rust-clippy/clippy_lints/src/int_plus_one.rs
2021-03-15 15:34:15 -05:00

172 lines
6 KiB
Rust

//! lint on blocks unnecessarily using >= with a + 1 or - 1
use clippy_utils::source::snippet_opt;
use rustc_ast::ast::{BinOpKind, Expr, ExprKind, Lit, LitKind};
use rustc_errors::Applicability;
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use crate::utils::span_lint_and_sugg;
declare_clippy_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
/// # let x = 1;
/// # let y = 1;
/// if x >= y + 1 {}
/// ```
///
/// Could be written as:
///
/// ```rust
/// # let x = 1;
/// # let y = 1;
/// if x > y {}
/// ```
pub INT_PLUS_ONE,
complexity,
"instead of using `x >= y + 1`, use `x > y`"
}
declare_lint_pass!(IntPlusOne => [INT_PLUS_ONE]);
// cases:
// BinOpKind::Ge
// x >= y + 1
// x - 1 >= y
//
// BinOpKind::Le
// x + 1 <= y
// x <= y - 1
#[derive(Copy, Clone)]
enum Side {
Lhs,
Rhs,
}
impl IntPlusOne {
#[allow(clippy::cast_sign_loss)]
fn check_lit(lit: &Lit, target_value: i128) -> bool {
if let LitKind::Int(value, ..) = lit.kind {
return value == (target_value as u128);
}
false
}
fn check_binop(cx: &EarlyContext<'_>, binop: BinOpKind, lhs: &Expr, rhs: &Expr) -> Option<String> {
match (binop, &lhs.kind, &rhs.kind) {
// case where `x - 1 >= ...` or `-1 + x >= ...`
(BinOpKind::Ge, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _) => {
match (lhskind.node, &lhslhs.kind, &lhsrhs.kind) {
// `-1 + x`
(BinOpKind::Add, &ExprKind::Lit(ref lit), _) if Self::check_lit(lit, -1) => {
Self::generate_recommendation(cx, binop, lhsrhs, rhs, Side::Lhs)
},
// `x - 1`
(BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) if Self::check_lit(lit, 1) => {
Self::generate_recommendation(cx, binop, lhslhs, rhs, Side::Lhs)
},
_ => None,
}
},
// case where `... >= y + 1` or `... >= 1 + y`
(BinOpKind::Ge, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs))
if rhskind.node == BinOpKind::Add =>
{
match (&rhslhs.kind, &rhsrhs.kind) {
// `y + 1` and `1 + y`
(&ExprKind::Lit(ref lit), _) if Self::check_lit(lit, 1) => {
Self::generate_recommendation(cx, binop, rhsrhs, lhs, Side::Rhs)
},
(_, &ExprKind::Lit(ref lit)) if Self::check_lit(lit, 1) => {
Self::generate_recommendation(cx, binop, rhslhs, lhs, Side::Rhs)
},
_ => None,
}
}
// case where `x + 1 <= ...` or `1 + x <= ...`
(BinOpKind::Le, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _)
if lhskind.node == BinOpKind::Add =>
{
match (&lhslhs.kind, &lhsrhs.kind) {
// `1 + x` and `x + 1`
(&ExprKind::Lit(ref lit), _) if Self::check_lit(lit, 1) => {
Self::generate_recommendation(cx, binop, lhsrhs, rhs, Side::Lhs)
},
(_, &ExprKind::Lit(ref lit)) if Self::check_lit(lit, 1) => {
Self::generate_recommendation(cx, binop, lhslhs, rhs, Side::Lhs)
},
_ => None,
}
}
// case where `... >= y - 1` or `... >= -1 + y`
(BinOpKind::Le, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs)) => {
match (rhskind.node, &rhslhs.kind, &rhsrhs.kind) {
// `-1 + y`
(BinOpKind::Add, &ExprKind::Lit(ref lit), _) if Self::check_lit(lit, -1) => {
Self::generate_recommendation(cx, binop, rhsrhs, lhs, Side::Rhs)
},
// `y - 1`
(BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) if Self::check_lit(lit, 1) => {
Self::generate_recommendation(cx, binop, rhslhs, lhs, Side::Rhs)
},
_ => None,
}
},
_ => None,
}
}
fn generate_recommendation(
cx: &EarlyContext<'_>,
binop: BinOpKind,
node: &Expr,
other_side: &Expr,
side: Side,
) -> Option<String> {
let binop_string = match binop {
BinOpKind::Ge => ">",
BinOpKind::Le => "<",
_ => return None,
};
if let Some(snippet) = snippet_opt(cx, node.span) {
if let Some(other_side_snippet) = snippet_opt(cx, other_side.span) {
let rec = match side {
Side::Lhs => Some(format!("{} {} {}", snippet, binop_string, other_side_snippet)),
Side::Rhs => Some(format!("{} {} {}", other_side_snippet, binop_string, snippet)),
};
return rec;
}
}
None
}
fn emit_warning(cx: &EarlyContext<'_>, block: &Expr, recommendation: String) {
span_lint_and_sugg(
cx,
INT_PLUS_ONE,
block.span,
"unnecessary `>= y + 1` or `x - 1 >=`",
"change it to",
recommendation,
Applicability::MachineApplicable, // snippet
);
}
}
impl EarlyLintPass for IntPlusOne {
fn check_expr(&mut self, cx: &EarlyContext<'_>, item: &Expr) {
if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = item.kind {
if let Some(rec) = Self::check_binop(cx, kind.node, lhs, rhs) {
Self::emit_warning(cx, item, rec);
}
}
}
}