3a309ba4eb
This PR improves the error message encountered in the case of a type class instance resolution failure, and adds an error explanation that discusses the common new-user case of binary operation overloading and points to the `trace.Meta.synthInstance` option for advanced debugging. ## Example ```lean4 def f (x : String) := x + x ``` Before: ``` failed to synthesize HAdd String String ?m.5 Hint: Additional diagnostic information may be available using the `set_option diagnostics true` command. ``` After: ``` failed to synthesize instance of type class HAdd String String ?m.5 Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command. Error code: lean.failedToSynthesizeTypeclassInstance [View explanation](https://lean-lang.org/doc/reference/latest/find/?domain=Manual.errorExplanation&name=lean.failedToSynthesizeTypeclassInstance) ``` The error message is changed in three important ways: * Explains *what* failed to synthesize, using the "type class" terminology that's more likely to be recognized than the "instance" terminology * Points to the `trace.Meta.synthInstance` option which is otherwise nearly undiscoverable but is quite powerful (see also leanprover/reference-manual#663 which is adding commentary on this option) * Gives an error explanation link (which won't actually work until the next release after this is merged) which prioritizes the common-case explanation of using the wrong binary operation
18 lines
794 B
Text
18 lines
794 B
Text
setLit.lean:22:19-22:21: error: overloaded, errors
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failed to synthesize instance of type class
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EmptyCollection String
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Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command.
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Fields missing: `bytes`, `isValidUTF8`
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Hint: Add missing fields:
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̲b̲y̲t̲e̲s̲ ̲:̲=̲ ̲_̲
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̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲i̲s̲V̲a̲l̲i̲d̲U̲T̲F̲8̲ ̲:̲=̲ ̲_̲ ̲
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setLit.lean:24:31-24:38: error: overloaded, errors
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failed to synthesize instance of type class
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Singleton Nat String
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Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command.
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24:33 `val` is not a field of structure `String`
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