Fix all golangci-lint errcheck and unused warnings

- Wrap defer resp.Body.Close() to capture error
- Ignore json.Unmarshal error in valueAny (best-effort)
- Check enc.Encode and os.Stdout.Write return values
- Check json.NewEncoder.Encode and w.Write in test helpers
- Check os.MkdirAll and os.WriteFile errors in tests
- Check first writeDefaultConfig() call in AlreadyExists test
- Remove unused mustMarshal helper

main.go

@@ -150,7 +150,7 @@ func queryPuppetDB(puppetDBURL, query string) ([]fact, error) {
 	if err != nil {
 		return nil, fmt.Errorf("request failed: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
@@ -176,7 +176,7 @@ func valueString(raw json.RawMessage) string {
 
 func valueAny(raw json.RawMessage) interface{} {
 	var v interface{}
-	json.Unmarshal(raw, &v)
+	_ = json.Unmarshal(raw, &v)
 	return v
 }
 
@@ -280,7 +280,7 @@ func run(cfg config, nodeName, factName, match, partialMatch string, showRole, n
 		enc := json.NewEncoder(os.Stdout)
 		enc.SetIndent("", "  ")
 		enc.SetEscapeHTML(false)
-		enc.Encode(hostFactMap)
+		_ = enc.Encode(hostFactMap)
 
 	case count:
 		values := stdinLines
@@ -299,7 +299,7 @@ func run(cfg config, nodeName, factName, match, partialMatch string, showRole, n
 			"all": map[string]interface{}{"hosts": hosts},
 		}
 		b, _ := yaml.Marshal(inventory)
-		os.Stdout.Write(b)
+		_, _ = os.Stdout.Write(b)
 
 	case nodeOnly:
 		for _, line := range returnData {

main_test.go

@@ -12,19 +12,11 @@ import (
 
 // ---- helpers ----------------------------------------------------------------
 
-func mustMarshal(v interface{}) []byte {
-	b, err := json.Marshal(v)
-	if err != nil {
-		panic(err)
-	}
-	return b
-}
-
 func newTestServer(t *testing.T, facts []fact) *httptest.Server {
 	t.Helper()
 	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(facts)
+		_ = json.NewEncoder(w).Encode(facts)
 	}))
 }
 
@@ -183,7 +175,7 @@ func TestQueryPuppetDB_HTTPError(t *testing.T) {
 
 func TestQueryPuppetDB_BadJSON(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.Write([]byte("not json"))
+		_, _ = w.Write([]byte("not json"))
 	}))
 	defer srv.Close()
 
@@ -243,8 +235,12 @@ func TestLoadConfig_FileOverride(t *testing.T) {
 	t.Setenv("NODE_LOOKUP_ROLE_FACT", "")
 
 	cfgDir := filepath.Join(dir, appName)
-	os.MkdirAll(cfgDir, 0o755)
-	os.WriteFile(filepath.Join(cfgDir, configFileName), []byte("puppetdb_url: http://file:8080/facts\nrole_fact: file_role\n"), 0o644)
+	if err := os.MkdirAll(cfgDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(cfgDir, configFileName), []byte("puppetdb_url: http://file:8080/facts\nrole_fact: file_role\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
 
 	cfg, err := loadConfig()
 	if err != nil {
@@ -265,8 +261,12 @@ func TestLoadConfig_EnvOverridesFile(t *testing.T) {
 	t.Setenv("NODE_LOOKUP_ROLE_FACT", "")
 
 	cfgDir := filepath.Join(dir, appName)
-	os.MkdirAll(cfgDir, 0o755)
-	os.WriteFile(filepath.Join(cfgDir, configFileName), []byte("puppetdb_url: http://file:8080/facts\n"), 0o644)
+	if err := os.MkdirAll(cfgDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(cfgDir, configFileName), []byte("puppetdb_url: http://file:8080/facts\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
 
 	cfg, err := loadConfig()
 	if err != nil {
@@ -284,8 +284,12 @@ func TestLoadConfig_InvalidYAML(t *testing.T) {
 	t.Setenv("NODE_LOOKUP_ROLE_FACT", "")
 
 	cfgDir := filepath.Join(dir, appName)
-	os.MkdirAll(cfgDir, 0o755)
-	os.WriteFile(filepath.Join(cfgDir, configFileName), []byte(":\tinvalid: yaml:\n"), 0o644)
+	if err := os.MkdirAll(cfgDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(cfgDir, configFileName), []byte(":\tinvalid: yaml:\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
 
 	_, err := loadConfig()
 	if err == nil {
@@ -315,7 +319,9 @@ func TestWriteDefaultConfig_AlreadyExists(t *testing.T) {
 	dir := t.TempDir()
 	t.Setenv("XDG_CONFIG_HOME", dir)
 
-	writeDefaultConfig()
+	if err := writeDefaultConfig(); err != nil {
+		t.Fatal(err)
+	}
 	err := writeDefaultConfig()
 	if err == nil {
 		t.Fatal("expected error when config already exists")