compute cyclomatic complexity (adjusted to not punish Rust's match)

.gitignore

@@ -12,3 +12,6 @@
 
 # We don't pin yet
 Cargo.lock
+
+# Generated by dogfood
+/target_recur/

README.md

@@ -6,7 +6,7 @@ A collection of lints to catch common mistakes and improve your Rust code.
 [Jump to usage instructions](#usage)
 
 ##Lints
-There are 79 lints included in this crate:
+There are 80 lints included in this crate:
 
 name                                                                                                     | default | meaning
 ---------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
@@ -22,6 +22,7 @@ name
 [cmp_nan](https://github.com/Manishearth/rust-clippy/wiki#cmp_nan)                                       | deny    | comparisons to NAN (which will always return false, which is probably not intended)
 [cmp_owned](https://github.com/Manishearth/rust-clippy/wiki#cmp_owned)                                   | warn    | creating owned instances for comparing with others, e.g. `x == "foo".to_string()`
 [collapsible_if](https://github.com/Manishearth/rust-clippy/wiki#collapsible_if)                         | warn    | two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` can be written as `if x && y { foo() }`
+[cyclomatic_complexity](https://github.com/Manishearth/rust-clippy/wiki#cyclomatic_complexity)           | warn    | finds functions that should be split up into multiple functions
 [empty_loop](https://github.com/Manishearth/rust-clippy/wiki#empty_loop)                                 | warn    | empty `loop {}` detected
 [eq_op](https://github.com/Manishearth/rust-clippy/wiki#eq_op)                                           | warn    | equal operands on both sides of a comparison or bitwise combination (e.g. `x == x`)
 [explicit_counter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_counter_loop)           | warn    | for-looping with an explicit counter when `_.enumerate()` would do

src/cyclomatic_complexity.rs

@@ -0,0 +1,105 @@
+//! calculate cyclomatic complexity and warn about overly complex functions
+
+use rustc::lint::*;
+use rustc_front::hir::*;
+use rustc::middle::cfg::CFG;
+use syntax::codemap::Span;
+use syntax::attr::*;
+use syntax::ast::Attribute;
+use rustc_front::intravisit::{Visitor, walk_expr};
+
+use utils::{in_macro, LimitStack};
+
+declare_lint! { pub CYCLOMATIC_COMPLEXITY, Warn,
+    "finds functions that should be split up into multiple functions" }
+
+pub struct CyclomaticComplexity {
+    limit: LimitStack,
+}
+
+impl CyclomaticComplexity {
+    pub fn new(limit: u64) -> Self {
+        CyclomaticComplexity {
+            limit: LimitStack::new(limit),
+        }
+    }
+}
+
+impl LintPass for CyclomaticComplexity {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(CYCLOMATIC_COMPLEXITY)
+    }
+}
+
+impl CyclomaticComplexity {
+    fn check(&mut self, cx: &LateContext, block: &Block, span: Span) {
+        if in_macro(cx, span) { return; }
+        let cfg = CFG::new(cx.tcx, block);
+        let n = cfg.graph.len_nodes() as u64;
+        let e = cfg.graph.len_edges() as u64;
+        let cc = e + 2 - n;
+        let mut arm_counter = MatchArmCounter(0);
+        arm_counter.visit_block(block);
+        let mut narms = arm_counter.0;
+        if narms > 0 {
+            narms = narms - 1;
+        }
+        if cc < narms {
+            println!("cc = {}, arms = {}", cc, narms);
+            println!("{:?}", block);
+            println!("{:?}", span);
+            panic!("cc = {}, arms = {}", cc, narms);
+        }
+        let rust_cc = cc - narms;
+        if rust_cc > self.limit.limit() {
+            cx.span_lint_help(CYCLOMATIC_COMPLEXITY, span,
+            &format!("The function has a cyclomatic complexity of {}.", rust_cc),
+            "You could split it up into multiple smaller functions");
+        }
+    }
+}
+
+impl LateLintPass for CyclomaticComplexity {
+    fn check_item(&mut self, cx: &LateContext, item: &Item) {
+        if let ItemFn(_, _, _, _, _, ref block) = item.node {
+            self.check(cx, block, item.span);
+        }
+    }
+
+    fn check_impl_item(&mut self, cx: &LateContext, item: &ImplItem) {
+        if let ImplItemKind::Method(_, ref block) = item.node {
+            self.check(cx, block, item.span);
+        }
+    }
+
+    fn check_trait_item(&mut self, cx: &LateContext, item: &TraitItem) {
+        if let MethodTraitItem(_, Some(ref block)) = item.node {
+            self.check(cx, block, item.span);
+        }
+    }
+
+    fn enter_lint_attrs(&mut self, cx: &LateContext, attrs: &[Attribute]) {
+        self.limit.push_attrs(cx.sess(), attrs, "cyclomatic_complexity");
+    }
+    fn exit_lint_attrs(&mut self, cx: &LateContext, attrs: &[Attribute]) {
+        self.limit.pop_attrs(cx.sess(), attrs, "cyclomatic_complexity");
+    }
+}
+
+struct MatchArmCounter(u64);
+
+impl<'a> Visitor<'a> for MatchArmCounter {
+    fn visit_expr(&mut self, e: &'a Expr) {
+        match e.node {
+            ExprMatch(_, ref arms, _) => {
+                walk_expr(self, e);
+                let arms_n: u64 = arms.iter().map(|arm| arm.pats.len() as u64).sum();
+                if arms_n > 0 {
+                    self.0 += arms_n - 1;
+                }
+            },
+            ExprClosure(..) => {},
+            _ => walk_expr(self, e),
+        }
+    }
+}

