fix never_loop

README.md

@@ -295,7 +295,7 @@ name
 [needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return)                                     | warn    | using a return statement like `return expr;` where an expression would suffice
 [needless_update](https://github.com/Manishearth/rust-clippy/wiki#needless_update)                                     | warn    | using `Foo { ..base }` when there are no missing fields
 [neg_multiply](https://github.com/Manishearth/rust-clippy/wiki#neg_multiply)                                           | warn    | multiplying integers with -1
-[never_loop](https://github.com/Manishearth/rust-clippy/wiki#never_loop)                                               | allow   | any loop with an unconditional `break` or `return` statement
+[never_loop](https://github.com/Manishearth/rust-clippy/wiki#never_loop)                                               | warn    | any loop that will always `break` or `return`
 [new_ret_no_self](https://github.com/Manishearth/rust-clippy/wiki#new_ret_no_self)                                     | warn    | not returning `Self` in a `new` method
 [new_without_default](https://github.com/Manishearth/rust-clippy/wiki#new_without_default)                             | warn    | `fn new() -> Self` method without `Default` implementation
 [new_without_default_derive](https://github.com/Manishearth/rust-clippy/wiki#new_without_default_derive)               | warn    | `fn new() -> Self` without `#[derive]`able `Default` implementation

clippy_lints/src/lib.rs

@@ -324,7 +324,6 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         enum_variants::STUTTER,
         if_not_else::IF_NOT_ELSE,
         items_after_statements::ITEMS_AFTER_STATEMENTS,
-        loops::NEVER_LOOP,
         matches::SINGLE_MATCH_ELSE,
         mem_forget::MEM_FORGET,
         methods::FILTER_MAP,
@@ -420,6 +419,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         loops::FOR_LOOP_OVER_RESULT,
         loops::ITER_NEXT_LOOP,
         loops::NEEDLESS_RANGE_LOOP,
+        loops::NEVER_LOOP,
         loops::REVERSE_RANGE_LOOP,
         loops::UNUSED_COLLECT,
         loops::WHILE_LET_LOOP,

clippy_lints/src/loops.rs

@@ -285,15 +285,13 @@ declare_lint! {
     "looping on a map using `iter` when `keys` or `values` would do"
 }
 
-/// **What it does:** Checks for loops that contain an unconditional `break`
+/// **What it does:** Checks for loops that will always `break`, `return` or
-/// or `return`.
+/// `continue` an outer loop.
 ///
 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
 /// code.
 ///
-/// **Known problems:** Ignores `continue` statements in the loop that create
+/// **Known problems:** None
-/// nontrivial control flow. Therefore set to `Allow` by default.
-/// See https://github.com/Manishearth/rust-clippy/issues/1586
 ///
 /// **Example:**
 /// ```rust
@@ -301,8 +299,8 @@ declare_lint! {
 /// ```
 declare_lint! {
     pub NEVER_LOOP,
-    Allow,
+    Warn,
-    "any loop with an unconditional `break` or `return` statement"
+    "any loop that will always `break` or `return`"
 }
 
 #[derive(Copy, Clone)]
@@ -344,7 +342,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
                           "empty `loop {}` detected. You may want to either use `panic!()` or add \
                            `std::thread::sleep(..);` to the loop body.");
             }
-            if never_loop_block(block) {
+            if never_loop(block, &expr.id) {
                 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops");
             }
 
@@ -424,47 +422,100 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
     }
 }
 
-fn never_loop_block(block: &Block) -> bool {
+fn never_loop(block: &Block, id: &NodeId) -> bool {
-    block.stmts.iter().any(never_loop_stmt) || block.expr.as_ref().map_or(false, |e| never_loop_expr(e))
+    !contains_continue_block(block, id) && loop_exit_block(block)
 }
 
