Function to strip JSON comments

crates/yaak-templates/src/lib.rs

@@ -1,6 +1,7 @@
 pub mod error;
 pub mod escape;
 pub mod format_json;
+pub mod strip_json_comments;
 pub mod parser;
 pub mod renderer;
 pub mod wasm;

crates/yaak-templates/src/strip_json_comments.rs

@@ -0,0 +1,224 @@
+/// Strips comments from JSONC, preserving the original formatting as much as possible.
+///
+/// - Trailing comments on a line are removed (along with preceding whitespace)
+/// - Whole-line comments are removed, including the line itself
+/// - Block comments are removed, including any lines that become empty
+/// - Comments inside strings and template tags are left alone
+pub fn strip_json_comments(text: &str) -> String {
+    let mut chars = text.chars().peekable();
+    let mut result = String::with_capacity(text.len());
+    let mut in_string = false;
+    let mut in_template_tag = false;
+
+    loop {
+        let current_char = match chars.next() {
+            None => break,
+            Some(c) => c,
+        };
+
+        // Handle JSON strings
+        if in_string {
+            result.push(current_char);
+            match current_char {
+                '"' => in_string = false,
+                '\\' => {
+                    if let Some(c) = chars.next() {
+                        result.push(c);
+                    }
+                }
+                _ => {}
+            }
+            continue;
+        }
+
+        // Handle template tags
+        if in_template_tag {
+            result.push(current_char);
+            if current_char == ']' && chars.peek() == Some(&'}') {
+                result.push(chars.next().unwrap());
+                in_template_tag = false;
+            }
+            continue;
+        }
+
+        // Check for template tag start
+        if current_char == '$' && chars.peek() == Some(&'{') {
+            let mut lookahead = chars.clone();
+            lookahead.next(); // skip {
+            if lookahead.peek() == Some(&'[') {
+                in_template_tag = true;
+                result.push(current_char);
+                result.push(chars.next().unwrap()); // {
+                result.push(chars.next().unwrap()); // [
+                continue;
+            }
+        }
+
+        // Check for line comment
+        if current_char == '/' && chars.peek() == Some(&'/') {
+            chars.next(); // skip second /
+            // Consume until newline
+            loop {
+                match chars.peek() {
+                    Some(&'\n') | None => break,
+                    Some(_) => {
+                        chars.next();
+                    }
+                }
+            }
+            // Trim trailing whitespace that preceded the comment
+            let trimmed_len = result.trim_end_matches(|c: char| c == ' ' || c == '\t').len();
+            result.truncate(trimmed_len);
+            continue;
+        }
+
+        // Check for block comment
+        if current_char == '/' && chars.peek() == Some(&'*') {
+            chars.next(); // skip *
+            // Consume until */
+            loop {
+                match chars.next() {
+                    None => break,
+                    Some('*') if chars.peek() == Some(&'/') => {
+                        chars.next(); // skip /
+                        break;
+                    }
+                    Some(_) => {}
+                }
+            }
+            // Trim trailing whitespace that preceded the comment
+            let trimmed_len = result.trim_end_matches(|c: char| c == ' ' || c == '\t').len();
+            result.truncate(trimmed_len);
+            // Skip whitespace/newline after the block comment if the next line is content
+            // (this handles the case where the block comment is on its own line)
+            continue;
+        }
+
+        if current_char == '"' {
+            in_string = true;
+        }
+
+        result.push(current_char);
+    }
+
+    // Remove lines that are now empty (were comment-only lines)
+    result
+        .lines()
+        .filter(|line| !line.trim().is_empty())
+        .collect::<Vec<&str>>()
+        .join("\n")
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::strip_json_comments::strip_json_comments;
+
+    #[test]
+    fn test_no_comments() {
+        let input = r#"{
+  "foo": "bar",
+  "baz": 123
+}"#;
+        assert_eq!(strip_json_comments(input), input);
+    }
+
+    #[test]
+    fn test_trailing_line_comment() {
+        assert_eq!(
+            strip_json_comments(r#"{
+  "foo": "bar", // this is a comment
+  "baz": 123
+}"#),
+            r#"{
+  "foo": "bar",
+  "baz": 123
+}"#
+        );
+    }
+
+    #[test]
+    fn test_whole_line_comment() {
+        assert_eq!(
+            strip_json_comments(r#"{
+  // this is a comment
+  "foo": "bar"
+}"#),
+            r#"{
+  "foo": "bar"
+}"#
+        );
+    }
+
+    #[test]
+    fn test_inline_block_comment() {
+        assert_eq!(
+            strip_json_comments(r#"{
+  "foo": /* a comment */ "bar"
+}"#),
+            r#"{
+  "foo": "bar"
+}"#
+        );
+    }
+
+    #[test]
+    fn test_whole_line_block_comment() {
+        assert_eq!(
+            strip_json_comments(r#"{
+  /* a comment */
+  "foo": "bar"
+}"#),
+            r#"{
+  "foo": "bar"
+}"#
+        );
+    }
+
+    #[test]
+    fn test_multiline_block_comment() {
+        assert_eq!(
+            strip_json_comments(r#"{
+  /**
+   * Hello World!
+   */
+  "foo": "bar"
+}"#),
+            r#"{
+  "foo": "bar"
+}"#
+        );
+    }
+
+    #[test]
+    fn test_comment_inside_string_preserved() {
+        let input = r#"{
+  "foo": "// not a comment",
+  "bar": "/* also not */"
+}"#;
+        assert_eq!(strip_json_comments(input), input);
+    }
+
+    #[test]
+    fn test_comment_inside_template_tag_preserved() {
+        let input = r#"{
+  "foo": ${[ fn("// hi", "/* hey */") ]}
+}"#;
+        assert_eq!(strip_json_comments(input), input);
+    }
+
+    #[test]
+    fn test_multiple_comments() {
+        assert_eq!(
+            strip_json_comments(r#"{
+  // first comment
+  "foo": "bar", // trailing
+  /* block */
+  "baz": 123
+}"#),
+            r#"{
+  "foo": "bar",
+  "baz": 123
+}"#
+        );
+    }
+}