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Auto merge of #4569 - james9909:add-comparison-chain, r=oli-obk

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Add a new lint for comparison chains

changelog: Adds a new lint: `comparison_chain`.

`comparison_chain` lints all `if` conditional chains where all the conditions are binary comparisons on the same two operands and will suggest a rewrite with `match`.

Closes #4531.
This commit is contained in:
bors 2019-09-26 07:38:08 +00:00
commit 4d30b08027
13 changed files with 368 additions and 113 deletions
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1
CHANGELOG.md
View file

@ -962,6 +962,7 @@ Released 2018-09-13
[`cmp_owned`]: https://rust-lang.github.io/rust-clippy/master/index.html#cmp_owned
[`cognitive_complexity`]: https://rust-lang.github.io/rust-clippy/master/index.html#cognitive_complexity
[`collapsible_if`]: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_if
[`comparison_chain`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_chain
[`copy_iterator`]: https://rust-lang.github.io/rust-clippy/master/index.html#copy_iterator
[`crosspointer_transmute`]: https://rust-lang.github.io/rust-clippy/master/index.html#crosspointer_transmute
[`dbg_macro`]: https://rust-lang.github.io/rust-clippy/master/index.html#dbg_macro

2
README.md
View file

@ -6,7 +6,7 @@
A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
[There are 316 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
[There are 317 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:

107
clippy_lints/src/comparison_chain.rs Normal file
View file

@ -0,0 +1,107 @@
use crate::utils::{if_sequence, parent_node_is_if_expr, span_help_and_lint, SpanlessEq};
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks comparison chains written with `if` that can be
/// rewritten with `match` and `cmp`.
///
/// **Why is this bad?** `if` is not guaranteed to be exhaustive and conditionals can get
/// repetitive
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// # fn a() {}
/// # fn b() {}
/// # fn c() {}
/// fn f(x: u8, y: u8) {
/// if x > y {
/// a()
/// } else if x < y {
/// b()
/// } else {
/// c()
/// }
/// }
/// ```
///
/// Could be written:
///
/// ```rust,ignore
/// use std::cmp::Ordering;
/// # fn a() {}
/// # fn b() {}
/// # fn c() {}
/// fn f(x: u8, y: u8) {
/// match x.cmp(&y) {
/// Ordering::Greater => a(),
/// Ordering::Less => b(),
/// Ordering::Equal => c()
/// }
/// }
/// ```
pub COMPARISON_CHAIN,
style,
"`if`s that can be rewritten with `match` and `cmp`"
}
declare_lint_pass!(ComparisonChain => [COMPARISON_CHAIN]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ComparisonChain {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if expr.span.from_expansion() {
return;
}
// We only care about the top-most `if` in the chain
if parent_node_is_if_expr(expr, cx) {
return;
}
// Check that there exists at least one explicit else condition
let (conds, _) = if_sequence(expr);
if conds.len() < 2 {
return;
}
for cond in conds.windows(2) {
if let (
&ExprKind::Binary(ref kind1, ref lhs1, ref rhs1),
&ExprKind::Binary(ref kind2, ref lhs2, ref rhs2),
) = (&cond[0].node, &cond[1].node)
{
if !kind_is_cmp(kind1.node) || !kind_is_cmp(kind2.node) {
return;
}
// Check that both sets of operands are equal
let mut spanless_eq = SpanlessEq::new(cx);
if (!spanless_eq.eq_expr(lhs1, lhs2) || !spanless_eq.eq_expr(rhs1, rhs2))
&& (!spanless_eq.eq_expr(lhs1, rhs2) || !spanless_eq.eq_expr(rhs1, lhs2))
{
return;
}
} else {
// We only care about comparison chains
return;
}
}
span_help_and_lint(
cx,
COMPARISON_CHAIN,
expr.span,
"`if` chain can be rewritten with `match`",
"Consider rewriting the `if` chain to use `cmp` and `match`.",
)
}
}
fn kind_is_cmp(kind: BinOpKind) -> bool {
match kind {
BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq => true,
_ => false,
}
}