-fn never_loop_stmt(stmt: &Stmt) -> bool {
+fn contains_continue_block(block: &Block, dest: &NodeId) -> bool {
+    block.stmts.iter().any(|e| contains_continue_stmt(e, dest))
+        || block.expr.as_ref().map_or(false, |e| contains_continue_expr(e, dest))
+}
+
+fn contains_continue_stmt(stmt: &Stmt, dest: &NodeId) -> bool {
     match stmt.node {
         StmtSemi(ref e, _) |
-        StmtExpr(ref e, _) => never_loop_expr(e),
+        StmtExpr(ref e, _) => contains_continue_expr(e, dest),
-        StmtDecl(ref d, _) => never_loop_decl(d),
+        StmtDecl(ref d, _) => contains_continue_decl(d, dest),
     }
 }
 
-fn never_loop_decl(decl: &Decl) -> bool {
+fn contains_continue_decl(decl: &Decl, dest: &NodeId) -> bool {
-    if let DeclLocal(ref local) = decl.node {
+    match decl.node {
-        local.init.as_ref().map_or(false, |e| never_loop_expr(e))
+        DeclLocal(ref local) => local.init.as_ref().map_or(false, |e| contains_continue_expr(e, dest)),
-    } else {
+        _ => false
-        false
     }
 }
 
-fn never_loop_expr(expr: &Expr) -> bool {
+fn contains_continue_expr(expr: &Expr, dest: &NodeId) -> bool {
     match expr.node {
-        ExprBreak(..) | ExprRet(..) => true,
         ExprBox(ref e) |
         ExprUnary(_, ref e) |
-        ExprBinary(_, ref e, _) | // because short-circuiting
         ExprCast(ref e, _) |
         ExprType(ref e, _) |
         ExprField(ref e, _) |
         ExprTupField(ref e, _) |
-        ExprRepeat(ref e, _) |
+        ExprAddrOf(_, ref e) |
-        ExprAddrOf(_, ref e) => never_loop_expr(e),
+        ExprRepeat(ref e, _) => contains_continue_expr(e, dest),
+        ExprBinary(_, ref e1, ref e2) |
         ExprAssign(ref e1, ref e2) |
         ExprAssignOp(_, ref e1, ref e2) |
-        ExprIndex(ref e1, ref e2) => never_loop_expr(e1) || never_loop_expr(e2),
+        ExprIndex(ref e1, ref e2) => [e1, e2].iter().any(|e| contains_continue_expr(e, dest)),
         ExprArray(ref es) |
         ExprTup(ref es) |
-        ExprMethodCall(_, _, ref es) => es.iter().any(|e| never_loop_expr(e)),
+        ExprMethodCall(_, _, ref es) => es.iter().any(|e| contains_continue_expr(e, dest)),
-        ExprCall(ref e, ref es) => never_loop_expr(e) || es.iter().any(|e| never_loop_expr(e)),
+        ExprCall(ref e, ref es) => contains_continue_expr(e, dest) || es.iter().any(|e| contains_continue_expr(e, dest)),
-        ExprBlock(ref block) => never_loop_block(block),
+        ExprBlock(ref block) => contains_continue_block(block, dest),
-        ExprStruct(_, _, ref base) => base.as_ref().map_or(false, |e| never_loop_expr(e)),
+        ExprStruct(_, _, ref base) => base.as_ref().map_or(false, |e| contains_continue_expr(e, dest)),
+        ExprAgain(d) => d.target_id.opt_id().map_or(false, |id| id == *dest),
+        _ => false,
+    }
+}
+
+fn loop_exit_block(block: &Block) -> bool {
+    block.stmts.iter().any(|e| loop_exit_stmt(e))
+        || block.expr.as_ref().map_or(false, |e| loop_exit_expr(e))
+}
+
+fn loop_exit_stmt(stmt: &Stmt) -> bool {
+    match stmt.node {
+        StmtSemi(ref e, _) |
+        StmtExpr(ref e, _) => loop_exit_expr(e),
+        StmtDecl(ref d, _) => loop_exit_decl(d),
+    }
+}
+
+fn loop_exit_decl(decl: &Decl) -> bool {
+    match decl.node {
+        DeclLocal(ref local) => local.init.as_ref().map_or(false, |e| loop_exit_expr(e)),
+        _ => false
+    }
+}
+
+fn loop_exit_expr(expr: &Expr) -> bool {
+    match expr.node {
+        ExprBox(ref e) |
+        ExprUnary(_, ref e) |
+        ExprCast(ref e, _) |
+        ExprType(ref e, _) |
+        ExprField(ref e, _) |
+        ExprTupField(ref e, _) |
+        ExprAddrOf(_, ref e) |
+        ExprRepeat(ref e, _) => loop_exit_expr(e),
+        ExprMethodCall(_, _, ref es) => es.iter().any(|e| loop_exit_expr(e)),
+        ExprArray(ref es) |
+        ExprTup(ref es) => es.iter().any(|e| loop_exit_expr(e)),
+        ExprCall(ref e, ref es) => loop_exit_expr(e) || es.iter().any(|e| loop_exit_expr(e)),
+        ExprBinary(_, ref e1, ref e2) |
+        ExprAssign(ref e1, ref e2) |
+        ExprAssignOp(_, ref e1, ref e2) |
+        ExprIndex(ref e1, ref e2) => [e1, e2].iter().any(|e| loop_exit_expr(e)),
+        ExprIf(ref e, ref e2, ref e3) => loop_exit_expr(e) || e3.as_ref().map_or(false, |e| loop_exit_expr(e)) && loop_exit_expr(e2),
+        ExprWhile(ref e, ref b, _) => loop_exit_expr(e) || loop_exit_block(b),
+        ExprMatch(ref e, ref arms, _) => loop_exit_expr(e) || arms.iter().all(|a| loop_exit_expr(&a.body)),
+        ExprBlock(ref b) => loop_exit_block(b),
+        ExprBreak(_, _) |
+        ExprAgain(_) |
+        ExprRet(_) => true,
         _ => false,
     }
 }

