Lints and suggestions for the Nix programming language
new lint: empty_list_concat (#50)
`[] ++ something` should be reduced to just `something`
Simplify the check
Add unit tests
authored by
Stanisław Pitucha
and committed by
GitHub
cd187b2b
9cb88dd5
+124
-1
+16
bin/tests/data/empty_list_concat.nix
+16
bin/tests/data/empty_list_concat.nix
+2
-1
bin/tests/main.rs
+2
-1
bin/tests/main.rs
+41
bin/tests/snapshots/main__empty_list_concat.snap
+41
bin/tests/snapshots/main__empty_list_concat.snap
···
1
+
---
2
+
source: bin/tests/main.rs
3
+
expression: "&out"
4
+
5
+
---
6
+
[W23] Warning: Unnecessary concatenation with empty list
7
+
╭─[data/empty_list_concat.nix:6:4]
8
+
│
9
+
6 │ ([] ++ [1 2 3])
10
+
· ──────┬──────
11
+
· ╰──────── Concatenation with the empty list, [], is a no-op
12
+
───╯
13
+
[W23] Warning: Unnecessary concatenation with empty list
14
+
╭─[data/empty_list_concat.nix:9:4]
15
+
│
16
+
9 │ ([1 2 3] ++ [])
17
+
· ──────┬──────
18
+
· ╰──────── Concatenation with the empty list, [], is a no-op
19
+
───╯
20
+
[W23] Warning: Unnecessary concatenation with empty list
21
+
╭─[data/empty_list_concat.nix:12:4]
22
+
│
23
+
12 │ ([] ++ [])
24
+
· ────┬───
25
+
· ╰───── Concatenation with the empty list, [], is a no-op
26
+
────╯
27
+
[W23] Warning: Unnecessary concatenation with empty list
28
+
╭─[data/empty_list_concat.nix:15:4]
29
+
│
30
+
15 │ ([] ++ [] ++ [])
31
+
· ───────┬──────
32
+
· ╰──────── Concatenation with the empty list, [], is a no-op
33
+
────╯
34
+
[W23] Warning: Unnecessary concatenation with empty list
35
+
╭─[data/empty_list_concat.nix:15:4]
36
+
│
37
+
15 │ ([] ++ [] ++ [])
38
+
· ────┬───
39
+
· ╰───── Concatenation with the empty list, [], is a no-op
40
+
────╯
41
+
+1
lib/src/lints.rs
+1
lib/src/lints.rs
+64
lib/src/lints/empty_list_concat.rs
+64
lib/src/lints/empty_list_concat.rs
···
1
+
use crate::{session::SessionInfo, Metadata, Report, Rule, Suggestion};
2
+
3
+
use if_chain::if_chain;
4
+
use macros::lint;
5
+
use rnix::{
6
+
types::{BinOp, BinOpKind, List, TypedNode},
7
+
NodeOrToken, SyntaxElement, SyntaxKind, SyntaxNode,
8
+
};
9
+
10
+
/// ## What it does
11
+
/// Checks for concatenations to empty lists
12
+
///
13
+
/// ## Why is this bad?
14
+
/// Concatenation with the empty list is a no-op.
15
+
///
16
+
/// ## Example
17
+
/// ```nix
18
+
/// [] ++ something
19
+
/// ```
20
+
///
21
+
/// Remove the operation:
22
+
///
23
+
/// ```nix
24
+
/// something
25
+
/// ```
26
+
#[lint(
27
+
name = "empty_list_concat",
28
+
note = "Unnecessary concatenation with empty list",
29
+
code = 23,
30
+
match_with = SyntaxKind::NODE_BIN_OP
31
+
)]
32
+
struct EmptyListConcat;
33
+
34
+
impl Rule for EmptyListConcat {
35
+
fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
36
+
if_chain! {
37
+
if let NodeOrToken::Node(node) = node;
38
+
if let Some(bin_expr) = BinOp::cast(node.clone());
39
+
if let Some(lhs) = bin_expr.lhs();
40
+
if let Some(rhs) = bin_expr.rhs();
41
+
if let Some(op) = bin_expr.operator();
42
+
if let BinOpKind::Concat = op;
43
+
then {
44
+
let at = node.text_range();
45
+
let message = "Concatenation with the empty list, `[]`, is a no-op";
46
+
if is_empty_array(&lhs) {
47
+
Some(self.report().suggest(at, message, Suggestion::new(at, rhs)))
48
+
} else if is_empty_array(&rhs) {
49
+
Some(self.report().suggest(at, message, Suggestion::new(at, lhs)))
50
+
} else {
51
+
None
52
+
}
53
+
} else {
54
+
None
55
+
}
56
+
}
57
+
}
58
+
}
59
+
60
+
fn is_empty_array(node: &SyntaxNode) -> bool {
61
+
List::cast(node.clone())
62
+
.map(|list| list.items().count() == 0)
63
+
.unwrap_or_default()
64
+
}