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Added final lint and tests
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@pmk21
pmk21 committed Apr 18, 2020
1 parent 7c52e51 commit 4d03b4d
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151 changes: 117 additions & 34 deletions clippy_lints/src/implicit_saturating_sub.rs
View file
@@ -1,4 +1,4 @@
use crate::utils::{higher, in_macro, span_lint_and_sugg};
use crate::utils::{higher, in_macro, match_qpath, span_lint_and_sugg, SpanlessEq};
use if_chain::if_chain;
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
Expand All @@ -9,17 +9,17 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks for implicit saturating subtraction.
///
/// **Why is this bad?** Simplicity and readability. Instead we can easily use an inbuilt function.
/// **Why is this bad?** Simplicity and readability. Instead we can easily use an builtin function.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let end = 10;
/// let start = 5;
/// let end: u32 = 10;
/// let start: u32 = 5;
///
/// let mut i = end - start;
/// let mut i: u32 = end - start;
///
/// // Bad
/// if i != 0 {
Expand All @@ -28,13 +28,13 @@ declare_clippy_lint! {
/// ```
/// Use instead:
/// ```rust
/// let end = 10;
/// let start = 5;
/// let end: u32 = 10;
/// let start: u32 = 5;
///
/// let mut i = end - start;
/// let mut i: u32 = end - start;
///
/// // Good
/// i.saturating_sub(1);
/// i = i.saturating_sub(1);
/// ```
pub IMPLICIT_SATURATING_SUB,
pedantic,
Expand All @@ -50,41 +50,124 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitSaturatingSub {
}
if_chain! {
if let Some((ref cond, ref then, None)) = higher::if_block(&expr);

// Check if the conditional expression is a binary operation
if let ExprKind::Binary(ref op, ref left, ref right) = cond.kind;
// Ensure that the binary operator is > or !=
if BinOpKind::Ne == op.node || BinOpKind::Gt == op.node;
if let ExprKind::Path(ref cond_path) = left.kind;
// Get the literal on the right hand side
if let ExprKind::Lit(ref lit) = right.kind;
if let LitKind::Int(0, _) = lit.node;
if let ExprKind::Binary(ref cond_op, ref cond_left, ref cond_right) = cond.kind;

// Ensure that the binary operator is >, != and <
if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;

// Check if the true condition block has only one statement
if let ExprKind::Block(ref block, _) = then.kind;
if block.stmts.len() == 1;
if block.stmts.len() == 1 && block.expr.is_none();

// Check if assign operation is done
if let StmtKind::Semi(ref e) = block.stmts[0].kind;
if let ExprKind::AssignOp(ref op1, ref target, ref value) = e.kind;
if BinOpKind::Sub == op1.node;
if let Some(target) = subtracts_one(cx, e);

// Extracting out the variable name
if let ExprKind::Path(ref assign_path) = target.kind;
// Check if the variable in the condition and assignment statement are the same
if let (QPath::Resolved(_, ref cres_path), QPath::Resolved(_, ref ares_path)) = (cond_path, assign_path);
if cres_path.res == ares_path.res;
if let ExprKind::Lit(ref lit1) = value.kind;
if let LitKind::Int(assign_lit, _) = lit1.node;
if let QPath::Resolved(_, ref ares_path) = assign_path;

then {
// Handle symmetric conditions in the if statement
let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
(cond_left, cond_right)
} else {
return;
}
} else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
(cond_right, cond_left)
} else {
return;
}
} else {
return;
};

// Check if the variable in the condition statement is an integer
if !cx.tables.expr_ty(cond_var).is_integral() {
return;
}

// Get the variable name
let var_name = ares_path.segments[0].ident.name.as_str();
let applicability = Applicability::MaybeIncorrect;
span_lint_and_sugg(
cx,
IMPLICIT_SATURATING_SUB,
expr.span,
"Implicitly performing saturating subtraction",
"try",
format!("{}.saturating_sub({});", var_name, assign_lit.to_string()),
applicability
);
const INT_TYPES: [&str; 5] = ["i8", "i16", "i32", "i64", "i128"];

match cond_num_val.kind {
ExprKind::Lit(ref cond_lit) => {
// Check if the constant is zero
if let LitKind::Int(0, _) = cond_lit.node {
if cx.tables.expr_ty(cond_left).is_signed() {
} else {
print_lint_and_sugg(cx, &var_name, expr);
};
}
},
ExprKind::Path(ref cond_num_path) => {
if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "MIN"])) {
print_lint_and_sugg(cx, &var_name, expr);
};
},
ExprKind::Call(ref func, _) => {
if let ExprKind::Path(ref cond_num_path) = func.kind {
if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "min_value"])) {
print_lint_and_sugg(cx, &var_name, expr);
}
};
},
_ => (),
}
}
}
}
}