clippy_tests/examples/never_loop.rs

@@ -2,33 +2,56 @@
 #![plugin(clippy)]
 
 #![warn(never_loop)]
-#![allow(dead_code, unused)]
+#![allow(single_match, while_true)]
 
-fn main() {
+fn break_stmt() {
     loop {
-        println!("This is only ever printed once");
         break;
     }
+}
 
-    let x = 1;
+fn conditional_break() {
+    let mut x = 5;
     loop {
-        println!("This, too"); // but that's OK
+        x -= 1;
         if x == 1 {
-            break;
+            break
-        }
-    }
-
-    loop {
-        loop {
-            // another one
-            break;
-        }
-        break;
-    }
-
-    loop {
-        loop {
-            if x == 1 { return; }
         }
     }
 }
+
+fn nested_loop() {
+    loop {
+        while true {
+            break
+        }
+        break
+    }
+}
+
+fn if_false() {
+    let x = 1;
+    loop {
+        if x == 1 {
+            return
+        }
+    }
+}
+
+fn match_false() {
+    let x = 1;
+    loop {
+        match x {
+            1 => return,
+            _ => (),
+        }
+    }
+}
+
+fn main() {
+    break_stmt();
+    conditional_break();
+    nested_loop();
+    if_false();
+    match_false();
+}

clippy_tests/examples/never_loop.stderr

@@ -2,38 +2,25 @@ error: this loop never actually loops
   --> never_loop.rs:8:5
    |
 8  | /     loop {
-9  | |         println!("This is only ever printed once");
+9  | |         break;
-10 | |         break;
+10 | |     }
-11 | |     }
    | |_____^
    |
    = note: `-D never-loop` implied by `-D warnings`
 
 error: this loop never actually loops
-  --> never_loop.rs:21:5
+  --> never_loop.rs:24:5
    |
-21 | /     loop {
+24 | /     loop {
-22 | |         loop {
+25 | |         while true {
-23 | |             // another one
+26 | |             break
-24 | |             break;
-25 | |         }
-26 | |         break;
 27 | |         }
+28 | |         break
+29 | |     }
    | |_____^
    |
    = note: `-D never-loop` implied by `-D warnings`
 
-error: this loop never actually loops
-  --> never_loop.rs:22:9
-   |
-22 | /         loop {
-23 | |             // another one
-24 | |             break;
-25 | |         }
-   | |_________^
-   |
-   = note: `-D never-loop` implied by `-D warnings`
-
 error: aborting due to previous error(s)
 
 error: Could not compile `clippy_tests`.