src/lib.rs

@@ -1,6 +1,6 @@
 #![feature(plugin_registrar, box_syntax)]
 #![feature(rustc_private, core, collections)]
-#![feature(num_bits_bytes)]
+#![feature(num_bits_bytes, iter_arith)]
 #![allow(unknown_lints)]
 
 #[macro_use]
@@ -59,6 +59,7 @@ pub mod needless_update;
 pub mod no_effect;
 pub mod temporary_assignment;
 pub mod transmute;
+pub mod cyclomatic_complexity;
 
 mod reexport {
     pub use syntax::ast::{Name, Ident, NodeId};
@@ -110,6 +111,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
     reg.register_late_lint_pass(box map_clone::MapClonePass);
     reg.register_late_lint_pass(box temporary_assignment::TemporaryAssignmentPass);
     reg.register_late_lint_pass(box transmute::UselessTransmute);
+    reg.register_late_lint_pass(box cyclomatic_complexity::CyclomaticComplexity::new(25));
 
     reg.register_lint_group("clippy_pedantic", vec![
         methods::OPTION_UNWRAP_USED,
@@ -138,6 +140,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
         block_in_if_condition::BLOCK_IN_IF_CONDITION_EXPR,
         block_in_if_condition::BLOCK_IN_IF_CONDITION_STMT,
         collapsible_if::COLLAPSIBLE_IF,
+        cyclomatic_complexity::CYCLOMATIC_COMPLEXITY,
         eq_op::EQ_OP,
         eta_reduction::REDUNDANT_CLOSURE,
         identity_op::IDENTITY_OP,

src/lifetimes.rs

@@ -108,7 +108,7 @@ fn could_use_elision(cx: &LateContext, func: &FnDecl, slf: Option<&ExplicitSelf>
 
     // no input lifetimes? easy case!
     if input_lts.is_empty() {
-        return false;
+        false
     } else if output_lts.is_empty() {
         // no output lifetimes, check distinctness of input lifetimes
 
