helpers/runJSON: unmarshal JSON

Author: alyraffauf

src/helpers.go

@@ -29,14 +29,11 @@ func loadDeployments(cfg string) (map[string]JobSpec, error) {
 	flakeReference := fmt.Sprintf("%s#nynxDeployments", cfg)
 
 	// Nix -> JSON
-	data, err := runJSON("nix", "eval", "--json", flakeReference)
+	data, err := runJSON[map[string]JobSpec]("nix", "eval", "--json", flakeReference)
 	if err != nil {
 		return nil, fmt.Errorf("failed to run nix eval on %s: %w", cfg, err)
 	}
-	jobs := make(map[string]JobSpec)
-	if err := json.Unmarshal(data, &jobs); err != nil {
-		return nil, fmt.Errorf("invalid JSON in %s: %w", cfg, err)
-	}
+	jobs := data
 
 	// Perform validation and system inference
 	for name, spec := range jobs {
@@ -84,16 +81,22 @@ func run(cmd string, args ...string) ([]byte, error) {
 	return out, nil
 }
 
-func runJSON(cmd string, args ...string) ([]byte, error) {
+func runJSON[T any](cmd string, args ...string) (T, error) {
 	c := exec.Command(cmd, args...)
 	out, err := c.Output() // only capture stdout
 	if err != nil {
+		var zero T
 		if ee, ok := err.(*exec.ExitError); ok {
-			return nil, fmt.Errorf("`%s %v` failed: %s", cmd, args, string(ee.Stderr))
+			return zero, fmt.Errorf("`%s %v` failed: %s", cmd, args, string(ee.Stderr))
 		}
-		return nil, fmt.Errorf("`%s %v` failed: %v", cmd, args, err)
+		return zero, fmt.Errorf("`%s %v` failed: %v", cmd, args, err)
 	}
-	return out, nil
+	var result T
+	if err := json.Unmarshal(out, &result); err != nil {
+		var zero T
+		return zero, fmt.Errorf("failed to unmarshal JSON: %w\nRaw: %s", err, string(out))
+	}
+	return result, nil
 }
 
 func validateOperations(jobs map[string]JobSpec, op string) ([]string, error) {

src/nixbuild.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"encoding/json"
 	"fmt"
 )
 
@@ -11,24 +10,20 @@ type BuildResult struct {
 }
 
 func buildClosure(spec JobSpec, drvPath string, builder string) (string, error) {
-	var buildOut []byte
 	var err error
+	var results []BuildResult
 
 	// Build the closure locally or on the remote builder
 	if builder != "localhost" {
-		buildOut, err = runJSON("nix", "build", "--no-link", "--json", "--store", "ssh-ng://"+builder, drvPath+"^*")
+		results, err = runJSON[[]BuildResult]("nix", "build", "--no-link", "--json", "--store", "ssh-ng://"+builder, drvPath+"^*")
 	} else {
-		buildOut, err = runJSON("nix", "build", "--no-link", "--json", drvPath+"^*")
+		results, err = runJSON[[]BuildResult]("nix", "build", "--no-link", "--json", drvPath+"^*")
 	}
 	if err != nil {
 		return "", fmt.Errorf("failed to build %s on %s: %w", spec.Output, builder, err)
 	}
 
 	// Parse the output path
-	var results []BuildResult
-	if err := json.Unmarshal(buildOut, &results); err != nil {
-		return "", fmt.Errorf("invalid build JSON for %s: %w\nRaw: %s", spec.Output, err, string(buildOut))
-	}
 	if len(results) == 0 {
 		return "", fmt.Errorf("build result for %s was empty", spec.Output)
 	}
@@ -83,14 +78,13 @@ func instantiateDrvPath(flake string, name string, builder string) (string, erro
 	drvExpr := expr + ".drvPath"
 
 	// Evaluate the .drv path locally
-	data, err := runJSON("nix", "eval", "--json", drvExpr)
+	drvPath, err := runJSON[string]("nix", "eval", "--json", drvExpr)
 	if err != nil {
 		return "", fmt.Errorf("failed to evaluate drvPath for job '%s': %w", name, err)
 	}
 
-	var drvPath string
-	if err := json.Unmarshal(data, &drvPath); err != nil {
-		return "", fmt.Errorf("failed to parse JSON for job '%s': %w", name, err)
+	if err != nil {
+		return "", fmt.Errorf("failed to evaluate drvPath for job '%s': %w", name, err)
 	}
 
 	// Copy the .drv to the remote builder (if needed)