[rustc.git] / src / tools / clippy / clippy_lints / src / needless_pass_by_value.rs

use rustc::hir::*;
use rustc::hir::map::*;
use rustc::hir::intravisit::FnKind;
use rustc::lint::*;
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::{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
/// unnecessary allocations.
///
/// **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,
    Warn,
    "functions taking arguments by value, but not consuming them in its body"
}

pub struct NeedlessPassByValue;

impl LintPass for NeedlessPassByValue {
    fn get_lints(&self) -> LintArray {
        lint_array![NEEDLESS_PASS_BY_VALUE]
    }
}

macro_rules! need {
    ($e: expr) => { if let Some(x) = $e { x } else { return; } };
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
    fn check_fn(
        &mut self,
        cx: &LateContext<'a, 'tcx>,
        kind: FnKind<'tcx>,
        decl: &'tcx FnDecl,
        body: &'tcx Body,
        span: Span,
        node_id: NodeId,
    ) {
        if in_macro(span) {
            return;
        }

        match kind {
            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,
        }

        // 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(..) |
                ItemTrait(..))
            {
                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 sized_trait = need!(cx.tcx.lang_items().sized_trait());

        let fn_def_id = cx.tcx.hir.local_def_id(node_id);

        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_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.fn_sig(fn_def_id);
        let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);

        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;
            }

            // Ignore `self`s.
            if idx == 0 {
                if let PatKind::Binding(_, _, name, ..) = arg.pat.node {
                    if name.node.as_str() == "self" {
                        continue;
                    }
                }
            }

            // * 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;
                    }

                    // 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| &params.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;
                            }
                        }

                        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<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 {
        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 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 mc::Categorization::Local(vid) = cmt.cat {
            let mut id = matched_pat.id;
            loop {
                let parent = self.cx.tcx.hir.get_parent_node(id);
                if id == parent {
                    // no parent
                    return;
                }
                id = parent;

                if let Some(node) = self.cx.tcx.hir.find(id) {
                    match node {
                        map::Node::NodeExpr(e) => {
                            // `match` and `if let`
                            if let ExprMatch(ref c, ..) = e.node {
                                self.spans_need_deref
                                    .entry(vid)
                                    .or_insert_with(HashSet::new)
                                    .insert(c.span);
                            }
                        },

                        map::Node::NodeStmt(s) => {
                            // `let <pat> = x;`
                            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"));
                                }
                            }
                        },

                        _ => {},
                    }
                }
            }
        }
    }
}

impl<'a, 'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> {
    fn consume(&mut self, consume_id: NodeId, consume_span: Span, cmt: mc::cmt<'tcx>, mode: euv::ConsumeMode) {
        if let euv::ConsumeMode::Move(_) = mode {
            self.move_common(consume_id, consume_span, cmt);
        }
    }

    fn matched_pat(&mut self, matched_pat: &Pat, cmt: mc::cmt<'tcx>, mode: euv::MatchMode) {
        if let euv::MatchMode::MovingMatch = mode {
            self.move_common(matched_pat.id, matched_pat.span, cmt);
        } else {
            self.non_moving_pat(matched_pat, cmt);
        }
    }

    fn consume_pat(&mut self, consume_pat: &Pat, cmt: mc::cmt<'tcx>, mode: euv::ConsumeMode) {
        if let euv::ConsumeMode::Move(_) = mode {
            self.move_common(consume_pat.id, consume_pat.span, cmt);
        }
    }

    fn borrow(&mut self, _: NodeId, _: Span, _: mc::cmt<'tcx>, _: ty::Region, _: ty::BorrowKind, _: euv::LoanCause) {}

    fn mutate(&mut self, _: NodeId, _: Span, _: mc::cmt<'tcx>, _: euv::MutateMode) {}

