Return only partial text edits on formatting request

Author: Xanewok

rls/src/actions/format.rs

@@ -9,8 +9,9 @@ use std::process::{Command, Stdio};
 use std::string::FromUtf8Error;
 
 use log::debug;
+use lsp_types::{Position, Range, TextEdit};
 use rand::{distributions, thread_rng, Rng};
-use rustfmt_nightly::{Config, Input, Session};
+use rustfmt_nightly::{Config, Input, ModifiedLines, NewlineStyle, Session};
 use serde_json;
 
 /// Specifies which `rustfmt` to use.
@@ -66,6 +67,41 @@ impl Rustfmt {
             Rustfmt::External { path, cwd } => format_external(path, cwd, input, cfg),
         }
     }
+
+    pub fn calc_text_edits(&self, input: String, mut cfg: Config) -> Result<Vec<TextEdit>, Error> {
+        cfg.set().emit_mode(rustfmt_nightly::EmitMode::ModifiedLines);
+
+        let native = if cfg!(windows) { "\r\n" } else { "\n" };
+        let newline = match cfg.newline_style() {
+            NewlineStyle::Windows => "\r\n",
+            NewlineStyle::Unix | NewlineStyle::Auto => "\n",
+            NewlineStyle::Native => native,
+        };
+
+        let output = self.format(input, cfg)?;
+        let ModifiedLines { chunks } = output.parse().map_err(|_| Error::Failed)?;
+
+        Ok(chunks
+            .into_iter()
+            .map(|item| {
+                // Rustfmt's line indices are 1-based
+                let start_line = u64::from(item.line_number_orig) - 1;
+                let removed = u64::from(item.lines_removed);
+                // If there is only one line and we add them, we may underflow.
+                let removed = if removed == 0 { 0 } else { removed - 1 };
+                TextEdit {
+                    range: Range {
+                        start: Position::new(start_line, 0),
+                        // We don't extend the range past the last line because
+                        // sometimes it may not exist, skewing the diff and
+                        // making us add an invalid additional trailing newline.
+                        end: Position::new(start_line + removed, u64::max_value()),
+                    },
+                    new_text: item.lines.join(newline),
+                }
+            })
+            .collect())
+    }
 }
 
 fn format_external(

rls/src/actions/requests.rs

@@ -620,7 +620,7 @@ impl RequestAction for CodeAction {
 }
 
 impl RequestAction for Formatting {
-    type Response = [TextEdit; 1];
+    type Response = Vec<TextEdit>;
 
     fn fallback_response() -> Result<Self::Response, ResponseError> {
         Err(ResponseError::Message(
@@ -638,7 +638,7 @@ impl RequestAction for Formatting {
 }
 
 impl RequestAction for RangeFormatting {
-    type Response = [TextEdit; 1];
+    type Response = Vec<TextEdit>;
 
     fn fallback_response() -> Result<Self::Response, ResponseError> {
         Err(ResponseError::Message(
@@ -660,7 +660,7 @@ fn reformat(
     selection: Option<Range>,
     opts: &FormattingOptions,
     ctx: &InitActionContext,
-) -> Result<[TextEdit; 1], ResponseError> {
+) -> Result<Vec<TextEdit>, ResponseError> {
     ctx.quiescent.store(true, Ordering::SeqCst);
     trace!("Reformat: {:?} {:?} {} {}", doc, selection, opts.tab_size, opts.insert_spaces);
     let path = parse_file_path!(&doc.uri, "reformat")?;
@@ -683,7 +683,6 @@ fn reformat(
         }
     };
 
-    let range_whole_file = ls_util::range_from_file_string(&input);
     let mut config = ctx.fmt_config().get_rustfmt_config().clone();
     if !config.was_set().hard_tabs() {
         config.set().hard_tabs(!opts.insert_spaces);
@@ -722,9 +721,9 @@ fn reformat(
         config.set().file_lines(file_lines);
     };
 
-    let formatted_text = ctx
+    let text_edits = ctx
         .formatter()
-        .format(input, config)
+        .calc_text_edits(input, config)
         .map_err(|msg| ResponseError::Message(ErrorCode::InternalError, msg.to_string()))?;
 
     // Note that we don't need to update the VFS, the client echos back the
@@ -737,9 +736,7 @@ fn reformat(
         ));
     }
 
-    // If Rustfmt returns range of text that changed,
-    // we will be able to pass only range of changed text to the client.
-    Ok([TextEdit { range: range_whole_file, new_text: formatted_text }])
+    Ok(text_edits)
 }
 
 impl RequestAction for ResolveCompletion {

tests/client.rs

@@ -1758,7 +1758,7 @@ fn client_reformat() {
             start: Position { line: 0, character: 0 },
             end: Position { line: 2, character: 0 },
         },
-        new_text: "pub mod foo;\npub fn main() {\n    let world = \"world\";\n    println!(\"Hello, {}!\", world);\n}\n".to_string(),
+        new_text: "pub mod foo;\npub fn main() {\n    let world = \"world\";\n    println!(\"Hello, {}!\", world);\n}".to_string(),
     });
 }