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Merge pull request #913 from oli-obk/assign_ops
suggest `a op= b` over `a = a op b`
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‎CHANGELOG.md

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@@ -76,6 +76,8 @@ All notable changes to this project will be documented in this file.
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[`absurd_extreme_comparisons`]: https://github.com/Manishearth/rust-clippy/wiki#absurd_extreme_comparisons
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[`almost_swapped`]: https://github.com/Manishearth/rust-clippy/wiki#almost_swapped
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[`approx_constant`]: https://github.com/Manishearth/rust-clippy/wiki#approx_constant
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[`assign_op_pattern`]: https://github.com/Manishearth/rust-clippy/wiki#assign_op_pattern
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[`assign_ops`]: https://github.com/Manishearth/rust-clippy/wiki#assign_ops
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[`bad_bit_mask`]: https://github.com/Manishearth/rust-clippy/wiki#bad_bit_mask
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[`blacklisted_name`]: https://github.com/Manishearth/rust-clippy/wiki#blacklisted_name
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[`block_in_if_condition_expr`]: https://github.com/Manishearth/rust-clippy/wiki#block_in_if_condition_expr

‎README.md

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@@ -17,13 +17,15 @@ Table of contents:
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## Lints
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There are 147 lints included in this crate:
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There are 149 lints included in this crate:
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name | default | meaning
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---------------------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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[absurd_extreme_comparisons](https://github.com/Manishearth/rust-clippy/wiki#absurd_extreme_comparisons) | warn | a comparison involving a maximum or minimum value involves a case that is always true or always false
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[almost_swapped](https://github.com/Manishearth/rust-clippy/wiki#almost_swapped) | warn | `foo = bar; bar = foo` sequence
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[approx_constant](https://github.com/Manishearth/rust-clippy/wiki#approx_constant) | warn | the approximate of a known float constant (in `std::f64::consts` or `std::f32::consts`) is found; suggests to use the constant
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[assign_op_pattern](https://github.com/Manishearth/rust-clippy/wiki#assign_op_pattern) | warn | assigning the result of an operation on a variable to that same variable
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[assign_ops](https://github.com/Manishearth/rust-clippy/wiki#assign_ops) | allow | Any assignment operation
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[bad_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#bad_bit_mask) | warn | expressions of the form `_ & mask == select` that will only ever return `true` or `false` (because in the example `select` containing bits that `mask` doesn't have)
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[blacklisted_name](https://github.com/Manishearth/rust-clippy/wiki#blacklisted_name) | warn | usage of a blacklisted/placeholder name
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[block_in_if_condition_expr](https://github.com/Manishearth/rust-clippy/wiki#block_in_if_condition_expr) | warn | braces can be eliminated in conditions that are expressions, e.g `if { true } ...`

