Simplified yaml parser to have fewer dependencies

refs https://linear.app/tryghost/issue/CORE-35/refactor-route-and-redirect-settings
refs 5715aa2155 (diff-48644be82a9b957e5e627bf7b0f2f73cdb1d63851ffad68c7c178c5886495bb8R52-R57)

- Simplified the yaml parser implementation to take in a single parameter, this move will allove to simplify the logic in the route settings + opens a door to unify handling with redirects yaml parsing!
- We loose the "filename" from the error information but that was a generic "routes.yaml" anyway and would be thrown only when somebody uploaded a routes.yaml file (no real added value).
- The debug statement should be moved to contain related filepath+other info to the calling module instead
- An additional error handler was borrowed from the redirects yaml parsing logic that was introduced in a referenced commit - it still makes sense to keep it for routes.yaml configuration

core/server/services/route-settings/yaml-parser.js

@@ -1,36 +1,49 @@
 const yaml = require('js-yaml');
-const debug = require('@tryghost/debug')('frontend:services:settings:yaml-parser');
 const tpl = require('@tryghost/tpl');
 const errors = require('@tryghost/errors');
 
 const messages = {
-    error: 'Could not parse {file}: {context}.',
-    help: 'Check your {file} file for typos and fix the named issues.'
+    error: 'Could not parse provided YAML file: {context}.',
+    help: 'Check provided file for typos and fix the named issues.',
+    yamlParse: 'YAML input cannot be a plain string. Check the format of your YAML file.',
+    yamlParseHelp: 'https://ghost.org/docs/themes/routing/'
 };
 
 /**
- * Takes a YAML file, parses it and returns a JSON Object
- * @param {YAML} file the YAML file utf8 encoded
- * @param {String} fileName the name of the file incl. extension
+ * Takes a YAML formatted string and parses it and returns a JSON Object
+ * @param {String} file the YAML file utf8 encoded
  * @returns {Object} parsed
  */
-module.exports = function parseYaml(file, fileName) {
+module.exports = function parseYaml(file) {
     try {
         const parsed = yaml.load(file);
 
-        debug('YAML settings file parsed:', fileName);
+        // yaml.load passes almost every yaml code.
+        // Because of that, it's hard to detect if there's an error in the file.
+        // But one of the obvious errors is the plain string output.
+        // Here we check if the user made this mistake.
+        if (typeof parsed === 'string') {
+            throw new errors.BadRequestError({
+                message: messages.yamlParse,
+                help: messages.yamlParseHelp
+            });
+        }
 
         return parsed;
     } catch (error) {
+        if (errors.utils.isIgnitionError(error)) {
+            throw error;
+        }
+
         // CASE: parsing failed, `js-yaml` tells us exactly what and where in the
         // `reason` property as well as in the message.
         // As the file uploaded is invalid, the person uploading must fix this - it's a 4xx error
         throw new errors.IncorrectUsageError({
-            message: tpl(messages.error, {file: fileName, context: error.reason}),
+            message: tpl(messages.error, {context: error.reason}),
             code: 'YAML_PARSER_ERROR',
             context: error.message,
             err: error,
-            help: tpl(messages.help, {file: fileName})
+            help: messages.help
         });
     }
 };

test/unit/services/settings/yaml-parser.test.js

@@ -20,7 +20,7 @@ describe('UNIT > Settings Service yaml parser:', function () {
         it('parses correct yaml file', function () {
             const file = fs.readFileSync(path.join(__dirname, '../../../utils/fixtures/settings/', 'goodroutes.yaml'), 'utf8');
 
-            const result = yamlParser(file, 'goodroutes.yaml');
+            const result = yamlParser(file);
             should.exist(result);
             result.should.be.an.Object().with.properties('routes', 'collections', 'taxonomies');
             yamlSpy.calledOnce.should.be.true();
@@ -30,13 +30,13 @@ describe('UNIT > Settings Service yaml parser:', function () {
             const file = fs.readFileSync(path.join(__dirname, '../../../utils/fixtures/settings/', 'badroutes.yaml'), 'utf8');
 
             try {
-                const result = yamlParser(file, 'badroutes.yaml');
+                const result = yamlParser(file);
                 should.not.exist(result);
             } catch (error) {
                 should.exist(error);
-                error.message.should.eql('Could not parse badroutes.yaml: bad indentation of a mapping entry.');
+                error.message.should.eql('Could not parse provided YAML file: bad indentation of a mapping entry.');
                 error.context.should.containEql('bad indentation of a mapping entry (5:14)');
-                error.help.should.eql('Check your badroutes.yaml file for typos and fix the named issues.');
+                error.help.should.eql('Check provided file for typos and fix the named issues.');
                 yamlSpy.calledOnce.should.be.true();
             }
         });