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