Closed
Description
Summary
collapisble_match warning gives an incorrect suggestion for code that cannot compile. Even with some tweaks, I haven't been able to compress the statement.
I suspect the syn crate may be doing something interesting, but I haven't investigated it deeply.
Lint Name
collapsible_match
Reproducer
I tried this code:
use syn::{parse, Field, Type, Expr, Result, ExprLit, Lit, TypePath};
pub fn parse_type(field: &Field, ft: Type) -> Result<(TypePath, usize)> {
match ft {
Type::Array(a) => {
let mut size: usize = 0;
if let Expr::Lit(ExprLit { lit, .. }) = a.len {
if let = lit {
if let Ok(num) = lit.base10_parse::<usize>() {
size = num;
}
}
}
if size == 0 {
Err(
parse::Error::new(field.ident.as_ref().unwrap().span(), "`#[gen_hid_descriptor]` array has invalid length")
)
} else {
Ok((parse_type(field, *a.elem)?.0, size))
}
}
Type::Path(p) => {
Ok((p, 1))
}
_ => {
Err(
parse::Error::new(field.ident.as_ref().unwrap().span(),"`#[gen_hid_descriptor]` cannot handle field type")
)
}
}
}I saw this happen:
warning: this `if let` can be collapsed into the outer `if let`
--> src/main.rs:13:17
|
13 | / if let Lit::Int(lit) = lit {
14 | | if let Ok(num) = lit.base10_parse::<usize>() {
15 | | size = num;
16 | | }
17 | | }
| |_________________^
|
help: the outer pattern can be modified to include the inner pattern
--> src/main.rs:12:40
|
12 | if let Expr::Lit(ExprLit { lit, .. }) = a.len {
| ^^^ replace this binding
13 | if let Lit::Int(lit) = lit {
| ^^^^^^^^^^^^^ with this pattern
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match
= note: `#[warn(clippy::collapsible_match)]` on by default
warning: `collapsible_match` (bin "collapsible_match") generated 1 warning
Finished dev [unoptimized + debuginfo] target(s) in 0.09s
I changed the code to the suggestion:
if let Expr::Lit(ExprLit { Lit::Int(lit), .. }) = a.len {
if let Ok(num) = lit.base10_parse::<usize>() {
size = num;
}
}This happened:
Checking collapsible_match v0.1.0 (/home/hyatt/git/examples/collapsible_match)
error: expected `,`
--> src/main.rs:11:43
|
11 | if let Expr::Lit(ExprLit { Lit::Int(lit), .. }) = a.len {
| ------- ^^
| |
| while parsing the fields for this pattern
error[E0425]: cannot find value `lit` in this scope
--> src/main.rs:12:38
|
12 | if let Ok(num) = lit.base10_parse::<usize>() {
| ^^^ help: a function with a similar name exists: `Lit`
|
::: /home/hyatt/.cargo/registry/src/github.colasdn.workers.dev-1ecc6299db9ec823/syn-1.0.102/src/lit.rs:733:1
|
733 | pub fn Lit(marker: lookahead::TokenMarker) -> Lit {
| ------------------------------------------------- similarly named function `Lit` defined here
warning: unused import: `Lit`
--> src/main.rs:1:54
|
1 | use syn::{parse, Field, Type, Expr, Result, ExprLit, Lit, TypePath};
| ^^^
|
= note: `#[warn(unused_imports)]` on by default
For more information about this error, try `rustc --explain E0425`.
warning: `collapsible_match` (bin "collapsible_match") generated 1 warning
error: could not compile `collapsible_match` due to 2 previous errors; 1 warning emitted
Version
rustc 1.66.0-nightly (6b3ede3f7 2022-10-13)
binary: rustc
commit-hash: 6b3ede3f7bc502eba7bbd202b4b9312d812adcd7
commit-date: 2022-10-13
host: x86_64-unknown-linux-gnu
release: 1.66.0-nightly
LLVM version: 15.0.2
Additional Labels
@rustbot label +l-suggestion-causes-error