cmd/nixbuild: implement command frontend

.gitignore

@@ -5,6 +5,7 @@
 *.so
 *.dylib
 *.pkg
+/nixbuild
 
 # Test binary, built with `go test -c`
 *.test

cmd/nixbuild/main.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+
+	"git.gensokyo.uk/yonah/nixbuild"
+	"hakurei.app/command"
+)
+
+type commandHandlerError string
+
+func (c commandHandlerError) Error() string { return string(c) }
+
+func main() {
+	var (
+		flagNixOS   bool
+		flagVerbose bool
+		flagJSON    bool
+	)
+	c := command.New(os.Stderr, log.Printf, "nixbuild", func(args []string) error {
+		log.SetFlags(0)
+		log.SetPrefix("nixbuild: ")
+		nixbuild.Stdout = os.Stdout
+		if flagVerbose {
+			nixbuild.Stderr = os.Stderr
+		}
+		return nil
+	}).
+		Flag(&flagNixOS, "nixos", command.BoolFlag(false), "Interpret input as NixOS flake installable").
+		Flag(&flagVerbose, "v", command.BoolFlag(false), "Connect nix stderr").
+		Flag(&flagJSON, "json", command.BoolFlag(false), "Serialise output in JSON when applicable")
+
+	c.Command("instantiated", "Evaluate an installable and output all derivations it instantiated", func(args []string) error {
+		if len(args) != 1 {
+			return commandHandlerError("instantiated requires exactly 1 argument")
+		}
+
+		installable := args[0]
+		if flagNixOS {
+			fields := strings.SplitN(installable, "#", 2)
+			switch len(fields) {
+			case 2:
+				installable = nixbuild.NixOSInstallable(fields[0], fields[1])
+			case 1:
+				hostname, err := os.Hostname()
+				if err != nil {
+					return commandHandlerError(fmt.Sprintf("cannot get hostname: %v", err))
+				}
+				installable = nixbuild.NixOSInstallable(fields[0], hostname)
+			default:
+				return commandHandlerError("unexpected installable")
+			}
+		}
+
+		ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+		defer stop()
+
+		if v, err := nixbuild.EvalInstantiated(ctx, installable); err != nil {
+			return commandHandlerError(fmt.Sprintf("cannot evaluate for instantiated derivations: %v", err))
+		} else if flagJSON {
+			if err = json.NewEncoder(os.Stdout).Encode(v); err != nil {
+				return commandHandlerError(fmt.Sprintf("cannot serialise JSON: %v", err))
+			}
+			return nil
+		} else {
+			for _, drv := range v {
+				if strings.HasSuffix(drv, ".drv") {
+					fmt.Println(drv + "^*")
+				} else {
+					fmt.Println(drv)
+				}
+			}
+			return nil
+		}
+	})
+
+	c.MustParse(os.Args[1:], func(err error) {
+		var ce commandHandlerError
+		if errors.As(err, &ce) {
+			log.Fatal(ce.Error())
+			return
+		}
+		log.Fatalf("cannot parse command: %v", err)
+	})
+}

go.mod

@@ -1,3 +1,5 @@
 module git.gensokyo.uk/yonah/nixbuild
 
 go 1.24.4
+
+require hakurei.app v0.1.1

go.sum

@@ -0,0 +1,2 @@
+hakurei.app v0.1.1 h1:b1ooWWIdvvBRj0BCOmK2wLfVs3nvYbxEHtQX5DP6bos=
+hakurei.app v0.1.1/go.mod h1:bWcF0vCO+ZOtZ2zK7L3e08sNb0kIkv1CBcdWTZtu1Gs=