use rustc::hir::*;
+use rustc::hir::map::*;
use rustc::hir::intravisit::FnKind;
-use rustc::hir::def_id::DefId;
use rustc::lint::*;
-use rustc::ty::{self, TypeFoldable};
+use rustc::ty::{self, RegionKind, TypeFoldable};
use rustc::traits;
use rustc::middle::expr_use_visitor as euv;
use rustc::middle::mem_categorization as mc;
use syntax::ast::NodeId;
use syntax_pos::Span;
use syntax::errors::DiagnosticBuilder;
-use utils::{in_macro, is_self, is_copy, implements_trait, get_trait_def_id, match_type, snippet, span_lint_and_then,
- multispan_sugg, paths};
-use std::collections::{HashSet, HashMap};
-
-/// **What it does:** Checks for functions taking arguments by value, but not consuming them in its
+use utils::{get_trait_def_id, implements_trait, in_macro, is_copy, is_self, match_type, multispan_sugg, paths,
+ snippet, snippet_opt, span_lint_and_then};
+use utils::ptr::get_spans;
+use std::collections::{HashMap, HashSet};
+use std::borrow::Cow;
+
+/// **What it does:** Checks for functions taking arguments by value, but not
+/// consuming them in its
/// body.
///
-/// **Why is this bad?** Taking arguments by reference is more flexible and can sometimes avoid
+/// **Why is this bad?** Taking arguments by reference is more flexible and can
+/// sometimes avoid
/// unnecessary allocations.
///
-/// **Known problems:** Hopefully none.
+/// **Known problems:**
+/// * This lint suggests taking an argument by reference,
+/// however sometimes it is better to let users decide the argument type
+/// (by using `Borrow` trait, for example), depending on how the function is used.
///
/// **Example:**
/// ```rust
/// fn foo(v: Vec<i32>) {
/// assert_eq!(v.len(), 42);
/// }
+/// // should be
+/// fn foo(v: &[i32]) {
+/// assert_eq!(v.len(), 42);
+/// }
/// ```
declare_lint! {
pub NEEDLESS_PASS_BY_VALUE,
decl: &'tcx FnDecl,
body: &'tcx Body,
span: Span,
- node_id: NodeId
+ node_id: NodeId,
) {
if in_macro(span) {
return;
}
match kind {
- FnKind::ItemFn(.., attrs) => {
- for a in attrs {
- if_let_chain!{[
- a.meta_item_list().is_some(),
- let Some(name) = a.name(),
- name == "proc_macro_derive",
- ], {
+ FnKind::ItemFn(.., attrs) => for a in attrs {
+ if_chain! {
+ if a.meta_item_list().is_some();
+ if let Some(name) = a.name();
+ if name == "proc_macro_derive";
+ then {
return;
- }}
+ }
}
},
+ FnKind::Method(..) => (),
_ => return,
}
- // Allows these to be passed by value.
- let fn_trait = need!(cx.tcx.lang_items.fn_trait());
- let asref_trait = need!(get_trait_def_id(cx, &paths::ASREF_TRAIT));
+ // Exclude non-inherent impls
+ if let Some(NodeItem(item)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(node_id)) {
+ if matches!(item.node, ItemImpl(_, _, _, _, Some(_), _, _) | ItemAutoImpl(..)) {
+ return;
+ }
+ }
+
+ // Allow `Borrow` or functions to be taken by value
let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
+ let fn_traits = [
+ need!(cx.tcx.lang_items().fn_trait()),
+ need!(cx.tcx.lang_items().fn_once_trait()),
+ need!(cx.tcx.lang_items().fn_mut_trait()),
+ ];
- let fn_def_id = cx.tcx.hir.local_def_id(node_id);
+ let sized_trait = need!(cx.tcx.lang_items().sized_trait());
- let preds: Vec<ty::Predicate> = {
- traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
- .filter(|p| !p.is_global())
- .collect()
- };
+ let fn_def_id = cx.tcx.hir.local_def_id(node_id);
- // Collect moved variables and spans which will need dereferencings from the function body.
