Detect bad number of generics caused by bad derive - #160695
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HIR ty lowering was modified cc @fmease |
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When a derive macro expands the annotated item's name directly using `quote!`, it keep the item's Span context (instead of having a new context). This means that the generic Span context machinery which provides feedback that an error happened due to a derive doesn't kick in. If a derive macro isn't written to take into account the existence of type parameters, an error for "mismatched number of type parameters" will be emitted. We now detect the case when this happens due to the derive macro, and customize the output to point that out, as well as avoid giving suggestions that will always be wrong.
CenTdemeern1
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| "it looks like this derive macro might not support annotating items with type \ | ||
| parameters", | ||
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it might be more accurate to say "generic parameters" as this applies to the other types of generic parameters too (lifetimes, const params)
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When a derive macro expands the annotated item's name directly using
quote!, it keep the item's Span context (instead of having a new context). This means that the generic Span context machinery which provides feedback that an error happened due to a derive doesn't kick in.If a derive macro isn't written to take into account the existence of type parameters, an error for "mismatched number of type parameters" will be emitted. We now detect the case when this happens due to the derive macro, and customize the output to point that out, as well as avoid giving suggestions that will always be wrong.
Partially address #160463 (this doesn't detect a nameres error caused by referencing type parameter within a derive).
r? @petrochenkov