    fn decl_without_init(&mut self, _: NodeId, _: Span) {}
}


fn unwrap_downcast_or_interior(mut cmt: mc::cmt) -> mc::cmt {
    loop {
        match cmt.cat.clone() {
            mc::Categorization::Downcast(c, _) | mc::Categorization::Interior(c, _) => {
                cmt = c;
            },
            _ => return cmt,
        }
    }
}
Commit	Line	Data
ea8adc8c	1	use rustc::hir::*;
abe05a73	2	use rustc::hir::map::*;
ea8adc8c	3	use rustc::hir::intravisit::FnKind;
ea8adc8c	4	use rustc::lint::*;
abe05a73	5	use rustc::ty::{self, RegionKind, TypeFoldable};
ea8adc8c XL	6	use rustc::traits;
	7	use rustc::middle::expr_use_visitor as euv;
	8	use rustc::middle::mem_categorization as mc;
	9	use syntax::ast::NodeId;
	10	use syntax_pos::Span;
	11	use syntax::errors::DiagnosticBuilder;
abe05a73 XL	12	use utils::{get_trait_def_id, implements_trait, in_macro, is_copy, is_self, match_type, multispan_sugg, paths,
	13	snippet, snippet_opt, span_lint_and_then};
	14	use utils::ptr::get_spans;
	15	use std::collections::{HashMap, HashSet};
	16	use std::borrow::Cow;
ea8adc8c XL	17
	18	/// What it does: Checks for functions taking arguments by value, but not
	19	/// consuming them in its
	20	/// body.
	21	///
	22	/// Why is this bad? Taking arguments by reference is more flexible and can
	23	/// sometimes avoid
	24	/// unnecessary allocations.
	25	///
abe05a73 XL	26	/// Known problems:
	27	/// * This lint suggests taking an argument by reference,
	28	/// however sometimes it is better to let users decide the argument type
	29	/// (by using `Borrow` trait, for example), depending on how the function is used.
ea8adc8c XL	30	///
	31	/// Example:
	32	/// ```rust
	33	/// fn foo(v: Vec<i32>) {
	34	/// assert_eq!(v.len(), 42);
	35	/// }
abe05a73 XL	36	/// // should be
	37	/// fn foo(v: &[i32]) {
	38	/// assert_eq!(v.len(), 42);
	39	/// }
ea8adc8c XL	40	/// ```
	41	declare_lint! {
	42	pub NEEDLESS_PASS_BY_VALUE,
	43	Warn,
	44	"functions taking arguments by value, but not consuming them in its body"
	45	}
	46
	47	pub struct NeedlessPassByValue;
	48
	49	impl LintPass for NeedlessPassByValue {
	50	fn get_lints(&self) -> LintArray {
	51	lint_array![NEEDLESS_PASS_BY_VALUE]
	52	}
	53	}
	54
	55	macro_rules! need {
	56	($e: expr) => { if let Some(x) = $e { x } else { return; } };
	57	}
	58
	59	impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
	60	fn check_fn(
	61	&mut self,
	62	cx: &LateContext<'a, 'tcx>,
	63	kind: FnKind<'tcx>,
	64	decl: &'tcx FnDecl,
	65	body: &'tcx Body,
	66	span: Span,
	67	node_id: NodeId,
	68	) {
	69	if in_macro(span) {
	70	return;
	71	}
	72
	73	match kind {
abe05a73 XL	74	FnKind::ItemFn(.., attrs) => for a in attrs {
	75	if_chain! {
	76	if a.meta_item_list().is_some();
	77	if let Some(name) = a.name();
	78	if name == "proc_macro_derive";
	79	then {
ea8adc8c	80	return;
abe05a73	81	}
ea8adc8c XL	82	}
ea8adc8c XL	83	},
abe05a73	84	FnKind::Method(..) => (),
ea8adc8c XL	85	_ => return,
	86	}
	87
abe05a73 XL	88	// Exclude non-inherent impls
	89	if let Some(NodeItem(item)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(node_id)) {
