| use crate::consts::{constant, Constant}; |
| use crate::utils::sugg::Sugg; |
| use crate::utils::{span_lint, span_lint_and_then}; |
| use if_chain::if_chain; |
| use rustc::hir::*; |
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| use rustc::{declare_tool_lint, impl_lint_pass}; |
| use rustc_errors::Applicability; |
| use syntax::ast::LitKind; |
| use syntax::source_map::Span; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for incompatible bit masks in comparisons. |
| /// |
| /// The formula for detecting if an expression of the type `_ <bit_op> m |
| /// <cmp_op> c` (where `<bit_op>` is one of {`&`, `|`} and `<cmp_op>` is one of |
| /// {`!=`, `>=`, `>`, `!=`, `>=`, `>`}) can be determined from the following |
| /// table: |
| /// |
| /// |Comparison |Bit Op|Example |is always|Formula | |
| /// |------------|------|------------|---------|----------------------| |
| /// |`==` or `!=`| `&` |`x & 2 == 3`|`false` |`c & m != c` | |
| /// |`<` or `>=`| `&` |`x & 2 < 3` |`true` |`m < c` | |
| /// |`>` or `<=`| `&` |`x & 1 > 1` |`false` |`m <= c` | |
| /// |`==` or `!=`| `|` |`x | 1 == 0`|`false` |`c | m != c` | |
| /// |`<` or `>=`| `|` |`x | 1 < 1` |`false` |`m >= c` | |
| /// |`<=` or `>` | `|` |`x | 1 > 0` |`true` |`m > c` | |
| /// |
| /// **Why is this bad?** If the bits that the comparison cares about are always |
| /// set to zero or one by the bit mask, the comparison is constant `true` or |
| /// `false` (depending on mask, compared value, and operators). |
| /// |
| /// So the code is actively misleading, and the only reason someone would write |
| /// this intentionally is to win an underhanded Rust contest or create a |
| /// test-case for this lint. |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// # let x = 1; |
| /// if (x & 1 == 2) { } |
| /// ``` |
| pub BAD_BIT_MASK, |
| correctness, |
| "expressions of the form `_ & mask == select` that will only ever return `true` or `false`" |
| } |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for bit masks in comparisons which can be removed |
| /// without changing the outcome. The basic structure can be seen in the |
| /// following table: |
| /// |
| /// |Comparison| Bit Op |Example |equals | |
| /// |----------|---------|-----------|-------| |
| /// |`>` / `<=`|`|` / `^`|`x | 2 > 3`|`x > 3`| |
| /// |`<` / `>=`|`|` / `^`|`x ^ 1 < 4`|`x < 4`| |
| /// |
| /// **Why is this bad?** Not equally evil as [`bad_bit_mask`](#bad_bit_mask), |
| /// but still a bit misleading, because the bit mask is ineffective. |
| /// |
| /// **Known problems:** False negatives: This lint will only match instances |
| /// where we have figured out the math (which is for a power-of-two compared |
| /// value). This means things like `x | 1 >= 7` (which would be better written |
| /// as `x >= 6`) will not be reported (but bit masks like this are fairly |
| /// uncommon). |
| /// |
| /// **Example:** |
| /// ```rust |
| /// # let x = 1; |
| /// if (x | 1 > 3) { } |
| /// ``` |
| pub INEFFECTIVE_BIT_MASK, |
| correctness, |
| "expressions where a bit mask will be rendered useless by a comparison, e.g., `(x | 1) > 2`" |
| } |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for bit masks that can be replaced by a call |