fn subtracts_one<'a>(cx: &LateContext<'_, '_>, expr: &Expr<'a>) -> Option<&'a Expr<'a>> {
match expr.kind {
ExprKind::AssignOp(ref op1, ref target, ref value) => {
if_chain! {
if BinOpKind::Sub == op1.node;
// Check if literal being subtracted is one
if let ExprKind::Lit(ref lit1) = value.kind;
if let LitKind::Int(1, _) = lit1.node;
then {
Some(target)
} else {
None
}
}
},
ExprKind::Assign(ref target, ref value, _) => {
if_chain! {
if let ExprKind::Binary(ref op1, ref left1, ref right1) = value.kind;
if BinOpKind::Sub == op1.node;

if SpanlessEq::new(cx).eq_expr(left1, target);

if let ExprKind::Lit(ref lit1) = right1.kind;
if let LitKind::Int(1, _) = lit1.node;
then {
Some(target)
} else {
None
}
}
},
_ => None,
}
}

fn print_lint_and_sugg(cx: &LateContext<'_, '_>, var_name: &str, expr: &Expr<'_>) {
span_lint_and_sugg(
cx,
IMPLICIT_SATURATING_SUB,
expr.span,
"Implicitly performing saturating subtraction",
"try",
format!("{} = {}.saturating_sub({});", var_name, var_name, 1.to_string()),
Applicability::MachineApplicable,
);
}
160 changes: 160 additions & 0 deletions tests/ui/implicit_saturating_sub.fixed
View file
@@ -0,0 +1,160 @@
// run-rustfix
#![allow(unused_assignments, unused_mut)]
#![warn(clippy::implicit_saturating_sub)]

fn main() {
// Tests for unsigned integers

let end_8: u8 = 10;
let start_8: u8 = 5;
let mut u_8: u8 = end_8 - start_8;

// Lint
u_8 = u_8.saturating_sub(1);

match end_8 {
10 => {
// Lint
u_8 = u_8.saturating_sub(1);
},
11 => u_8 += 1,
_ => u_8 = 0,
}

let end_16: u16 = 35;
let start_16: u16 = 40;

let mut u_16: u16 = end_16 - start_16;

// Lint
u_16 = u_16.saturating_sub(1);

let mut end_32: u32 = 7000;
let mut start_32: u32 = 7010;

let mut u_32: u32 = end_32 - start_32;

// Lint
u_32 = u_32.saturating_sub(1);

// No Lint
if u_32 > 0 {
u_16 += 1;
}

// No Lint
if u_32 != 0 {
end_32 -= 1;
start_32 += 1;
}

let mut end_64: u64 = 75001;
let mut start_64: u64 = 75000;

let mut u_64: u64 = end_64 - start_64;

// Lint
u_64 = u_64.saturating_sub(1);

// Lint
u_64 = u_64.saturating_sub(1);

// Lint
u_64 = u_64.saturating_sub(1);

// No Lint
if u_64 >= 1 {
u_64 -= 1;
}

// No Lint
if u_64 > 0 {
end_64 -= 1;
}

// Tests for usize
let end_usize: usize = 8054;
let start_usize: usize = 8050;

let mut u_usize: usize = end_usize - start_usize;

// Lint
u_usize = u_usize.saturating_sub(1);

// Tests for signed integers

let endi_8: i8 = 10;
let starti_8: i8 = 50;

let mut i_8: i8 = endi_8 - starti_8;

// Lint
i_8 = i_8.saturating_sub(1);

// Lint
i_8 = i_8.saturating_sub(1);

// Lint
i_8 = i_8.saturating_sub(1);

// Lint
i_8 = i_8.saturating_sub(1);

let endi_16: i16 = 45;
let starti_16: i16 = 44;

let mut i_16: i16 = endi_16 - starti_16;

// Lint
i_16 = i_16.saturating_sub(1);

// Lint
i_16 = i_16.saturating_sub(1);

// Lint
i_16 = i_16.saturating_sub(1);

// Lint
i_16 = i_16.saturating_sub(1);

let endi_32: i32 = 45;
let starti_32: i32 = 44;

let mut i_32: i32 = endi_32 - starti_32;

// Lint
i_32 = i_32.saturating_sub(1);

// Lint
i_32 = i_32.saturating_sub(1);

// Lint
i_32 = i_32.saturating_sub(1);

// Lint
i_32 = i_32.saturating_sub(1);

let endi_64: i64 = 45;
let starti_64: i64 = 44;

let mut i_64: i64 = endi_64 - starti_64;

// Lint
i_64 = i_64.saturating_sub(1);

// Lint
i_64 = i_64.saturating_sub(1);

// Lint
i_64 = i_64.saturating_sub(1);

// No Lint
if i_64 > 0 {
i_64 -= 1;
}

// No Lint
if i_64 != 0 {
i_64 -= 1;
}
}

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