Truncate repl output as length crosses threshold

Calvas performance can be drastically affected as the size of the repl
output window grows.

This commit adds a config entry `replOutputMaxLines` which if set to a
non-0 number will cause the output window to be truncated if it grows
beyond this threshold.

Fixes #804

CHANGELOG.md

@@ -5,6 +5,9 @@ Changes to Calva.
 ## [Unreleased]
 
 - Fix: [Rogue loops that print output to stdout cause Calva to hang](https://github.com/BetterThanTomorrow/calva/issues/2010)
+- Fix: [Output window becomes very slow when number of lines of content is very high](https://github.com/BetterThanTomorrow/calva/issues/804)
+- Partial Fix: [Output window becomes very slow when number of lines of content is very high](https://github.com/BetterThanTomorrow/calva/issues/942)
+
 ## [2.0.323] - 2023-01-07
 
 - Fix: [Provider completions not handling errors gracefully](https://github.com/BetterThanTomorrow/calva/issues/2006)

package.json

@@ -775,6 +775,11 @@
             "type": "number",
             "default": 100
           },
+          "calva.replOutputMaxLines": {
+            "markdownDescription": "The maximum number of lines to retain in the repl output window. Having the repl output window grow too large can significantly affect performance. Setting this to 0 will disable truncating",
+            "type": "number",
+            "default": 1000
+          },
           "calva.depsEdnJackInExecutable": {
             "markdownDescription": "Which executable should Calva Jack-in use for starting a deps.edn project? The default is to let Calva choose. It will choose `clojure` if that is installed and working. Otherwise `deps.clj`, which is bundled with Calva, will be used. (This settings has no effect on Windows, where `deps.clj` will always be used.)",
             "enum": [

src/config.ts

@@ -15,6 +15,7 @@ const KEYBINDINGS_ENABLED_CONFIG_KEY = 'calva.keybindingsEnabled';
 const KEYBINDINGS_ENABLED_CONTEXT_KEY = 'calva:keybindingsEnabled';
 
 const REPL_OUTPUT_THROTTLE_RATE_CONFIG_KEY = 'calva.replOutputThrottleRate';
+const REPL_OUTPUT_MAX_LINES_CONFIG_KEY = 'calva.replOutputMaxLines';
 
 type ReplSessionType = 'clj' | 'cljs';
 
@@ -237,6 +238,7 @@ export {
   KEYBINDINGS_ENABLED_CONFIG_KEY,
   KEYBINDINGS_ENABLED_CONTEXT_KEY,
   REPL_OUTPUT_THROTTLE_RATE_CONFIG_KEY,
+  REPL_OUTPUT_MAX_LINES_CONFIG_KEY,
   documentSelector,
   ReplSessionType,
   getConfig,

src/results-output/results-doc.ts

@@ -20,6 +20,10 @@ const RESULTS_DOC_NAME = `output.${config.REPL_FILE_EXT}`;
 const REPL_OUTPUT_THROTTLE_RATE = vscode.workspace
   .getConfiguration()
   .get<number>(config.REPL_OUTPUT_THROTTLE_RATE_CONFIG_KEY);
+const REPL_OUTPUT_MAX_LINES = vscode.workspace
+  .getConfiguration()
+  .get<number>(config.REPL_OUTPUT_MAX_LINES_CONFIG_KEY);
+
 const PROMPT_HINT = 'Use `alt+enter` to evaluate';
 
 const START_GREETINGS = [
@@ -306,10 +310,22 @@ async function writeToResultsDoc({ text, onAppended }: ResultsBufferEntry): Prom
   const insertPosition = doc.positionAt(Infinity);
   const edit = new vscode.WorkspaceEdit();
   const editText = util.stripAnsi(text);
+
+  if (REPL_OUTPUT_MAX_LINES > 0 && doc.lineCount > REPL_OUTPUT_MAX_LINES) {
+    edit.delete(
+      docUri,
+      new vscode.Range(
+        new vscode.Position(0, 0),
+        new vscode.Position(doc.lineCount - REPL_OUTPUT_MAX_LINES, 0)
+      )
+    );
+  }
+
   edit.insert(docUri, insertPosition, editText);
   if (!((await vscode.workspace.applyEdit(edit)) && (await doc.save()))) {
     return;
   }
+
   onAppended?.(
     new vscode.Location(docUri, insertPosition),
     new vscode.Location(docUri, doc.positionAt(Infinity))

src/results-output/util.ts

@@ -24,7 +24,7 @@ function splitEditQueueForTextBatching(
   const nextBatch = takeWhile(editQueue, (value, index) => {
     return index < maxBatchSize && !value.onAppended;
   }).map((x) => x.text);
-  const remainingEditQueue = [...editQueue].slice(nextBatch.length);
+  const remainingEditQueue = editQueue.slice(nextBatch.length);
   return [nextBatch, remainingEditQueue];
 }