@@ -117,9 +117,7 @@ fn could_use_elision(cx: &LateContext, func: &FnDecl, slf: Option<&ExplicitSelf>
             return false;
         }
         // we have no output reference, so we only need all distinct lifetimes
-        if input_lts.len() == unique_lifetimes(&input_lts) {
+        input_lts.len() == unique_lifetimes(&input_lts)
-            return true;
-        }
     } else {
         // we have output references, so we need one input reference,
         // and all output lifetimes must be the same
@@ -128,15 +126,16 @@ fn could_use_elision(cx: &LateContext, func: &FnDecl, slf: Option<&ExplicitSelf>
         }
         if input_lts.len() == 1 {
             match (&input_lts[0], &output_lts[0]) {
-                (&Named(n1), &Named(n2)) if n1 == n2 => { return true; }
+                (&Named(n1), &Named(n2)) if n1 == n2 => true,
-                (&Named(_), &Unnamed) => { return true; }
+                (&Named(_), &Unnamed) => true,
-                (&Unnamed, &Named(_)) => { return true; }
+                (&Unnamed, &Named(_)) => true,
-                _ => { } // already elided, different named lifetimes
+                _ => false // already elided, different named lifetimes
-                         // or something static going on
+                           // or something static going on
             }
+        } else {
+            false
         }
     }
-    false
 }
 
