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in which the unused shorthand field pattern debacle/saga continues
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In e4b1a79 (#47922), we corrected erroneous suggestions for unused
shorthand field pattern bindings, suggesting `field: _` where the
previous suggestion of `_field` wouldn't even have compiled
(#47390). Soon, it was revealed that this was insufficient (#50303), and
the fix was extended to references, slices, &c. (#50327) But even this
proved inadequate, as the erroneous suggestions were still being issued
for patterns in local (`let`) bindings (#50804). Here, we yank the
shorthand-detection and variable/node registration code into a new
common function that can be called while visiting both match arms and
`let` bindings.

Resolves #50804.
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@zackmdavis
zackmdavis committed May 18, 2018
1 parent dfc07a4 commit 59782f4
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Showing 3 changed files with 80 additions and 71 deletions.
106 changes: 50 additions & 56 deletions src/librustc/middle/liveness.rs
View file
Expand Up @@ -117,6 +117,7 @@ use std::io::prelude::*;
use std::io;
use std::rc::Rc;
use syntax::ast::{self, NodeId};
use syntax::ptr::P;
use syntax::symbol::keywords;
use syntax_pos::Span;

Expand Down Expand Up @@ -398,72 +399,65 @@ fn visit_fn<'a, 'tcx: 'a>(ir: &mut IrMaps<'a, 'tcx>,
lsets.warn_about_unused_args(body, entry_ln);
}

fn visit_local<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, local: &'tcx hir::Local) {
local.pat.each_binding(|_, p_id, sp, path1| {
debug!("adding local variable {}", p_id);
fn add_from_pat<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, pat: &P<hir::Pat>) {
// For struct patterns, take note of which fields used shorthand
// (`x` rather than `x: x`).
//
// FIXME: according to the rust-lang-nursery/rustc-guide book, `NodeId`s are to be
// phased out in favor of `HirId`s; however, we need to match the signature of
// `each_binding`, which uses `NodeIds`.
let mut shorthand_field_ids = NodeSet();
let mut pats = VecDeque::new();
pats.push_back(pat);
while let Some(pat) = pats.pop_front() {
use hir::PatKind::*;
match pat.node {
Binding(_, _, _, ref inner_pat) => {
pats.extend(inner_pat.iter());
}
Struct(_, ref fields, _) => {
for field in fields {
if field.node.is_shorthand {
shorthand_field_ids.insert(field.node.pat.id);
}
}
}
Ref(ref inner_pat, _) |
Box(ref inner_pat) => {
pats.push_back(inner_pat);
}
TupleStruct(_, ref inner_pats, _) |
Tuple(ref inner_pats, _) => {
pats.extend(inner_pats.iter());
}
Slice(ref pre_pats, ref inner_pat, ref post_pats) => {
pats.extend(pre_pats.iter());
pats.extend(inner_pat.iter());
pats.extend(post_pats.iter());
}
_ => {}
}
}

pat.each_binding(|_bm, p_id, _sp, path1| {
let name = path1.node;
ir.add_live_node_for_node(p_id, VarDefNode(sp));
ir.add_live_node_for_node(p_id, VarDefNode(path1.span));
ir.add_variable(Local(LocalInfo {
id: p_id,
name,
is_shorthand: false,
is_shorthand: shorthand_field_ids.contains(&p_id)
}));
});
}

fn visit_local<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, local: &'tcx hir::Local) {
add_from_pat(ir, &local.pat);
intravisit::walk_local(ir, local);
}

fn visit_arm<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, arm: &'tcx hir::Arm) {
for mut pat in &arm.pats {
// For struct patterns, take note of which fields used shorthand
// (`x` rather than `x: x`).
//
// FIXME: according to the rust-lang-nursery/rustc-guide book, `NodeId`s are to be
// phased out in favor of `HirId`s; however, we need to match the signature of
// `each_binding`, which uses `NodeIds`.
let mut shorthand_field_ids = NodeSet();
let mut pats = VecDeque::new();
pats.push_back(pat);
while let Some(pat) = pats.pop_front() {
use hir::PatKind::*;
match pat.node {
Binding(_, _, _, ref inner_pat) => {
pats.extend(inner_pat.iter());
}
Struct(_, ref fields, _) => {
for field in fields {
if field.node.is_shorthand {
shorthand_field_ids.insert(field.node.pat.id);
}
}
}
Ref(ref inner_pat, _) |
Box(ref inner_pat) => {
pats.push_back(inner_pat);
}
TupleStruct(_, ref inner_pats, _) |
Tuple(ref inner_pats, _) => {
pats.extend(inner_pats.iter());
}
Slice(ref pre_pats, ref inner_pat, ref post_pats) => {
pats.extend(pre_pats.iter());
pats.extend(inner_pat.iter());
pats.extend(post_pats.iter());
}
_ => {}
}
}