‎src/assign_ops.rs

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@@ -0,0 +1,158 @@
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use rustc::hir;
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use rustc::lint::*;
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use utils::{span_lint_and_then, span_lint, snippet_opt, SpanlessEq, get_trait_def_id, implements_trait};
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/// **What it does:** This lint checks for `+=` operations and similar
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///
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/// **Why is this bad?** Projects with many developers from languages without those operations
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/// may find them unreadable and not worth their weight
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///
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/// **Known problems:** Types implementing `OpAssign` don't necessarily implement `Op`
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///
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/// **Example:**
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/// ```
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/// a += 1;
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/// ```
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declare_restriction_lint! {
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pub ASSIGN_OPS,
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"Any assignment operation"
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}
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/// **What it does:** Check for `a = a op b` or `a = b commutative_op a` patterns
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///
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/// **Why is this bad?** These can be written as the shorter `a op= b`
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///
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/// **Known problems:** While forbidden by the spec, `OpAssign` traits may have implementations that differ from the regular `Op` impl
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///
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/// **Example:**
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///
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/// ```
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/// let mut a = 5;
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/// ...
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/// a = a + b;
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/// ```
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declare_lint! {
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pub ASSIGN_OP_PATTERN,
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Warn,
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"assigning the result of an operation on a variable to that same variable"
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}
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#[derive(Copy, Clone, Default)]
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pub struct AssignOps;
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impl LintPass for AssignOps {
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fn get_lints(&self) -> LintArray {
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lint_array!(ASSIGN_OPS, ASSIGN_OP_PATTERN)
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}
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}
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impl LateLintPass for AssignOps {
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fn check_expr(&mut self, cx: &LateContext, expr: &hir::Expr) {
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match expr.node {
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hir::ExprAssignOp(op, ref lhs, ref rhs) => {
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if let (Some(l), Some(r)) = (snippet_opt(cx, lhs.span), snippet_opt(cx, rhs.span)) {
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span_lint_and_then(cx,
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ASSIGN_OPS,
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expr.span,
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"assign operation detected",
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|db| {
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match rhs.node {
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hir::ExprBinary(op2, _, _) if op2 != op => {
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db.span_suggestion(expr.span,
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"replace it with",
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format!("{} = {} {} ({})", l, l, op.node.as_str(), r));
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},
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_ => {
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db.span_suggestion(expr.span,
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"replace it with",
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format!("{} = {} {} {}", l, l, op.node.as_str(), r));
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}
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}
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});
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} else {
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span_lint(cx,
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ASSIGN_OPS,
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expr.span,
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"assign operation detected");
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}
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},
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hir::ExprAssign(ref assignee, ref e) => {
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if let hir::ExprBinary(op, ref l, ref r) = e.node {
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let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
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let ty = cx.tcx.expr_ty(assignee);
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if ty.walk_shallow().next().is_some() {
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return; // implements_trait does not work with generics
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}
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let rty = cx.tcx.expr_ty(rhs);
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if rty.walk_shallow().next().is_some() {
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return; // implements_trait does not work with generics
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}
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macro_rules! ops {
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($op:expr, $cx:expr, $ty:expr, $rty:expr, $($trait_name:ident:$full_trait_name:ident),+) => {
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match $op {
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$(hir::$full_trait_name => {
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let [krate, module] = ::utils::paths::OPS_MODULE;
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let path = [krate, module, concat!(stringify!($trait_name), "Assign")];
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let trait_id = if let Some(trait_id) = get_trait_def_id($cx, &path) {
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trait_id
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} else {
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return; // useless if the trait doesn't exist
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};
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implements_trait($cx, $ty, trait_id, vec![$rty])
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},)*
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_ => false,
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}
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}
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}
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if ops!(op.node, cx, ty, rty, Add:BiAdd,
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Sub:BiSub,
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Mul:BiMul,
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Div:BiDiv,
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Rem:BiRem,
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And:BiAnd,
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Or:BiOr,
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BitAnd:BiBitAnd,
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BitOr:BiBitOr,
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BitXor:BiBitXor,
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Shr:BiShr,
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Shl:BiShl
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) {
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if let (Some(snip_a), Some(snip_r)) = (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) {
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span_lint_and_then(cx,
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ASSIGN_OP_PATTERN,
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expr.span,
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"manual implementation of an assign operation",
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|db| {
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db.span_suggestion(expr.span,
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"replace it with",
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format!("{} {}= {}", snip_a, op.node.as_str(), snip_r));
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});
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} else {
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span_lint(cx,
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ASSIGN_OP_PATTERN,
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expr.span,
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"manual implementation of an assign operation");
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}
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}
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};
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// a = a op b
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if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, l) {
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lint(assignee, r);
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}
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// a = b commutative_op a
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if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, r) {
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match op.node {
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hir::BiAdd | hir::BiMul |
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hir::BiAnd | hir::BiOr |
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hir::BiBitXor | hir::BiBitAnd | hir::BiBitOr => {
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lint(assignee, l);
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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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_ => {},
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}
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}
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}

