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Auto merge of rust-lang#5427 - pmk21:implicit-sat-sub, r=flip1995
Add lint named implicit_saturating_sub Fixes: rust-lang#5399 I've made a basic skeleton of the lint, would love more feedback on how to make it better. changelog: Add lint [`implicit_saturating_sub`]
2 parents 1c0e4e5 + 1c11035 commit 891e1a8

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‎CHANGELOG.md

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@@ -1293,6 +1293,7 @@ Released 2018-09-13
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[`ifs_same_cond`]: https://rust-lang.github.io/rust-clippy/master/index.html#ifs_same_cond
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[`implicit_hasher`]: https://rust-lang.github.io/rust-clippy/master/index.html#implicit_hasher
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[`implicit_return`]: https://rust-lang.github.io/rust-clippy/master/index.html#implicit_return
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[`implicit_saturating_sub`]: https://rust-lang.github.io/rust-clippy/master/index.html#implicit_saturating_sub
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[`imprecise_flops`]: https://rust-lang.github.io/rust-clippy/master/index.html#imprecise_flops
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[`inconsistent_digit_grouping`]: https://rust-lang.github.io/rust-clippy/master/index.html#inconsistent_digit_grouping
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[`indexing_slicing`]: https://rust-lang.github.io/rust-clippy/master/index.html#indexing_slicing

‎clippy_lints/src/implicit_saturating_sub.rs

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use crate::utils::{higher, in_macro, match_qpath, span_lint_and_sugg, SpanlessEq};
2+
use if_chain::if_chain;
3+
use rustc_ast::ast::LitKind;
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use rustc_errors::Applicability;
5+
use rustc_hir::{BinOpKind, Expr, ExprKind, QPath, StmtKind};
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use rustc_lint::{LateContext, LateLintPass};
7+
use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// **What it does:** Checks for implicit saturating subtraction.
11+
///
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/// **Why is this bad?** Simplicity and readability. Instead we can easily use an builtin function.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// let end: u32 = 10;
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/// let start: u32 = 5;
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///
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/// let mut i: u32 = end - start;
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///
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/// // Bad
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/// if i != 0 {
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/// i -= 1;
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/// }
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/// ```
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/// Use instead:
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/// ```rust
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/// let end: u32 = 10;
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/// let start: u32 = 5;
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///
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/// let mut i: u32 = end - start;
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///
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/// // Good
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/// i = i.saturating_sub(1);
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/// ```
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pub IMPLICIT_SATURATING_SUB,
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pedantic,
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"Perform saturating subtraction instead of implicitly checking lower bound of data type"
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}
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declare_lint_pass!(ImplicitSaturatingSub => [IMPLICIT_SATURATING_SUB]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitSaturatingSub {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'tcx>) {
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if in_macro(expr.span) {
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return;
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}
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if_chain! {
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if let Some((ref cond, ref then, None)) = higher::if_block(&expr);
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// Check if the conditional expression is a binary operation
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if let ExprKind::Binary(ref cond_op, ref cond_left, ref cond_right) = cond.kind;
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// Ensure that the binary operator is >, != and <
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if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;
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// Check if the true condition block has only one statement
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if let ExprKind::Block(ref block, _) = then.kind;
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if block.stmts.len() == 1 && block.expr.is_none();
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// Check if assign operation is done
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if let StmtKind::Semi(ref e) = block.stmts[0].kind;
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if let Some(target) = subtracts_one(cx, e);
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// Extracting out the variable name
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if let ExprKind::Path(ref assign_path) = target.kind;
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if let QPath::Resolved(_, ref ares_path) = assign_path;
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then {
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// Handle symmetric conditions in the if statement
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let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
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if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
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(cond_left, cond_right)
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} else {
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return;
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}
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} else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
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if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
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(cond_right, cond_left)
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} else {
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return;
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}
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} else {
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return;
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};
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// Check if the variable in the condition statement is an integer
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if !cx.tables.expr_ty(cond_var).is_integral() {
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return;
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}
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// Get the variable name
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let var_name = ares_path.segments[0].ident.name.as_str();
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const INT_TYPES: [&str; 5] = ["i8", "i16", "i32", "i64", "i128"];
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match cond_num_val.kind {
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ExprKind::Lit(ref cond_lit) => {
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// Check if the constant is zero
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if let LitKind::Int(0, _) = cond_lit.node {
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if cx.tables.expr_ty(cond_left).is_signed() {
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} else {
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print_lint_and_sugg(cx, &var_name, expr);
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};
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}
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},
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ExprKind::Path(ref cond_num_path) => {
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if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "MIN"])) {
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print_lint_and_sugg(cx, &var_name, expr);
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};
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},
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ExprKind::Call(ref func, _) => {
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if let ExprKind::Path(ref cond_num_path) = func.kind {
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if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "min_value"])) {
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print_lint_and_sugg(cx, &var_name, expr);
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}
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};
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},
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_ => (),
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}
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}
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}
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}
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}
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fn subtracts_one<'a>(cx: &LateContext<'_, '_>, expr: &Expr<'a>) -> Option<&'a Expr<'a>> {
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match expr.kind {
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ExprKind::AssignOp(ref op1, ref target, ref value) => {
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if_chain! {
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if BinOpKind::Sub == op1.node;
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// Check if literal being subtracted is one
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if let ExprKind::Lit(ref lit1) = value.kind;
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if let LitKind::Int(1, _) = lit1.node;
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then {
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Some(target)
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} else {
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None
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}
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}
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},
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ExprKind::Assign(ref target, ref value, _) => {
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if_chain! {
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if let ExprKind::Binary(ref op1, ref left1, ref right1) = value.kind;
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if BinOpKind::Sub == op1.node;
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if SpanlessEq::new(cx).eq_expr(left1, target);
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if let ExprKind::Lit(ref lit1) = right1.kind;
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if let LitKind::Int(1, _) = lit1.node;
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then {
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Some(target)
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} else {
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None
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}
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}
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},
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_ => None,
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}
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}
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fn print_lint_and_sugg(cx: &LateContext<'_, '_>, var_name: &str, expr: &Expr<'_>) {
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span_lint_and_sugg(
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cx,
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IMPLICIT_SATURATING_SUB,
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expr.span,
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"Implicitly performing saturating subtraction",
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"try",
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format!("{} = {}.saturating_sub({});", var_name, var_name, 1.to_string()),
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Applicability::MachineApplicable,
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);
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}

