tr.rs: replace split_once method with custom function

Author: SarcasticNastik

src/descriptor/tr.rs

@@ -203,7 +203,7 @@ where
     }
 }
 
-fn parse_tr<'a>(s: &'a str) -> Result<Tree<'a>, Error> {
+fn parse_tr(s: &str) -> Result<Tree, Error> {
     for ch in s.bytes() {
         if ch > 0x7f {
             return Err(Error::Unprintable(ch));
@@ -224,8 +224,8 @@ fn parse_tr<'a>(s: &'a str) -> Result<Tree<'a>, Error> {
                 args: vec![key_path],
             });
         }
-        let (key, script) = rest
-            .split_once(',')
+        // use str::split_once() method to refactor this when compiler version bumps up
+        let (key, script) = split_once(rest, ',')
             .ok_or_else(|| Error::BadDescriptor("invalid taproot descriptor".to_string()))?;
         let key_path = Tree {
             name: key,
@@ -237,7 +237,7 @@ fn parse_tr<'a>(s: &'a str) -> Result<Tree<'a>, Error> {
                 args: vec![key_path],
             });
         }
-        let (script_path, rest) = expression::Tree::from_slice_helper_curly(script, 0)?;
+        let (script_path, rest) = expression::Tree::from_slice_helper_curly(script, 1)?;
         if rest.is_empty() {
             Ok(Tree {
                 name: "tr",
@@ -250,3 +250,22 @@ fn parse_tr<'a>(s: &'a str) -> Result<Tree<'a>, Error> {
         Err(Error::Unexpected("invalid taproot descriptor".to_string()))
     };
 }
+
+fn split_once(inp: &str, delim: char) -> Option<(&str, &str)> {
+    return if inp.len() == 0 {
+        None
+    } else {
+        let mut found = 0;
+        for (idx, ch) in inp.chars().enumerate() {
+            if ch == delim {
+                found = idx;
+                break;
+            }
+        }
+        if found == inp.len() - 1 {
+            Some((&inp[..], &""))
+        } else {
+            Some((&inp[..found], &inp[found + 1..]))
+        }
+    };
+}