 fn allowed_lts_from(named_lts: &[LifetimeDef]) -> HashSet<RefLt> {

src/loops.rs

@@ -56,116 +56,7 @@ impl LintPass for LoopsPass {
 impl LateLintPass for LoopsPass {
     fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
         if let Some((pat, arg, body)) = recover_for_loop(expr) {
-            // check for looping over a range and then indexing a sequence with it
+            check_for_loop(cx, pat, arg, body, expr);
-            // -> the iteratee must be a range literal
-            if let ExprRange(Some(ref l), _) = arg.node {
-                // Range should start with `0`
-                if let ExprLit(ref lit) = l.node {
-                    if let LitInt(0, _) = lit.node {
-
-                        // the var must be a single name
-                        if let PatIdent(_, ref ident, _) = pat.node {
-                            let mut visitor = VarVisitor { cx: cx, var: ident.node.name,
-                                                           indexed: HashSet::new(), nonindex: false };
-                            walk_expr(&mut visitor, body);
-                            // linting condition: we only indexed one variable
-                            if visitor.indexed.len() == 1 {
-                                let indexed = visitor.indexed.into_iter().next().expect(
-                                    "Len was nonzero, but no contents found");
-                                if visitor.nonindex {
-                                    span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
-                                        "the loop variable `{}` is used to index `{}`. Consider using \
-                                         `for ({}, item) in {}.iter().enumerate()` or similar iterators",
-                                        ident.node.name, indexed, ident.node.name, indexed));
-                                } else {
-                                    span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
-                                        "the loop variable `{}` is only used to index `{}`. \
-                                         Consider using `for item in &{}` or similar iterators",
-                                        ident.node.name, indexed, indexed));
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-
-            // if this for loop is iterating over a two-sided range...
-            if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
-                // ...and both sides are compile-time constant integers...
-                if let Some(start_idx @ Constant::ConstantInt(..)) = constant_simple(start_expr) {
-                    if let Some(stop_idx @ Constant::ConstantInt(..)) = constant_simple(stop_expr) {
-                        // ...and the start index is greater than the stop index,
-                        // this loop will never run. This is often confusing for developers
-                        // who think that this will iterate from the larger value to the
-                        // smaller value.
-                        if start_idx > stop_idx {
-                            span_help_and_lint(cx, REVERSE_RANGE_LOOP, expr.span,
-                                "this range is empty so this for loop will never run",
-                                &format!("Consider using `({}..{}).rev()` if you are attempting to \
-                                iterate over this range in reverse", stop_idx, start_idx));
-                        } else if start_idx == stop_idx {
-                            // if they are equal, it's also problematic - this loop
-                            // will never run.
-                            span_lint(cx, REVERSE_RANGE_LOOP, expr.span,
-                                "this range is empty so this for loop will never run");
-                        }
-                    }
-                }
-            }
-
-            if let ExprMethodCall(ref method, _, ref args) = arg.node {
-                // just the receiver, no arguments
-                if args.len() == 1 {
-                    let method_name = method.node;
-                    // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
-                    if method_name.as_str() == "iter" || method_name.as_str() == "iter_mut" {
-                        if is_ref_iterable_type(cx, &args[0]) {
-                            let object = snippet(cx, args[0].span, "_");
-                            span_lint(cx, EXPLICIT_ITER_LOOP, expr.span, &format!(
-                                "it is more idiomatic to loop over `&{}{}` instead of `{}.{}()`",
-                                if method_name.as_str() == "iter_mut" { "mut " } else { "" },
-                                object, object, method_name));
-                        }
-                    }
-                    // check for looping over Iterator::next() which is not what you want
-                    else if method_name.as_str() == "next" &&
-                            match_trait_method(cx, arg, &["core", "iter", "Iterator"]) {
-                        span_lint(cx, ITER_NEXT_LOOP, expr.span,
-                                  "you are iterating over `Iterator::next()` which is an Option; \
-                                   this will compile but is probably not what you want");
-                    }
-                }
-            }
-
-            // Look for variables that are incremented once per loop iteration.
-            let mut visitor = IncrementVisitor { cx: cx, states: HashMap::new(), depth: 0, done: false };
-            walk_expr(&mut visitor, body);
-
-            // For each candidate, check the parent block to see if
-            // it's initialized to zero at the start of the loop.
-            let map = &cx.tcx.map;
-            let parent_scope = map.get_enclosing_scope(expr.id).and_then(|id| map.get_enclosing_scope(id) );
-            if let Some(parent_id) = parent_scope {
-                if let NodeBlock(block) = map.get(parent_id) {
-                    for (id, _) in visitor.states.iter().filter( |&(_,v)| *v == VarState::IncrOnce) {
-                        let mut visitor2 = InitializeVisitor { cx: cx, end_expr: expr, var_id: id.clone(),
-                                                               state: VarState::IncrOnce, name: None,
-                                                               depth: 0,
-                                                               past_loop: false };
-                        walk_block(&mut visitor2, block);
-
-                        if visitor2.state == VarState::Warn {
-                            if let Some(name) = visitor2.name {
-                                span_lint(cx, EXPLICIT_COUNTER_LOOP, expr.span,
-                                          &format!("the variable `{0}` is used as a loop counter. Consider \
-                                                    using `for ({0}, item) in {1}.enumerate()` \
-                                                    or similar iterators",
-                                                   name, snippet(cx, arg.span, "_")));
-                            }
-                        }
-                    }
-                }
-            }
         }
         // check for `loop { if let {} else break }` that could be `while let`
         // (also matches an explicit "match" instead of "if let")
@@ -271,6 +162,119 @@ impl LateLintPass for LoopsPass {
     }
 }
 
+fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
+    // check for looping over a range and then indexing a sequence with it
+    // -> the iteratee must be a range literal
+    if let ExprRange(Some(ref l), _) = arg.node {
+        // Range should start with `0`
+        if let ExprLit(ref lit) = l.node {
+            if let LitInt(0, _) = lit.node {
+
+                // the var must be a single name
+                if let PatIdent(_, ref ident, _) = pat.node {
+                    let mut visitor = VarVisitor { cx: cx, var: ident.node.name,
+                                                   indexed: HashSet::new(), nonindex: false };
+                    walk_expr(&mut visitor, body);
+                    // linting condition: we only indexed one variable
+                    if visitor.indexed.len() == 1 {
+                        let indexed = visitor.indexed.into_iter().next().expect(
+                            "Len was nonzero, but no contents found");
+                        if visitor.nonindex {
+                            span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
+                                "the loop variable `{}` is used to index `{}`. Consider using \
+                                 `for ({}, item) in {}.iter().enumerate()` or similar iterators",
+                                ident.node.name, indexed, ident.node.name, indexed));
+                        } else {
+                            span_lint(cx, NEEDLESS_RANGE_LOOP, expr.span, &format!(
+                                "the loop variable `{}` is only used to index `{}`. \
+                                 Consider using `for item in &{}` or similar iterators",
+                                ident.node.name, indexed, indexed));
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    // if this for loop is iterating over a two-sided range...
+    if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
+        // ...and both sides are compile-time constant integers...
+        if let Some(start_idx @ Constant::ConstantInt(..)) = constant_simple(start_expr) {
+            if let Some(stop_idx @ Constant::ConstantInt(..)) = constant_simple(stop_expr) {
+                // ...and the start index is greater than the stop index,
+                // this loop will never run. This is often confusing for developers
+                // who think that this will iterate from the larger value to the
+                // smaller value.
+                if start_idx > stop_idx {
+                    span_help_and_lint(cx, REVERSE_RANGE_LOOP, expr.span,
+                        "this range is empty so this for loop will never run",
+                        &format!("Consider using `({}..{}).rev()` if you are attempting to \
+                        iterate over this range in reverse", stop_idx, start_idx));
+                } else if start_idx == stop_idx {
+                    // if they are equal, it's also problematic - this loop
+                    // will never run.
+                    span_lint(cx, REVERSE_RANGE_LOOP, expr.span,
+                        "this range is empty so this for loop will never run");
+                }
+            }
+        }
+    }
+
+    if let ExprMethodCall(ref method, _, ref args) = arg.node {
+        // just the receiver, no arguments
+        if args.len() == 1 {
+            let method_name = method.node;
+            // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
+            if method_name.as_str() == "iter" || method_name.as_str() == "iter_mut" {
+                if is_ref_iterable_type(cx, &args[0]) {
+                    let object = snippet(cx, args[0].span, "_");
+                    span_lint(cx, EXPLICIT_ITER_LOOP, expr.span, &format!(
+                        "it is more idiomatic to loop over `&{}{}` instead of `{}.{}()`",
+                        if method_name.as_str() == "iter_mut" { "mut " } else { "" },
+                        object, object, method_name));
+                }
+            }
+            // check for looping over Iterator::next() which is not what you want
+            else if method_name.as_str() == "next" &&
+                    match_trait_method(cx, arg, &["core", "iter", "Iterator"]) {
+                span_lint(cx, ITER_NEXT_LOOP, expr.span,
+                          "you are iterating over `Iterator::next()` which is an Option; \
+                           this will compile but is probably not what you want");
+            }
+        }
+    }
+
+    // Look for variables that are incremented once per loop iteration.
+    let mut visitor = IncrementVisitor { cx: cx, states: HashMap::new(), depth: 0, done: false };
+    walk_expr(&mut visitor, body);
+
+    // For each candidate, check the parent block to see if
+    // it's initialized to zero at the start of the loop.
+    let map = &cx.tcx.map;
+    let parent_scope = map.get_enclosing_scope(expr.id).and_then(|id| map.get_enclosing_scope(id) );
+    if let Some(parent_id) = parent_scope {
+        if let NodeBlock(block) = map.get(parent_id) {
+            for (id, _) in visitor.states.iter().filter( |&(_,v)| *v == VarState::IncrOnce) {
+                let mut visitor2 = InitializeVisitor { cx: cx, end_expr: expr, var_id: id.clone(),
+                                                       state: VarState::IncrOnce, name: None,
+                                                       depth: 0,
+                                                       past_loop: false };
+                walk_block(&mut visitor2, block);
+
+                if visitor2.state == VarState::Warn {
+                    if let Some(name) = visitor2.name {
+                        span_lint(cx, EXPLICIT_COUNTER_LOOP, expr.span,
+                                  &format!("the variable `{0}` is used as a loop counter. Consider \
+                                            using `for ({0}, item) in {1}.enumerate()` \
+                                            or similar iterators",
+                                           name, snippet(cx, arg.span, "_")));
+                    }
+                }
+            }
+        }
+    }
+}
+
 /// Recover the essential nodes of a desugared for loop:
 /// `for pat in arg { body }` becomes `(pat, arg, body)`.
 fn recover_for_loop(expr: &Expr) -> Option<(&Pat, &Expr, &Expr)> {

