && true && false || true && false && true && false
+LL | | }
+   | |_^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: the function has a cognitive complexity of 2
+  --> $DIR/cognitive_complexity.rs:376:1
+   |
+LL | / fn osscilating_logical_chain_3() -> bool {
+LL | |     (true && false) || (true && false)
+LL | | }
+   | |_^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: the function has a cognitive complexity of 4
+  --> $DIR/cognitive_complexity.rs:381:1
+   |
+LL | / fn nested_functions_are_counted(n: usize) -> usize {
+LL | |     fn lucas_number(n: usize) -> usize {
+LL | |         match n {
+LL | |             0 => 2,
+...  |
+LL | |     lucas_number(n)
+LL | | }
+   | |_^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: the function has a cognitive complexity of 3
+  --> $DIR/cognitive_complexity.rs:382:5
+   |
+LL | /     fn lucas_number(n: usize) -> usize {
+LL | |         match n {
+LL | |             0 => 2,
+LL | |             1 => 1,
+LL | |             _ => lucas_number(n - 1) + lucas_number(n - 2),
+LL | |         }
+LL | |     }
+   | |_____^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: aborting due to 23 previous errors