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Add errorcontext to unmarshalString() #856

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Add errorcontext to unmarshalString() #856

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6 changes: 6 additions & 0 deletions unmarshaler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -979,12 +979,18 @@ func (d *decoder) unmarshalString(value *unstable.Node, v reflect.Value) error {
case reflect.Interface:
v.Set(reflect.ValueOf(string(value.Data)))
default:
ctx := d.errorContext
if ctx != nil && ctx.Struct != nil {
f := ctx.Struct.FieldByIndex(ctx.Field)
return unstable.NewParserErrorWithContext(d.p.Raw(value.Raw), "cannot store TOML string into struct field %s.%s of type %s", f.Name, f.Type, v.Kind())
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Unless I missed something, you should be able to use d.typeMismatchError() to generate an error that resulted from a mismatch between the expected Go type and the type found in the TOML document. It will take care of creating the human readable error based on whether the decoder is targeting a struct.

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Hey @pelletier,

Pardon my ignorance. I'm a newbie. Is there a way to get a human-readable error string when the type of a field mismatches? d.typeMismatchError() is internal, and I can't use it in my code. And, DecodeError.String() is multi-line, which is not something I want.

This is what I'm trying:
If my config looks like this,

[server]
path = "/my/path"
port = 50

and, I read it like this,

if err := toml.NewDecoder(file).Decode(&cfg); err != nil {
    return Cfg{}, fmt.Errorf("load toml: %w", err)
}

I'm getting the error message load toml: cannot store TOML string into a Go int when the port is set to a string. How can I get the error message to mention the field server.port that is causing the problem?

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@arkn98 sorry I didn't see this. You're doing it right; the error message should contain the name of the field causing problem. Seems like this specific error is not constructed properly to include it.

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@arkn98 arkn98 Aug 29, 2023 •
edited
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No worries at all. Your fix seems to work. Let me test it out. Thanks for looking into this!

}
return unstable.NewParserError(d.p.Raw(value.Raw), "cannot store TOML string into a Go %s", v.Kind())
}

return nil
}


func (d *decoder) handleKeyValue(expr *unstable.Node, v reflect.Value) (reflect.Value, error) {
d.strict.EnterKeyValue(expr)

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