47
clippy_lints/src/copies.rs
View file

@ -1,11 +1,11 @@
use crate::utils::{get_parent_expr, higher, same_tys, snippet, span_lint_and_then, span_note_and_lint};
use crate::utils::{get_parent_expr, higher, if_sequence, same_tys, snippet, span_lint_and_then, span_note_and_lint};
use crate::utils::{SpanlessEq, SpanlessHash};
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::ty::Ty;
use rustc::{declare_lint_pass, declare_tool_lint};
use rustc_data_structures::fx::FxHashMap;
use smallvec::SmallVec;
use std::cmp::Ordering;
use std::collections::hash_map::Entry;
use std::hash::BuildHasherDefault;
use syntax::symbol::Symbol;
@ -236,39 +236,6 @@ fn lint_match_arms<'tcx>(cx: &LateContext<'_, 'tcx>, expr: &Expr) {
}
}
/// Returns the list of condition expressions and the list of blocks in a
/// sequence of `if/else`.
/// E.g., this returns `([a, b], [c, d, e])` for the expression
/// `if a { c } else if b { d } else { e }`.
fn if_sequence(mut expr: &Expr) -> (SmallVec<[&Expr; 1]>, SmallVec<[&Block; 1]>) {
let mut conds = SmallVec::new();
let mut blocks: SmallVec<[&Block; 1]> = SmallVec::new();
while let Some((ref cond, ref then_expr, ref else_expr)) = higher::if_block(&expr) {
conds.push(&**cond);
if let ExprKind::Block(ref block, _) = then_expr.node {
blocks.push(block);
} else {
panic!("ExprKind::If node is not an ExprKind::Block");
}
if let Some(ref else_expr) = *else_expr {
expr = else_expr;
} else {
break;
}
}
// final `else {..}`
if !blocks.is_empty() {
if let ExprKind::Block(ref block, _) = expr.node {
blocks.push(&**block);
}
}
(conds, blocks)
}
/// Returns the list of bindings in a pattern.
fn bindings<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, pat: &Pat) -> FxHashMap<Symbol, Ty<'tcx>> {
fn bindings_impl<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, pat: &Pat, map: &mut FxHashMap<Symbol, Ty<'tcx>>) {
@ -333,14 +300,8 @@ fn search_common_cases<'a, T, Eq>(exprs: &'a [T], eq: &Eq) -> Option<(&'a T, &'a
where
Eq: Fn(&T, &T) -> bool,
{
if exprs.len() < 2 {
None
} else if exprs.len() == 2 {
if eq(&exprs[0], &exprs[1]) {
Some((&exprs[0], &exprs[1]))
} else {
None
}
if exprs.len() == 2 && eq(&exprs[0], &exprs[1]) {
Some((&exprs[0], &exprs[1]))
} else {
None
}

4
clippy_lints/src/lib.rs
View file

@ -159,6 +159,7 @@ pub mod cargo_common_metadata;
pub mod checked_conversions;
pub mod cognitive_complexity;
pub mod collapsible_if;
pub mod comparison_chain;
pub mod copies;
pub mod copy_iterator;
pub mod dbg_macro;
@ -600,6 +601,7 @@ pub fn register_plugins(reg: &mut rustc_driver::plugin::Registry<'_>, conf: &Con
reg.register_late_lint_pass(box integer_division::IntegerDivision);
reg.register_late_lint_pass(box inherent_to_string::InherentToString);
reg.register_late_lint_pass(box trait_bounds::TraitBounds);
reg.register_late_lint_pass(box comparison_chain::ComparisonChain);
reg.register_lint_group("clippy::restriction", Some("clippy_restriction"), vec![
arithmetic::FLOAT_ARITHMETIC,
@ -706,6 +708,7 @@ pub fn register_plugins(reg: &mut rustc_driver::plugin::Registry<'_>, conf: &Con
bytecount::NAIVE_BYTECOUNT,
cognitive_complexity::COGNITIVE_COMPLEXITY,
collapsible_if::COLLAPSIBLE_IF,
comparison_chain::COMPARISON_CHAIN,
copies::IFS_SAME_COND,
copies::IF_SAME_THEN_ELSE,
derive::DERIVE_HASH_XOR_EQ,
@ -932,6 +935,7 @@ pub fn register_plugins(reg: &mut rustc_driver::plugin::Registry<'_>, conf: &Con
block_in_if_condition::BLOCK_IN_IF_CONDITION_EXPR,
block_in_if_condition::BLOCK_IN_IF_CONDITION_STMT,
collapsible_if::COLLAPSIBLE_IF,
comparison_chain::COMPARISON_CHAIN,
doc::MISSING_SAFETY_DOC,
enum_variants::ENUM_VARIANT_NAMES,
enum_variants::MODULE_INCEPTION,

