Add support for regex patterns in template schema (#768)

## Changes
This PR introduces support for regex pattern validation in our custom
jsonschema validator. This allows us to fail early if a user enters an
invalid value for a field.

For example, now this is what initializing the default template looks
like with an invalid project name:
```
shreyas.goenka@THW32HFW6T bricks % cli bundle init
Template to use [default-python]: 
Unique name for this project [my_project]: (_*_)
Error: invalid value for project_name: (_*_). Must consist of letter and underscores only.
```

## Tests
New unit tests and manually.

libs/jsonschema/extension.go

@@ -11,4 +11,8 @@ type Extension struct {
 	// If not defined, the field is ordered alphabetically after all fields
 	// that do have an order defined.
 	Order *int `json:"order,omitempty"`
+
+	// PatternMatchFailureMessage is a user defined message that is displayed to the
+	// user if a JSON schema pattern match fails.
+	PatternMatchFailureMessage string `json:"pattern_match_failure_message,omitempty"`
 }

libs/jsonschema/instance.go

@@ -45,6 +45,7 @@ func (s *Schema) ValidateInstance(instance map[string]any) error {
 		s.validateEnum,
 		s.validateRequired,
 		s.validateTypes,
+		s.validatePattern,
 	} {
 		err := fn(instance)
 		if err != nil {
@@ -111,3 +112,14 @@ func (s *Schema) validateEnum(instance map[string]any) error {
 	}
 	return nil
 }
+
+func (s *Schema) validatePattern(instance map[string]any) error {
+	for k, v := range instance {
+		fieldInfo, ok := s.Properties[k]
+		if !ok {
+			continue
+		}
+		return ValidatePatternMatch(k, v, fieldInfo)
+	}
+	return nil
+}

libs/jsonschema/instance_test.go

@@ -153,3 +153,43 @@ func TestValidateInstanceEnum(t *testing.T) {
 	assert.EqualError(t, schema.validateEnum(invalidIntInstance), "expected value of property bar to be one of [2 4 6]. Found: 1")
 	assert.EqualError(t, schema.ValidateInstance(invalidIntInstance), "expected value of property bar to be one of [2 4 6]. Found: 1")
 }
+
+func TestValidateInstancePattern(t *testing.T) {
+	schema, err := Load("./testdata/instance-validate/test-schema-pattern.json")
+	require.NoError(t, err)
+
+	validInstance := map[string]any{
+		"foo": "axyzc",
+	}
+	assert.NoError(t, schema.validatePattern(validInstance))
+	assert.NoError(t, schema.ValidateInstance(validInstance))
+
+	invalidInstanceValue := map[string]any{
+		"foo": "xyz",
+	}
+	assert.EqualError(t, schema.validatePattern(invalidInstanceValue), "invalid value for foo: \"xyz\". Expected to match regex pattern: a.*c")
+	assert.EqualError(t, schema.ValidateInstance(invalidInstanceValue), "invalid value for foo: \"xyz\". Expected to match regex pattern: a.*c")
+
+	invalidInstanceType := map[string]any{
+		"foo": 1,
+	}
+	assert.EqualError(t, schema.validatePattern(invalidInstanceType), "invalid value for foo: 1. Expected a value of type string")
+	assert.EqualError(t, schema.ValidateInstance(invalidInstanceType), "incorrect type for property foo: expected type string, but value is 1")
+}
+
+func TestValidateInstancePatternWithCustomMessage(t *testing.T) {
+	schema, err := Load("./testdata/instance-validate/test-schema-pattern-with-custom-message.json")
+	require.NoError(t, err)
+
+	validInstance := map[string]any{
+		"foo": "axyzc",
+	}
+	assert.NoError(t, schema.validatePattern(validInstance))
+	assert.NoError(t, schema.ValidateInstance(validInstance))
+
+	invalidInstanceValue := map[string]any{
+		"foo": "xyz",
+	}
+	assert.EqualError(t, schema.validatePattern(invalidInstanceValue), "invalid value for foo: \"xyz\". Please enter a string starting with 'a' and ending with 'c'")
+	assert.EqualError(t, schema.ValidateInstance(invalidInstanceValue), "invalid value for foo: \"xyz\". Please enter a string starting with 'a' and ending with 'c'")
+}

libs/jsonschema/schema.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"regexp"
 	"slices"
 )
 
@@ -45,6 +46,11 @@ type Schema struct {
 	// List of valid values for a JSON instance for this schema.
 	Enum []any `json:"enum,omitempty"`
 
