Fix flat json front matter

CHANGELOG.md

@@ -9,6 +9,8 @@
 
 ## Unreleased
 
+* Fix parsing of flat JSON front matter objects
+
 ## v0.1.1 (October 11, 2024)
 
 * Automated release setup

README.md

@@ -1,3 +1,65 @@
 # Matterhorn
 
 A lenient front matter parsing crate that supports files prefixed with YAML, JSON, and TOML front matter.
+The type of front matter is detected automatically.
+
+The order of input keys is retained, and parsing is lenient where possible.
+Notably, duplicate keys are supported in YAML front matter.
+
+All parsed front matter is returned as a `serde_json` Value.
+
+## Usage
+
+```bash
+cargo add matterhorn
+```
+
+```rust
+const YAML_SOURCE_FILE: &str = r#"
+---
+title: Hello World
+order: 12
+---
+# Main Title
+
+Cras mattis consectetur purus sit amet fermentum.
+"#;
+
+const TOML_SOURCE_FILE: &str = r#"
++++
+title = "Hello World"
+order = 12
++++
+# Main Title
+
+Cras mattis consectetur purus sit amet fermentum.
+"#;
+
+const JSON_SOURCE_FILE: &str = r#"
+{
+  "title": "Hello World",
+  "order": 12
+}
+# Main Title
+
+Cras mattis consectetur purus sit amet fermentum.
+"#;
+
+fn main() {
+    let document = matterhorn::parse_document(YAML_SOURCE_FILE).expect("Input should be valid");
+
+    println!("{:#?}", document.front_matter);
+    // Returns:
+    // serde_json::Value::Object {
+    //     "title": serde_json::Value::String("Hello World"),
+    //     "order": serde_json::Value::Number(12),
+    // }
+
+    println!("{:#?}", document.content);
+    // Returns:
+    // "# Main Title\n\nCras mattis consectetur purus sit amet fermentum.\n"
+
+    assert_eq!(matterhorn::parse_document(YAML_SOURCE_FILE), matterhorn::parse_document(TOML_SOURCE_FILE));
+    assert_eq!(matterhorn::parse_document(TOML_SOURCE_FILE), matterhorn::parse_document(JSON_SOURCE_FILE));
+}
+```

src/lib.rs

@@ -49,7 +49,10 @@ pub fn parse_document<'d>(
         document_start + separator.len()
     };
 
-    for (pre_fm_end, _) in original_content.match_indices(separator).skip(1) {
+    for (pre_fm_end, _) in original_content
+        .match_indices(separator)
+        .filter(|(i, _)| *i > fm_start)
+    {
         let post_fm_end = pre_fm_end + separator.len();
         let potential_front_matter = if should_parse_separator {
             &original_content[fm_start..post_fm_end]