rust-clippy/clippy_lints/src/ptr.rs
2020-11-02 11:46:37 -06:00

329 lines
13 KiB
Rust

//! Checks for usage of `&Vec[_]` and `&String`.
use crate::utils::ptr::get_spans;
use crate::utils::{
is_allowed, is_type_diagnostic_item, match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_sugg,
span_lint_and_then, walk_ptrs_hir_ty,
};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{
BinOpKind, BodyId, Expr, ExprKind, FnDecl, FnRetTy, GenericArg, HirId, ImplItem, ImplItemKind, Item, ItemKind,
Lifetime, MutTy, Mutability, Node, PathSegment, QPath, TraitFn, TraitItem, TraitItemKind, Ty, TyKind,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use rustc_span::{sym, MultiSpan};
use std::borrow::Cow;
declare_clippy_lint! {
/// **What it does:** This lint checks for function arguments of type `&String`
/// or `&Vec` unless the references are mutable. It will also suggest you
/// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
/// calls.
///
/// **Why is this bad?** Requiring the argument to be of the specific size
/// makes the function less useful for no benefit; slices in the form of `&[T]`
/// or `&str` usually suffice and can be obtained from other types, too.
///
/// **Known problems:** The lint does not follow data. So if you have an
/// argument `x` and write `let y = x; y.clone()` the lint will not suggest
/// changing that `.clone()` to `.to_owned()`.
///
/// Other functions called from this function taking a `&String` or `&Vec`
/// argument may also fail to compile if you change the argument. Applying
/// this lint on them will fix the problem, but they may be in other crates.
///
/// One notable example of a function that may cause issues, and which cannot
/// easily be changed due to being in the standard library is `Vec::contains`.
/// when called on a `Vec<Vec<T>>`. If a `&Vec` is passed to that method then
/// it will compile, but if a `&[T]` is passed then it will not compile.
///
/// ```ignore
/// fn cannot_take_a_slice(v: &Vec<u8>) -> bool {
/// let vec_of_vecs: Vec<Vec<u8>> = some_other_fn();
///
/// vec_of_vecs.contains(v)
/// }
/// ```
///
/// Also there may be `fn(&Vec)`-typed references pointing to your function.
/// If you have them, you will get a compiler error after applying this lint's
/// suggestions. You then have the choice to undo your changes or change the
/// type of the reference.
///
/// Note that if the function is part of your public interface, there may be
/// other crates referencing it, of which you may not be aware. Carefully
/// deprecate the function before applying the lint suggestions in this case.
///
/// **Example:**
/// ```ignore
/// // Bad
/// fn foo(&Vec<u32>) { .. }
///
/// // Good
/// fn foo(&[u32]) { .. }
/// ```
pub PTR_ARG,
style,
"fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
}
declare_clippy_lint! {
/// **What it does:** This lint checks for equality comparisons with `ptr::null`
///
/// **Why is this bad?** It's easier and more readable to use the inherent
/// `.is_null()`
/// method instead
///
/// **Known problems:** None.
///
/// **Example:**
/// ```ignore
/// // Bad
/// if x == ptr::null {
/// ..
/// }
///
/// // Good
/// if x.is_null() {
/// ..
/// }
/// ```
pub CMP_NULL,
style,
"comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
}
declare_clippy_lint! {
/// **What it does:** This lint checks for functions that take immutable
/// references and return mutable ones.
///
/// **Why is this bad?** This is trivially unsound, as one can create two
/// mutable references from the same (immutable!) source.
/// This [error](https://github.com/rust-lang/rust/issues/39465)
/// actually lead to an interim Rust release 1.15.1.
///
/// **Known problems:** To be on the conservative side, if there's at least one
/// mutable reference with the output lifetime, this lint will not trigger.
/// In practice, this case is unlikely anyway.
