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rust-clippy/clippy_lints/src/booleans.rs

404 lines
14 KiB
Rust

use rustc::lint::{LintArray, LateLintPass, LateContext, LintPass};
use rustc::hir::*;
use rustc::hir::intravisit::*;
use syntax::ast::{LitKind, DUMMY_NODE_ID};
use syntax::codemap::{DUMMY_SP, dummy_spanned};
use syntax::util::ThinVec;
use utils::{span_lint_and_then, in_macro, snippet_opt, SpanlessEq};
/// **What it does:** Checks for boolean expressions that can be written more
/// concisely.
///
/// **Why is this bad?** Readability of boolean expressions suffers from
/// unnecessary duplication.
///
/// **Known problems:** Ignores short circuiting behavior of `||` and
/// `&&`. Ignores `|`, `&` and `^`.
///
/// **Example:**
/// ```rust
/// if a && true // should be: if a
/// if !(a == b) // should be: if a != b
/// ```
declare_lint! {
pub NONMINIMAL_BOOL,
Allow,
"boolean expressions that can be written more concisely"
}
/// **What it does:** Checks for boolean expressions that contain terminals that
/// can be eliminated.
///
/// **Why is this bad?** This is most likely a logic bug.
///
/// **Known problems:** Ignores short circuiting behavior.
///
/// **Example:**
/// ```rust
/// if a && b || a { ... }
/// ```
/// The `b` is unnecessary, the expression is equivalent to `if a`.
declare_lint! {
pub LOGIC_BUG,
Warn,
"boolean expressions that contain terminals which can be eliminated"
}
#[derive(Copy,Clone)]
pub struct NonminimalBool;
impl LintPass for NonminimalBool {
fn get_lints(&self) -> LintArray {
lint_array!(NONMINIMAL_BOOL, LOGIC_BUG)
}
}
impl LateLintPass for NonminimalBool {
fn check_item(&mut self, cx: &LateContext, item: &Item) {
NonminimalBoolVisitor(cx).visit_item(item)
}
}
struct NonminimalBoolVisitor<'a, 'tcx: 'a>(&'a LateContext<'a, 'tcx>);
use quine_mc_cluskey::Bool;
struct Hir2Qmm<'a, 'tcx: 'a, 'v> {
terminals: Vec<&'v Expr>,
cx: &'a LateContext<'a, 'tcx>,
}
impl<'a, 'tcx, 'v> Hir2Qmm<'a, 'tcx, 'v> {
fn extract(&mut self, op: BinOp_, a: &[&'v Expr], mut v: Vec<Bool>) -> Result<Vec<Bool>, String> {
for a in a {
if let ExprBinary(binop, ref lhs, ref rhs) = a.node {
if binop.node == op {
v = self.extract(op, &[lhs, rhs], v)?;
continue;
}
}
v.push(self.run(a)?);
}
Ok(v)
}
fn run(&mut self, e: &'v Expr) -> Result<Bool, String> {
// prevent folding of `cfg!` macros and the like
if !in_macro(self.cx, e.span) {
match e.node {
ExprUnary(UnNot, ref inner) => return Ok(Bool::Not(box self.run(inner)?)),
ExprBinary(binop, ref lhs, ref rhs) => {
match binop.node {
BiOr => return Ok(Bool::Or(self.extract(BiOr, &[lhs, rhs], Vec::new())?)),
BiAnd => return Ok(Bool::And(self.extract(BiAnd, &[lhs, rhs], Vec::new())?)),
_ => (),
}
}
ExprLit(ref lit) => {
match lit.node {
LitKind::Bool(true) => return Ok(Bool::True),
LitKind::Bool(false) => return Ok(Bool::False),
_ => (),
}
}
_ => (),
}
}
for (n, expr) in self.terminals.iter().enumerate() {
if SpanlessEq::new(self.cx).ignore_fn().eq_expr(e, expr) {
#[allow(cast_possible_truncation)]
return Ok(Bool::Term(n as u8));
}
let negated = match e.node {
ExprBinary(binop, ref lhs, ref rhs) => {