	90	if matches!(item.node, ItemImpl(_, _, _, _, Some(_), _, _) \| ItemAutoImpl(..) \|
	91	ItemTrait(..))
	92	{
	93	return;
	94	}
	95	}
	96
	97	// Allow `Borrow` or functions to be taken by value
ea8adc8c	98	let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
abe05a73 XL	99	let fn_traits = [
	100	need!(cx.tcx.lang_items().fn_trait()),
	101	need!(cx.tcx.lang_items().fn_once_trait()),
	102	need!(cx.tcx.lang_items().fn_mut_trait()),
	103	];
	104
	105	let sized_trait = need!(cx.tcx.lang_items().sized_trait());
ea8adc8c XL	106
	107	let fn_def_id = cx.tcx.hir.local_def_id(node_id);
	108
abe05a73 XL	109	let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
	110	.filter(\|p\| !p.is_global())
	111	.filter_map(\|pred\| {
	112	if let ty::Predicate::Trait(poly_trait_ref) = pred {
	113	if poly_trait_ref.def_id() == sized_trait \|\| poly_trait_ref.skip_binder().has_escaping_regions() {
	114	return None;
	115	}
	116	Some(poly_trait_ref)
	117	} else {
	118	None
	119	}
	120	})
	121	.collect::<Vec<_>>();
ea8adc8c XL	122
	123	// Collect moved variables and spans which will need dereferencings from the
	124	// function body.
	125	let MovedVariablesCtxt {
	126	moved_vars,
	127	spans_need_deref,
	128	..
	129	} = {
	130	let mut ctx = MovedVariablesCtxt::new(cx);
abe05a73 XL	131	let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id);
	132	euv::ExprUseVisitor::new(&mut ctx, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None)
	133	.consume_body(body);
ea8adc8c XL	134	ctx
	135	};
	136
	137	let fn_sig = cx.tcx.fn_sig(fn_def_id);
	138	let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);
	139
abe05a73 XL	140	for (idx, ((input, &ty), arg)) in decl.inputs
	141	.iter()
	142	.zip(fn_sig.inputs())
	143	.zip(&body.arguments)
	144	.enumerate()
	145	{
	146	// All spans generated from a proc-macro invocation are the same...
	147	if span == input.span {
	148	return;
	149	}
ea8adc8c	150
abe05a73 XL	151	// Ignore `self`s.
	152	if idx == 0 {
	153	if let PatKind::Binding(_, _, name, ..) = arg.pat.node {
	154	if name.node.as_str() == "self" {
	155	continue;
	156	}
ea8adc8c	157	}
abe05a73	158	}
ea8adc8c	159
abe05a73 XL	160	// * Exclude a type that is specifically bounded by `Borrow`.
	161	// * Exclude a type whose reference also fulfills its bound.
	162	// (e.g. `std::convert::AsRef`, `serde::Serialize`)
	163	let (implements_borrow_trait, all_borrowable_trait) = {
	164	let preds = preds
	165	.iter()
	166	.filter(\|t\| t.skip_binder().self_ty() == ty)
	167	.collect::<Vec<_>>();
	168
	169	(
	170	preds.iter().any(\|t\| t.def_id() == borrow_trait),
	171	!preds.is_empty() && preds.iter().all(\|t\| {
	172	implements_trait(
	173	cx,
	174	cx.tcx.mk_imm_ref(&RegionKind::ReErased, ty),
	175	t.def_id(),
	176	&t.skip_binder().input_types().skip(1).collect::<Vec<_>>(),
	177	)
	178	}),
	179	)
	180	};
	181
	182	if_chain! {
	183	if !is_self(arg);
	184	if !ty.is_mutable_pointer();
	185	if !is_copy(cx, ty);
	186	if !fn_traits.iter().any(\|&t\| implements_trait(cx, ty, t, &[]));
	187	if !implements_borrow_trait;
	188	if !all_borrowable_trait;
	189
