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
39 lines
1.2 KiB
Text
39 lines
1.2 KiB
Text
import Lean
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open Lean Elab Tactic
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macro "obviously1" : tactic => `(tactic| exact sorryAx _ false)
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theorem result1 : False := by obviously1
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elab "obviously2" : tactic =>
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liftMetaTactic1 fun mvarId => mvarId.admit *> pure none
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theorem result2 : False := by obviously2
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/--
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error: failed to synthesize instance of type class
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OfNat Bool 0
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numerals are polymorphic in Lean, but the numeral `0` cannot be used in a context where the expected type is
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Bool
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due to the absence of the instance above
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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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-/
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#guard_msgs in
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def x : Bool := 0
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theorem result3 : False := by obviously2
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/--
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error: failed to synthesize instance of type class
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OfNat Bool 0
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numerals are polymorphic in Lean, but the numeral `0` cannot be used in a context where the expected type is
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Bool
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due to the absence of the instance above
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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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-/
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#guard_msgs in
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theorem result4 : False := by -- Does not generate a `sorry` warning because there is an error
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let x : Bool := 0
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obviously2
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