13
clippy_lints/src/needless_bool.rs
View file

@ -3,7 +3,7 @@
//! This lint is **warn** by default
use crate::utils::sugg::Sugg;
use crate::utils::{higher, span_lint, span_lint_and_sugg};
use crate::utils::{higher, parent_node_is_if_expr, span_lint, span_lint_and_sugg};
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_lint_pass, declare_tool_lint};
@ -118,17 +118,6 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
}
}
fn parent_node_is_if_expr<'a, 'b>(expr: &Expr, cx: &LateContext<'a, 'b>) -> bool {
let parent_id = cx.tcx.hir().get_parent_node(expr.hir_id);
let parent_node = cx.tcx.hir().get(parent_id);
match parent_node {
rustc::hir::Node::Expr(e) => higher::if_block(&e).is_some(),
rustc::hir::Node::Arm(e) => higher::if_block(&e.body).is_some(),
_ => false,
}
}
declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {

115
clippy_lints/src/non_expressive_names.rs
View file

@ -1,6 +1,7 @@
use crate::utils::{span_lint, span_lint_and_then};
use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
use rustc::{declare_tool_lint, impl_lint_pass};
use std::cmp::Ordering;
use syntax::ast::*;
use syntax::attr;
use syntax::source_map::Span;
@ -206,63 +207,67 @@ impl<'a, 'tcx, 'b> SimilarNamesNameVisitor<'a, 'tcx, 'b> {
continue;
}
let mut split_at = None;
if existing_name.len > count {
if existing_name.len - count != 1 || levenstein_not_1(&interned_name, &existing_name.interned) {
continue;
}
} else if existing_name.len < count {
if count - existing_name.len != 1 || levenstein_not_1(&existing_name.interned, &interned_name) {
continue;
}
} else {
let mut interned_chars = interned_name.chars();
let mut existing_chars = existing_name.interned.chars();
let first_i = interned_chars.next().expect("we know we have at least one char");
let first_e = existing_chars.next().expect("we know we have at least one char");
let eq_or_numeric = |(a, b): (char, char)| a == b || a.is_numeric() && b.is_numeric();
if eq_or_numeric((first_i, first_e)) {
let last_i = interned_chars.next_back().expect("we know we have at least two chars");
let last_e = existing_chars.next_back().expect("we know we have at least two chars");
if eq_or_numeric((last_i, last_e)) {
if interned_chars
.zip(existing_chars)
.filter(|&ie| !eq_or_numeric(ie))
.count()
!= 1
{
continue;
}
} else {
let second_last_i = interned_chars
.next_back()
.expect("we know we have at least three chars");
let second_last_e = existing_chars
.next_back()
.expect("we know we have at least three chars");
if !eq_or_numeric((second_last_i, second_last_e))
|| second_last_i == '_'
|| !interned_chars.zip(existing_chars).all(eq_or_numeric)
{
// allowed similarity foo_x, foo_y
// or too many chars differ (foo_x, boo_y) or (foox, booy)
continue;
}
split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
}
} else {
let second_i = interned_chars.next().expect("we know we have at least two chars");
let second_e = existing_chars.next().expect("we know we have at least two chars");
if !eq_or_numeric((second_i, second_e))
|| second_i == '_'
|| !interned_chars.zip(existing_chars).all(eq_or_numeric)
{
// allowed similarity x_foo, y_foo
// or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
match existing_name.len.cmp(&count) {
Ordering::Greater => {
if existing_name.len - count != 1 || levenstein_not_1(&interned_name, &existing_name.interned) {
continue;
}
split_at = interned_name.chars().next().map(char::len_utf8);
}
},
Ordering::Less => {
if count - existing_name.len != 1 || levenstein_not_1(&existing_name.interned, &interned_name) {
continue;
}
},
Ordering::Equal => {
let mut interned_chars = interned_name.chars();
let mut existing_chars = existing_name.interned.chars();
let first_i = interned_chars.next().expect("we know we have at least one char");
let first_e = existing_chars.next().expect("we know we have at least one char");
let eq_or_numeric = |(a, b): (char, char)| a == b || a.is_numeric() && b.is_numeric();
if eq_or_numeric((first_i, first_e)) {
let last_i = interned_chars.next_back().expect("we know we have at least two chars");
let last_e = existing_chars.next_back().expect("we know we have at least two chars");
if eq_or_numeric((last_i, last_e)) {
if interned_chars
.zip(existing_chars)
.filter(|&ie| !eq_or_numeric(ie))
.count()
!= 1
{
continue;
}
} else {
let second_last_i = interned_chars
.next_back()
.expect("we know we have at least three chars");
let second_last_e = existing_chars
.next_back()
.expect("we know we have at least three chars");
if !eq_or_numeric((second_last_i, second_last_e))
|| second_last_i == '_'
|| !interned_chars.zip(existing_chars).all(eq_or_numeric)
{
// allowed similarity foo_x, foo_y
// or too many chars differ (foo_x, boo_y) or (foox, booy)
continue;
}
split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
}
} else {
let second_i = interned_chars.next().expect("we know we have at least two chars");
let second_e = existing_chars.next().expect("we know we have at least two chars");
if !eq_or_numeric((second_i, second_e))
|| second_i == '_'
|| !interned_chars.zip(existing_chars).all(eq_or_numeric)
{
// allowed similarity x_foo, y_foo
// or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
continue;
}
split_at = interned_name.chars().next().map(char::len_utf8);
}
},
}
span_lint_and_then(
self.0.cx,

