fix(validator): property names in custom error messages (#63)

fixes #50

packages/validator/src/humanizer/ErrorHumanizer.ts

@@ -1,5 +1,6 @@
 import {
   ArrayFormatter,
+  CustomErrorMessageFormatter,
   Formatter,
   NumericFormatter,
   ObjectFormatter,
@@ -14,6 +15,7 @@ import { ErrorObject } from 'ajv';
 export class ErrorHumanizer {
   private readonly formatters: ReadonlyArray<Formatter> = [
     new ArrayFormatter(),
+    new CustomErrorMessageFormatter(),
     new NumericFormatter(),
     new ObjectFormatter(),
     new StringFormatter(),

packages/validator/src/humanizer/formatters/CustomErrorMessageFormatter.ts

@@ -0,0 +1,18 @@
+import { Formatter } from './Formatter';
+import { WordingHelper } from './WordingHelper';
+import { ErrorObject } from 'ajv';
+
+export class CustomErrorMessageFormatter implements Formatter {
+  public format(error: ErrorObject<'errorMessage'>): string {
+    if (error.keyword !== 'errorMessage') {
+      return;
+    }
+
+    const propName = WordingHelper.extractPropertyName(error.instancePath);
+
+    return error.message.replace(
+      /^The property must/,
+      `The property \`${propName}\` must`
+    );
+  }
+}

packages/validator/src/humanizer/formatters/index.ts

@@ -1,4 +1,5 @@
 export { ArrayFormatter } from './ArrayFormatter';
+export { CustomErrorMessageFormatter } from './CustomErrorMessageFormatter';
 export { Formatter } from './Formatter';
 export { NumericFormatter } from './NumericFormatter';
 export { ObjectFormatter } from './ObjectFormatter';

packages/validator/tests/error-humanizer.spec.ts

@@ -77,6 +77,49 @@ describe('ErrorHumanizer', () => {
       result.should.deep.eq([expected]);
     });
 
+    it('should parameterize original "errorMessage" if necessary', async () => {
+      const input: OpenAPIV3.Document = {
+        ...getBaseOasDoc(),
+        components: {
+          headers: {
+            CustomHeader: {
+              schema: {},
+              content: {
+                'application/json': {
+                  example: 42
+                }
+              }
+            }
+          }
+        }
+      };
+
+      const expected = {
+        message:
+          'Error at /components/headers/CustomHeader: The property `CustomHeader` must have either a `schema` or `content` option',
+        locationParts: [
+          {
+            text: 'Error at'
+          },
+          {
+            text: '/components/headers/CustomHeader',
+            jsonPointer: '/components/headers/CustomHeader'
+          }
+        ],
+        messageParts: [
+          {
+            text: 'The property `CustomHeader` must have either a `schema` or `content` option'
+          }
+        ]
+      };
+
+      const result = humanizer
+        .humanizeErrors(await oasValidator.verify(input))
+        .map(({ originalError, ...rest }) => ({ ...rest }));
+
+      result.should.deep.eq([expected]);
+    });
+
     it('should humanize "required" error on root path', async () => {
       const { host, ...input } = getBaseSwaggerDoc();