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(#1955): Suggests x > y
over x >= y + 1
for ints
This module handles the following cases: - `... >= ... + 1` and `... >= 1 + ...` - `... - 1 >= ...` and `-1 + ... >= ...` - `... + 1 <= ...` and `... + 1 <= ...` - `... <= ... - 1` and `... <= -1 + ...` Note: this only goes 1 level deep (i.e., does not constant-fold) and does not currently simplify expressions. Examples of these cases include: ```rust let x = 1; y >= y + x; // won't catch this case or any permutation x + 1 >= y + 2; // won't catch this case x + 1 - 1 >= y - 1 + 1; // WILL catch this case when it likely shouldn't ```
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clippy_lints/src/int_plus_one.rs
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115
clippy_lints/src/int_plus_one.rs
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@ -0,0 +1,115 @@
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//! lint on blocks unnecessarily using >= with a + 1 or - 1
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use rustc::lint::*;
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use syntax::ast::*;
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use utils::span_help_and_lint;
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/// **What it does:** Checks for usage of `x >= y + 1` or `x - 1 >= y` (and `<=`) in a block
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///
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///
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/// **Why is this bad?** Readability -- better to use `> y` instead of `>= y + 1`.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// x >= y + 1
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/// ```
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///
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/// Could be written:
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///
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/// ```rust
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/// x > y
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/// ```
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declare_lint! {
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pub INT_PLUS_ONE,
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Allow,
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"instead of using x >= y + 1, use x > y"
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}
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pub struct IntPlusOne;
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impl LintPass for IntPlusOne {
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fn get_lints(&self) -> LintArray {
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lint_array!(INT_PLUS_ONE)
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}
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}
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// cases:
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// BinOpKind::Ge
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// x >= y + 1
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// x - 1 >= y
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//
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// BinOpKind::Le
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// x + 1 <= y
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// x <= y - 1
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impl IntPlusOne {
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#[allow(cast_sign_loss)]
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fn check_lit(&self, lit: &Lit, target_value: i128) -> bool {
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if let LitKind::Int(value, ..) = lit.node {
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return value == (target_value as u128)
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}
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false
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}
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fn check_binop(&self, binop: BinOpKind, lhs: &Expr, rhs: &Expr) -> bool {
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match (binop, &lhs.node, &rhs.node) {
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// case where `x - 1 >= ...` or `-1 + x >= ...`
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(BinOpKind::Ge, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _) => {
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match (lhskind.node, &lhslhs.node, &lhsrhs.node) {
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// `-1 + x`
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(BinOpKind::Add, &ExprKind::Lit(ref lit), _) => self.check_lit(lit, -1),
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// `x - 1`
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(BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
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_ => false
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}
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},
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// case where `... >= y + 1` or `... >= 1 + y`
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(BinOpKind::Ge, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs)) if rhskind.node == BinOpKind::Add => {
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match (&rhslhs.node, &rhsrhs.node) {
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// `y + 1` and `1 + y`
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(&ExprKind::Lit(ref lit), _)|(_, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
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_ => false
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}
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},
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// case where `x + 1 <= ...` or `1 + x <= ...`
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(BinOpKind::Le, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _) if lhskind.node == BinOpKind::Add => {
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match (&lhslhs.node, &lhsrhs.node) {
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// `1 + x` and `x + 1`
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(&ExprKind::Lit(ref lit), _)|(_, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
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_ => false
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}
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},
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// case where `... >= y - 1` or `... >= -1 + y`
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(BinOpKind::Le, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs)) => {
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match (rhskind.node, &rhslhs.node, &rhsrhs.node) {
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// `-1 + y`
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(BinOpKind::Add, &ExprKind::Lit(ref lit), _) => self.check_lit(lit, -1),
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// `y - 1`
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(BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) => self.check_lit(lit, 1),
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_ => false
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}
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},
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_ => false
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}
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}
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}
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impl EarlyLintPass for IntPlusOne {
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fn check_expr(&mut self, cx: &EarlyContext, item: &Expr) {
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if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = item.node {
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if self.check_binop(kind.node, lhs, rhs) {
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span_help_and_lint(
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cx,
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INT_PLUS_ONE,
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item.span,
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"Unnecessary `>= y + 1` or `x - 1 >=`",
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"Consider reducing `x >= y + 1` or `x - 1 >= y` to `x > y`",
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);
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}
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}
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}
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}
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