--- /dev/null
+//! lint on blocks unnecessarily using >= with a + 1 or - 1
+
+use rustc::lint::*;
+use syntax::ast::*;
+
+use utils::span_help_and_lint;
+
+/// **What it does:** Checks for usage of `x >= y + 1` or `x - 1 >= y` (and `<=`) in a block
+///
+///
+/// **Why is this bad?** Readability -- better to use `> y` instead of `>= y + 1`.
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust
+/// x >= y + 1
+/// ```
+///
+/// Could be written:
+///
+/// ```rust
+/// x > y
+/// ```
+declare_lint! {
+ pub INT_PLUS_ONE,
+ Allow,
+ "instead of using x >= y + 1, use x > y"
+}
+
+pub struct IntPlusOne;
+
+impl LintPass for IntPlusOne {
+ fn get_lints(&self) -> LintArray {
+ lint_array!(INT_PLUS_ONE)
+ }
+}
+
+// cases:
+// BinOpKind::Ge
+// x >= y + 1
+// x - 1 >= y
+//
+// BinOpKind::Le
+// x + 1 <= y
+// x <= y - 1
+
+impl IntPlusOne {
+ #[allow(cast_sign_loss)]
+ fn check_lit(&self, lit: &Lit, target_value: i128) -> bool {
+ if let LitKind::Int(value, ..) = lit.node {
+ return value == (target_value as u128)
+ }
+ false
+ }
+
+ fn check_binop(&self, binop: BinOpKind, lhs: &Expr, rhs: &Expr) -> bool {
+ match (binop, &lhs.node, &rhs.node) {
+ // case where `x - 1 >= ...` or `-1 + x >= ...`
+ (BinOpKind::Ge, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _) => {
+ match (lhskind.node, &lhslhs.node, &lhsrhs.node) {
+ // `-1 + x`
+ (BinOpKind::Add, &ExprKind::Lit(ref lit), _) => self.check_lit(lit, -1),
+ // `x - 1`
+ (BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
+ _ => false
+ }
+ },
+ // case where `... >= y + 1` or `... >= 1 + y`
+ (BinOpKind::Ge, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs)) if rhskind.node == BinOpKind::Add => {
+ match (&rhslhs.node, &rhsrhs.node) {
+ // `y + 1` and `1 + y`
+ (&ExprKind::Lit(ref lit), _)|(_, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
+ _ => false
+ }
+ },
+ // case where `x + 1 <= ...` or `1 + x <= ...`
+ (BinOpKind::Le, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _) if lhskind.node == BinOpKind::Add => {
+ match (&lhslhs.node, &lhsrhs.node) {
+ // `1 + x` and `x + 1`
+ (&ExprKind::Lit(ref lit), _)|(_, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
+ _ => false
+ }
+ },
+ // case where `... >= y - 1` or `... >= -1 + y`
+ (BinOpKind::Le, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs)) => {
+ match (rhskind.node, &rhslhs.node, &rhsrhs.node) {
+ // `-1 + y`
+ (BinOpKind::Add, &ExprKind::Lit(ref lit), _) => self.check_lit(lit, -1),
+ // `y - 1`
+ (BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
+ _ => false
+ }
+ },
+ _ => false
+ }
+ }
+
+}
+
+impl EarlyLintPass for IntPlusOne {
+ fn check_expr(&mut self, cx: &EarlyContext, item: &Expr) {
+ if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = item.node {
+ if self.check_binop(kind.node, lhs, rhs) {
+ span_help_and_lint(
+ cx,
+ INT_PLUS_ONE,
+ item.span,
+ "Unnecessary `>= y + 1` or `x - 1 >=`",
+ "Consider reducing `x >= y + 1` or `x - 1 >= y` to `x > y`",
+ );
+ }
+ }
+ }
+}