///
/// **Example:**
/// ```ignore
/// fn foo(&Foo) -> &mut Bar { .. }
/// ```
pub MUT_FROM_REF,
correctness,
"fns that create mutable refs from immutable ref args"
}
declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF]);
impl<'tcx> LateLintPass<'tcx> for Ptr {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
if let ItemKind::Fn(ref sig, _, body_id) = item.kind {
check_fn(cx, &sig.decl, item.hir_id, Some(body_id));
}
}
fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
if let ImplItemKind::Fn(ref sig, body_id) = item.kind {
let parent_item = cx.tcx.hir().get_parent_item(item.hir_id);
if let Some(Node::Item(it)) = cx.tcx.hir().find(parent_item) {
if let ItemKind::Impl { of_trait: Some(_), .. } = it.kind {
return; // ignore trait impls
}
}
check_fn(cx, &sig.decl, item.hir_id, Some(body_id));
}
}
fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
if let TraitItemKind::Fn(ref sig, ref trait_method) = item.kind {
let body_id = if let TraitFn::Provided(b) = *trait_method {
Some(b)
} else {
None
};
check_fn(cx, &sig.decl, item.hir_id, body_id);
}
}
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::Binary(ref op, ref l, ref r) = expr.kind {
if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(l) || is_null_path(r)) {
span_lint(
cx,
CMP_NULL,
expr.span,
"comparing with null is better expressed by the `.is_null()` method",
);
}
}
}
}
#[allow(clippy::too_many_lines)]
fn check_fn(cx: &LateContext<'_>, decl: &FnDecl<'_>, fn_id: HirId, opt_body_id: Option<BodyId>) {
let fn_def_id = cx.tcx.hir().local_def_id(fn_id);
let sig = cx.tcx.fn_sig(fn_def_id);
let fn_ty = sig.skip_binder();
let body = opt_body_id.map(|id| cx.tcx.hir().body(id));
for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
// Honor the allow attribute on parameters. See issue 5644.
if let Some(body) = &body {
if is_allowed(cx, PTR_ARG, body.params[idx].hir_id) {
continue;
}
}
if let ty::Ref(_, ty, Mutability::Not) = ty.kind() {
if is_type_diagnostic_item(cx, ty, sym::vec_type) {
let mut ty_snippet = None;
if_chain! {
if let TyKind::Path(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).kind;
if let Some(&PathSegment{args: Some(ref parameters), ..}) = path.segments.last();
then {
let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
}).collect();
if types.len() == 1 {
ty_snippet = snippet_opt(cx, types[0].span);
}
}
};
if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
span_lint_and_then(
cx,
PTR_ARG,
arg.span,
"writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
with non-Vec-based slices.",
|diag| {
if let Some(ref snippet) = ty_snippet {
diag.span_suggestion(
arg.span,
"change this to",
format!("&[{}]", snippet),
Applicability::Unspecified,
);
}
for (clonespan, suggestion) in spans {
diag.span_suggestion(
clonespan,
&snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
Cow::Owned(format!("change `{}` to", x))
}),
suggestion.into(),
Applicability::Unspecified,
);
}
},
);
}
} else if is_type_diagnostic_item(cx, ty, sym::string_type) {
if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
span_lint_and_then(
cx,
PTR_ARG,
arg.span,
"writing `&String` instead of `&str` involves a new object where a slice will do.",
|diag| {
diag.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
for (clonespan, suggestion) in spans {
diag.span_suggestion_short(
clonespan,
&snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
Cow::Owned(format!("change `{}` to", x))
}),
suggestion.into(),
Applicability::Unspecified,
);
}
},
);
}
} else if match_type(cx, ty, &paths::COW) {
if_chain! {
if let TyKind::Rptr(_, MutTy { ref ty, ..} ) = arg.kind;
if let TyKind::Path(ref path) = ty.kind;
if let QPath::Resolved(None, ref pp) = *path;
if let [ref bx] = *pp.segments;
if let Some(ref params) = bx.args;
if !params.parenthesized;
if let Some(inner) = params.args.iter().find_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
});
then {
let replacement = snippet_opt(cx, inner.span);
if let Some(r) = replacement {
span_lint_and_sugg(
cx,
PTR_ARG,
arg.span,
"using a reference to `Cow` is not recommended.",
"change this to",
"&".to_owned() + &r,
Applicability::Unspecified,
);
}
}
}
}
}
}
if let FnRetTy::Return(ref ty) = decl.output {
if let Some((out, Mutability::Mut, _)) = get_rptr_lm(ty) {
let mut immutables = vec![];
for (_, ref mutbl, ref argspan) in decl
.inputs
.iter()
.filter_map(|ty| get_rptr_lm(ty))
.filter(|&(lt, _, _)| lt.name == out.name)
{
if *mutbl == Mutability::Mut {
return;
}
immutables.push(*argspan);
}
if immutables.is_empty() {
return;
}
span_lint_and_then(
cx,
MUT_FROM_REF,
ty.span,
"mutable borrow from immutable input(s)",
|diag| {
let ms = MultiSpan::from_spans(immutables);
diag.span_note(ms, "immutable borrow here");
},
);
}
}
}
fn get_rptr_lm<'tcx>(ty: &'tcx Ty<'tcx>) -> Option<(&'tcx Lifetime, Mutability, Span)> {
if let TyKind::Rptr(ref lt, ref m) = ty.kind {
Some((lt, m.mutbl, ty.span))
} else {
None
}
}
fn is_null_path(expr: &Expr<'_>) -> bool {
if let ExprKind::Call(ref pathexp, ref args) = expr.kind {
if args.is_empty() {
if let ExprKind::Path(ref path) = pathexp.kind {
return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);
}
}
}
false
}