Add JSON schema for package index

This schema defines the data structure of the Arduino package index at three compliance levels:

- permissive: the minimum accepted format. This allows for a gradual deprecation following specification changes.
- specification: the format as defined in the official specification
- strict: best practices

Helper functions for reading package indexes and validating them against the schema are added, at this point for use in
the tests, but also for the schema-based rules to come.

Author: per1234

Diff for: etc/schemas/arduino-package-index-definitions-schema.json

@@ -0,0 +1,11 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/schemas/arduino-package-index-permissive-schema.json",
+  "title": "Arduino Package Index JSON permissive schema",
+  "description": "Package indexes define Arduino hardware packages. See: https://arduino.github.io/arduino-cli/latest/package_index_json-specification/. This schema defines the minimum accepted data format.",
+  "allOf": [
+    {
+      "$ref": "arduino-package-index-definitions-schema.json#/definitions/root/permissive/object"
+    }
+  ]
+}

Diff for: etc/schemas/arduino-package-index-permissive-schema.json

@@ -0,0 +1,11 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/schemas/arduino-package-index-schema.json",
+  "title": "Arduino Package Index JSON schema",
+  "description": "Package indexes define Arduino hardware packages. See: https://arduino.github.io/arduino-cli/latest/package_index_json-specification/. This schema defines the data format per the specification.",
+  "allOf": [
+    {
+      "$ref": "arduino-package-index-definitions-schema.json#/definitions/root/specification/object"
+    }
+  ]
+}

Diff for: etc/schemas/arduino-package-index-schema.json

@@ -0,0 +1,11 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/schemas/arduino-package-index-strict-schema.json",
+  "title": "Arduino Package Index JSON strict schema",
+  "description": "Package indexes define Arduino hardware packages. See: https://arduino.github.io/arduino-cli/latest/package_index_json-specification/. This schema defines the best practices for the data format, above and beyond the specification.",
+  "allOf": [
+    {
+      "$ref": "arduino-package-index-definitions-schema.json#/definitions/root/strict/object"
+    }
+  ]
+}

Diff for: etc/schemas/arduino-package-index-strict-schema.json

@@ -20,12 +20,55 @@ See: https://arduino.github.io/arduino-cli/latest/package_index_json-specificati
 package packageindex
 
 import (
+	"encoding/json"
 	"fmt"
 	"regexp"
 
+	"github.com/arduino/arduino-lint/internal/rule/schema"
+	"github.com/arduino/arduino-lint/internal/rule/schema/compliancelevel"
+	"github.com/arduino/arduino-lint/internal/rule/schema/schemadata"
 	"github.com/arduino/go-paths-helper"
 )
 
+// Properties parses the package index from the given path and returns the data.
+func Properties(packageIndexPath *paths.Path) (map[string]interface{}, error) {
+	rawIndex, err := packageIndexPath.ReadFile()
+	if err != nil {
+		panic(err)
+	}
+	var indexData map[string]interface{}
+	err = json.Unmarshal(rawIndex, &indexData)
+	if err != nil {
+		return nil, err
+	}
+
+	return indexData, nil
+}
+
+var schemaObject = make(map[compliancelevel.Type]schema.Schema)
+
+// Validate validates boards.txt data against the JSON schema and returns a map of the result for each compliance level.
+func Validate(packageIndex map[string]interface{}) map[compliancelevel.Type]schema.ValidationResult {
+	referencedSchemaFilenames := []string{
+		"general-definitions-schema.json",
+		"arduino-package-index-definitions-schema.json",
+	}
+
+	var validationResults = make(map[compliancelevel.Type]schema.ValidationResult)
+
+	if schemaObject[compliancelevel.Permissive].Compiled == nil { // Only compile the schemas once.
+		schemaObject[compliancelevel.Permissive] = schema.Compile("arduino-package-index-permissive-schema.json", referencedSchemaFilenames, schemadata.Asset)
+		schemaObject[compliancelevel.Specification] = schema.Compile("arduino-package-index-schema.json", referencedSchemaFilenames, schemadata.Asset)
+		schemaObject[compliancelevel.Strict] = schema.Compile("arduino-package-index-strict-schema.json", referencedSchemaFilenames, schemadata.Asset)
+	}
+
+	validationResults[compliancelevel.Permissive] = schema.Validate(packageIndex, schemaObject[compliancelevel.Permissive])
+	validationResults[compliancelevel.Specification] = schema.Validate(packageIndex, schemaObject[compliancelevel.Specification])
+	validationResults[compliancelevel.Strict] = schema.Validate(packageIndex, schemaObject[compliancelevel.Strict])
+
+	return validationResults
+}
+
 var empty struct{}
 
 // Reference: https://arduino.github.io/arduino-cli/latest/package_index_json-specification/#naming-of-the-json-index-file

Diff for: internal/project/packageindex/packageindex.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/arduino/go-paths-helper"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 var testDataPath *paths.Path
@@ -33,6 +34,13 @@ func init() {
 	testDataPath = paths.New(workingDirectory, "testdata")
 }
 
+func TestProperties(t *testing.T) {
+	packageIndex, err := Properties(testDataPath.Join("package_valid_index.json"))
+	require.Nil(t, err)
+
+	assert.NotNil(t, packageIndex)
+}
+
 func TestHasValidExtension(t *testing.T) {
 	assert.True(t, HasValidExtension(paths.New("/foo", "bar.json")))
 	assert.False(t, HasValidExtension(paths.New("/foo", "bar.baz")))