src/matches.rs

@@ -59,7 +59,7 @@ impl LateLintPass for MatchPass {
                 if arms.len() == 2 && arms[0].pats.len() == 1 { // no guards
                     let exprs = if let PatLit(ref arm_bool) = arms[0].pats[0].node {
                         if let ExprLit(ref lit) = arm_bool.node {
-                            if let LitBool(val) = lit.node { 
+                            if let LitBool(val) = lit.node {
                                 if val {
                                     Some((&*arms[0].body, &*arms[1].body))
                                 } else {

src/utils.rs

@@ -9,6 +9,9 @@ use std::borrow::Cow;
 use syntax::ast::Lit_::*;
 use syntax::ast;
 
+use rustc::session::Session;
+use std::str::FromStr;
+
 // module DefPaths for certain structs/enums we check for
 pub const OPTION_PATH: [&'static str; 3] = ["core", "option", "Option"];
 pub const RESULT_PATH: [&'static str; 3] = ["core", "result", "Result"];
@@ -65,8 +68,8 @@ macro_rules! if_let_chain {
     };
 }
 
-/// returns true this expn_info was expanded by any macro
+/// returns true if this expn_info was expanded by any macro
-pub fn in_macro(cx: &LateContext, span: Span) -> bool {
+pub fn in_macro<T: LintContext>(cx: &T, span: Span) -> bool {
     cx.sess().codemap().with_expn_info(span.expn_id,
             |info| info.is_some())
 }
@@ -397,3 +400,62 @@ macro_rules! if_let_chain {
         }
     };
 }
+
+pub struct LimitStack {
+    stack: Vec<u64>,
+}
+
+impl Drop for LimitStack {
+    fn drop(&mut self) {
+        assert_eq!(self.stack.len(), 1);
+    }
+}
+
+impl LimitStack {
+    pub fn new(limit: u64) -> LimitStack {
+        LimitStack {
+            stack: vec![limit],
+        }
+    }
+    pub fn limit(&self) -> u64 {
+        *self.stack.last().expect("there should always be a value in the stack")
+    }
+    pub fn push_attrs(&mut self, sess: &Session, attrs: &[ast::Attribute], name: &'static str) {
+        let stack = &mut self.stack;
+        parse_attrs(
+            sess,
+            attrs,
+            name,
+            |val| stack.push(val),
+        );
+    }
+    pub fn pop_attrs(&mut self, sess: &Session, attrs: &[ast::Attribute], name: &'static str) {
+        let stack = &mut self.stack;
+        parse_attrs(
+            sess,
+            attrs,
+            name,
+            |val| assert_eq!(stack.pop(), Some(val)),
+        );
+    }
+}
+
+fn parse_attrs<F: FnMut(u64)>(sess: &Session, attrs: &[ast::Attribute], name: &'static str, mut f: F) {
+    for attr in attrs {
+        let attr = &attr.node;
+        if attr.is_sugared_doc { continue; }
+        if let ast::MetaNameValue(ref key, ref value) = attr.value.node {
+            if *key == name {
+                if let LitStr(ref s, _) = value.node {
+                    if let Ok(value) = FromStr::from_str(s) {
+                        f(value)
+                    } else {
+                        sess.span_err(value.span, "not a number");
+                    }
+                } else {
+                    unreachable!()
+                }
+            }
+        }
+    }
+}

