build: use vite to get default mermaid config

Adds a vitepress JsonSchema plugin that automatically loads
the Mermaid Config JSON Schema from a .schema.yaml file and
gets the default values from it.

.vite/build.ts

@@ -2,6 +2,7 @@ import { build, InlineConfig, type PluginOption } from 'vite';
 import { resolve } from 'path';
 import { fileURLToPath } from 'url';
 import jisonPlugin from './jisonPlugin.js';
+import jsonSchemaPlugin from './jsonSchemaPlugin.js';
 import { readFileSync } from 'fs';
 import typescript from '@rollup/plugin-typescript';
 import { visualizer } from 'rollup-plugin-visualizer';
@@ -121,6 +122,7 @@ export const getBuildConfig = ({ minify, core, watch, entryName }: BuildOptions)
     },
     plugins: [
       jisonPlugin(),
+      jsonSchemaPlugin(), // handles `.schema.yaml` files
       // @ts-expect-error According to the type definitions, rollup plugins are incompatible with vite
       typescript({ compilerOptions: { declaration: false } }),
       istanbul({

.vite/jsonSchemaPlugin.ts

@@ -0,0 +1,150 @@
+import { load, JSON_SCHEMA } from 'js-yaml';
+import assert from 'node:assert';
+import Ajv2019, { type JSONSchemaType } from 'ajv/dist/2019.js';
+import { PluginOption } from 'vite';
+
+import type { MermaidConfig, BaseDiagramConfig } from '../packages/mermaid/src/config.type.js';
+
+/**
+ * All of the keys in the mermaid config that have a mermaid diagram config.
+ */
+const MERMAID_CONFIG_DIAGRAM_KEYS = [
+  'flowchart',
+  'sequence',
+  'gantt',
+  'journey',
+  'class',
+  'state',
+  'er',
+  'pie',
+  'quadrantChart',
+  'requirement',
+  'mindmap',
+  'timeline',
+  'gitGraph',
+  'c4',
+  'sankey',
+] as const;
+
+/**
+ * Generate default values from the JSON Schema.
+ *
+ * AJV does not support nested default values yet (or default values with $ref),
+ * so we need to manually find them (this may be fixed in ajv v9).
+ *
+ * @param mermaidConfigSchema - The Mermaid JSON Schema to use.
+ * @returns The default mermaid config object.
+ */
+function generateDefaults(mermaidConfigSchema: JSONSchemaType<MermaidConfig>) {
+  const ajv = new Ajv2019({
+    useDefaults: true,
+    allowUnionTypes: true,
+    strict: true,
+  });
+
+  ajv.addKeyword({
+    keyword: 'meta:enum', // used by jsonschema2md
+    errors: false,
+  });
+  ajv.addKeyword({
+    keyword: 'tsType', // used by json-schema-to-typescript
+    errors: false,
+  });
+
+  // ajv currently doesn't support nested default values, see https://github.com/ajv-validator/ajv/issues/1718
+  // (may be fixed in v9) so we need to manually use sub-schemas
+  const mermaidDefaultConfig = {};
+
+  assert.ok(mermaidConfigSchema.$defs);
+  const baseDiagramConfig = mermaidConfigSchema.$defs.BaseDiagramConfig;
+
+  for (const key of MERMAID_CONFIG_DIAGRAM_KEYS) {
+    const subSchemaRef = mermaidConfigSchema.properties[key].$ref;
+    const [root, defs, defName] = subSchemaRef.split('/');
+    assert.strictEqual(root, '#');
+    assert.strictEqual(defs, '$defs');
+    const subSchema = {
+      $schema: mermaidConfigSchema.$schema,
+      $defs: mermaidConfigSchema.$defs,
+      ...mermaidConfigSchema.$defs[defName],
+    } as JSONSchemaType<BaseDiagramConfig>;
+
+    const validate = ajv.compile(subSchema);
+
+    mermaidDefaultConfig[key] = {};
+
+    for (const required of subSchema.required ?? []) {
+      if (subSchema.properties[required] === undefined && baseDiagramConfig.properties[required]) {
+        mermaidDefaultConfig[key][required] = baseDiagramConfig.properties[required].default;
+      }
+    }
+    if (!validate(mermaidDefaultConfig[key])) {
+      throw new Error(
+        `schema for subconfig ${key} does not have valid defaults! Errors were ${JSON.stringify(
+          validate.errors,
+          undefined,
+          2
+        )}`
+      );
+    }
+  }
+
+  const validate = ajv.compile(mermaidConfigSchema);
+
+  if (!validate(mermaidDefaultConfig)) {
+    throw new Error(
+      `Mermaid config JSON Schema does not have valid defaults! Errors were ${JSON.stringify(
+        validate.errors,
+        undefined,
+        2
+      )}`
+    );
+  }
+
+  return mermaidDefaultConfig;
+}
+
+/**
+ * Vite plugin that handles JSON Schemas saved as a `.schema.yaml` file.
+ *
+ * Use `my-example.schema.yaml?only-defaults=true` to only load the default values.
+ */
+export default function jsonSchemaPlugin(): PluginOption {
+  return {
+    name: 'json-schema-plugin',
+    transform(src: string, id: string) {
+      const idAsUrl = new URL(id, 'file:///');
+
+      if (!idAsUrl.pathname.endsWith('schema.yaml')) {
+        return;
+      }
+
+      if (idAsUrl.searchParams.get('only-defaults')) {
+        const jsonSchema = load(src, {
+          filename: idAsUrl.pathname,
+          // only allow JSON types in our YAML doc (will probably be default in YAML 1.3)
+          // e.g. `true` will be parsed a boolean `true`, `True` will be parsed as string `"True"`.
+          schema: JSON_SCHEMA,
+        }) as JSONSchemaType<MermaidConfig>;
+        return {
+          code: `export default ${JSON.stringify(generateDefaults(jsonSchema), undefined, 2)};`,
+          map: null, // no source map
+        };
+      } else {
+        return {
+          code: `export default ${JSON.stringify(
+            load(src, {
+              filename: idAsUrl.pathname,
+              // only allow JSON types in our YAML doc (will probably be default in YAML 1.3)
+              // e.g. `true` will be parsed a boolean `true`, `True` will be parsed as string `"True"`.
+              schema: JSON_SCHEMA,
+            }),
+            undefined,
+            2
+          )};`,
+          map: null, // provide source map if available
+        };
+      }
+    },
+  };
+}