diff --git a/src/rustc/middle/lint.rs b/src/rustc/middle/lint.rs
index 0768a09252247..192b2924cb14d 100644
--- a/src/rustc/middle/lint.rs
+++ b/src/rustc/middle/lint.rs
@@ -54,6 +54,7 @@ enum lint {
deprecated_pattern,
non_camel_case_types,
structural_records,
+ type_limits,
managed_heap_memory,
owned_heap_memory,
@@ -186,6 +187,11 @@ fn get_lint_dict() -> lint_dict {
desc: ~"allow legacy modes",
default: forbid}),
+ (~"type_limits",
+ @{lint: type_limits,
+ desc: ~"comparisons made useless by limits of the types involved",
+ default: warn})
+
/* FIXME(#3266)--make liveness warnings lintable
(~"unused_variable",
@{lint: unused_variable,
@@ -397,6 +403,7 @@ fn check_item(i: @ast::item, cx: ty::ctxt) {
check_item_heap(cx, i);
check_item_structural_records(cx, i);
check_item_deprecated_modes(cx, i);
+ check_item_type_limits(cx, i);
}
// Take a visitor, and modify it so that it will not proceed past subitems.
@@ -430,6 +437,122 @@ fn check_item_while_true(cx: ty::ctxt, it: @ast::item) {
visit::visit_item(it, (), visit);
}
+fn check_item_type_limits(cx: ty::ctxt, it: @ast::item) {
+ pure fn is_valid<T: cmp::Ord>(binop: ast::binop, v: T,
+ min: T, max: T) -> bool {
+ match binop {
+ ast::lt => v <= max,
+ ast::le => v < max,
+ ast::gt => v >= min,
+ ast::ge => v > min,
+ ast::eq | ast::ne => v >= min && v <= max,
+ _ => fail
+ }
+ }
+
+ pure fn rev_binop(binop: ast::binop) -> ast::binop {
+ match binop {
+ ast::lt => ast::gt,
+ ast::le => ast::ge,
+ ast::gt => ast::lt,
+ ast::ge => ast::le,
+ _ => binop
+ }
+ }
+
+ pure fn int_ty_range(int_ty: ast::int_ty) -> (i64, i64) {
+ match int_ty {
+ ast::ty_i => (int::min_value as i64, int::max_value as i64),
+ ast::ty_char => (u32::min_value as i64, u32::max_value as i64),
+ ast::ty_i8 => (i8::min_value as i64, i8::max_value as i64),
+ ast::ty_i16 => (i16::min_value as i64, i16::max_value as i64),
+ ast::ty_i32 => (i32::min_value as i64, i32::max_value as i64),
+ ast::ty_i64 => (i64::min_value, i64::max_value)
+ }
+ }
+
+ pure fn uint_ty_range(uint_ty: ast::uint_ty) -> (u64, u64) {
+ match uint_ty {
+ ast::ty_u => (uint::min_value as u64, uint::max_value as u64),
+ ast::ty_u8 => (u8::min_value as u64, u8::max_value as u64),
+ ast::ty_u16 => (u16::min_value as u64, u16::max_value as u64),
+ ast::ty_u32 => (u32::min_value as u64, u32::max_value as u64),
+ ast::ty_u64 => (u64::min_value, u64::max_value)
+ }
+ }
+
+ fn check_limits(cx: ty::ctxt, binop: ast::binop, l: &ast::expr,
+ r: &ast::expr) -> bool {
+ let (lit, expr, swap) = match (l.node, r.node) {
+ (ast::expr_lit(_), _) => (l, r, true),
+ (_, ast::expr_lit(_)) => (r, l, false),
+ _ => return true
+ };
+ // Normalize the binop so that the literal is always on the RHS in
+ // the comparison
+ let norm_binop = if (swap) {
+ rev_binop(binop)
+ } else {
+ binop
+ };
+ match ty::get(ty::expr_ty(cx, @*expr)).sty {
+ ty::ty_int(int_ty) => {
+ let (min, max) = int_ty_range(int_ty);
+ let lit_val: i64 = match lit.node {
+ ast::expr_lit(@li) => match li.node {
+ ast::lit_int(v, _) => v,
+ ast::lit_uint(v, _) => v as i64,
+ ast::lit_int_unsuffixed(v) => v,
+ _ => return true
+ },
+ _ => fail
+ };
+ is_valid(norm_binop, lit_val, min, max)
+ }
+ ty::ty_uint(uint_ty) => {
+ let (min, max): (u64, u64) = uint_ty_range(uint_ty);
+ let lit_val: u64 = match lit.node {
+ ast::expr_lit(@li) => match li.node {
+ ast::lit_int(v, _) => v as u64,
+ ast::lit_uint(v, _) => v,
+ ast::lit_int_unsuffixed(v) => v as u64,
+ _ => return true
+ },
+ _ => fail
+ };
+ is_valid(norm_binop, lit_val, min, max)
+ }
+ _ => true
+ }
+ }
+
+ pure fn is_comparison(binop: ast::binop) -> bool {
+ match binop {
+ ast::eq | ast::lt | ast::le |
+ ast::ne | ast::ge | ast::gt => true,
+ _ => false
+ }
+ }
+
+ let visit = item_stopping_visitor(visit::mk_simple_visitor(@{
+ visit_expr: fn@(e: @ast::expr) {
+ match e.node {
+ ast::expr_binary(binop, @l, @r) => {
+ if is_comparison(binop)
+ && !check_limits(cx, binop, &l, &r) {
+ cx.sess.span_lint(
+ type_limits, e.id, it.id, e.span,
+ ~"comparison is useless due to type limits");
+ }
+ }
+ _ => ()
+ }
+ },
+ .. *visit::default_simple_visitor()
+ }));
+ visit::visit_item(it, (), visit);
+}
+
fn check_item_structural_records(cx: ty::ctxt, it: @ast::item) {
let visit = item_stopping_visitor(visit::mk_simple_visitor(@{
visit_expr: fn@(e: @ast::expr) {
diff --git a/src/test/compile-fail/lint-type-limits.rs b/src/test/compile-fail/lint-type-limits.rs
new file mode 100644
index 0000000000000..14bffdca241be
--- /dev/null
+++ b/src/test/compile-fail/lint-type-limits.rs
@@ -0,0 +1,25 @@
+// compile-flags: -D type-limits
+fn main() { }
+
+fn foo() {
+ let mut i = 100u;
+ while i >= 0 { //~ ERROR comparison is useless due to type limits
+ i -= 1;
+ }
+}
+
+fn bar() -> i8 {
+ return 123;
+}
+
+fn baz() -> bool {
+ 128 > bar() //~ ERROR comparison is useless due to type limits
+}
+
+fn qux() {
+ let mut i = 1i8;
+ while 200 != i { //~ ERROR comparison is useless due to type limits
+ i += 1;
+ }
+}
+