trap cases where the YAML indent is incorrect.

Signed-off-by: Matt Butcher <matt.butcher@microsoft.com>

pkg/lint/rules/template.go

@@ -17,6 +17,8 @@ limitations under the License.
 package rules
 
 import (
+	"bufio"
+	"bytes"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -121,7 +123,7 @@ func Templates(linter *support.Linter, values map[string]interface{}, namespace
 
 		renderedContent := renderedContentMap[filepath.Join(chart.Name(), fileName)]
 		if strings.TrimSpace(renderedContent) != "" {
-			fmt.Printf("Template %s: \n %s", path, renderedContent)
+			linter.RunLinterRule(support.WarningSev, path, validateTopIndentLevel(renderedContent))
 			var yamlStruct K8sYamlStruct
 			// Even though K8sYamlStruct only defines a few fields, an error in any other
 			// key will be raised as well
@@ -137,6 +139,32 @@ func Templates(linter *support.Linter, values map[string]interface{}, namespace
 	}
 }
 
+// validateTopIndentLevel checks that the content does not start with an indent level > 0.
+//
+// This error can occur when a template accidentally inserts space. It can cause
+// unpredictable errors dependening on whether the text is normalized before being passed
+// into the YAML parser. So we trap it here.
+//
+// See https://github.com/helm/helm/issues/8467
+func validateTopIndentLevel(content string) error {
+	// Read lines until we get to a non-empty one
+	scanner := bufio.NewScanner(bytes.NewBufferString(content))
+	for scanner.Scan() {
+		line := scanner.Text()
+		// If line is empty, skip
+		if strings.TrimSpace(line) == "" {
+			continue
+		}
+		// If it starts with one or more spaces, this is an error
+		if strings.HasPrefix(line, " ") || strings.HasPrefix(line, "\t") {
+			return fmt.Errorf("document starts with an illegal indent: %q, which may cause parsing problems", line)
+		}
+		// Any other condition passes.
+		return nil
+	}
+	return scanner.Err()
+}
+
 // Validation functions
 func validateTemplatesDir(templatesPath string) error {
 	if fi, err := os.Stat(templatesPath); err != nil {

pkg/lint/rules/template_test.go

@@ -305,3 +305,20 @@ spec:
 		t.Error("expected Deployment with no selector to fail")
 	}
 }
+
+func TestValidateTopIndentLevel(t *testing.T) {
+	for doc, shouldFail := range map[string]bool{
+		// Should not fail
+		"\n\n\n\t\n   \t\n":          false,
+		"apiVersion:foo\n  bar:baz":  false,
+		"\n\n\napiVersion:foo\n\n\n": false,
+		// Should fail
+		"  apiVersion:foo":         true,
+		"\n\n  apiVersion:foo\n\n": true,
+	} {
+		if err := validateTopIndentLevel(doc); (err == nil) == shouldFail {
+			t.Errorf("Expected %t for %q", shouldFail, doc)
+		}
+	}
+
+}