Re-add ability to parse frontmatter like ---json.

src/formats/frontmatter.js

@@ -2,21 +2,42 @@ import matter from 'gray-matter';
 import tomlEng from 'toml';
 import YAML from './yaml';
 
+const parsers = {
+  toml: tomlEng.parse.bind(tomlEng),
+  json: (input) => {
+    let JSONinput = input.trim();
+    // Fix JSON if leading and trailing brackets were trimmed.
+    if (JSONinput.substr(0, 1) !== '{') {
+      JSONinput = '{' + JSONinput;
+    }
+    if (JSONinput.substr(-1) !== '}') {
+      JSONinput = JSONinput + '}';
+    }
+    return matter.engines.json.parse(JSONinput);
+  },
+}
+
 function inferFrontmatterFormat(str) {
   const firstLine = str.substr(0, str.indexOf('\n')).trim();
+  if ((firstLine.length > 3) && (firstLine.substr(0, 3) === "---")) {
+    // No need to infer, `gray-matter` will handle things like `---toml` for us.
+    return;
+  }
   switch (firstLine) {
     case "---":
       return { language: "yaml", delimiters: "---" };
     case "+++":
-      return { language: "toml", delimiters: "+++", engines: { toml: tomlEng.parse.bind(tomlEng) } };
+      return { language: "toml", delimiters: "+++" };
     case "{":
-      return { language: "json", delimiters: ["{", "}"], engines: { json: ((input) => matter.engines.json.parse('{' + input + '}')) } };
+      return { language: "json", delimiters: ["{", "}"] };
+    default:
+      throw "Unrecgonized front-matter format.";
   }
 }
 
 export default class Frontmatter {
   fromFile(content) {
-    const result = matter(content, inferFrontmatterFormat(content));
+    const result = matter(content, { engines: parsers, ...inferFrontmatterFormat(content) });
     const data = result.data;
     data.body = result.content;
     return data;