rust-clippy/clippy_lints/src/mut_reference.rs

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use rustc::lint::*;
use rustc::ty::{TypeAndMut, TypeVariants, MethodCall, TyS};
use rustc::hir::*;
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use utils::span_lint;
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/// **What it does:** Detects giving a mutable reference to a function that only
/// requires an immutable reference.
///
/// **Why is this bad?** The immutable reference rules out all other references
/// to the value. Also the code misleads about the intent of the call site.
///
/// **Known problems:** None.
///
/// **Example:**
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/// ```rust
/// my_vec.push(&mut value)
/// ```
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declare_lint! {
pub UNNECESSARY_MUT_PASSED,
Warn,
"an argument passed as a mutable reference although the callee only demands an \
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immutable reference"
}
#[derive(Copy,Clone)]
pub struct UnnecessaryMutPassed;
impl LintPass for UnnecessaryMutPassed {
fn get_lints(&self) -> LintArray {
lint_array!(UNNECESSARY_MUT_PASSED)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnecessaryMutPassed {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
let borrowed_table = cx.tcx.tables.borrow();
match e.node {
ExprCall(ref fn_expr, ref arguments) => {
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let function_type = borrowed_table.node_types
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.get(&fn_expr.id)
.expect("A function with an unknown type is called. If this happened, the compiler would have \
aborted the compilation long ago");
if let ExprPath(ref path) = fn_expr.node {
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check_arguments(cx,
arguments,
function_type,
&print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)));
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}
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},
ExprMethodCall(ref name, _, ref arguments) => {
let method_call = MethodCall::expr(e.id);
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let method_type = borrowed_table.method_map.get(&method_call).expect("This should never happen.");
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check_arguments(cx, arguments, method_type.ty, &name.node.as_str())
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},
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_ => (),
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}
}
}
fn check_arguments(cx: &LateContext, arguments: &[Expr], type_definition: &TyS, name: &str) {
match type_definition.sty {
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TypeVariants::TyFnDef(_, _, fn_type) |
TypeVariants::TyFnPtr(fn_type) => {
let parameters = fn_type.sig.skip_binder().inputs();
for (argument, parameter) in arguments.iter().zip(parameters.iter()) {
match parameter.sty {
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TypeVariants::TyRef(_, TypeAndMut { mutbl: MutImmutable, .. }) |
TypeVariants::TyRawPtr(TypeAndMut { mutbl: MutImmutable, .. }) => {
if let ExprAddrOf(MutMutable, _) = argument.node {
span_lint(cx,
UNNECESSARY_MUT_PASSED,
argument.span,
&format!("The function/method \"{}\" doesn't need a mutable reference", name));
}
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},
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_ => (),
}
}
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},
_ => (),
}
}