internal/codegen: add Enum.Valid and AllEnumValues

[josharian]

This commit adds a Valid method for enum types
and an All...Values function to get all enum values.

This makes it easier to work with enums.

Fixes #1607

[kyleconroy]

Thanks for making a first pass at this. A few things before this is ready to merge.

For enums with many values, the generated code takes up a large amount of horizontal space. Can we put each enum on its own line for both methods?

func (e BooksBookType) Valid() bool {
	switch e {
	case BooksBookTypeFICTION:
		return true
	case BooksBookTypeNONFICTION:
		return true
	}
	return false
}

func AllBooksBookTypeValues() []BooksBookType {
	return []BooksBookType{
		BooksBookTypeFICTION,
		BooksBookTypeNONFICTION,
	}
}

This feature has only been requested by a few people. I'd like to put both behind a feature flag. Let's go with emit_enum_valid_method and emit_all_enum_values. I know the emit prefixes are a bit weird, but it's what we use for other options.

[josharian]

Can we put each enum on its own line for both methods?

We can, although for the Valid method the compiler will generate better code if we can make them part of a single case statement, so it can unify the return statements. (That's also the reason not to write the code return e == EnumA || e == EnumB || ... || e == EnumX.)

What do you think about this:

func (e BooksBookType) Valid() bool {
	switch e {
	case BooksBookTypeFICTION,
                 BooksBookTypeNONFICTION:
		return true
	}
	return false
}

It's also not too hard to put (say) 4 items on a line, which might be nicer yet. WDYT?

[kyleconroy]

I think it's more straightforward to put one on each line. The comma style with a single case statement looks good to me.

[josharian]

OK, there's now one per line. Go's templates sure don't make that easy.

This is now gated by config parameters. There's a surprising amount required to add a config parameter; I hope I didn't miss anything.

There is also an additional commit to make debugging regeneration failures easier to diagnose. (I'd like to do https://twitter.com/commaok/status/1345977948453490688 as well, but this is a good first start.)

[jakoguta]

The test data emit_enum_valid_and_values added is for PostgreSQL. I recommend we put them in the folder postgresql/pgx.

[josharian]

The test data emit_enum_valid_and_values added is for PostgreSQL. I recommend we put them in the folder postgresql/pgx.

Genuine question: Does it matter? This codegen change is DB-agnostic.

[josharian]

Ping.

What expectations should I have for review and issue comment turnaround time? It’d be useful to know so that I can plan accordingly and also not pester pointlessly.

[kyleconroy]

One small issue in the regen script, going to merge anyways

[kyleconroy]

out is a byte slice, so I think this will print out gibberish.

[josharian]

If the verb were %v then it would. With %s it prints as a string.