Show lines where parsing error happened if available

internal/glance/config-fields.go

@@ -48,6 +48,7 @@ func (c1 *hslColorField) SameAs(c2 *hslColorField) bool {
 
 func (c *hslColorField) UnmarshalYAML(node *yaml.Node) error {
 	var value string
+	errorLine := fmt.Sprintf("line %d:", node.Line)
 
 	if err := node.Decode(&value); err != nil {
 		return err
@@ -56,7 +57,7 @@ func (c *hslColorField) UnmarshalYAML(node *yaml.Node) error {
 	matches := hslColorFieldPattern.FindStringSubmatch(value)
 
 	if len(matches) != 4 {
-		return fmt.Errorf("invalid HSL color format: %s", value)
+		return fmt.Errorf("%s invalid HSL color format: %s", errorLine, value)
 	}
 
 	hue, err := strconv.ParseFloat(matches[1], 64)
@@ -65,7 +66,7 @@ func (c *hslColorField) UnmarshalYAML(node *yaml.Node) error {
 	}
 
 	if hue > hslHueMax {
-		return fmt.Errorf("HSL hue must be between 0 and %d", hslHueMax)
+		return fmt.Errorf("%s HSL hue must be between 0 and %d", errorLine, hslHueMax)
 	}
 
 	saturation, err := strconv.ParseFloat(matches[2], 64)
@@ -74,7 +75,7 @@ func (c *hslColorField) UnmarshalYAML(node *yaml.Node) error {
 	}
 
 	if saturation > hslSaturationMax {
-		return fmt.Errorf("HSL saturation must be between 0 and %d", hslSaturationMax)
+		return fmt.Errorf("%s HSL saturation must be between 0 and %d", errorLine, hslSaturationMax)
 	}
 
 	lightness, err := strconv.ParseFloat(matches[3], 64)
@@ -83,7 +84,7 @@ func (c *hslColorField) UnmarshalYAML(node *yaml.Node) error {
 	}
 
 	if lightness > hslLightnessMax {
-		return fmt.Errorf("HSL lightness must be between 0 and %d", hslLightnessMax)
+		return fmt.Errorf("%s HSL lightness must be between 0 and %d", errorLine, hslLightnessMax)
 	}
 
 	c.H = hue
@@ -99,6 +100,7 @@ type durationField time.Duration
 
 func (d *durationField) UnmarshalYAML(node *yaml.Node) error {
 	var value string
+	errorLine := fmt.Sprintf("line %d:", node.Line)
 
 	if err := node.Decode(&value); err != nil {
 		return err
@@ -107,12 +109,12 @@ func (d *durationField) UnmarshalYAML(node *yaml.Node) error {
 	matches := durationFieldPattern.FindStringSubmatch(value)
 
 	if len(matches) != 3 {
-		return fmt.Errorf("invalid duration format: %s", value)
+		return fmt.Errorf("%s invalid duration format for value `%s`", errorLine, value)
 	}
 
 	duration, err := strconv.Atoi(matches[1])
 	if err != nil {
-		return err
+		return fmt.Errorf("%s invalid duration value: %s", errorLine, matches[1])
 	}
 
 	switch matches[2] {
@@ -245,6 +247,8 @@ func (q *queryParametersField) UnmarshalYAML(node *yaml.Node) error {
 
 	*q = make(queryParametersField)
 
+	errorLine := fmt.Sprintf("line %d:", node.Line)
+
 	// TODO: refactor the duplication in the switch cases if any more types get added
 	for key, value := range decoded {
 		switch v := value.(type) {
@@ -266,11 +270,11 @@ func (q *queryParametersField) UnmarshalYAML(node *yaml.Node) error {
 				case bool:
 					(*q)[key] = append((*q)[key], fmt.Sprintf("%t", item))
 				default:
-					return fmt.Errorf("invalid query parameter value type: %T", item)
+					return fmt.Errorf("%s invalid query parameter value type: %T", errorLine, item)
 				}
 			}
 		default:
-			return fmt.Errorf("invalid query parameter value type: %T", value)
+			return fmt.Errorf("%s invalid query parameter value type: %T", errorLine, value)
 		}
 	}
 

internal/glance/main.go

@@ -6,6 +6,9 @@ import (
 	"log"
 	"net/http"
 	"os"
+	"regexp"
+	"strconv"
+	"strings"
 
 	"golang.org/x/crypto/bcrypt"
 )
@@ -105,7 +108,12 @@ func serveApp(configPath string) error {
 
 		config, err := newConfigFromYAML(newContents)
 		if err != nil {
-			log.Printf("Config has errors: %v", err)
+			errStr := strings.ReplaceAll(err.Error(), "\n", "")
+			errStr = sequentialWhitespacePattern.ReplaceAllString(errStr, " ")
+			errStr = strings.ReplaceAll(errStr, "!!seq", "array")
+
+			log.Printf("Config has errors: %v", errStr)
+			printConfigLinesNearErrorIfAvailable(err, newContents)
 
 			if !hadValidConfigOnStartup {
 				close(exitChannel)
@@ -180,6 +188,41 @@ func serveApp(configPath string) error {
 	return nil
 }
 
+var errorLinePattern = regexp.MustCompile(`line (\d+)`)
+
+func printConfigLinesNearErrorIfAvailable(err error, configContents []byte) {
+	if err == nil {
+		return
+	}
+
+	matches := errorLinePattern.FindStringSubmatch(err.Error())
+	if len(matches) < 2 {
+		return
+	}
+
+	errorAtLine, err := strconv.Atoi(matches[1])
+	if err != nil {
+		return
+	}
+
+	contents := strings.ReplaceAll(string(configContents), "\r\n", "\n")
+	lines := strings.Split(contents, "\n")
+
+	if errorAtLine < 1 || errorAtLine > len(lines) {
+		return
+	}
+
+	contextLength := 3
+
+	for i := max(0, errorAtLine-contextLength-1); i < min(len(lines), errorAtLine+contextLength); i++ {
+		if i == errorAtLine-1 {
+			fmt.Printf("-> %s\n", lines[i])
+		} else {
+			fmt.Printf("|  %s\n", lines[i])
+		}
+	}
+}
+
 func serveUpdateNoticeIfConfigLocationNotMigrated(configPath string) bool {
 	if !isRunningInsideDockerContainer() {
 		return false