44
clippy_lints/src/utils/mod.rs
View file

@ -1168,3 +1168,47 @@ pub fn match_def_path<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, did: DefId, syms: &[
let path = cx.get_def_path(did);
path.len() == syms.len() && path.into_iter().zip(syms.iter()).all(|(a, &b)| a.as_str() == b)
}
/// Returns the list of condition expressions and the list of blocks in a
/// sequence of `if/else`.
/// E.g., this returns `([a, b], [c, d, e])` for the expression
/// `if a { c } else if b { d } else { e }`.
pub fn if_sequence(mut expr: &Expr) -> (SmallVec<[&Expr; 1]>, SmallVec<[&Block; 1]>) {
let mut conds = SmallVec::new();
let mut blocks: SmallVec<[&Block; 1]> = SmallVec::new();
while let Some((ref cond, ref then_expr, ref else_expr)) = higher::if_block(&expr) {
conds.push(&**cond);
if let ExprKind::Block(ref block, _) = then_expr.node {
blocks.push(block);
} else {
panic!("ExprKind::If node is not an ExprKind::Block");
}
if let Some(ref else_expr) = *else_expr {
expr = else_expr;
} else {
break;
}
}
// final `else {..}`
if !blocks.is_empty() {
if let ExprKind::Block(ref block, _) = expr.node {
blocks.push(&**block);
}
}
(conds, blocks)
}
pub fn parent_node_is_if_expr<'a, 'b>(expr: &Expr, cx: &LateContext<'a, 'b>) -> bool {
let parent_id = cx.tcx.hir().get_parent_node(expr.hir_id);
let parent_node = cx.tcx.hir().get(parent_id);
match parent_node {
rustc::hir::Node::Expr(e) => higher::if_block(&e).is_some(),
rustc::hir::Node::Arm(e) => higher::if_block(&e.body).is_some(),
_ => false,
}
}