pat.each_binding(|bm, p_id, _sp, path1| {
debug!("adding local variable {} from match with bm {:?}",
p_id, bm);
let name = path1.node;
ir.add_live_node_for_node(p_id, VarDefNode(path1.span));
ir.add_variable(Local(LocalInfo {
id: p_id,
name: name,
is_shorthand: shorthand_field_ids.contains(&p_id)
}));
})
for pat in &arm.pats {
add_from_pat(ir, pat);
}
intravisit::walk_arm(ir, arm);
}
Expand Down
9 changes: 9 additions & 0 deletions src/test/ui/lint/issue-47390-unused-variable-in-struct-pattern.rs
View file
Expand Up @@ -20,6 +20,11 @@ struct SoulHistory {
endless_and_singing: bool
}

struct LovelyAmbition {
lips: usize,
fire: usize
}

#[derive(Clone, Copy)]
enum Large {
Suit { case: () }
Expand All @@ -45,6 +50,10 @@ fn main() {
hours_are_suns = false;
}

let the_spirit = LovelyAmbition { lips: 1, fire: 2 };
let LovelyAmbition { lips, fire } = the_spirit;
println!("{}", lips);

let bag = Large::Suit {
case: ()
};
Expand Down
36 changes: 21 additions & 15 deletions src/test/ui/lint/issue-47390-unused-variable-in-struct-pattern.stderr
View file
@@ -1,5 +1,5 @@
warning: unused variable: `i_think_continually`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:31:9
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:36:9
|
LL | let i_think_continually = 2;
| ^^^^^^^^^^^^^^^^^^^ help: consider using `_i_think_continually` instead
Expand All @@ -12,39 +12,39 @@ LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
= note: #[warn(unused_variables)] implied by #[warn(unused)]

warning: unused variable: `mut_unused_var`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:38:13
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:43:13
|
LL | let mut mut_unused_var = 1;
| ^^^^^^^^^^^^^^ help: consider using `_mut_unused_var` instead

warning: unused variable: `var`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:40:14
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:45:14
|
LL | let (mut var, unused_var) = (1, 2);
| ^^^ help: consider using `_var` instead

warning: unused variable: `unused_var`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:40:19
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:45:19
|
LL | let (mut var, unused_var) = (1, 2);
| ^^^^^^^^^^ help: consider using `_unused_var` instead

warning: unused variable: `corridors_of_light`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:42:26
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:47:26
|
LL | if let SoulHistory { corridors_of_light,
| ^^^^^^^^^^^^^^^^^^ help: try ignoring the field: `corridors_of_light: _`

warning: variable `hours_are_suns` is assigned to, but never used
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:43:30
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:48:30
|
LL | mut hours_are_suns,
| ^^^^^^^^^^^^^^
|
= note: consider using `_hours_are_suns` instead

warning: value assigned to `hours_are_suns` is never read
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:45:9
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:50:9
|
LL | hours_are_suns = false;
| ^^^^^^^^^^^^^^
Expand All @@ -56,44 +56,50 @@ LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
| ^^^^^^
= note: #[warn(unused_assignments)] implied by #[warn(unused)]

warning: unused variable: `fire`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:54:32
|
LL | let LovelyAmbition { lips, fire } = the_spirit;
| ^^^^ help: try ignoring the field: `fire: _`

warning: unused variable: `case`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:54:23
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:63:23
|
LL | Large::Suit { case } => {}
| ^^^^ help: try ignoring the field: `case: _`

warning: unused variable: `case`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:59:24
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:68:24
|
LL | &Large::Suit { case } => {}
| ^^^^ help: try ignoring the field: `case: _`

warning: unused variable: `case`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:64:27
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:73:27
|
LL | box Large::Suit { case } => {}
| ^^^^ help: try ignoring the field: `case: _`

warning: unused variable: `case`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:69:24
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:78:24
|
LL | (Large::Suit { case },) => {}
| ^^^^ help: try ignoring the field: `case: _`

warning: unused variable: `case`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:74:24
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:83:24
|
LL | [Large::Suit { case }] => {}
| ^^^^ help: try ignoring the field: `case: _`

warning: unused variable: `case`
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:79:29
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:88:29
|
LL | Tuple(Large::Suit { case }, ()) => {}
| ^^^^ help: try ignoring the field: `case: _`

warning: variable does not need to be mutable
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:38:9
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:43:9
|
LL | let mut mut_unused_var = 1;
| ----^^^^^^^^^^^^^^
Expand All @@ -108,7 +114,7 @@ LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
= note: #[warn(unused_mut)] implied by #[warn(unused)]

warning: variable does not need to be mutable
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:40:10
--> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:45:10
|
LL | let (mut var, unused_var) = (1, 2);
| ----^^^
Expand Down

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