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
27 lines
870 B
Text
27 lines
870 B
Text
macroStack.lean:4:5-4:6: error(lean.unknownIdentifier): Unknown identifier `x`
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macroStack.lean:8:6-8:7: error: Unknown identifier `x`
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with resulting expansion
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binrel% GT.gt✝ x 0
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while expanding
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x > 0
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while expanding
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(x > 0)
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while expanding
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if h : (x > 0) then 1 else 0
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macroStack.lean:11:9-11:15: error: invalid use of `(<- ...)`, must be nested inside a 'do' expression
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macroStack.lean:17:0-17:6: error: failed to synthesize instance of type class
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HAdd Nat String ?m
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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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with resulting expansion
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binop% HAdd.hAdd✝ (x + x✝) x✝¹
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while expanding
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(x + x✝) + x✝¹
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while expanding
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foo!(x + x✝)
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while expanding
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foo!(x + x✝) < 1
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while expanding
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if foo!(x + x✝) < 1 then true✝ else false✝
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while expanding
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bla! x
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