feat: add format range functionality for partial code formatting

malva/src/error.rs

@@ -8,6 +8,12 @@ pub enum Error {
     /// and the second component is error line number,
     /// and the third component is error column number.
     Parser(raffia::error::Error, usize, usize),
+
+    /// The specified range is outside of the source file bounds.
+    RangeOutOfBounds {
+        range: std::ops::Range<usize>,
+        source_len: usize,
+    },
 }
 
 impl Display for Error {
@@ -16,6 +22,13 @@ impl Display for Error {
             Error::Parser(error, line, col) => {
                 write!(f, "syntax error at line {line}, col {col}: {}", error.kind)
             }
+            Error::RangeOutOfBounds { range, source_len } => {
+                write!(
+                    f,
+                    "range {}..{} is out of bounds (source length: {})",
+                    range.start, range.end, source_len
+                )
+            }
         }
     }
 }

malva/src/lib.rs

@@ -6,8 +6,10 @@ mod doc_gen;
 mod error;
 mod helpers;
 mod line_bounds;
+pub mod range;
 mod state;
 
+pub use crate::range::FormatRangeResult;
 use crate::{config::FormatOptions, ctx::Ctx, doc_gen::DocGen, state::State};
 pub use crate::{error::Error, line_bounds::LineBounds};
 pub use raffia::Syntax;
@@ -107,3 +109,18 @@ pub fn detect_syntax(path: impl AsRef<Path>) -> Option<Syntax> {
         _ => None,
     }
 }
+
+/// Format a specific range of CSS code.
+///
+/// This function formats only the specified range of code, which is useful for
+/// editor integrations where users select a portion of code to format.
+///
+/// See [`crate::range::format_range`] for more details.
+pub fn format_range(
+    source: &str,
+    range: std::ops::Range<usize>,
+    syntax: Syntax,
+    options: &FormatOptions,
+) -> Result<FormatRangeResult, Error> {
+    crate::range::format_range(source, range, syntax, options)
+}