build: wrap nix build

These things currently require manual testing unfortunately since writing a nix stub would take a long time.

build.go

@@ -0,0 +1,51 @@
+package nixbuild
+
+import (
+	"context"
+	"iter"
+	"strings"
+)
+
+// Build builds all entries yielded by installables.
+func Build(ctx context.Context, installables iter.Seq[string]) error {
+	c, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	cmd := Nix(c, CommandBuild,
+		FlagKeepGoing, FlagNoLink, FlagStdin)
+	if Stdout != nil {
+		cmd.Stdout = Stdout
+		cmd.Args = append(cmd.Args, FlagPrintBuildLogs)
+	} else {
+		cmd.Args = append(cmd.Args, FlagQuiet)
+	}
+	if Stderr != nil {
+		cmd.Stderr = Stderr
+		cmd.Args = append(cmd.Args, FlagVerbose)
+	}
+
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return err
+	}
+
+	if err = cmd.Start(); err != nil {
+		return err
+	}
+
+	for drv := range installables {
+		if strings.HasSuffix(drv, ".drv") {
+			// this is just what nix requires now :c
+			drv += "^*"
+		}
+		if _, err = stdin.Write([]byte(drv + "\n")); err != nil {
+			return err
+		}
+	}
+
+	if err = stdin.Close(); err != nil {
+		return err
+	}
+
+	return cmd.Wait()
+}

cmd/nixbuild/main.go

@@ -8,6 +8,7 @@ import (
 	"log"
 	"os"
 	"os/signal"
+	"slices"
 	"strings"
 	"syscall"
 
@@ -20,6 +21,9 @@ type commandHandlerError string
 func (c commandHandlerError) Error() string { return string(c) }
 
 func main() {
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+
 	var (
 		flagNixOS   bool
 		flagVerbose bool
@@ -38,7 +42,18 @@ func main() {
 		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 {
+	c.Command("build", "Build a list of installables", func(args []string) error {
+		if len(args) < 1 {
+			return commandHandlerError("build requires at least 1 argument")
+		}
+
+		if err := nixbuild.Build(ctx, slices.Values(args)); err != nil {
+			return commandHandlerError(fmt.Sprintf("cannot build: %v", err))
+		}
+		return nil
+	})
+
+	c.Command("instantiated", "Evaluate an installable and output all derivations instantiated during evaluation", func(args []string) error {
 		if len(args) != 1 {
 			return commandHandlerError("instantiated requires exactly 1 argument")
 		}
@@ -60,9 +75,6 @@ func main() {
 			}
 		}
 
-		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 {

format.go

@@ -48,6 +48,13 @@ const (
 	// FlagVersion show version information.
 	FlagVersion = "--version"
 
+	// FlagKeepGoing keep going in case of failed builds, to the greatest extent possible.
+	// That is, if building an input of some derivation fails, Nix will still build the other inputs,
+	// but not the derivation itself.
+	// Without this option, Nix stops if any build fails (except for builds of substitutes),
+	// possibly killing builds in progress (in case of parallel or distributed builds).
+	FlagKeepGoing = "--keep-going"
+
 	// OptionEvalCache whether to use the flake evaluation cache.
 	// Certain commands won’t have to evaluate when invoked for the second time with a particular version of a flake.
 	// Intermediate results are not cached.