Using usql as a library (or subprocess) about usql

[kenshaw]

So: the usql code is very modular, as its constiuent packages don't have many interdependencies (thank you Go!). You could easily conjure up a different frontend that uses the Handler to do exactly what you've described. Please see the main.go and args.go, it's really a trivial amount of code involved.

With regards to completions and a \complete command, please note that completions in usql aren't complete (no pun intended). They currently only work on a few databases, and only complete some entity names. As such, I can't really see how the benefit of a \complete command. You can dig into the code and use the actual completer engine, as it's also modular and completely separable from the usql code.

[astoff]

@kenshaw: Thanks for the explanation. What you describe should work indeed.

Still regarding the use of usql as a library, perhaps you can help me with a question about the build tags (I'm new to Go).

The installation instructions involving go install -tags somedriver github.com/xo/usql work as expected. However, if I create a simple program that imports usql like the one below, the resulting binary is quite small and prints 0; that is, no drivers are linked.

package main

import (
	"fmt"
	"github.com/xo/usql/drivers"
)

func main() {
	available := drivers.Available()
	fmt.Printf("%v\n", len(available))
}

How am I supposed to pass build tags to usql when it is used as a dependency?

[kenshaw]

You don't need the build tags when building it as a library. That's a hack I whipped up to change the configuration at build time, but without needing to modify the source code.

You can manually import any of the drivers you want, via the following:

package main

import (
	"fmt"
	"sort"

	"github.com/xo/usql/drivers"
	_ "github.com/xo/usql/drivers/mysql"
	"golang.org/x/exp/maps"
)

func main() {
	available := drivers.Available()
	keys := maps.Keys(available)
	sort.Strings(keys)
	for _, key := range keys {
		fmt.Println(key)
	}
}

You can import any (or none) of the drivers you'd like to import. Good luck!

[astoff]

Thanks for the hints! My usql integration for Emacs is working; for the record, it can be found here.

As a friendly piece of feedback, I wanted to say again that you like the idea of supporting other types of UIs, it would be nice to provide a dedicated "eval" function. In my case, it was enough to hack into the usql read-eval-print loop and manipulate the strings it receives, but a different situation might have required to copy and adapt the whole of Handler.Run, which is a rather long function. Conceptually, it does both the "E" and "L" of REPL at once.

[kenshaw]

Handler.Run is the entire REPL. A third-party package (github.com/gohxs/readline) is used to actually do the line reading, and other packages within usql handle the bulk of the operations, but it's that Run func that the main hands off to after setting up the environment that does the majority of the the "work".