	190	if let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node;
	191	if !moved_vars.contains(&canonical_id);
	192	then {
	193	if mode == BindingAnnotation::Mutable \|\| mode == BindingAnnotation::RefMut {
	194	continue;
ea8adc8c XL	195	}
ea8adc8c XL	196
abe05a73 XL	197	// Dereference suggestion
	198	let sugg = \|db: &mut DiagnosticBuilder\| {
	199	let deref_span = spans_need_deref.get(&canonical_id);
	200	if_chain! {
	201	if match_type(cx, ty, &paths::VEC);
	202	if let Some(clone_spans) =
	203	get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]);
	204	if let TyPath(QPath::Resolved(_, ref path)) = input.node;
	205	if let Some(elem_ty) = path.segments.iter()
	206	.find(\|seg\| seg.name == "Vec")
	207	.and_then(\|ps\| ps.parameters.as_ref())
	208	.map(\|params\| &params.types[0]);
	209	then {
	210	let slice_ty = format!("&[{}]", snippet(cx, elem_ty.span, "_"));
	211	db.span_suggestion(input.span,
	212	"consider changing the type to",
	213	slice_ty);
	214
	215	for (span, suggestion) in clone_spans {
	216	db.span_suggestion(
	217	span,
	218	&snippet_opt(cx, span)
	219	.map_or(
	220	"change the call to".into(),
	221	\|x\| Cow::from(format!("change `{}` to", x)),
	222	),
	223	suggestion.into()
	224	);
	225	}
	226
	227	// cannot be destructured, no need for `*` suggestion
	228	assert!(deref_span.is_none());
	229	return;
	230	}
	231	}
ea8adc8c	232
abe05a73 XL	233	if match_type(cx, ty, &paths::STRING) {
	234	if let Some(clone_spans) =
	235	get_spans(cx, Some(body.id()), idx, &[("clone", ".to_string()"), ("as_str", "")]) {
	236	db.span_suggestion(input.span, "consider changing the type to", "&str".to_string());
	237
	238	for (span, suggestion) in clone_spans {
	239	db.span_suggestion(
	240	span,
	241	&snippet_opt(cx, span)
	242	.map_or(
	243	"change the call to".into(),
	244	\|x\| Cow::from(format!("change `{}` to", x))
	245	),
	246	suggestion.into(),
	247	);
	248	}
	249
	250	assert!(deref_span.is_none());
	251	return;
	252	}
	253	}
	254
	255	let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
	256
	257	// Suggests adding `*` to dereference the added reference.
	258	if let Some(deref_span) = deref_span {
	259	spans.extend(
	260	deref_span
	261	.iter()
	262	.cloned()
	263	.map(\|span\| (span, format!("*{}", snippet(cx, span, "<expr>")))),
	264	);
	265	spans.sort_by_key(\|&(span, _)\| span);
	266	}
	267	multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
	268	};
	269
	270	span_lint_and_then(
	271	cx,
	272	NEEDLESS_PASS_BY_VALUE,
	273	input.span,
	274	"this argument is passed by value, but not consumed in the function body",
	275	sugg,
	276	);
	277	}
	278	}
ea8adc8c XL	279	}
	280	}
	281	}
	282
	283	struct MovedVariablesCtxt<'a, 'tcx: 'a> {
	284	cx: &'a LateContext<'a, 'tcx>,
abe05a73	285	moved_vars: HashSet<NodeId>,
ea8adc8c	286	/// Spans which need to be prefixed with `*` for dereferencing the
abe05a73 XL	287	/// suggested additional reference.
abe05a73 XL	288	spans_need_deref: HashMap<NodeId, HashSet<Span>>,
ea8adc8c XL	289	}
	290
	291	impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
