fix(options): improved ValidationError messages

Author: michael-ciniawsky

src/options.json

@@ -11,6 +11,12 @@
           "type": "object"
         }
       },
+      "errorMessage": {
+        "properties": {
+          "ctx": "should be {Object} (https://github.com/postcss/postcss-loader#context-ctx)",
+          "path": "should be {String} (https://github.com/postcss/postcss-loader#path)"
+        }
+      },
       "additionalProperties": false
     },
     "exec": {
@@ -39,5 +45,17 @@
       "type": [ "string", "boolean" ]
     }
   },
+  "errorMessage": {
+    "properties": {
+      "exec": "should be {Boolean} (https://github.com/postcss/postcss-loader#exec)",
+      "ident": "should be {String} (https://github.com/postcss/postcss-loader#plugins)",
+      "config": "should be {Object} (https://github.com/postcss/postcss-loader#config)",
+      "parser": "should be {String|Object} (https://github.com/postcss/postcss-loader#parser)",
+      "syntax": "should be {String|Object} (https://github.com/postcss/postcss-loader#syntax)",
+      "stringifier": "should be {String|Object} (https://github.com/postcss/postcss-loader#stringifier)",
+      "plugins": "should be {Array|Object|Function} (https://github.com/postcss/postcss-loader#plugins)",
+      "sourceMap": "should be {String|Boolean} (https://github.com/postcss/postcss-loader#sourcemap)"
+    }
+  },
   "additionalProperties": true
 }

test/__snapshots__/Errors.test.js.snap

@@ -1,7 +1,7 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`Errors Syntax Error 1`] = `
-"Syntax Error 
+"Syntax Error
 
 (1:3) Unexpected separator in property
 
@@ -14,6 +14,8 @@ exports[`Errors Syntax Error 1`] = `
 exports[`Errors Validation Error 1`] = `
 "ValidationError: PostCSS Loader Invalid Options
 
-options.sourceMap should be string,boolean
-"
+options.sourceMap should be {String|Boolean} (https://github.com/postcss/postcss-loader#sourcemap)
+
+    at validateOptions (/Users/Cini/Github/webpack/loaders/postcss/node_modules/@webpack-utilities/schema/src/validateOptions.js:25:11)
+    at Object.loader (/Users/Cini/Github/webpack/loaders/postcss/src/index.js:44:3)"
 `;