fix(config): apply defaults to generators-list entries (PIPE-1493)

cmd/blitz/main.go

@@ -121,6 +121,10 @@ func run(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
+	if err := config.ValidateExclusiveGeneratorConfig(viper.GetViper()); err != nil {
+		return err
+	}
+
 	cfg := config.NewConfig()
 	if err := viper.Unmarshal(cfg); err != nil {
 		return fmt.Errorf("failed to unmarshal config: %w", err)

internal/config/config.go

@@ -40,7 +40,14 @@ func (c *Config) Validate() error {
 	if err := c.Logging.Validate(); err != nil {
 		return err
 	}
-	if err := c.Generator.Validate(); err != nil {
+	if len(c.Generators) > 0 {
+		// Validate the defaulted entries, since that is what runs.
+		for i, g := range c.EffectiveGenerators() {
+			if err := g.Validate(); err != nil {
+				return fmt.Errorf("generators[%d] validation failed: %w", i, err)
+			}
+		}
+	} else if err := c.Generator.Validate(); err != nil {
 		return err
 	}
 	if len(c.Outputs) > 0 {
@@ -70,12 +77,21 @@ func (c *Config) Validate() error {
 
 // EffectiveGenerators returns the list of generators to use.
 // If Generators is set, it takes precedence over the singular Generator field.
+// The singular Generator carries the defaults applied by the override system,
+// so each list entry inherits any field it leaves unset (workers, and so on)
+// from it, while user-set fields win.
 // Comma-separated HostMetrics OS values are expanded into separate generators.
 func (c *Config) EffectiveGenerators() []Generator {
-	if len(c.Generators) > 0 {
-		return expandGenerators(c.Generators)
+	if len(c.Generators) == 0 {
+		return expandGenerators([]Generator{c.Generator})
+	}
+	merged := make([]Generator, len(c.Generators))
+	for i, g := range c.Generators {
+		m := g
+		fillZeroFields(reflect.ValueOf(&m).Elem(), reflect.ValueOf(c.Generator))
+		merged[i] = m
 	}
-	return expandGenerators([]Generator{c.Generator})
+	return expandGenerators(merged)
 }
 
 // EffectiveOutputs returns the list of outputs to use.

internal/config/generator_multi_test.go

@@ -0,0 +1,52 @@
+package config
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEffectiveGenerators_ListEntriesInheritDefaults(t *testing.T) {
+	// c.Generator is the viper-defaulted template (workers filled). A list
+	// entry that omits workers must inherit that default; user-set fields win.
+	cfg := &Config{
+		Generator: Generator{JSON: JSONGeneratorConfig{Workers: 1}},
+		Generators: []Generator{
+			{Type: GeneratorTypeJSON, JSON: JSONGeneratorConfig{Rate: time.Second}},
+		},
+	}
+
+	gens := cfg.EffectiveGenerators()
+	require.Len(t, gens, 1)
+	assert.Equal(t, 1, gens[0].JSON.Workers, "unset workers should inherit the template default")
+	assert.Equal(t, time.Second, gens[0].JSON.Rate, "user-set rate must be preserved")
+}
+
+func TestEffectiveGenerators_ListEntryUserValueOverridesDefault(t *testing.T) {
+	cfg := &Config{
+		Generator: Generator{JSON: JSONGeneratorConfig{Workers: 1}},
+		Generators: []Generator{
+			{Type: GeneratorTypeJSON, JSON: JSONGeneratorConfig{Workers: 8, Rate: time.Second}},
+		},
+	}
+
+	gens := cfg.EffectiveGenerators()
+	assert.Equal(t, 8, gens[0].JSON.Workers, "explicit workers must win over the template default")
+}
+
+func TestValidateExclusiveGeneratorConfig_BothSetFails(t *testing.T) {
+	v := viperFrom(t, "generator:\n  type: json\ngenerators:\n  - type: json\n")
+	require.Error(t, ValidateExclusiveGeneratorConfig(v))
+}
+
+func TestValidateExclusiveGeneratorConfig_OnlyGeneratorsOK(t *testing.T) {
+	v := viperFrom(t, "generators:\n  - type: json\n")
+	require.NoError(t, ValidateExclusiveGeneratorConfig(v))
+}
+
+func TestValidateExclusiveGeneratorConfig_OnlyGeneratorOK(t *testing.T) {
+	v := viperFrom(t, "generator:\n  type: json\n")
+	require.NoError(t, ValidateExclusiveGeneratorConfig(v))
+}

internal/config/output_exclusive.go

@@ -18,6 +18,13 @@ func ValidateExclusiveOutputConfig(v *viper.Viper) error {
 	return rejectBothForms(v, "output", "outputs")
 }
 
+// ValidateExclusiveGeneratorConfig rejects a config that sets both the
+// singular `generator` and the plural `generators`, the same ambiguity the
+// output check guards against.
+func ValidateExclusiveGeneratorConfig(v *viper.Viper) error {
+	return rejectBothForms(v, "generator", "generators")
+}
+
 // rejectBothForms errors when both the singular and plural forms of a config
 // key are present in the parsed config. Shared by the output check here and,
 // later, the generator/generators check.