- let MovedVariablesCtxt { moved_vars, spans_need_deref, .. } = {
+ let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
+ .filter(|p| !p.is_global())
+ .filter_map(|pred| {
+ if let ty::Predicate::Trait(poly_trait_ref) = pred {
+ if poly_trait_ref.def_id() == sized_trait || poly_trait_ref.skip_binder().has_escaping_regions() {
+ return None;
+ }
+ Some(poly_trait_ref)
+ } else {
+ None
+ }
+ })
+ .collect::<Vec<_>>();
+
+ // Collect moved variables and spans which will need dereferencings from the
+ // function body.
+ let MovedVariablesCtxt {
+ moved_vars,
+ spans_need_deref,
+ ..
+ } = {
let mut ctx = MovedVariablesCtxt::new(cx);
- let region_maps = &cx.tcx.region_maps(fn_def_id);
- euv::ExprUseVisitor::new(&mut ctx, cx.tcx, cx.param_env, region_maps, cx.tables).consume_body(body);
+ let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id);
+ euv::ExprUseVisitor::new(&mut ctx, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None)
+ .consume_body(body);
ctx
};
- let fn_sig = cx.tcx.type_of(fn_def_id).fn_sig();
+ let fn_sig = cx.tcx.fn_sig(fn_def_id);
let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);
- for ((input, &ty), arg) in decl.inputs.iter().zip(fn_sig.inputs()).zip(&body.arguments) {
+ for (idx, ((input, &ty), arg)) in decl.inputs
+ .iter()
+ .zip(fn_sig.inputs())
+ .zip(&body.arguments)
+ .enumerate()
+ {
+ // All spans generated from a proc-macro invocation are the same...
+ if span == input.span {
+ return;
+ }
- // Determines whether `ty` implements `Borrow<U>` (U != ty) specifically.
- // This is needed due to the `Borrow<T> for T` blanket impl.
- let implements_borrow_trait = preds.iter()
- .filter_map(|pred| if let ty::Predicate::Trait(ref poly_trait_ref) = *pred {
- Some(poly_trait_ref.skip_binder())
- } else {
- None
- })
- .filter(|tpred| tpred.def_id() == borrow_trait && tpred.self_ty() == ty)
- .any(|tpred| tpred.input_types().nth(1).expect("Borrow trait must have an parameter") != ty);
-
- if_let_chain! {[
- !is_self(arg),
- !ty.is_mutable_pointer(),
- !is_copy(cx, ty),
- !implements_trait(cx, ty, fn_trait, &[]),
- !implements_trait(cx, ty, asref_trait, &[]),
- !implements_borrow_trait,
-
- let PatKind::Binding(mode, defid, ..) = arg.pat.node,
- !moved_vars.contains(&defid),
- ], {
- // Note: `toplevel_ref_arg` warns if `BindByRef`
- let m = match mode {
- BindingMode::BindByRef(m) | BindingMode::BindByValue(m) => m,
- };
- if m == Mutability::MutMutable {
- continue;
+ // Ignore `self`s.
+ if idx == 0 {
+ if let PatKind::Binding(_, _, name, ..) = arg.pat.node {
+ if name.node.as_str() == "self" {
+ continue;
+ }
}
+ }
- // Suggestion logic
- let sugg = |db: &mut DiagnosticBuilder| {
- let deref_span = spans_need_deref.get(&defid);
- if_let_chain! {[
- match_type(cx, ty, &paths::VEC),
- let TyPath(QPath::Resolved(_, ref path)) = input.node,
- let Some(elem_ty) = path.segments.iter()
- .find(|seg| seg.name == "Vec")
- .map(|ps| ps.parameters.types()[0]),
- ], {
- let slice_ty = format!("&[{}]", snippet(cx, elem_ty.span, "_"));
- db.span_suggestion(input.span,
- "consider changing the type to",
- slice_ty);
- assert!(deref_span.is_none());
- return; // `Vec` and `String` cannot be destructured - no need for `*` suggestion
- }}
-
- if match_type(cx, ty, &paths::STRING) {
- db.span_suggestion(input.span,
- "consider changing the type to",
- "&str".to_string());
- assert!(deref_span.is_none());
- return;
+ // * Exclude a type that is specifically bounded by `Borrow`.