+	// A pattern is a regular expression the object will be validated against.
+	// Can only be used with type "string". The regex syntax supported is available
+	// here: https://github.com/google/re2/wiki/Syntax
+	Pattern string `json:"pattern,omitempty"`
+
 	// Extension embeds our custom JSON schema extensions.
 	Extension
 }
@@ -112,6 +118,38 @@ func (schema *Schema) validate() error {
 			return fmt.Errorf("list of enum values for property %s does not contain default value %v: %v", name, property.Default, property.Enum)
 		}
 	}
+
+	// Validate usage of "pattern" is consistent.
+	for name, property := range schema.Properties {
+		pattern := property.Pattern
+		if pattern == "" {
+			continue
+		}
+
+		// validate property type is string
+		if property.Type != StringType {
+			return fmt.Errorf("property %q has a non-empty regex pattern %q specified. Patterns are only supported for string properties", name, pattern)
+		}
+
+		// validate regex pattern syntax
+		r, err := regexp.Compile(pattern)
+		if err != nil {
+			return fmt.Errorf("invalid regex pattern %q provided for property %q: %w", pattern, name, err)
+		}
+
+		// validate default value against the pattern
+		if property.Default != nil && !r.MatchString(property.Default.(string)) {
+			return fmt.Errorf("default value %q for property %q does not match specified regex pattern: %q", property.Default, name, pattern)
+		}
+
+		// validate enum values against the pattern
+		for i, enum := range property.Enum {
+			if !r.MatchString(enum.(string)) {
+				return fmt.Errorf("enum value %q at index %v for property %q does not match specified regex pattern: %q", enum, i, name, pattern)
+			}
+		}
+	}
+
 	return nil
 }
 

libs/jsonschema/schema_test.go

@@ -139,3 +139,86 @@ func TestSchemaValidateErrorWhenDefaultValueIsNotInEnums(t *testing.T) {
 	err = validSchema.validate()
 	assert.NoError(t, err)
 }
+
+func TestSchemaValidatePatternType(t *testing.T) {
+	s := &Schema{
+		Properties: map[string]*Schema{
+			"foo": {
+				Type:    "number",
+				Pattern: "abc",
+			},
+		},
+	}
+	assert.EqualError(t, s.validate(), "property \"foo\" has a non-empty regex pattern \"abc\" specified. Patterns are only supported for string properties")
+
+	s = &Schema{
+		Properties: map[string]*Schema{
+			"foo": {
+				Type:    "string",
+				Pattern: "abc",
+			},
+		},
+	}
+	assert.NoError(t, s.validate())
+}
+
+func TestSchemaValidateIncorrectRegex(t *testing.T) {
+	s := &Schema{
+		Properties: map[string]*Schema{
+			"foo": {
+				Type: "string",
+				// invalid regex, missing the closing brace
+				Pattern: "(abc",
+			},
+		},
+	}
+	assert.EqualError(t, s.validate(), "invalid regex pattern \"(abc\" provided for property \"foo\": error parsing regexp: missing closing ): `(abc`")
+}
+
+func TestSchemaValidatePatternDefault(t *testing.T) {
+	s := &Schema{
+		Properties: map[string]*Schema{
+			"foo": {
+				Type:    "string",
+				Pattern: "abc",
+				Default: "def",
+			},
+		},
+	}
+	assert.EqualError(t, s.validate(), "default value \"def\" for property \"foo\" does not match specified regex pattern: \"abc\"")
+
+	s = &Schema{
+		Properties: map[string]*Schema{
+			"foo": {
+				Type:    "string",
+				Pattern: "a.*d",
+				Default: "axyzd",
+			},
+		},
+	}
+	assert.NoError(t, s.validate())
+}
+
+func TestSchemaValidatePatternEnum(t *testing.T) {
+	s := &Schema{
+		Properties: map[string]*Schema{
+			"foo": {
+				Type:    "string",
+				Pattern: "a.*c",
+				Enum:    []any{"abc", "def", "abbc"},
+			},
+		},
+	}
+	assert.EqualError(t, s.validate(), "enum value \"def\" at index 1 for property \"foo\" does not match specified regex pattern: \"a.*c\"")
+
+	s = &Schema{
+		Properties: map[string]*Schema{
+			"foo": {
+				Type:    "string",
+				Pattern: "a.*d",
+				Enum:    []any{"abd", "axybgd", "abbd"},
+			},
+		},
+	}
+	assert.NoError(t, s.validate())
+}

libs/jsonschema/testdata/instance-validate/test-schema-pattern-with-custom-message.json

@@ -0,0 +1,9 @@
+{
+    "properties": {
+        "foo": {
+            "type": "string",
+            "pattern": "a.*c",
+            "pattern_match_failure_message": "Please enter a string starting with 'a' and ending with 'c'"
+        }
+    }
+}

libs/jsonschema/testdata/instance-validate/test-schema-pattern.json

@@ -0,0 +1,8 @@
+{
+    "properties": {
+        "foo": {
+            "type": "string",
+            "pattern": "a.*c"
+        }
+    }
+}

libs/jsonschema/utils.go

@@ -3,6 +3,7 @@ package jsonschema
 import (
 	"errors"
 	"fmt"
+	"regexp"
 	"strconv"
 )
 