9
src/lintlist/mod.rs
View file

@ -6,7 +6,7 @@ pub use lint::Lint;
pub use lint::LINT_LEVELS;
// begin lint list, do not remove this comment, it’s used in `update_lints`
pub const ALL_LINTS: [Lint; 316] = [
pub const ALL_LINTS: [Lint; 317] = [
Lint {
name: "absurd_extreme_comparisons",
group: "correctness",
@ -252,6 +252,13 @@ pub const ALL_LINTS: [Lint; 316] = [
deprecation: None,
module: "collapsible_if",
},
Lint {
name: "comparison_chain",
group: "style",
desc: "`if`s that can be rewritten with `match` and `cmp`",
deprecation: None,
module: "comparison_chain",
},
Lint {
name: "copy_iterator",
group: "pedantic",

79
tests/ui/comparison_chain.rs Normal file
View file

@ -0,0 +1,79 @@
#![allow(dead_code)]
#![warn(clippy::comparison_chain)]
fn a() {}
fn b() {}
fn c() {}
fn f(x: u8, y: u8, z: u8) {
// Ignored: Only one branch
if x > y {
a()
}
if x > y {
a()
} else if x < y {
b()
}
// Ignored: Only one explicit conditional
if x > y {
a()
} else {
b()
}
if x > y {
a()
} else if x < y {
b()
} else {
c()
}
if x > y {
a()
} else if y > x {
b()
} else {
c()
}
if x > 1 {
a()
} else if x < 1 {
b()
} else if x == 1 {
c()
}
// Ignored: Binop args are not equivalent
if x > 1 {
a()
} else if y > 1 {
b()
} else {
c()
}
// Ignored: Binop args are not equivalent
if x > y {
a()
} else if x > z {
b()
} else if y > z {
c()
}
// Ignored: Not binary comparisons
if true {
a()
} else if false {
b()
} else {
c()
}
}
fn main() {}

57
tests/ui/comparison_chain.stderr Normal file
View file

@ -0,0 +1,57 @@
error: `if` chain can be rewritten with `match`
--> $DIR/comparison_chain.rs:14:5
|
LL | / if x > y {
LL | | a()
LL | | } else if x < y {
LL | | b()
LL | | }
| |_____^
|
= note: `-D clippy::comparison-chain` implied by `-D warnings`
= help: Consider rewriting the `if` chain to use `cmp` and `match`.
error: `if` chain can be rewritten with `match`
--> $DIR/comparison_chain.rs:27:5
|
LL | / if x > y {
LL | | a()
LL | | } else if x < y {
LL | | b()
LL | | } else {
LL | | c()
LL | | }
| |_____^
|
= help: Consider rewriting the `if` chain to use `cmp` and `match`.
error: `if` chain can be rewritten with `match`
--> $DIR/comparison_chain.rs:35:5
|
LL | / if x > y {
LL | | a()
LL | | } else if y > x {
LL | | b()
LL | | } else {
LL | | c()
LL | | }
| |_____^
|
= help: Consider rewriting the `if` chain to use `cmp` and `match`.
error: `if` chain can be rewritten with `match`
--> $DIR/comparison_chain.rs:43:5
|
LL | / if x > 1 {
LL | | a()
LL | | } else if x < 1 {
LL | | b()
LL | | } else if x == 1 {
LL | | c()
LL | | }
| |_____^
|
= help: Consider rewriting the `if` chain to use `cmp` and `match`.
error: aborting due to 4 previous errors

1
tests/ui/crashes/if_same_then_else.rs
View file

@ -1,5 +1,6 @@
// run-pass
#![allow(clippy::comparison_chain)]
#![deny(clippy::if_same_then_else)]
/// Test for https://github.com/rust-lang/rust-clippy/issues/2426

2
tests/ui/ifs_same_cond.rs
View file

@ -1,5 +1,5 @@
#![warn(clippy::ifs_same_cond)]
#![allow(clippy::if_same_then_else)] // all empty blocks
#![allow(clippy::if_same_then_else, clippy::comparison_chain)] // all empty blocks
fn ifs_same_cond() {
let a = 0;