	292	fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
	293	Self {
	294	cx: cx,
	295	moved_vars: HashSet::new(),
	296	spans_need_deref: HashMap::new(),
	297	}
	298	}
	299
	300	fn move_common(&mut self, _consume_id: NodeId, _span: Span, cmt: mc::cmt<'tcx>) {
	301	let cmt = unwrap_downcast_or_interior(cmt);
	302
abe05a73 XL	303	if let mc::Categorization::Local(vid) = cmt.cat {
	304	self.moved_vars.insert(vid);
	305	}
ea8adc8c XL	306	}
	307
	308	fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: mc::cmt<'tcx>) {
	309	let cmt = unwrap_downcast_or_interior(cmt);
	310
abe05a73	311	if let mc::Categorization::Local(vid) = cmt.cat {
ea8adc8c XL	312	let mut id = matched_pat.id;
	313	loop {
	314	let parent = self.cx.tcx.hir.get_parent_node(id);
	315	if id == parent {
	316	// no parent
	317	return;
	318	}
	319	id = parent;
	320
	321	if let Some(node) = self.cx.tcx.hir.find(id) {
	322	match node {
	323	map::Node::NodeExpr(e) => {
	324	// `match` and `if let`
	325	if let ExprMatch(ref c, ..) = e.node {
	326	self.spans_need_deref
abe05a73	327	.entry(vid)
ea8adc8c XL	328	.or_insert_with(HashSet::new)
	329	.insert(c.span);
	330	}
abe05a73	331	},
ea8adc8c XL	332
	333	map::Node::NodeStmt(s) => {
	334	// `let <pat> = x;`
abe05a73 XL	335	if_chain! {
	336	if let StmtDecl(ref decl, _) = s.node;
	337	if let DeclLocal(ref local) = decl.node;
	338	then {
	339	self.spans_need_deref
	340	.entry(vid)
	341	.or_insert_with(HashSet::new)
	342	.insert(local.init
	343	.as_ref()
	344	.map(\|e\| e.span)
	345	.expect("`let` stmt without init aren't caught by match_pat"));
	346	}
	347	}
	348	},
ea8adc8c	349
abe05a73	350	_ => {},
ea8adc8c XL	351	}
	352	}
	353	}
abe05a73	354	}
ea8adc8c XL	355	}
	356	}
	357
	358	impl<'a, 'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> {
	359	fn consume(&mut self, consume_id: NodeId, consume_span: Span, cmt: mc::cmt<'tcx>, mode: euv::ConsumeMode) {
	360	if let euv::ConsumeMode::Move(_) = mode {
	361	self.move_common(consume_id, consume_span, cmt);
	362	}
	363	}
	364
	365	fn matched_pat(&mut self, matched_pat: &Pat, cmt: mc::cmt<'tcx>, mode: euv::MatchMode) {
	366	if let euv::MatchMode::MovingMatch = mode {
	367	self.move_common(matched_pat.id, matched_pat.span, cmt);
	368	} else {
	369	self.non_moving_pat(matched_pat, cmt);
	370	}
	371	}
	372
	373	fn consume_pat(&mut self, consume_pat: &Pat, cmt: mc::cmt<'tcx>, mode: euv::ConsumeMode) {
	374	if let euv::ConsumeMode::Move(_) = mode {
	375	self.move_common(consume_pat.id, consume_pat.span, cmt);
	376	}
	377	}
	378
	379	fn borrow(&mut self, _: NodeId, _: Span, _: mc::cmt<'tcx>, _: ty::Region, _: ty::BorrowKind, _: euv::LoanCause) {}
	380
	381	fn mutate(&mut self, _: NodeId, _: Span, _: mc::cmt<'tcx>, _: euv::MutateMode) {}
	382
	383	fn decl_without_init(&mut self, _: NodeId, _: Span) {}
	384	}
	385
	386
	387	fn unwrap_downcast_or_interior(mut cmt: mc::cmt) -> mc::cmt {
	388	loop {
	389	match cmt.cat.clone() {
abe05a73	390	mc::Categorization::Downcast(c, _) \| mc::Categorization::Interior(c, _) => {
ea8adc8c XL	391	cmt = c;
	392	},
	393	_ => return cmt,
	394	}
	395	}
	396	}