@@ -111,3 +112,32 @@ func FromString(s string, T Type) (any, error) {
 	}
 	return v, err
 }
+
+func ValidatePatternMatch(name string, value any, propertySchema *Schema) error {
+	if propertySchema.Pattern == "" {
+		// Return early if no pattern is specified
+		return nil
+	}
+
+	// Expect type of value to be a string
+	stringValue, ok := value.(string)
+	if !ok {
+		return fmt.Errorf("invalid value for %s: %v. Expected a value of type string", name, value)
+	}
+
+	match, err := regexp.MatchString(propertySchema.Pattern, stringValue)
+	if err != nil {
+		return err
+	}
+	if match {
+		// successful match
+		return nil
+	}
+
+	// If custom user error message is defined, return error with the custom message
+	msg := propertySchema.PatternMatchFailureMessage
+	if msg == "" {
+		msg = fmt.Sprintf("Expected to match regex pattern: %s", propertySchema.Pattern)
+	}
+	return fmt.Errorf("invalid value for %s: %q. %s", name, value, msg)
+}

libs/jsonschema/utils_test.go

@@ -128,3 +128,40 @@ func TestTemplateToStringSlice(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, []string{"1.1", "2.2", "3.3"}, s)
 }
+
+func TestValidatePropertyPatternMatch(t *testing.T) {
+	var err error
+
+	// Expect no error if no pattern is specified.
+	err = ValidatePatternMatch("foo", 1, &Schema{Type: "integer"})
+	assert.NoError(t, err)
+
+	// Expect error because value is not a string.
+	err = ValidatePatternMatch("bar", 1, &Schema{Type: "integer", Pattern: "abc"})
+	assert.EqualError(t, err, "invalid value for bar: 1. Expected a value of type string")
+
+	// Expect error because the pattern is invalid.
+	err = ValidatePatternMatch("bar", "xyz", &Schema{Type: "string", Pattern: "(abc"})
+	assert.EqualError(t, err, "error parsing regexp: missing closing ): `(abc`")
+
+	// Expect no error because the pattern matches.
+	err = ValidatePatternMatch("bar", "axyzd", &Schema{Type: "string", Pattern: "(a*.d)"})
+	assert.NoError(t, err)
+
+	// Expect custom error message on match fail
+	err = ValidatePatternMatch("bar", "axyze", &Schema{
+		Type:    "string",
+		Pattern: "(a*.d)",
+		Extension: Extension{
+			PatternMatchFailureMessage: "my custom msg",
+		},
+	})
+	assert.EqualError(t, err, "invalid value for bar: \"axyze\". my custom msg")
+
+	// Expect generic message on match fail
+	err = ValidatePatternMatch("bar", "axyze", &Schema{
+		Type:    "string",
+		Pattern: "(a*.d)",
+	})
+	assert.EqualError(t, err, "invalid value for bar: \"axyze\". Expected to match regex pattern: (a*.d)")
+}

libs/template/config.go

@@ -121,6 +121,11 @@ func (c *config) promptForValues() error {
 
 		}
 
+		// Validate the property matches any specified regex pattern.
+		if err := jsonschema.ValidatePatternMatch(name, userInput, property); err != nil {
+			return err
+		}
+
 		// Convert user input string back to a value
 		c.values[name], err = jsonschema.FromString(userInput, property.Type)
 		if err != nil {

libs/template/templates/default-python/databricks_template_schema.json

@@ -4,7 +4,9 @@
             "type": "string",
             "default": "my_project",
             "description": "Unique name for this project",
-            "order": 1
+            "order": 1,
+            "pattern": "^[A-Za-z0-9_]*$",
+            "pattern_match_failure_message": "Must consist of letter and underscores only."
         },
         "include_notebook": {
             "type": "string",

libs/template/templates/default-python/template/__preamble.tmpl

@@ -4,13 +4,6 @@ This file only template directives; it is skipped for the actual output.
 
 {{skip "__preamble"}}
 
-{{ $value := .project_name }}
-{{with (regexp "^[A-Za-z0-9_]*$")}}
-  {{if not (.MatchString $value)}}
-    {{fail "Invalid project_name: %s. Must consist of letter and underscores only." $value}}
-  {{end}}
-{{end}}
-
 {{$notDLT := not (eq .include_dlt "yes")}}
 {{$notNotebook := not (eq .include_notebook "yes")}}
 {{$notPython := not (eq .include_python "yes")}}