enh(parser): Better errors when one language requires another (#2311)

joshgoebel · web-flow · commit 2d003576d5d9 · 2019-12-07T17:28:52.000-05:00
diff --git a/CHANGES.md b/CHANGES.md
@@ -7,6 +7,7 @@ New styles:
   none.
 
 Improvements:
+- enh(parser): add better error when a language requirement is missing () [Josh Goebel][]
 - fix(sql): backslash is not used to escape in strings in standard SQL (#1748) [Mike Schall][]
 - enh(ebnf) add backticks as additional string variant (#2290) [Chris Marchesi][]
 - fix(themes): fix inconsistencies between some themes padding/spacing (#2300) [Josh Goebel][]
diff --git a/docs/api.rst b/docs/api.rst
@@ -126,6 +126,18 @@ Looks up a language by name or alias.
 Returns the language object if found, ``undefined`` otherwise.
 
 
+``requireLanguage(name)``
+---------------------
+
+Looks up a language by name or alias.
+
+This should be used when one language definition depends on another.
+Using this function (vs ``getLanguage``) will provide better error messaging
+when a required language is missing.
+
+Returns the language object if found, raises a hard error otherwise.
+
+
 ``debugMode()``
 ---------------
 
diff --git a/src/highlight.js b/src/highlight.js
@@ -958,6 +958,20 @@ https://highlightjs.org/
     return objectKeys(languages);
   }
 
+  /*
+    intended usage: When one language truly requires another
+
+    Unlike `getLanguage`, this will throw when the requested language
+    is not available.
+  */
+  function requireLanguage(name) {
+    var lang = getLanguage(name);
+    if (lang) { return lang; }
+
+    var err = new Error('The \'{}\' language is required, but not loaded.'.replace('{}',name));
+    throw err;
+  }
+
   function getLanguage(name) {
     name = (name || '').toLowerCase();
     return languages[name] || languages[aliases[name]];
@@ -980,6 +994,7 @@ https://highlightjs.org/
   hljs.registerLanguage = registerLanguage;
   hljs.listLanguages = listLanguages;
   hljs.getLanguage = getLanguage;
+  hljs.requireLanguage = requireLanguage;
   hljs.autoDetection = autoDetection;
   hljs.inherit = inherit;
   hljs.debugMode = function() { SAFE_MODE = false; }
diff --git a/src/languages/arduino.js b/src/languages/arduino.js
@@ -94,7 +94,7 @@ function(hljs) {
         'DEFAULT OUTPUT INPUT HIGH LOW'
   };
 
-  var ARDUINO = hljs.getLanguage('cpp').rawDefinition();
+  var ARDUINO = hljs.requireLanguage('cpp').rawDefinition();
 
   var kws = ARDUINO.keywords;
 
