feature: export functions and remove internal package

[switchupcb]

How can you increase the library's usage and contributions?

Problem

You are limiting the library's usage and contributions by using an internal package and unexported functions.

dbgo uses a modified version of jet to interpret a Go file and output type-safe SQL.

Here are the issues experienced while implementing this functionality:

1. Use of internal: Using jet programmatically with an interpreter requires you to use functions which reference internal, when functions in an internal package cannot be referenced. So, the developer must rename the entire internal package to use jet with an interpreter.
2. Unexported functions
   1. genTemplate is unexported which requires the developer to inline a definition or export the function to use jet programmatically.
   2. postgres package contains unexported functions which requires the developer to export them when using jet with an interpreter.

Implementation

You can increase the library's usage and contributions by replacing the internal package and exporting certain unexported functions.

https://github.com/switchupcb/jet/tree/dbgo is a version of jet which has these problems fixed for PostgreSQL functionality.

Implementation: Internal Usage

The solution to this problem requires further discussion among maintainers.

Implementation: Export Unexported Functions

You can approve the decision to export unexported fuinctions required for usage of jet in an interpreter (e.g., functions in import "github.com/go-jet/jet/v2/postgres") and I can create a pull request to solve this problem.

Here are example commits:

• switchupcb@1ba2f4d
• switchupcb@26ee4c5

[go-jet]

If everything is exported, then everything becomes part of the public API, which limits maintainability. For instance if we need to refactor something which is often the case, we might break someones build.

There might be cases where certain elements aren't exported and they should, but these will be evaluated individually.

Making everything public is out of question.

[switchupcb]

There might be cases where certain elements aren't exported and they should, but these will be evaluated individually.
— @go-jet

What is the evaluation of the exporting the unexported functions listed in the original issue?

1. genTemplate functions for MySQL, SQLITE, and Postgres to call Generate
2. functions in import "github.com/go-jet/jet/v2/postgres" (example commits provided)

— @switchupcb

[go-jet]

genTemplate functions for MySQL, SQLITE, and Postgres to call Generate

genTemplate in ./cmd/jet/main.go ?

functions in import "github.com/go-jet/jet/v2/postgres" (example commits provided)

windowExpand - is not an expression, just start of building an expression, so it doesn't make sense to export it.

[switchupcb]

genTemplate in ./cmd/jet/main.go ?
— @go-jet

You cannot call Generate from programmatic usage of jet without defining a template.Template.

jet/generator/postgres/postgres_generator.go

Line 40 in fb7c376

return GenerateDSN(dsn, dbConn.SchemaName, destDir, genTemplate...)

There is no documentation explaining how to define a template other than genTemplate, which is returned as a parameter from an exported function GenerateDSN.

jet/cmd/jet/main.go

Line 242 in fb7c376

func genTemplate(dialect jet.Dialect, ignoreTables []string, ignoreViews []string, ignoreEnums []string) template.Template {

Here is how jet defines a template using the unexported function.

jet/cmd/jet/main.go

Line 101 in fb7c376

generatorTemplate := genTemplate(postgres2.Dialect, ignoreTablesList, ignoreViewsList, ignoreEnumsList)

[switchupcb]

windowExpand - is not an expression, just start of building an expression, so it doesn't make sense to export it.
— @go-jet

When does exporting a struct required to implement an exported interface make sense?

Nothing can implement a jet.SelectStatement interface because windowExpand is returned from a function referenced by the exported SelectStatement interface.

• The same logic applies to fetchExpand.

jet/postgres/select_statement.go

Line 42 in fb7c376

type SelectStatement interface {