Reuse queries struct

[MartyHub]

Hello,

reading #2607, I can see that sqlc is able to reuse a table struct when generating queries output.
To fix #755, maybe the same process can be extended to allow a query output struct to be reused?

Regards

[andrewmbenton]

This is a nice solution I think, but we should have @kyleconroy weigh in as well.

It's a breaking change, so I think if we do merge this we'll want it behind a configuration parameter like reuse_query_structs or reuse_structs. But that brings up an interesting question I guess. Should we try to have sqlc reuse the query parameter structs as well? A quick search doesn't turn up anyone asking for this in GH issues, but I think it would make sense.

A minor suggestion would be to name the slice of query structs queryStructs instead of structsQueries.

And then one more question, after looking over the testdata output, are you certain that the choice of struct name is deterministic? That is, can we be sure that we're always iterating over the queries in the same order so that the reused struct will always have the same name? I think the answer is yes but just want to be sure.

[MartyHub]

I agree a configuration parameter would be useful to keep compatibility!

Good point regarding deterministic structs iteration order, I'll try to have a look.

Since my PR, I also discovered that it does not play nicely with sqlc.embed, this needs more test cases.

[fnsne]

Hello, @MartyHub
The PR error looks like not add "reuse_structs": false in the internal/endtoend/testdata/process_plugin_sqlc_gen_json/gen/codegen.json.
But I don't know how to help to fixed that.