Auto merge of #81103 - zackmdavis:comma_trail, r=davidtwco
don't suggest erroneous trailing comma after `..`
In #76612, suggestions were added for missing fields in patterns. However, the suggestions are being inserted just at the end
of the last field in the pattern—before any trailing comma after the last field. This resulted in the "if you don't care about missing fields" suggestion to recommend code with a trailing comma after the field ellipsis (`..,`), which is actually not legal ("`..` must be at the end and cannot have a trailing comma")!
Incidentally, the doc-comment on `error_unmentioned_fields` was using `you_cant_use_this_field` as an example field name (presumably copy-paste inherited from the description of Issue #76077), but the present author found this confusing, because unmentioned fields aren't necessarily unusable.
The suggested code in the diff this commit introduces to `destructuring-assignment/struct_destructure_fail.stderr` doesn't work, but it didn't work beforehand, either (because of the "found reserved identifier `_`" thing), so you can't really call it a regression; it could be fixed in a separate PR.
Resolves #78511.
r? `@davidtwco` or `@estebank`
diff --git a/compiler/rustc_typeck/src/check/pat.rs b/compiler/rustc_typeck/src/check/pat.rs
index ecc6e85..79234f0 100644
--- a/compiler/rustc_typeck/src/check/pat.rs
+++ b/compiler/rustc_typeck/src/check/pat.rs
@@ -1486,11 +1486,11 @@
/// Returns a diagnostic reporting a struct pattern which does not mention some fields.
///
/// ```text
- /// error[E0027]: pattern does not mention field `you_cant_use_this_field`
+ /// error[E0027]: pattern does not mention field `bar`
/// --> src/main.rs:15:9
/// |
/// LL | let foo::Foo {} = foo::Foo::new();
- /// | ^^^^^^^^^^^ missing field `you_cant_use_this_field`
+ /// | ^^^^^^^^^^^ missing field `bar`
/// ```
fn error_unmentioned_fields(
&self,
@@ -1524,14 +1524,26 @@
}
_ => return err,
},
- [.., field] => (
- match pat.kind {
- PatKind::Struct(_, [_, ..], _) => ", ",
- _ => "",
- },
- "",
- field.span.shrink_to_hi(),
- ),
+ [.., field] => {
+ // if last field has a trailing comma, use the comma
+ // as the span to avoid trailing comma in ultimate
+ // suggestion (Issue #78511)
+ let tail = field.span.shrink_to_hi().until(pat.span.shrink_to_hi());
+ let tail_through_comma = self.tcx.sess.source_map().span_through_char(tail, ',');
+ let sp = if tail_through_comma == tail {
+ field.span.shrink_to_hi()
+ } else {
+ tail_through_comma
+ };
+ (
+ match pat.kind {
+ PatKind::Struct(_, [_, ..], _) => ", ",
+ _ => "",
+ },
+ "",
+ sp,
+ )
+ }
};
err.span_suggestion(
sp,
diff --git a/src/test/ui/destructuring-assignment/struct_destructure_fail.stderr b/src/test/ui/destructuring-assignment/struct_destructure_fail.stderr
index 81661a3..c0955ef 100644
--- a/src/test/ui/destructuring-assignment/struct_destructure_fail.stderr
+++ b/src/test/ui/destructuring-assignment/struct_destructure_fail.stderr
@@ -32,11 +32,11 @@
|
help: include the missing field in the pattern
|
-LL | Struct { a, b, _ } = Struct { a: 1, b: 2 };
+LL | Struct { a, b _ } = Struct { a: 1, b: 2 };
| ^^^
help: if you don't care about this missing field, you can explicitly ignore it
|
-LL | Struct { a, .., _ } = Struct { a: 1, b: 2 };
+LL | Struct { a, .. _ } = Struct { a: 1, b: 2 };
| ^^^^
error: aborting due to 5 previous errors
diff --git a/src/test/ui/error-codes/E0027.rs b/src/test/ui/error-codes/E0027.rs
index 8d08e17..e7eca1c 100644
--- a/src/test/ui/error-codes/E0027.rs
+++ b/src/test/ui/error-codes/E0027.rs
@@ -3,6 +3,7 @@
age: u32,
}
+
fn main() {
let d = Dog { name: "Rusty".to_string(), age: 8 };
@@ -10,6 +11,14 @@
Dog { age: x } => {} //~ ERROR pattern does not mention field `name`
}
match d {
+ // trailing comma
+ Dog { name: x, } => {} //~ ERROR pattern does not mention field `age`
+ }
+ match d {
+ // trailing comma with weird whitespace
+ Dog { name: x , } => {} //~ ERROR pattern does not mention field `age`
+ }
+ match d {
Dog {} => {} //~ ERROR pattern does not mention fields `name`, `age`
}
}
diff --git a/src/test/ui/error-codes/E0027.stderr b/src/test/ui/error-codes/E0027.stderr
index cf0ff63..694bbc3 100644
--- a/src/test/ui/error-codes/E0027.stderr
+++ b/src/test/ui/error-codes/E0027.stderr
@@ -1,5 +1,5 @@
error[E0027]: pattern does not mention field `name`
- --> $DIR/E0027.rs:10:9
+ --> $DIR/E0027.rs:11:9
|
LL | Dog { age: x } => {}
| ^^^^^^^^^^^^^^ missing field `name`
@@ -13,8 +13,38 @@
LL | Dog { age: x, .. } => {}
| ^^^^
+error[E0027]: pattern does not mention field `age`
+ --> $DIR/E0027.rs:15:9
+ |
+LL | Dog { name: x, } => {}
+ | ^^^^^^^^^^^^^^^^ missing field `age`
+ |
+help: include the missing field in the pattern
+ |
+LL | Dog { name: x, age } => {}
+ | ^^^^^
+help: if you don't care about this missing field, you can explicitly ignore it
+ |
+LL | Dog { name: x, .. } => {}
+ | ^^^^
+
+error[E0027]: pattern does not mention field `age`
+ --> $DIR/E0027.rs:19:9
+ |
+LL | Dog { name: x , } => {}
+ | ^^^^^^^^^^^^^^^^^^ missing field `age`
+ |
+help: include the missing field in the pattern
+ |
+LL | Dog { name: x, age } => {}
+ | ^^^^^
+help: if you don't care about this missing field, you can explicitly ignore it
+ |
+LL | Dog { name: x, .. } => {}
+ | ^^^^
+
error[E0027]: pattern does not mention fields `name`, `age`
- --> $DIR/E0027.rs:13:9
+ --> $DIR/E0027.rs:22:9
|
LL | Dog {} => {}
| ^^^^^^ missing fields `name`, `age`
@@ -28,6 +58,6 @@
LL | Dog { .. } => {}
| ^^^^^^
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors
For more information about this error, try `rustc --explain E0027`.
