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Fix suggestion for let <pat>
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@sinkuu
sinkuu committed Feb 20, 2017
1 parent 263e60c commit 627d24c
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Showing 3 changed files with 109 additions and 69 deletions.
151 changes: 89 additions & 62 deletions clippy_lints/src/needless_pass_by_value.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ 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,
paths};
use std::collections::{HashSet, HashMap};
Expand Down Expand Up @@ -59,7 +60,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
return;
}

// These are usually passed by value and only used by reference
// Allows these to be passed by value.
let fn_trait = cx.tcx.lang_items.fn_trait().expect("failed to find `Fn` trait");
let asref_trait = get_trait_def_id(cx, &paths::ASREF_TRAIT).expect("failed to find `AsRef` trait");
let borrow_trait = get_trait_def_id(cx, &paths::BORROW_TRAIT).expect("failed to find `Borrow` trait");
Expand All @@ -71,8 +72,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
.collect()
};

// Collect moved variables and non-moving usages at `match`es from the function body
let MovedVariablesCtxt { moved_vars, non_moving_matches, .. } = {
// 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 infcx = cx.tcx.borrowck_fake_infer_ctxt(body.id());
{
Expand Down Expand Up @@ -119,11 +120,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
continue;
}

span_lint_and_then(cx,
NEEDLESS_PASS_BY_VALUE,
input.span,
"this argument is passed by value, but not consumed in the function body",
|db| {
// Suggestion logic
let sugg = |db: &mut DiagnosticBuilder| {
if_let_chain! {[
match_type(cx, ty, &paths::VEC),
let TyPath(QPath::Resolved(_, ref path)) = input.node,
Expand All @@ -148,24 +146,27 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
format!("&{}", snippet(cx, input.span, "_")));
}

// For non-moving consumption at `match`es,
// suggests adding `*` to dereference the added reference.
// e.g. `match x { Some(_) => 1, None => 2 }`
// -> `match *x { .. }`
if let Some(matches) = non_moving_matches.get(&defid) {
for (i, m) in matches.iter().enumerate() {
if let ExprMatch(ref e, ..) = cx.tcx.hir.expect_expr(*m).node {
db.span_suggestion(e.span,
if i == 0 {
"...and dereference it here"
} else {
"...and here"
},
format!("*{}", snippet(cx, e.span, "<expr>")));
}
// Suggests adding `*` to dereference the added reference.
if let Some(spans) = spans_need_deref.get(&defid) {
let mut spans: Vec<_> = spans.iter().cloned().collect();
spans.sort();
for (i, span) in spans.into_iter().enumerate() {
db.span_suggestion(span,
if i == 0 {
"...and dereference it here"
} else {
"...and here"
},
format!("*{}", snippet(cx, span, "<expr>")));
}
}
});
};

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);
}}
}
}
Expand All @@ -174,15 +175,17 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
struct MovedVariablesCtxt<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
moved_vars: HashSet<DefId>,
non_moving_matches: HashMap<DefId, HashSet<NodeId>>,
/// Spans which need to be prefixed with `*` for dereferencing the suggested additional
/// reference.
spans_need_deref: HashMap<DefId, HashSet<Span>>,
}

impl<'a, 'tcx: 'a> MovedVariablesCtxt<'a, 'tcx> {
fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
MovedVariablesCtxt {
cx: cx,
moved_vars: HashSet::new(),
non_moving_matches: HashMap::new(),
spans_need_deref: HashMap::new(),
}
}

Expand All @@ -196,6 +199,57 @@ impl<'a, 'tcx: 'a> MovedVariablesCtxt<'a, 'tcx> {
self.moved_vars.insert(def_id);
}}
}

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),
], {
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(def_id)
.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"));
}}
}

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

impl<'a, 'tcx: 'a> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> {
Expand All @@ -209,27 +263,7 @@ impl<'a, 'tcx: 'a> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> {
if let euv::MatchMode::MovingMatch = mode {
self.move_common(matched_pat.id, matched_pat.span, cmt);
} else {
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),
], {
// Find the `ExprMatch` which contains this pattern
let mut match_id = matched_pat.id;
loop {
match_id = self.cx.tcx.hir.get_parent_node(match_id);
if_let_chain! {[
let Some(map::Node::NodeExpr(e)) = self.cx.tcx.hir.find(match_id),
let ExprMatch(..) = e.node,
], {
break;
}}
}

self.non_moving_matches.entry(def_id).or_insert_with(HashSet::new)
.insert(match_id);
}}
self.non_moving_pat(matched_pat, cmt);
}
}

Expand All @@ -241,25 +275,18 @@ impl<'a, 'tcx: 'a> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> {

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

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

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


Expand Down
10 changes: 6 additions & 4 deletions tests/ui/needless_pass_by_value.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
#![plugin(clippy)]

#![deny(needless_pass_by_value)]
#![allow(dead_code, single_match)]
#![allow(dead_code, single_match, if_let_redundant_pattern_matching, many_single_char_names)]

// `v` should be warned
// `w`, `x` and `y` are allowed (moved or mutated)
Expand Down Expand Up @@ -49,10 +49,12 @@ fn test_match(x: Option<Option<String>>, y: Option<Option<String>>) {
};
}

// x should be warned, but y is ok
fn test_destructure(x: Wrapper, y: Wrapper) {
let Wrapper(s) = y; // moved
// x and y should be warned, but z is ok
fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
let Wrapper(s) = z; // moved
let Wrapper(ref t) = y; // not moved
assert_eq!(x.0.len(), s.len());
println!("{}", t);
}

fn main() {}
17 changes: 14 additions & 3 deletions tests/ui/needless_pass_by_value.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -53,11 +53,22 @@ help: ...and dereference it here
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:53:24
|
53 | fn test_destructure(x: Wrapper, y: Wrapper) {
53 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
| ^^^^^^^
|
help: consider taking a reference instead
| fn test_destructure(x: &Wrapper, y: Wrapper) {
| fn test_destructure(x: &Wrapper, y: Wrapper, z: Wrapper) {

error: aborting due to 6 previous errors
error: this argument is passed by value, but not consumed in the function body
--> $DIR/needless_pass_by_value.rs:53:36
|
53 | fn test_destructure(x: Wrapper, y: Wrapper, z: Wrapper) {
| ^^^^^^^
|
help: consider taking a reference instead
| fn test_destructure(x: Wrapper, y: &Wrapper, z: Wrapper) {
help: ...and dereference it here
| let Wrapper(ref t) = *y; // not moved

error: aborting due to 7 previous errors

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