let mk_expr = |op| {
Expr {
id: DUMMY_NODE_ID,
span: DUMMY_SP,
attrs: ThinVec::new(),
node: ExprBinary(dummy_spanned(op), lhs.clone(), rhs.clone()),
}
};
match binop.node {
BiEq => mk_expr(BiNe),
BiNe => mk_expr(BiEq),
BiGt => mk_expr(BiLe),
BiGe => mk_expr(BiLt),
BiLt => mk_expr(BiGe),
BiLe => mk_expr(BiGt),
_ => continue,
}
}
_ => continue,
};
if SpanlessEq::new(self.cx).ignore_fn().eq_expr(&negated, expr) {
#[allow(cast_possible_truncation)]
return Ok(Bool::Not(Box::new(Bool::Term(n as u8))));
}
}
let n = self.terminals.len();
self.terminals.push(e);
if n < 32 {
#[allow(cast_possible_truncation)]
Ok(Bool::Term(n as u8))
} else {
Err("too many literals".to_owned())
}
}
}
fn suggest(cx: &LateContext, suggestion: &Bool, terminals: &[&Expr]) -> String {
fn recurse(brackets: bool, cx: &LateContext, suggestion: &Bool, terminals: &[&Expr], mut s: String) -> String {
use quine_mc_cluskey::Bool::*;
let snip = |e: &Expr| snippet_opt(cx, e.span).expect("don't try to improve booleans created by macros");
match *suggestion {
True => {
s.push_str("true");
s
}
False => {
s.push_str("false");
s
}
Not(ref inner) => {
match **inner {
And(_) | Or(_) => {
s.push('!');
recurse(true, cx, inner, terminals, s)
}
Term(n) => {
if let ExprBinary(binop, ref lhs, ref rhs) = terminals[n as usize].node {
let op = match binop.node {
BiEq => " != ",
BiNe => " == ",
BiLt => " >= ",
BiGt => " <= ",
BiLe => " > ",
BiGe => " < ",
_ => {
s.push('!');
return recurse(true, cx, inner, terminals, s);
}
};
s.push_str(&snip(lhs));
s.push_str(op);
s.push_str(&snip(rhs));
s
} else {
s.push('!');
recurse(false, cx, inner, terminals, s)
}
}
_ => {
s.push('!');
recurse(false, cx, inner, terminals, s)
}
}
}
And(ref v) => {
if brackets {
s.push('(');
}
if let Or(_) = v[0] {
s = recurse(true, cx, &v[0], terminals, s);
} else {
s = recurse(false, cx, &v[0], terminals, s);
}
for inner in &v[1..] {
s.push_str(" && ");
if let Or(_) = *inner {
s = recurse(true, cx, inner, terminals, s);
} else {
s = recurse(false, cx, inner, terminals, s);
}
}
if brackets {
s.push(')');
}
s
}
Or(ref v) => {
if brackets {
s.push('(');
}
s = recurse(false, cx, &v[0], terminals, s);
for inner in &v[1..] {
s.push_str(" || ");
s = recurse(false, cx, inner, terminals, s);
}
if brackets {
s.push(')');
}
s
}
Term(n) => {
if brackets {
if let ExprBinary(..) = terminals[n as usize].node {
s.push('(');
}
}
s.push_str(&snip(terminals[n as usize]));
if brackets {
if let ExprBinary(..) = terminals[n as usize].node {
s.push(')');
}
}
s
}
}
}
recurse(false, cx, suggestion, terminals, String::new())
}
fn simple_negate(b: Bool) -> Bool {
use quine_mc_cluskey::Bool::*;
match b {
True => False,
False => True,
t @ Term(_) => Not(Box::new(t)),
And(mut v) => {
for el in &mut v {
*el = simple_negate(::std::mem::replace(el, True));
}
Or(v)
}
Or(mut v) => {
for el in &mut v {
*el = simple_negate(::std::mem::replace(el, True));
}
And(v)
}
Not(inner) => *inner,
}
}
#[derive(Default)]
struct Stats {
terminals: [usize; 32],
negations: usize,
ops: usize,
}
fn terminal_stats(b: &Bool) -> Stats {
fn recurse(b: &Bool, stats: &mut Stats) {
match *b {