‎clippy_lints/src/lib.rs

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@@ -225,6 +225,7 @@ mod identity_op;
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mod if_let_some_result;
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mod if_not_else;
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mod implicit_return;
228+
mod implicit_saturating_sub;
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mod indexing_slicing;
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mod infinite_iter;
230231
mod inherent_impl;
@@ -574,6 +575,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
574575
&if_let_some_result::IF_LET_SOME_RESULT,
575576
&if_not_else::IF_NOT_ELSE,
576577
&implicit_return::IMPLICIT_RETURN,
578+
&implicit_saturating_sub::IMPLICIT_SATURATING_SUB,
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&indexing_slicing::INDEXING_SLICING,
578580
&indexing_slicing::OUT_OF_BOUNDS_INDEXING,
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&infinite_iter::INFINITE_ITER,
@@ -888,6 +890,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
888890
store.register_late_pass(|| box unicode::Unicode);
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store.register_late_pass(|| box strings::StringAdd);
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store.register_late_pass(|| box implicit_return::ImplicitReturn);
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store.register_late_pass(|| box implicit_saturating_sub::ImplicitSaturatingSub);
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store.register_late_pass(|| box methods::Methods);
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store.register_late_pass(|| box map_clone::MapClone);
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store.register_late_pass(|| box shadow::Shadow);
@@ -1111,6 +1114,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&functions::MUST_USE_CANDIDATE),
11121115
LintId::of(&functions::TOO_MANY_LINES),
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LintId::of(&if_not_else::IF_NOT_ELSE),
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LintId::of(&implicit_saturating_sub::IMPLICIT_SATURATING_SUB),
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LintId::of(&infinite_iter::MAYBE_INFINITE_ITER),
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LintId::of(&items_after_statements::ITEMS_AFTER_STATEMENTS),
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LintId::of(&large_stack_arrays::LARGE_STACK_ARRAYS),

‎src/lintlist/mod.rs

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@@ -773,6 +773,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
773773
deprecation: None,
774774
module: "implicit_return",
775775
},
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Lint {
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name: "implicit_saturating_sub",
778+
group: "pedantic",
779+
desc: "Perform saturating subtraction instead of implicitly checking lower bound of data type",
780+
deprecation: None,
781+
module: "implicit_saturating_sub",
782+
},
776783
Lint {
777784
name: "imprecise_flops",
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group: "nursery",

