lint: while immutable condition: do not lint constants

clippy_lints/src/loops.rs

@@ -22,6 +22,8 @@ use syntax::codemap::Span;
 use utils::sugg;
 use utils::const_to_u64;
 
+use consts::constant;
+
 use utils::{get_enclosing_block, get_parent_expr, higher, in_external_macro, is_integer_literal, is_refutable,
             last_path_segment, match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt,
             span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then};
@@ -2142,6 +2144,11 @@ fn path_name(e: &Expr) -> Option<Name> {
 }
 
 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, block: &'tcx Block, expr: &'tcx Expr) {
+    if constant(cx, cond).is_some() {
+        // A pure constant condition (e.g. while false) is not linted.
+        return;
+    }
+
     let mut mut_var_visitor = MutableVarsVisitor {
         cx,
         ids: HashMap::new(),
@@ -2152,12 +2159,12 @@ fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, b
         return;
     }
 
-    if mut_var_visitor.ids.len() == 0 {
+    if mut_var_visitor.ids.is_empty() {
         span_lint(
             cx,
             WHILE_IMMUTABLE_CONDITION,
             cond.span,
-            "all variables in condition are immutable. This might lead to infinite loops.",
+            "all variables in condition are immutable. This either leads to an infinite or to a never running loop.",
         );
         return;
     }
@@ -2175,7 +2182,7 @@ fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, b
             cx,
             WHILE_IMMUTABLE_CONDITION,
             expr.span,
-            "Variable in the condition are not mutated in the loop body. This might lead to infinite loops.",
+            "Variable in the condition are not mutated in the loop body. This either leads to an infinite or to a never running loop.",
         );
     }
 }

tests/ui/infinite_loop.rs

@@ -94,6 +94,23 @@ fn used_immutable() {
     }
 }
 
+const N: i32 = 5;
+const B: bool = false;
+
+fn consts() {
+    while false {
+        println!("Constants are not linted");
+    }
+
+    while B {
+        println!("Constants are not linted");
+    }
+
+    while N > 0 {
+        println!("Constants are not linted");
+    }
+}
+
 use std::cell::Cell;
 
 fn maybe_i_mutate(i: &Cell<bool>) { unimplemented!() }

tests/ui/infinite_loop.stderr

@@ -1,4 +1,4 @@
-error: all variables in condition are immutable. This might lead to infinite loops.
+error: all variables in condition are immutable. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:10:11
    |
 10 |     while y < 10 {
@@ -6,19 +6,19 @@ error: all variables in condition are immutable. This might lead to infinite loo
    |
    = note: `-D while-immutable-condition` implied by `-D warnings`
 
-error: all variables in condition are immutable. This might lead to infinite loops.
+error: all variables in condition are immutable. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:15:11
    |
 15 |     while y < 10 && x < 3 {
    |           ^^^^^^^^^^^^^^^
 
-error: all variables in condition are immutable. This might lead to infinite loops.
+error: all variables in condition are immutable. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:22:11
    |
 22 |     while !cond {
    |           ^^^^^
 
-error: Variable in the condition are not mutated in the loop body. This might lead to infinite loops.
+error: Variable in the condition are not mutated in the loop body. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:52:5
    |
 52 | /     while i < 3 {
@@ -27,7 +27,7 @@ error: Variable in the condition are not mutated in the loop body. This might le
 55 | |     }
    | |_____^
 
-error: Variable in the condition are not mutated in the loop body. This might lead to infinite loops.
+error: Variable in the condition are not mutated in the loop body. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:57:5
    |
 57 | /     while i < 3 && j > 0 {
@@ -35,7 +35,7 @@ error: Variable in the condition are not mutated in the loop body. This might le
 59 | |     }
    | |_____^
 
-error: Variable in the condition are not mutated in the loop body. This might lead to infinite loops.
+error: Variable in the condition are not mutated in the loop body. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:61:5
    |
 61 | /     while i < 3 {
@@ -45,7 +45,7 @@ error: Variable in the condition are not mutated in the loop body. This might le
 65 | |     }
    | |_____^
 
-error: Variable in the condition are not mutated in the loop body. This might lead to infinite loops.
+error: Variable in the condition are not mutated in the loop body. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:76:5
    |
 76 | /     while i < 3 {
@@ -54,7 +54,7 @@ error: Variable in the condition are not mutated in the loop body. This might le
 79 | |     }
    | |_____^
 
-error: Variable in the condition are not mutated in the loop body. This might lead to infinite loops.
+error: Variable in the condition are not mutated in the loop body. This either leads to an infinite or to a never running loop.
   --> $DIR/infinite_loop.rs:81:5
    |
 81 | /     while i < 3 {