//! Checks for usage of `&Vec[_]` and `&String`.
use std::borrow::Cow;
use rustc::hir::*;
use rustc::hir::map::NodeItem;
use rustc::hir::QPath;
use rustc::lint::*;
use rustc::ty;
use syntax::ast::NodeId;
use syntax::codemap::Span;
use syntax_pos::MultiSpan;
use utils::{match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then, walk_ptrs_hir_ty};
use utils::ptr::get_spans;
/// **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.
///
/// 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 you may not be aware. Carefully deprecate the
/// function before applying the lint suggestions in this case.
///
/// **Example:**
/// ```rust
/// fn foo(&Vec<u32>) { .. }
/// ```
declare_clippy_lint! {
pub PTR_ARG,
style,
"fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` \
instead, respectively"
}
/// **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:**
/// ```rust
/// if x == ptr::null { .. }
/// ```
declare_clippy_lint! {
pub CMP_NULL,
style,
"comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
}
/// **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:**
/// ```rust
/// fn foo(&Foo) -> &mut Bar { .. }
/// ```
declare_clippy_lint! {
pub MUT_FROM_REF,
correctness,
"fns that create mutable refs from immutable ref args"
}
#[derive(Copy, Clone)]
pub struct PointerPass;
impl LintPass for PointerPass {
fn get_lints(&self) -> LintArray {
lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass {
fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
if let ItemFn(ref decl, _, _, _, _, body_id) = item.node {
check_fn(cx, decl, item.id, Some(body_id));
}
}
fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
if let ImplItemKind::Method(ref sig, body_id) = item.node {
if let Some(NodeItem(it)) = cx.tcx.hir.find(cx.tcx.hir.get_parent(item.id)) {
if let ItemImpl(_, _, _, _, Some(_), _, _) = it.node {
return; // ignore trait impls
}
}
check_fn(cx, &sig.decl, item.id, Some(body_id));
}
}
fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
if let TraitItemKind::Method(ref sig, ref trait_method) = item.node {
let body_id = if let TraitMethod::Provided(b) = *trait_method {
Some(b)
} else {
None
};
check_fn(cx, &sig.decl, item.id, body_id);
}
}
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let ExprBinary(ref op, ref l, ref r) = expr.node {
if (op.node == BiEq || op.node == BiNe) && (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",
);
}
}
}
}
fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, 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();
for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
if let ty::TyRef(
_,
ty,
MutImmutable
) = ty.sty
{
if match_type(cx, ty, &paths::VEC) {
let mut ty_snippet = None;
if_chain! {
if let TyPath(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node;
if let Some(&PathSegment{parameters: Some(ref parameters), ..}) = path.segments.last();
if parameters.types.len() == 1;
then {
ty_snippet = snippet_opt(cx, parameters.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.",
|db| {
if let Some(ref snippet) = ty_snippet {
db.span_suggestion(arg.span, "change this to", format!("&[{}]", snippet));
}
for (clonespan, suggestion) in spans {
db.span_suggestion(
clonespan,
&snippet_opt(cx, clonespan).map_or(
"change the call to".into(),
|x| Cow::Owned(format!("change `{}` to", x)),
),
suggestion.into(),
);
}
},
);
}
} else if match_type(cx, ty, &paths::STRING) {
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.",
|db| {
db.span_suggestion(arg.span, "change this to", "&str".into());
for (clonespan, suggestion) in spans {
db.span_suggestion_short(
clonespan,
&snippet_opt(cx, clonespan).map_or(
"change the call to".into(),
|x| Cow::Owned(format!("change `{}` to", x)),
),
suggestion.into(),
);
}
},
);
}
} else if match_type(cx, ty, &paths::COW) {
if_chain! {
if let TyRptr(_, MutTy { ref ty, ..} ) = arg.node;
if let TyPath(ref path) = ty.node;
if let QPath::Resolved(None, ref pp) = *path;
if let [ref bx] = *pp.segments;
if let Some(ref params) = bx.parameters;
if !params.parenthesized;
if let [ref inner] = *params.types;
then {
let replacement = snippet_opt(cx, inner.span);
if let Some(r) = replacement {
span_lint_and_then(
cx,
PTR_ARG,
arg.span,
"using a reference to `Cow` is not recommended.",
|db| {
db.span_suggestion(arg.span, "change this to", "&".to_owned() + &r);
},
);
}
}
}
}
}
}
if let FunctionRetTy::Return(ref ty) = decl.output {
if let Some((out, MutMutable, _)) = 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 == MutMutable {
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)", |db| {
let ms = MultiSpan::from_spans(immutables);
db.span_note(ms, "immutable borrow here");
});
}
}
}
fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
if let Ty_::TyRptr(ref lt, ref m) = ty.node {
Some((lt, m.mutbl, ty.span))
} else {
None
}
}
fn is_null_path(expr: &Expr) -> bool {
if let ExprCall(ref pathexp, ref args) = expr.node {
if args.is_empty() {
if let ExprPath(ref path) = pathexp.node {
return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);
}
}
}
false
}