‎tests/ui/implicit_saturating_sub.fixed

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// run-rustfix
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#![allow(unused_assignments, unused_mut, clippy::assign_op_pattern)]
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#![warn(clippy::implicit_saturating_sub)]
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fn main() {
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// Tests for unsigned integers
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let end_8: u8 = 10;
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let start_8: u8 = 5;
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let mut u_8: u8 = end_8 - start_8;
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// Lint
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u_8 = u_8.saturating_sub(1);
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match end_8 {
16+
10 => {
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// Lint
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u_8 = u_8.saturating_sub(1);
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},
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11 => u_8 += 1,
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_ => u_8 = 0,
22+
}
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let end_16: u16 = 35;
25+
let start_16: u16 = 40;
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let mut u_16: u16 = end_16 - start_16;
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// Lint
30+
u_16 = u_16.saturating_sub(1);
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let mut end_32: u32 = 7000;
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let mut start_32: u32 = 7010;
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let mut u_32: u32 = end_32 - start_32;
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// Lint
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u_32 = u_32.saturating_sub(1);
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// No Lint
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if u_32 > 0 {
42+
u_16 += 1;
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}
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// No Lint
46+
if u_32 != 0 {
47+
end_32 -= 1;
48+
start_32 += 1;
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}
50+
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let mut end_64: u64 = 75001;
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let mut start_64: u64 = 75000;
53+
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let mut u_64: u64 = end_64 - start_64;
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// Lint
57+
u_64 = u_64.saturating_sub(1);
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// Lint
60+
u_64 = u_64.saturating_sub(1);
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// Lint
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u_64 = u_64.saturating_sub(1);
64+
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// No Lint
66+
if u_64 >= 1 {
67+
u_64 -= 1;
68+
}
69+
70+
// No Lint
71+
if u_64 > 0 {
72+
end_64 -= 1;
73+
}
74+
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// Tests for usize
76+
let end_usize: usize = 8054;
77+
let start_usize: usize = 8050;
78+
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let mut u_usize: usize = end_usize - start_usize;
80+
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// Lint
82+
u_usize = u_usize.saturating_sub(1);
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// Tests for signed integers
85+
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let endi_8: i8 = 10;
87+
let starti_8: i8 = 50;
88+
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let mut i_8: i8 = endi_8 - starti_8;
90+
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// Lint
92+
i_8 = i_8.saturating_sub(1);
93+
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// Lint
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i_8 = i_8.saturating_sub(1);
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// Lint
98+
i_8 = i_8.saturating_sub(1);
99+
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// Lint
101+
i_8 = i_8.saturating_sub(1);
102+
103+
let endi_16: i16 = 45;
104+
let starti_16: i16 = 44;
105+
106+
let mut i_16: i16 = endi_16 - starti_16;
107+
108+
// Lint
109+
i_16 = i_16.saturating_sub(1);
110+
111+
// Lint
112+
i_16 = i_16.saturating_sub(1);
113+
114+
// Lint
115+
i_16 = i_16.saturating_sub(1);
116+
117+
// Lint
118+
i_16 = i_16.saturating_sub(1);
119+
120+
let endi_32: i32 = 45;
121+
let starti_32: i32 = 44;
122+
123+
let mut i_32: i32 = endi_32 - starti_32;
124+
125+
// Lint
126+
i_32 = i_32.saturating_sub(1);
127+
128+
// Lint
129+
i_32 = i_32.saturating_sub(1);
130+
131+
// Lint
132+
i_32 = i_32.saturating_sub(1);
133+
134+
// Lint
135+
i_32 = i_32.saturating_sub(1);
136+
137+
let endi_64: i64 = 45;
138+
let starti_64: i64 = 44;
139+
140+
let mut i_64: i64 = endi_64 - starti_64;
141+
142+
// Lint
143+
i_64 = i_64.saturating_sub(1);
144+
145+
// Lint
146+
i_64 = i_64.saturating_sub(1);
147+
148+
// Lint
149+
i_64 = i_64.saturating_sub(1);
150+
151+
// No Lint
152+
if i_64 > 0 {
153+
i_64 -= 1;
154+
}
155+
156+
// No Lint
157+
if i_64 != 0 {
158+
i_64 -= 1;
159+
}
160+
}

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