+ // * Exclude a type whose reference also fulfills its bound.
+ // (e.g. `std::convert::AsRef`, `serde::Serialize`)
+ let (implements_borrow_trait, all_borrowable_trait) = {
+ let preds = preds
+ .iter()
+ .filter(|t| t.skip_binder().self_ty() == ty)
+ .collect::<Vec<_>>();
+
+ (
+ preds.iter().any(|t| t.def_id() == borrow_trait),
+ !preds.is_empty() && preds.iter().all(|t| {
+ implements_trait(
+ cx,
+ cx.tcx.mk_imm_ref(&RegionKind::ReErased, ty),
+ t.def_id(),
+ &t.skip_binder().input_types().skip(1).collect::<Vec<_>>(),
+ )
+ }),
+ )
+ };
+
+ if_chain! {
+ if !is_self(arg);
+ if !ty.is_mutable_pointer();
+ if !is_copy(cx, ty);
+ if !fn_traits.iter().any(|&t| implements_trait(cx, ty, t, &[]));
+ if !implements_borrow_trait;
+ if !all_borrowable_trait;
+
+ if let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node;
+ if !moved_vars.contains(&canonical_id);
+ then {
+ if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut {
+ continue;
}
- let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
+ // Dereference suggestion
+ let sugg = |db: &mut DiagnosticBuilder| {
+ let deref_span = spans_need_deref.get(&canonical_id);
+ if_chain! {
+ if match_type(cx, ty, &paths::VEC);
+ if let Some(clone_spans) =
+ get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]);
+ if let TyPath(QPath::Resolved(_, ref path)) = input.node;
+ if let Some(elem_ty) = path.segments.iter()
+ .find(|seg| seg.name == "Vec")
+ .and_then(|ps| ps.parameters.as_ref())
+ .map(|params| ¶ms.types[0]);
+ then {
+ let slice_ty = format!("&[{}]", snippet(cx, elem_ty.span, "_"));
+ db.span_suggestion(input.span,
+ "consider changing the type to",
+ slice_ty);
+
+ for (span, suggestion) in clone_spans {
+ db.span_suggestion(
+ span,
+ &snippet_opt(cx, span)
+ .map_or(
+ "change the call to".into(),
+ |x| Cow::from(format!("change `{}` to", x)),
+ ),
+ suggestion.into()
+ );
+ }
+
+ // cannot be destructured, no need for `*` suggestion
+ assert!(deref_span.is_none());
+ return;
+ }
+ }
- // Suggests adding `*` to dereference the added reference.
- if let Some(deref_span) = deref_span {
- spans.extend(deref_span.iter().cloned()
- .map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))));
- spans.sort_by_key(|&(span, _)| span);
- }
- multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
- };
-
- span_lint_and_then(cx,
- NEEDLESS_PASS_BY_VALUE,
- input.span,
- "this argument is passed by value, but not consumed in the function body",
- sugg);
- }}
+ if match_type(cx, ty, &paths::STRING) {
+ if let Some(clone_spans) =
+ get_spans(cx, Some(body.id()), idx, &[("clone", ".to_string()"), ("as_str", "")]) {
+ db.span_suggestion(input.span, "consider changing the type to", "&str".to_string());
+
+ for (span, suggestion) in clone_spans {
+ db.span_suggestion(
+ span,
+ &snippet_opt(cx, span)
+ .map_or(
+ "change the call to".into(),
+ |x| Cow::from(format!("change `{}` to", x))
+ ),
+ suggestion.into(),
+ );
+ }
+
+ assert!(deref_span.is_none());
+ return;
+ }
+ }
+
+ let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
+
+ // Suggests adding `*` to dereference the added reference.
