3b58a7d36b
This PR improves a confusing error message that occurred when attempting to project from a zero-field structure. Closes #9312
31 lines
572 B
Text
31 lines
572 B
Text
/-!
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# Projections on types without fields
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https://github.com/leanprover/lean4/issues/9312
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Ensures that a suitable error message is displayed when attempting to project from a type that has
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no fields.
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-/
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structure MyEmpty where
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/--
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error: Invalid projection: Projections are not supported on this type because it has no fields
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{ }
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has type
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MyEmpty
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-/
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#guard_msgs in
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#check (MyEmpty.mk).1
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inductive T where
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/--
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error: Invalid projection: Projections are not supported on this type because it has no fields
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T.a
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has type
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T
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-/
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#guard_msgs in
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#check (T.a).1
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