| /// to `trailing_zeros` |
| /// |
| /// **Why is this bad?** `x.trailing_zeros() > 4` is much clearer than `x & 15 |
| /// == 0` |
| /// |
| /// **Known problems:** llvm generates better code for `x & 15 == 0` on x86 |
| /// |
| /// **Example:** |
| /// ```rust |
| /// # let x = 1; |
| /// if x & 0x1111 == 0 { } |
| /// ``` |
| pub VERBOSE_BIT_MASK, |
| style, |
| "expressions where a bit mask is less readable than the corresponding method call" |
| } |
| |
| #[derive(Copy, Clone)] |
| pub struct BitMask { |
| verbose_bit_mask_threshold: u64, |
| } |
| |
| impl BitMask { |
| #[must_use] |
| pub fn new(verbose_bit_mask_threshold: u64) -> Self { |
| Self { |
| verbose_bit_mask_threshold, |
| } |
| } |
| } |
| |
| impl_lint_pass!(BitMask => [BAD_BIT_MASK, INEFFECTIVE_BIT_MASK, VERBOSE_BIT_MASK]); |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask { |
| fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) { |
| if let ExprKind::Binary(cmp, left, right) = &e.kind { |
| if cmp.node.is_comparison() { |
| if let Some(cmp_opt) = fetch_int_literal(cx, right) { |
| check_compare(cx, left, cmp.node, cmp_opt, e.span) |
| } else if let Some(cmp_val) = fetch_int_literal(cx, left) { |
| check_compare(cx, right, invert_cmp(cmp.node), cmp_val, e.span) |
| } |
| } |
| } |
| if_chain! { |
| if let ExprKind::Binary(op, left, right) = &e.kind; |
| if BinOpKind::Eq == op.node; |
| if let ExprKind::Binary(op1, left1, right1) = &left.kind; |
| if BinOpKind::BitAnd == op1.node; |
| if let ExprKind::Lit(lit) = &right1.kind; |
| if let LitKind::Int(n, _) = lit.node; |
| if let ExprKind::Lit(lit1) = &right.kind; |
| if let LitKind::Int(0, _) = lit1.node; |
| if n.leading_zeros() == n.count_zeros(); |
| if n > u128::from(self.verbose_bit_mask_threshold); |
| then { |
| span_lint_and_then(cx, |
| VERBOSE_BIT_MASK, |
| e.span, |
| "bit mask could be simplified with a call to `trailing_zeros`", |
| |db| { |
| let sugg = Sugg::hir(cx, left1, "...").maybe_par(); |
| db.span_suggestion( |
| e.span, |
| "try", |
| format!("{}.trailing_zeros() >= {}", sugg, n.count_ones()), |
| Applicability::MaybeIncorrect, |
| ); |
| }); |
| } |
| } |
| } |
| } |
| |
| #[must_use] |
| fn invert_cmp(cmp: BinOpKind) -> BinOpKind { |
| match cmp { |
| BinOpKind::Eq => BinOpKind::Eq, |
| BinOpKind::Ne => BinOpKind::Ne, |
| BinOpKind::Lt => BinOpKind::Gt, |
| BinOpKind::Gt => BinOpKind::Lt, |
| BinOpKind::Le => BinOpKind::Ge, |
| BinOpKind::Ge => BinOpKind::Le, |
| _ => BinOpKind::Or, // Dummy |
| } |
| } |
| |
| fn check_compare(cx: &LateContext<'_, '_>, bit_op: &Expr, cmp_op: BinOpKind, cmp_value: u128, span: Span) { |
| if let ExprKind::Binary(op, left, right) = &bit_op.kind { |
| if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr { |
| return; |
| } |
| fetch_int_literal(cx, right) |
| .or_else(|| fetch_int_literal(cx, left)) |
| .map_or((), |mask| check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span)) |
| } |
| } |
| |
| #[allow(clippy::too_many_lines)] |
| fn check_bit_mask( |
| cx: &LateContext<'_, '_>, |
| bit_op: BinOpKind, |
| cmp_op: BinOpKind, |
| mask_value: u128, |
| cmp_value: u128, |
| span: Span, |
| ) { |
| match cmp_op { |