+ if let Some(deref_span) = deref_span {
+ spans.extend(
+ deref_span
+ .iter()
+ .cloned()
+ .map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))),
+ );
+ spans.sort_by_key(|&(span, _)| span);
+ }
+ multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
+ };
+
+ span_lint_and_then(
+ cx,
+ NEEDLESS_PASS_BY_VALUE,
+ input.span,
+ "this argument is passed by value, but not consumed in the function body",
+ sugg,
+ );
+ }
+ }
}
}
}
struct MovedVariablesCtxt<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
- moved_vars: HashSet<DefId>,
- /// Spans which need to be prefixed with `*` for dereferencing the suggested additional
- /// reference.
- spans_need_deref: HashMap<DefId, HashSet<Span>>,
+ moved_vars: HashSet<NodeId>,
+ /// Spans which need to be prefixed with `*` for dereferencing the
+ /// suggested additional reference.
+ spans_need_deref: HashMap<NodeId, HashSet<Span>>,
}
impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
- MovedVariablesCtxt {
+ Self {
cx: cx,
moved_vars: HashSet::new(),
spans_need_deref: HashMap::new(),
fn move_common(&mut self, _consume_id: NodeId, _span: Span, cmt: mc::cmt<'tcx>) {
let cmt = unwrap_downcast_or_interior(cmt);
- if_let_chain! {[
- let mc::Categorization::Local(vid) = cmt.cat,
- let Some(def_id) = self.cx.tcx.hir.opt_local_def_id(vid),
- ], {
- self.moved_vars.insert(def_id);
- }}
+ if let mc::Categorization::Local(vid) = cmt.cat {
+ self.moved_vars.insert(vid);
+ }
}
fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: mc::cmt<'tcx>) {
let cmt = unwrap_downcast_or_interior(cmt);
- if_let_chain! {[
- let mc::Categorization::Local(vid) = cmt.cat,
- let Some(def_id) = self.cx.tcx.hir.opt_local_def_id(vid),
- ], {
+ if let mc::Categorization::Local(vid) = cmt.cat {
let mut id = matched_pat.id;
loop {
let parent = self.cx.tcx.hir.get_parent_node(id);
// `match` and `if let`
if let ExprMatch(ref c, ..) = e.node {
self.spans_need_deref
- .entry(def_id)
+ .entry(vid)
.or_insert_with(HashSet::new)
.insert(c.span);
}
- }
+ },
map::Node::NodeStmt(s) => {
// `let <pat> = x;`
- if_let_chain! {[
- let StmtDecl(ref decl, _) = s.node,
- let DeclLocal(ref local) = decl.node,
- ], {
- self.spans_need_deref
- .entry(def_id)
- .or_insert_with(HashSet::new)
- .insert(local.init
- .as_ref()
- .map(|e| e.span)
- .expect("`let` stmt without init aren't caught by match_pat"));
- }}
- }
+ if_chain! {
+ if let StmtDecl(ref decl, _) = s.node;
+ if let DeclLocal(ref local) = decl.node;
+ then {
+ self.spans_need_deref
+ .entry(vid)
+ .or_insert_with(HashSet::new)
+ .insert(local.init
+ .as_ref()
+ .map(|e| e.span)
+ .expect("`let` stmt without init aren't caught by match_pat"));
+ }
+ }
+ },
- _ => {}
+ _ => {},
}
}
}
- }}
+ }
}
}
fn unwrap_downcast_or_interior(mut cmt: mc::cmt) -> mc::cmt {
loop {
match cmt.cat.clone() {
- mc::Categorization::Downcast(c, _) |
- mc::Categorization::Interior(c, _) => {
+ mc::Categorization::Downcast(c, _) | mc::Categorization::Interior(c, _) => {
cmt = c;
},
_ => return cmt,
projects / rust.git / blobdiff