465 lines
16 KiB
Rust
465 lines
16 KiB
Rust
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::{declare_tool_lint, lint_array};
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use rustc::hir::*;
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use rustc::hir::intravisit::*;
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use syntax::ast::{LitKind, NodeId, DUMMY_NODE_ID};
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use syntax::source_map::{dummy_spanned, Span, DUMMY_SP};
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use rustc_data_structures::thin_vec::ThinVec;
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use crate::utils::{in_macro, paths, match_type, snippet_opt, span_lint_and_then, SpanlessEq, get_trait_def_id, implements_trait};
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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_clippy_lint! {
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pub NONMINIMAL_BOOL,
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complexity,
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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_clippy_lint! {
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pub LOGIC_BUG,
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correctness,
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"boolean expressions that contain terminals which can be eliminated"
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}
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// For each pairs, both orders are considered.
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const METHODS_WITH_NEGATION: [(&str, &str); 2] = [
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("is_some", "is_none"),
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("is_err", "is_ok"),
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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 }.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: BinOpKind, 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 ExprKind::Binary(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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ExprKind::Unary(UnNot, ref inner) => return Ok(Bool::Not(box self.run(inner)?)),
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ExprKind::Binary(binop, ref lhs, ref rhs) => match binop.node {
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BinOpKind::Or => return Ok(Bool::Or(self.extract(BinOpKind::Or, &[lhs, rhs], Vec::new())?)),
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BinOpKind::And => return Ok(Bool::And(self.extract(BinOpKind::And, &[lhs, rhs], Vec::new())?)),
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_ => (),
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},
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ExprKind::Lit(ref lit) => 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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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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ExprKind::Binary(binop, ref lhs, ref rhs) => {
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if !implements_ord(self.cx, lhs) {
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continue;
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}
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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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hir_id: DUMMY_HIR_ID,
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span: DUMMY_SP,
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attrs: ThinVec::new(),
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node: ExprKind::Binary(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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BinOpKind::Eq => mk_expr(BinOpKind::Ne),
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BinOpKind::Ne => mk_expr(BinOpKind::Eq),
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BinOpKind::Gt => mk_expr(BinOpKind::Le),
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BinOpKind::Ge => mk_expr(BinOpKind::Lt),
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BinOpKind::Lt => mk_expr(BinOpKind::Ge),
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BinOpKind::Le => mk_expr(BinOpKind::Gt),
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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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struct SuggestContext<'a, 'tcx: 'a, 'v> {
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terminals: &'v [&'v Expr],
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cx: &'a LateContext<'a, 'tcx>,
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output: String,
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simplified: bool,
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}
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impl<'a, 'tcx, 'v> SuggestContext<'a, 'tcx, 'v> {
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fn snip(&self, e: &Expr) -> Option<String> {
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snippet_opt(self.cx, e.span)
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}
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fn simplify_not(&self, expr: &Expr) -> Option<String> {
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match expr.node {
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ExprKind::Binary(binop, ref lhs, ref rhs) => {
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if !implements_ord(self.cx, lhs) {
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return None;
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}
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match binop.node {
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BinOpKind::Eq => Some(" != "),
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BinOpKind::Ne => Some(" == "),
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BinOpKind::Lt => Some(" >= "),
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BinOpKind::Gt => Some(" <= "),
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BinOpKind::Le => Some(" > "),
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BinOpKind::Ge => Some(" < "),
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_ => None,
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}.and_then(|op| Some(format!("{}{}{}", self.snip(lhs)?, op, self.snip(rhs)?)))
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},
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ExprKind::MethodCall(ref path, _, ref args) if args.len() == 1 => {
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let type_of_receiver = self.cx.tables.expr_ty(&args[0]);
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if !match_type(self.cx, type_of_receiver, &paths::OPTION) &&
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!match_type(self.cx, type_of_receiver, &paths::RESULT) {
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return None;
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}
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METHODS_WITH_NEGATION
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.iter().cloned()
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.flat_map(|(a, b)| vec![(a, b), (b, a)])
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.find(|&(a, _)| a == path.ident.as_str())
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.and_then(|(_, neg_method)| Some(format!("{}.{}()", self.snip(&args[0])?, neg_method)))
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},
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_ => None,
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}
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}
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fn recurse(&mut self, suggestion: &Bool) -> Option<()> {
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use quine_mc_cluskey::Bool::*;
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match *suggestion {
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True => {
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self.output.push_str("true");
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},
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False => {
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self.output.push_str("false");
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},
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Not(ref inner) => match **inner {
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And(_) | Or(_) => {
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self.output.push('!');
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self.output.push('(');
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self.recurse(inner);
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self.output.push(')');
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},
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Term(n) => {
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let terminal = self.terminals[n as usize];
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if let Some(str) = self.simplify_not(terminal) {
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self.simplified = true;
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self.output.push_str(&str)
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} else {
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self.output.push('!');
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let snip = self.snip(terminal)?;
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self.output.push_str(&snip);
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}
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},
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True | False | Not(_) => {
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self.output.push('!');
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self.recurse(inner)?;
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},
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},
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And(ref v) => {
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for (index, inner) in v.iter().enumerate() {
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if index > 0 {
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self.output.push_str(" && ");
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}
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if let Or(_) = *inner {
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self.output.push('(');
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self.recurse(inner);
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self.output.push(')');
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} else {
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self.recurse(inner);
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}
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}
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},
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Or(ref v) => {
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for (index, inner) in v.iter().enumerate() {
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if index > 0 {
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self.output.push_str(" || ");
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}
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self.recurse(inner);
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}
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},
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Term(n) => {
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let snip = self.snip(self.terminals[n as usize])?;
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self.output.push_str(&snip);
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},
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}
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Some(())
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}
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}
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// The boolean part of the return indicates whether some simplifications have been applied.
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fn suggest(cx: &LateContext<'_, '_>, suggestion: &Bool, terminals: &[&Expr]) -> (String, bool) {
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let mut suggest_context = SuggestContext {
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terminals,
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cx,
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output: String::new(),
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simplified: false,
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};
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suggest_context.recurse(suggestion);
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(suggest_context.output, suggest_context.simplified)
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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(
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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(
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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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);
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db.span_suggestion(
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e.span,
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"it would look like the following",
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suggest(self.cx, suggestion, &h2q.terminals).0,
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);
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},
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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 && 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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let nonminimal_bool_lint = |suggestions| {
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span_lint_and_then(
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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| { db.span_suggestions(e.span, "try", suggestions); },
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);
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};
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if improvements.is_empty() {
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let suggest = suggest(self.cx, &expr, &h2q.terminals);
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if suggest.1 {
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nonminimal_bool_lint(vec![suggest.0])
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}
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} else {
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nonminimal_bool_lint(
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improvements
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.into_iter()
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.map(|suggestion| suggest(self.cx, suggestion, &h2q.terminals).0)
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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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ExprKind::Binary(binop, _, _) if binop.node == BinOpKind::Or || binop.node == BinOpKind::And => self.bool_expr(e),
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ExprKind::Unary(UnNot, ref inner) => if self.cx.tables.node_types()[inner.hir_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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_ => 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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fn implements_ord<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &Expr) -> bool {
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let ty = cx.tables.expr_ty(expr);
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get_trait_def_id(cx, &paths::ORD)
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.map_or(false, |id| implements_trait(cx, ty, id, &[]))
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}
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