config-loader,cli: better presentation of config schema validation errors

packages/cli/src/lib/config.ts

@@ -40,15 +40,24 @@ export async function loadCliConfig(configArgs: string[]) {
     `Loaded config from ${appConfigs.map(c => c.context).join(', ')}`,
   );
 
-  const frontendAppConfigs = schema.process(appConfigs, {
-    visiblity: ['frontend'],
-  });
-  const frontendConfig = ConfigReader.fromConfigs(frontendAppConfigs);
+  try {
+    const frontendAppConfigs = schema.process(appConfigs, {
+      visiblity: ['frontend'],
+    });
+    const frontendConfig = ConfigReader.fromConfigs(frontendAppConfigs);
 
-  return {
-    schema,
-    appConfigs,
-    frontendConfig,
-    frontendAppConfigs,
-  };
+    return {
+      schema,
+      appConfigs,
+      frontendConfig,
+      frontendAppConfigs,
+    };
+  } catch (error) {
+    const maybeSchemaError = error as Error & { messages?: string[] };
+    if (maybeSchemaError.messages) {
+      const messages = maybeSchemaError.messages.join('\n  ');
+      throw new Error(`Configuration does not match schema\n\n  ${messages}`);
+    }
+    throw error;
+  }
 }

packages/config-loader/src/lib/schema/compile.ts

@@ -104,10 +104,14 @@ export function compileConfigSchemas(
 
     const valid = validate(config);
     if (!valid) {
-      // TODO(Rugvip): better messages here, with more context such as which file the error occurred in
-      const errors = ajv.errorsText(validate.errors);
+      const errors = validate.errors ?? [];
       return {
-        errors: [errors],
+        errors: errors.map(({ dataPath, message, params }) => {
+          const paramStr = Object.entries(params)
+            .map(([name, value]) => `${name}=${value}`)
+            .join(' ');
+          return `Config ${message || ''} { ${paramStr} } at ${dataPath}`;
+        }),
         visibilityByPath: new Map(),
       };
     }

packages/config-loader/src/lib/schema/load.ts

@@ -61,9 +61,11 @@ export async function loadConfigSchema(
     ): AppConfig[] {
       const result = validate(configs);
       if (result.errors) {
-        throw new Error(
+        const error = new Error(
           `Config validation failed, ${result.errors.join('; ')}`,
         );
+        (error as any).messages = result.errors;
+        throw error;
       }
 
       let processedConfigs = configs;