style: restore explanatory comments and fix indentation in regexp_match scalar path

Author: andygrove

datafusion/functions/src/regex/regexpmatch.rs

@@ -176,22 +176,25 @@ fn regexp_match_scalar_pattern(args: &[ColumnarValue]) -> Result<Option<ArrayRef
     else {
         return Ok(None);
     };
-let flags = match flags {
-    Some(ColumnarValue::Array(_)) => return Ok(None),
-    Some(ColumnarValue::Scalar(flags)) => Some(flags),
-    None => None,
-};
-
-let value_type = values.data_type();
-
-if !matches!(pattern.try_as_str(), Some(Some(_)))
-    || &pattern.data_type() != value_type
-    || flags.is_some_and(|flags| {
-        flags.try_as_str() == Some(Some("g")) || &flags.data_type() != value_type
-    })
-{
-    return Ok(None);
-}
+    let flags = match flags {
+        // An array of flags has to be zipped with the values row by row.
+        Some(ColumnarValue::Array(_)) => return Ok(None),
+        Some(ColumnarValue::Scalar(flags)) => Some(flags),
+        None => None,
+    };
+
+    // The kernel requires the values, the pattern and the flags to share one
+    // string type.
+    let value_type = values.data_type();
+
+    if !matches!(pattern.try_as_str(), Some(Some(_)))
+        || &pattern.data_type() != value_type
+        || flags.is_some_and(|flags| {
+            flags.try_as_str() == Some(Some("g")) || &flags.data_type() != value_type
+        })
+    {
+        return Ok(None);
+    }
 
     let pattern = pattern.to_scalar()?;
     let flags = flags.map(ScalarValue::to_scalar).transpose()?;