‎src/lib.rs

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@@ -7,7 +7,6 @@
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#![feature(question_mark)]
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#![feature(stmt_expr_attributes)]
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#![allow(indexing_slicing, shadow_reuse, unknown_lints)]
10-
#![allow(float_arithmetic, integer_arithmetic)]
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extern crate rustc_driver;
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extern crate getopts;
@@ -203,6 +202,7 @@ pub mod utils;
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pub mod approx_const;
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pub mod arithmetic;
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pub mod array_indexing;
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pub mod assign_ops;
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pub mod attrs;
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pub mod bit_mask;
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pub mod blacklisted_name;
@@ -394,10 +394,12 @@ pub fn plugin_registrar(reg: &mut Registry) {
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reg.register_late_lint_pass(box unsafe_removed_from_name::UnsafeNameRemoval);
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reg.register_late_lint_pass(box mem_forget::MemForget);
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reg.register_late_lint_pass(box arithmetic::Arithmetic::default());
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reg.register_late_lint_pass(box assign_ops::AssignOps);
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reg.register_lint_group("clippy_restrictions", vec![
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arithmetic::FLOAT_ARITHMETIC,
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arithmetic::INTEGER_ARITHMETIC,
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assign_ops::ASSIGN_OPS,
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]);
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reg.register_lint_group("clippy_pedantic", vec![
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reg.register_lint_group("clippy", vec![
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approx_const::APPROX_CONSTANT,
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array_indexing::OUT_OF_BOUNDS_INDEXING,
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assign_ops::ASSIGN_OP_PATTERN,
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attrs::DEPRECATED_SEMVER,
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attrs::INLINE_ALWAYS,
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bit_mask::BAD_BIT_MASK,

‎src/utils/paths.rs

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pub const MEM_FORGET: [&'static str; 3] = ["core", "mem", "forget"];
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pub const MUTEX: [&'static str; 4] = ["std", "sync", "mutex", "Mutex"];
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pub const OPEN_OPTIONS: [&'static str; 3] = ["std", "fs", "OpenOptions"];
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pub const OPS_MODULE: [&'static str; 2] = ["core", "ops"];
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pub const OPTION: [&'static str; 3] = ["core", "option", "Option"];
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pub const RANGE: [&'static str; 3] = ["core", "ops", "Range"];
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pub const RANGE_FROM: [&'static str; 3] = ["core", "ops", "RangeFrom"];

‎tests/compile-fail/assign_ops.rs

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#![feature(plugin)]
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#![plugin(clippy)]
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#[deny(assign_ops)]
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#[allow(unused_assignments)]
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fn main() {
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let mut i = 1i32;
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i += 2; //~ ERROR assign operation detected
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//~^ HELP replace it with
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//~| SUGGESTION i = i + 2
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i -= 6; //~ ERROR assign operation detected
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//~^ HELP replace it with
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//~| SUGGESTION i = i - 6
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i *= 5; //~ ERROR assign operation detected
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//~^ HELP replace it with
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//~| SUGGESTION i = i * 5
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i /= 32; //~ ERROR assign operation detected
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//~^ HELP replace it with
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//~| SUGGESTION i = i / 32
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i %= 42; //~ ERROR assign operation detected
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//~^ HELP replace it with
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//~| SUGGESTION i = i % 42
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i >>= i; //~ ERROR assign operation detected
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//~^ HELP replace it with
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//~| SUGGESTION i = i >> i
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i <<= 9 + 6 - 7; //~ ERROR assign operation detected
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//~^ HELP replace it with
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//~| SUGGESTION i = i << (9 + 6 - 7)
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}
30+
31+
#[allow(dead_code, unused_assignments)]
32+
#[deny(assign_op_pattern)]
33+
fn bla() {
34+
let mut a = 5;
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a = a + 1; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
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//~| SUGGESTION a += 1
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a = 1 + a; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
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//~| SUGGESTION a += 1
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a = a - 1; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
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//~| SUGGESTION a -= 1
44+
a = a * 99; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
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//~| SUGGESTION a *= 99
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a = 42 * a; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
49+
//~| SUGGESTION a *= 42
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a = a / 2; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
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//~| SUGGESTION a /= 2
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a = a % 5; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
55+
//~| SUGGESTION a %= 5
56+
a = a & 1; //~ ERROR manual implementation of an assign operation
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//~^ HELP replace it with
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//~| SUGGESTION a &= 1
59+
a = 1 - a;
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a = 5 / a;
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a = 42 % a;
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a = 6 << a;
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let mut s = String::new();
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s = s + "bla";
65+
}

‎tests/compile-fail/strings.rs

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@@ -65,6 +65,6 @@ fn main() {
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6666
// the add is only caught for String
6767
let mut x = 1;
68-
x = x + 1;
68+
x = x + 1; //~ WARN assign_op_pattern
6969
assert_eq!(2, x);
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}

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