True | False => stats.ops += 1,
Not(ref inner) => {
match **inner {
And(_) | Or(_) => stats.ops += 1, // brackets are also operations
_ => stats.negations += 1,
}
recurse(inner, stats);
}
And(ref v) | Or(ref v) => {
stats.ops += v.len() - 1;
for inner in v {
recurse(inner, stats);
}
}
Term(n) => stats.terminals[n as usize] += 1,
}
}
use quine_mc_cluskey::Bool::*;
let mut stats = Stats::default();
recurse(b, &mut stats);
stats
}
impl<'a, 'tcx> NonminimalBoolVisitor<'a, 'tcx> {
fn bool_expr(&self, e: &Expr) {
let mut h2q = Hir2Qmm {
terminals: Vec::new(),
cx: self.0,
};
if let Ok(expr) = h2q.run(e) {
if h2q.terminals.len() > 8 {
// QMC has exponentially slow behavior as the number of terminals increases
// 8 is reasonable, it takes approximately 0.2 seconds.
// See #825
return;
}
let stats = terminal_stats(&expr);
let mut simplified = expr.simplify();
for simple in Bool::Not(Box::new(expr.clone())).simplify() {
match simple {
Bool::Not(_) | Bool::True | Bool::False => {}
_ => simplified.push(Bool::Not(Box::new(simple.clone()))),
}
let simple_negated = simple_negate(simple);
if simplified.iter().any(|s| *s == simple_negated) {
continue;
}
simplified.push(simple_negated);
}
let mut improvements = Vec::new();
'simplified: for suggestion in &simplified {
let simplified_stats = terminal_stats(suggestion);
let mut improvement = false;
for i in 0..32 {
// ignore any "simplifications" that end up requiring a terminal more often
// than in the original expression
if stats.terminals[i] < simplified_stats.terminals[i] {
continue 'simplified;
}
if stats.terminals[i] != 0 && simplified_stats.terminals[i] == 0 {
span_lint_and_then(self.0,
LOGIC_BUG,
e.span,
"this boolean expression contains a logic bug",
|db| {
db.span_help(h2q.terminals[i].span,
"this expression can be optimized out by applying boolean operations to the \
outer expression");
db.span_suggestion(e.span,
"it would look like the following",
suggest(self.0, suggestion, &h2q.terminals));
});
// don't also lint `NONMINIMAL_BOOL`
return;
}
// if the number of occurrences of a terminal decreases or any of the stats
// decreases while none increases
improvement |= (stats.terminals[i] > simplified_stats.terminals[i]) ||
(stats.negations > simplified_stats.negations &&
stats.ops == simplified_stats.ops) ||
(stats.ops > simplified_stats.ops && stats.negations == simplified_stats.negations);
}
if improvement {
improvements.push(suggestion);
}
}
if !improvements.is_empty() {
span_lint_and_then(self.0,
NONMINIMAL_BOOL,
e.span,
"this boolean expression can be simplified",
|db| {
for suggestion in &improvements {
db.span_suggestion(e.span, "try", suggest(self.0, suggestion, &h2q.terminals));
}
});
}
}
}
}
impl<'a, 'v, 'tcx> Visitor<'v> for NonminimalBoolVisitor<'a, 'tcx> {
fn visit_expr(&mut self, e: &'v Expr) {
if in_macro(self.0, e.span) {
return;
}
match e.node {
ExprBinary(binop, _, _) if binop.node == BiOr || binop.node == BiAnd => self.bool_expr(e),
ExprUnary(UnNot, ref inner) => {
if self.0.tcx.tables.borrow().node_types[&inner.id].is_bool() {
self.bool_expr(e);
} else {
walk_expr(self, e);
}
}
_ => walk_expr(self, e),
}
}
}