tests/compile-fail/cyclomatic_complexity.rs

@@ -0,0 +1,181 @@
+#![feature(plugin, custom_attribute)]
+#![plugin(clippy)]
+#![deny(clippy)]
+#![deny(cyclomatic_complexity)]
+#![allow(unused)]
+
+fn main() { //~ ERROR: The function has a cyclomatic complexity of 28.
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+    if true {
+        println!("a");
+    }
+}
+
+#[cyclomatic_complexity = "0"]
+fn kaboom() {  //~ ERROR: The function has a cyclomatic complexity of 6
+    let n = 0;
+    'a: for i in 0..20 {
+        'b: for j in i..20 {
+            for k in j..20 {
+                if k == 5 {
+                    break 'b;
+                }
+                if j == 3 && k == 6 {
+                    continue 'a;
+                }
+                if k == j {
+                    continue;
+                }
+                println!("bake");
+            }
+        }
+        println!("cake");
+    }
+}
+
+fn bloo() {
+    match 42 {
+        0 => println!("hi"),
+        1 => println!("hai"),
+        2 => println!("hey"),
+        3 => println!("hallo"),
+        4 => println!("hello"),
+        5 => println!("salut"),
+        6 => println!("good morning"),
+        7 => println!("good evening"),
+        8 => println!("good afternoon"),
+        9 => println!("good night"),
+        10 => println!("bonjour"),
+        11 => println!("hej"),
+        12 => println!("hej hej"),
+        13 => println!("greetings earthling"),
+        14 => println!("take us to you leader"),
+        15 | 17 | 19 | 21 | 23 | 25 | 27 | 29 | 31 | 33 => println!("take us to you leader"),
+        35 | 37 | 39 | 41 | 43 | 45 | 47 | 49 | 51 | 53 => println!("there is no undefined behavior"),
+        55 | 57 | 59 | 61 | 63 | 65 | 67 | 69 | 71 | 73 => println!("I know borrow-fu"),
+        _ => println!("bye"),
+    }
+}
+
+#[cyclomatic_complexity = "0"]
+fn baa() { //~ ERROR: The function has a cyclomatic complexity of 2
+    let x = || match 99 {
+        0 => true,
+        1 => false,
+        2 => true,
+        4 => true,
+        6 => true,
+        9 => true,
+        _ => false,
+    };
+    if x() {
+        println!("x");
+    } else {
+        println!("not x");
+    }
+}
+
+#[cyclomatic_complexity = "0"]
+fn bar() { //~ ERROR: The function has a cyclomatic complexity of 2
+    match 99 {
+        0 => println!("hi"),
+        _ => println!("bye"),
+    }
+}
+
+#[cyclomatic_complexity = "0"]
+fn barr() { //~ ERROR: The function has a cyclomatic complexity of 2
+    match 99 {
+        0 => println!("hi"),
+        1 => println!("bla"),
+        2 | 3 => println!("blub"),
+        _ => println!("bye"),
+    }
+}
+
+enum Void {}
+
+#[cyclomatic_complexity = "0"]
+fn void(void: Void) { //~ ERROR: The function has a cyclomatic complexity of 1
+    if true {
+        match void {
+        }
+    }
+}

tests/compile-fail/for_loop.rs

@@ -16,7 +16,7 @@ impl Unrelated {
 
 #[deny(needless_range_loop, explicit_iter_loop, iter_next_loop, reverse_range_loop, explicit_counter_loop)]
 #[deny(unused_collect)]
-#[allow(linkedlist,shadow_unrelated,unnecessary_mut_passed)]
+#[allow(linkedlist,shadow_unrelated,unnecessary_mut_passed, cyclomatic_complexity)]
 fn main() {
     let mut vec = vec![1, 2, 3, 4];
     let vec2 = vec![1, 2, 3, 4];

tests/compile-fail/while_loop.rs

@@ -2,7 +2,7 @@
 #![plugin(clippy)]
 
 #![deny(while_let_loop, empty_loop, while_let_on_iterator)]
-#![allow(dead_code, unused)]
+#![allow(dead_code, unused, cyclomatic_complexity)]
 
 fn main() {
     let y = Some(true);