cmd/nixbuild: implement dependency resolver

This replaces the bash implementation of this hack.

cmd/nixbuild/format.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"git.gensokyo.uk/yonah/nixbuild"
+)
+
+func formatInstallable(name string, installable *string, flagNixOS bool, args []string) error {
+	if len(args) != 1 {
+		return commandHandlerError(name + " requires exactly 1 argument")
+	}
+
+	*installable = args[0]
+	if !flagNixOS {
+		return nil
+	}
+
+	fields := strings.SplitN(*installable, "#", 2)
+	switch len(fields) {
+	case 2:
+		*installable = nixbuild.NixOSInstallable(fields[0], fields[1])
+		return nil
+	case 1:
+		hostname, err := os.Hostname()
+		if err != nil {
+			return commandHandlerError(fmt.Sprintf("cannot get hostname: %v", err))
+		}
+		*installable = nixbuild.NixOSInstallable(fields[0], hostname)
+		return nil
+	default:
+		return commandHandlerError("unexpected installable")
+	}
+}

cmd/nixbuild/main.go

@@ -9,7 +9,6 @@ import (
 	"os"
 	"os/signal"
 	"slices"
-	"strings"
 	"syscall"
 
 	"git.gensokyo.uk/yonah/nixbuild"
@@ -44,7 +43,7 @@ func main() {
 
 	c.Command("show", command.UsageInternal, func(args []string) error {
 		if len(args) < 1 {
-			return commandHandlerError("usage requires at least 1 argument")
+			return commandHandlerError("show requires at least 1 argument")
 		}
 
 		if drv, err := nixbuild.DerivationShow(ctx, slices.Values(args)); err != nil {
@@ -66,26 +65,57 @@ func main() {
 		return nil
 	})
 
-	c.Command("instantiated", "Evaluate an installable and output all derivations instantiated during evaluation", func(args []string) error {
+	var (
-		if len(args) != 1 {
+		resolveFlagOut string
-			return commandHandlerError("instantiated requires exactly 1 argument")
+	)
+	c.Command("resolve", "Resolve possible build-time dependencies", func(args []string) error {
+		var installable string
+		if err := formatInstallable("resolve", &installable, flagNixOS, args); err != nil {
+			return err
 		}
 
-		installable := args[0]
+		log.Printf("evaluating %s", installable)
-		if flagNixOS {
+		var installables []string
-			fields := strings.SplitN(installable, "#", 2)
+		if v, err := nixbuild.EvalInstantiated(ctx, installable); err != nil {
-			switch len(fields) {
+			return commandHandlerError(fmt.Sprintf("cannot evaluate for instantiated derivations: %v", err))
-			case 2:
+		} else {
-				installable = nixbuild.NixOSInstallable(fields[0], fields[1])
+			installables = v
-			case 1:
+		}
-				hostname, err := os.Hostname()
+
+		log.Println("building instantiated derivations")
+		if err := nixbuild.Build(ctx, slices.Values(installables)); err != nil {
+			return commandHandlerError(fmt.Sprintf("cannot build: %v", err))
+		}
+
+		var collective []string
+		log.Println("collecting store paths")
+		if derivations, err := nixbuild.DerivationShow(ctx, slices.Values(installables)); err != nil {
+			return commandHandlerError(fmt.Sprintf("cannot show: %v", err))
+		} else {
+			collective = nixbuild.CollectFromDerivations(derivations)
+		}
+
+		f, err := os.Create(resolveFlagOut)
 		if err != nil {
-					return commandHandlerError(fmt.Sprintf("cannot get hostname: %v", err))
+			return commandHandlerError(fmt.Sprintf("cannot create store paths file: %v", err))
 		}
-				installable = nixbuild.NixOSInstallable(fields[0], hostname)
+		if flagJSON {
-			default:
+			if err = json.NewEncoder(f).Encode(collective); err != nil {
-				return commandHandlerError("unexpected installable")
+				return commandHandlerError(fmt.Sprintf("cannot serialise JSON: %v", err))
 			}
+		} else {
+			if _, err = nixbuild.WriteStdin(f, slices.Values(collective)); err != nil {
+				return commandHandlerError(fmt.Sprintf("cannot write store path list: %v", err))
+			}
+		}
+		return nil
+	}).
+		Flag(&resolveFlagOut, "o", command.StringFlag("store-paths"), "Path to write collected store paths")
+
+	c.Command("instantiated", "Evaluate an installable and output all derivations instantiated during evaluation", func(args []string) error {
+		var installable string
+		if err := formatInstallable("instantiated", &installable, flagNixOS, args); err != nil {
+			return err
 		}
 
 		if v, err := nixbuild.EvalInstantiated(ctx, installable); err != nil {
@@ -96,13 +126,7 @@ func main() {
 			}
 			return nil
 		} else {
-			for _, drv := range v {
+			_, _ = nixbuild.WriteStdin(os.Stdout, slices.Values(v))
-				if strings.HasSuffix(drv, ".drv") {
-					fmt.Println(drv + "^*")
-				} else {
-					fmt.Println(drv)
-				}
-			}
 			return nil
 		}
 	})