Ben KraftandGitHub
4c38cb7759
## Summary: In this commit I begin the journey to add the long-awaited support for interfaces (part of #8). Well, it's not the beginning: I already had some half-written broken code around. But it's the first fully functional support, and especially, the first *tested* support; it's probably best to review the nontrivially-changed code as if it were new. Conceptually, the code so far is pretty simple: we generate an interface type, and the implementations. (That code is in fact mostly unchanged.) The complexity comes in because encoding/json doesn't know how to unmarshal that. So we have to add an UnmarshalJSON method, which actually has to be on the types with interface-type fields, that knows how. I factored it into two methods, such that that UnmarshalJSON method is just glue, and then there's a separate function, corresponding to each interface-type, that actually does all the work. (If only one could just write it as an actual method!) The method uses the same trick suggested to me by a few others in another context to deserialize all but one field, then handle that field specially, which is discussed in the code. This still has some limitations, which will be lifted in future commits: - it doesn't allow for list-of-interface fields - it requires that you manually ask for `__typename` - it doesn't support fragments, i.e. you can only query for interface fields, not concrete-type-specific ones But it works, even in integration tests, which is progress! As a part of this, I added a proper config option for the "allow broken features" flag, since I need to be able to set it from the integration tests which are in a separate package (and actually shell out via `go generate`). I also renamed what was to be the first case (InterfaceNoFragments), and replaced it with a further-simplified version (avoiding list-of-interface fields. [1] https://github.com/benjaminjkraft/notes/blob/master/go-json-interfaces.md Issue: https://github.com/Khan/genqlient/issues/8 ## Test plan: make tesc Author: benjaminjkraft Reviewers: dnerdy, benjaminjkraft, aberkan, csilvers, MiguelCastillo Required Reviewers: Approved by: dnerdy Checks: ⌛ Test (1.17), ✅ Test (1.16), ⌛ Test (1.15), ⌛ Test (1.14), ⌛ Test (1.13), ✅ Lint, ✅ Test (1.17), ⌛ Test (1.16), ⌛ Test (1.15), ⌛ Test (1.14), ⌛ Test (1.13), ✅ Lint Pull request URL: https://github.com/Khan/genqlient/pull/52
44 lines
1.7 KiB
Cheetah
44 lines
1.7 KiB
Cheetah
{{/* (the blank lines at the start are intentional, to separate
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UnmarshalJSON from the function it follows) */}}
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func (v *{{.GoName}}) UnmarshalJSON(b []byte) error {
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{{/* We want to specially handle the abstract fields (.AbstractFields),
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but unmarshal everything else normally. To handle abstract fields,
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first we unmarshal them into a json.RawMessage, and then handle those
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further, below. For the rest, we just want to call json.Unmarshal.
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But if we do that naively on a value of type `.Type`, it will call
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this function again, and recurse infinitely. So we make a wrapper
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type -- with a different name, thus different methods, but the same
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fields, and unmarshal into that. For more on why this is so
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difficult, see
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https://github.com/benjaminjkraft/notes/blob/master/go-json-interfaces.md
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TODO(benkraft)): Ensure `{{.Type}}Wrapper` won't collide with any
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other type we need. (For the most part it being locally-scoped saves
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us; it's not clear if this can be a problem in practice.)
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*/}}
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type {{.GoName}}Wrapper {{.GoName}}
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var firstPass struct{
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*{{.GoName}}Wrapper
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{{range .AbstractFields -}}
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{{.GoName}} {{ref "encoding/json.RawMessage"}} `json:"{{.JSONName}}"`
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{{end}}
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}
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firstPass.{{.GoName}}Wrapper = (*{{.GoName}}Wrapper)(v)
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err := {{ref "encoding/json.Unmarshal"}}(b, &firstPass)
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if err != nil {
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return err
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}
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{{/* Now, for each field, call out to the unmarshal-helper. */}}
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{{range .AbstractFields -}}
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err = __unmarshal{{.GoType.Reference}}(
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&v.{{.GoName}}, firstPass.{{.GoName}})
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if err != nil {
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return err
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}
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{{end}}
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return nil
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}
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