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Fix miscounting fields when from and backtrace are same field

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This commit is contained in:
David Tolnay 2021-12-18 11:41:04 -08:00
parent 8602ca3dd2
commit c4d7c2b135
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2 changed files with 8 additions and 4 deletions
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6
impl/src/valid.rs
View file

@ -180,7 +180,11 @@ fn check_field_attrs(fields: &[Field]) -> Result<()> {
}
}
if let Some(from_field) = from_field {
if fields.len() > 1 + has_backtrace as usize {
let max_expected_fields = match backtrace_field {
Some(backtrace_field) => 1 + !same_member(from_field, backtrace_field) as usize,
None => 1 + has_backtrace as usize,
};
if fields.len() > max_expected_fields {
return Err(Error::new_spanned(
from_field.attrs.from,
"deriving From requires no fields other than source and backtrace",

6
tests/ui/from-backtrace-backtrace.stderr
View file

@ -1,5 +1,5 @@
error[E0063]: missing field `1` in initializer of `Error`
--> tests/ui/from-backtrace-backtrace.rs:10:12
error: deriving From requires no fields other than source and backtrace
--> tests/ui/from-backtrace-backtrace.rs:10:18
|
10 | pub struct Error(#[from] #[backtrace] std::io::Error, Backtrace);
| ^^^^^ missing `1`
| ^^^^^^^