Add support for reprompts if user input does not match template schema (#946)

## Changes
This PR adds retry logic to user input prompts, prompting users again if
the value does not match the requirements specified in the bundle
template schema.

## Tests
Manually. Here's an example UX. The first prompt expects an integer and
the second one a string made only from the letters "defg"

```
shreyas.goenka@THW32HFW6T cli % cli bundle init ~/mlops-stack

Please enter an integer [123]: abc
Validation failed: "abc" is not a integer

Please enter an integer [123]: 123

Please enter a string [dddd]: apple
Validation failed: invalid value for input_root_dir: "apple". Only characters the 'd', 'e', 'f', 'g' are allowed
```

libs/jsonschema/utils.go

@@ -7,6 +7,19 @@ import (
 	"strconv"
 )
 
+// This error indicates an failure to parse a string as a particular JSON schema type.
+type parseStringError struct {
+	// Expected JSON schema type for the value
+	ExpectedType Type
+
+	// The string value that failed to parse
+	Value string
+}
+
+func (e parseStringError) Error() string {
+	return fmt.Sprintf("%q is not a %s", e.Value, e.ExpectedType)
+}
+
 // function to check whether a float value represents an integer
 func isIntegerValue(v float64) bool {
 	return v == float64(int64(v))
@@ -108,11 +121,40 @@ func fromString(s string, T Type) (any, error) {
 
 	// Return more readable error incase of a syntax error
 	if errors.Is(err, strconv.ErrSyntax) {
-		return nil, fmt.Errorf("could not parse %q as a %s: %w", s, T, err)
+		return nil, parseStringError{
+			ExpectedType: T,
+			Value:        s,
+		}
 	}
 	return v, err
 }
 
+// Error indicates a value entered by the user failed to match the pattern specified
+// in the template schema.
+type patternMatchError struct {
+	// The name of the property that failed to match the pattern
+	PropertyName string
+
+	// The value of the property that failed to match the pattern
+	PropertyValue any
+
+	// The regex pattern that the property value failed to match
+	Pattern string
+
+	// Failure message to display to the user, if specified in the template
+	// schema
+	FailureMessage string
+}
+
+func (e patternMatchError) Error() string {
+	// If custom user error message is defined, return error with the custom message
+	msg := e.FailureMessage
+	if msg == "" {
+		msg = fmt.Sprintf("Expected to match regex pattern: %s", e.Pattern)
+	}
+	return fmt.Sprintf("invalid value for %s: %q. %s", e.PropertyName, e.PropertyValue, msg)
+}
+
 func validatePatternMatch(name string, value any, propertySchema *Schema) error {
 	if propertySchema.Pattern == "" {
 		// Return early if no pattern is specified
@@ -134,10 +176,10 @@ func validatePatternMatch(name string, value any, propertySchema *Schema) error
 		return nil
 	}
 
-	// If custom user error message is defined, return error with the custom message
+	return patternMatchError{
-	msg := propertySchema.PatternMatchFailureMessage
+		PropertyName:   name,
-	if msg == "" {
+		PropertyValue:  value,
-		msg = fmt.Sprintf("Expected to match regex pattern: %s", propertySchema.Pattern)
+		Pattern:        propertySchema.Pattern,
+		FailureMessage: propertySchema.PatternMatchFailureMessage,
 	}
-	return fmt.Errorf("invalid value for %s: %q. %s", name, value, msg)
 }

libs/jsonschema/utils_test.go

@@ -110,10 +110,10 @@ func TestTemplateFromString(t *testing.T) {
 	assert.EqualError(t, err, "cannot parse string as object of type array. Value of string: \"qrt\"")
 
 	_, err = fromString("abc", IntegerType)
-	assert.EqualError(t, err, "could not parse \"abc\" as a integer: strconv.ParseInt: parsing \"abc\": invalid syntax")
+	assert.EqualError(t, err, "\"abc\" is not a integer")
 
 	_, err = fromString("1.0", IntegerType)
-	assert.EqualError(t, err, "could not parse \"1.0\" as a integer: strconv.ParseInt: parsing \"1.0\": invalid syntax")
+	assert.EqualError(t, err, "\"1.0\" is not a integer")
 
 	_, err = fromString("1.0", "foobar")
 	assert.EqualError(t, err, "unknown json schema type: \"foobar\"")

libs/template/config.go

@@ -2,6 +2,7 @@ package template
 
 import (
 	"context"
+	"errors"
 	"fmt"
 
 	"github.com/databricks/cli/libs/cmdio"
@@ -12,6 +13,14 @@ import (
 // The latest template schema version supported by the CLI
 const latestSchemaVersion = 1
 
+type retriableError struct {
+	err error
+}
+
+func (e retriableError) Error() string {
+	return e.err.Error()
+}
+
 type config struct {
 	ctx    context.Context
 	values map[string]any
@@ -143,6 +152,45 @@ func (c *config) skipPrompt(p jsonschema.Property, r *renderer) (bool, error) {
 	return true, nil
 }
 
+func (c *config) promptOnce(property *jsonschema.Schema, name, defaultVal, description string) error {
+	var userInput string
+	if property.Enum != nil {
+		// List options for the user to select from
+		options, err := property.EnumStringSlice()
+		if err != nil {
+			return err
+		}
+		userInput, err = cmdio.AskSelect(c.ctx, description, options)
+		if err != nil {
+			return err
+		}
+	} else {
+		var err error
+		userInput, err = cmdio.Ask(c.ctx, description, defaultVal)
+		if err != nil {
+			return err
+		}
+	}
+
+	// Convert user input string back to a Go value
+	var err error
+	c.values[name], err = property.ParseString(userInput)
+	if err != nil {
+		// Show error and retry if validation fails
+		cmdio.LogString(c.ctx, fmt.Sprintf("Validation failed: %s", err.Error()))
+		return retriableError{err: err}
+	}
+
+	// Validate the partial config which includes the new value
+	err = c.schema.ValidateInstance(c.values)
+	if err != nil {
+		// Show error and retry if validation fails
+		cmdio.LogString(c.ctx, fmt.Sprintf("Validation failed: %s", err.Error()))
+		return retriableError{err: err}
+	}
+	return nil
+}
+
 // Prompts user for values for properties that do not have a value set yet
 func (c *config) promptForValues(r *renderer) error {
 	for _, p := range c.schema.OrderedProperties() {
@@ -171,39 +219,22 @@ func (c *config) promptForValues(r *renderer) error {
 			}
 		}
 
+		// Compute description for the prompt
 		description, err := r.executeTemplate(property.Description)
 		if err != nil {
 			return err
 		}
 
-		// Get user input by running the prompt
+		// We wrap this function in a retry loop to allow retries when the user
-		var userInput string
+		// entered value is invalid.
-		if property.Enum != nil {
+		for {
-			// convert list of enums to string slice
+			err = c.promptOnce(property, name, defaultVal, description)
-			enums, err := property.EnumStringSlice()
+			if err == nil {
-			if err != nil {
+				break
+			}
+			if !errors.As(err, &retriableError{}) {
 				return err
 			}
-			userInput, err = cmdio.AskSelect(c.ctx, description, enums)
-			if err != nil {
-				return err
-			}
-		} else {
-			userInput, err = cmdio.Ask(c.ctx, description, defaultVal)
-			if err != nil {
-				return err
-			}
-		}
-
-		// Convert user input string back to a value
-		c.values[name], err = property.ParseString(userInput)
-		if err != nil {
-			return err
-		}
-
-		// Validate the partial config based on this update
-		if err := c.schema.ValidateInstance(c.values); err != nil {
-			return err
 		}
 	}
 	return nil