| BinOpKind::Eq | BinOpKind::Ne => match bit_op { |
| BinOpKind::BitAnd => { |
| if mask_value & cmp_value != cmp_value { |
| if cmp_value != 0 { |
| span_lint( |
| cx, |
| BAD_BIT_MASK, |
| span, |
| &format!( |
| "incompatible bit mask: `_ & {}` can never be equal to `{}`", |
| mask_value, cmp_value |
| ), |
| ); |
| } |
| } else if mask_value == 0 { |
| span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero"); |
| } |
| }, |
| BinOpKind::BitOr => { |
| if mask_value | cmp_value != cmp_value { |
| span_lint( |
| cx, |
| BAD_BIT_MASK, |
| span, |
| &format!( |
| "incompatible bit mask: `_ | {}` can never be equal to `{}`", |
| mask_value, cmp_value |
| ), |
| ); |
| } |
| }, |
| _ => (), |
| }, |
| BinOpKind::Lt | BinOpKind::Ge => match bit_op { |
| BinOpKind::BitAnd => { |
| if mask_value < cmp_value { |
| span_lint( |
| cx, |
| BAD_BIT_MASK, |
| span, |
| &format!( |
| "incompatible bit mask: `_ & {}` will always be lower than `{}`", |
| mask_value, cmp_value |
| ), |
| ); |
| } else if mask_value == 0 { |
| span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero"); |
| } |
| }, |
| BinOpKind::BitOr => { |
| if mask_value >= cmp_value { |
| span_lint( |
| cx, |
| BAD_BIT_MASK, |
| span, |
| &format!( |
| "incompatible bit mask: `_ | {}` will never be lower than `{}`", |
| mask_value, cmp_value |
| ), |
| ); |
| } else { |
| check_ineffective_lt(cx, span, mask_value, cmp_value, "|"); |
| } |
| }, |
| BinOpKind::BitXor => check_ineffective_lt(cx, span, mask_value, cmp_value, "^"), |
| _ => (), |
| }, |
| BinOpKind::Le | BinOpKind::Gt => match bit_op { |
| BinOpKind::BitAnd => { |
| if mask_value <= cmp_value { |
| span_lint( |
| cx, |
| BAD_BIT_MASK, |
| span, |
| &format!( |
| "incompatible bit mask: `_ & {}` will never be higher than `{}`", |
| mask_value, cmp_value |
| ), |
| ); |
| } else if mask_value == 0 { |
| span_lint(cx, BAD_BIT_MASK, span, "&-masking with zero"); |
| } |
| }, |
| BinOpKind::BitOr => { |
| if mask_value > cmp_value { |
| span_lint( |
| cx, |
| BAD_BIT_MASK, |
| span, |
| &format!( |
| "incompatible bit mask: `_ | {}` will always be higher than `{}`", |
| mask_value, cmp_value |
| ), |
| ); |
| } else { |
| check_ineffective_gt(cx, span, mask_value, cmp_value, "|"); |
| } |
| }, |
| BinOpKind::BitXor => check_ineffective_gt(cx, span, mask_value, cmp_value, "^"), |
| _ => (), |
| }, |
| _ => (), |
| } |
| } |
| |
| fn check_ineffective_lt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) { |
| if c.is_power_of_two() && m < c { |
| span_lint( |
| cx, |
| INEFFECTIVE_BIT_MASK, |
| span, |
| &format!( |
| "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly", |
| op, m, c |
| ), |
| ); |
| } |
| } |
| |
| fn check_ineffective_gt(cx: &LateContext<'_, '_>, span: Span, m: u128, c: u128, op: &str) { |
| if (c + 1).is_power_of_two() && m <= c { |
| span_lint( |
| cx, |
| INEFFECTIVE_BIT_MASK, |
| span, |
| &format!( |
| "ineffective bit mask: `x {} {}` compared to `{}`, is the same as x compared directly", |
| op, m, c |
| ), |
| ); |
| } |
| } |
| |
| fn fetch_int_literal(cx: &LateContext<'_, '_>, lit: &Expr) -> Option<u128> { |
| match constant(cx, cx.tables, lit)?.0 { |
| Constant::Int(n) => Some(n), |
| _ => None, |
| } |
| } |
