Note expr being cast when encounter NonScalar cast error #140787
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Signed-off-by: xizheyin <[email protected]>
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Most of the time this results in a longer message but no extra information, e.g.:
LL | fn main() { let u = 0u32 as (); }
| ^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
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= note: casting expr `0u32` as `()`
It's obvious that 0u32 is cast as (), it's right there above. Is it possible to only add the note when the type being cast to is partially/fully unspecified?
Also, in the issue-73886.rs we see some cases where the type is partially unspecified but the error message doesn't give any extra information:
= note: casting expr `&&[0]` as `&[_]`
= note: casting expr `7u32` as `Option<_>`
It would be nice if the _ were actually expanded here.
BTW, two thumbs up for adding the new test in the first commit and then doing the rest of the changes in the second commit. That makes reviewing easier.
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| if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) { | ||
| err.note(format!( | ||
| "casting expr `{}` as `{}`", |
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Change expr to expression, please.
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Thanks for review ：）
Indeed, it doesn't seem necessary to add duplicate notes for some simple types, and we can add notes when expressions are composite types such as references, for example, are added. However, the type may not be what this PR needs to address, but rather should indicate which expression is being converted.
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Yes, this was handed to me the last time you reviewed my PR, and I've been doing this ever since. |
Signed-off-by: xizheyin <[email protected]>
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| if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) | ||
| && matches!(self.expr.kind, ExprKind::AddrOf(..)) | ||
| { | ||
| err.note(format!("casting reference expression `{}`", snippet)); | ||
| } | ||
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Now, it will emit note only when the expression is &....
| @@ -3,6 +3,8 @@ error[E0605]: non-primitive cast: `&&[i32; 1]` as `&[_]` | |||
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| LL | let _ = &&[0] as &[_]; | |||
| | ^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object | |||
| | | |||
| = note: casting reference expression `&&[0]` | |||
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The explicit note looks like making sense, bacause some body would mistake it as &(&[0] as &[_]) subconsciously.
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Fixes #140491
I added note for
exprso that it doesn't treat&x as Tas&(x as T)but(&x) as T. But I'm not sure if I want to add note for all NonScalar, maybe for specificexpr_ty?r? compiler