Fix: Skip TextEdit when document already formatted (#3864)

* Initial plan

* Fix: Return empty edits when document is already formatted

This change prevents returning unnecessary TextEdits when the formatted
output is identical to the source document. This could potentially fix
issues where empty lines appear to be added to files during formatting.

The minimalEdit function now:
1. Checks if the document text is identical to the formatted result
2. Returns null if no changes are needed
3. The provideEdits function returns an empty array when no edit is needed

This ensures VS Code doesn't apply empty TextEdits which could cause
unexpected behavior with line endings or cursor positioning.

Co-authored-by: ntotten <282782+ntotten@users.noreply.github.com>

* Add logging for when document is already formatted

Co-authored-by: ntotten <282782+ntotten@users.noreply.github.com>

* Address code review feedback

- Fix countTrailingNewlines to use continue instead of break for \r
- Clarify condition in forceFormatDocument to check > 1 instead of !== 1

Co-authored-by: ntotten <282782+ntotten@users.noreply.github.com>

* Update warning message to reflect that 0 edits is valid

Co-authored-by: ntotten <282782+ntotten@users.noreply.github.com>

* Update CHANGELOG.md with fix for unnecessary TextEdits

Added changelog entry documenting the fix for issue #3232 where
unnecessary TextEdits were applied when document was already formatted.

Co-authored-by: ntotten <282782+ntotten@users.noreply.github.com>

* Fix test to format via extension twice for idempotency

Updated the markdown test to call format() twice instead of calling
format() once and prettier.format() once. This better reproduces the
original bug where formatting via the extension multiple times would
add spurious empty lines.

Co-authored-by: ntotten <282782+ntotten@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ntotten <282782+ntotten@users.noreply.github.com>
Co-authored-by: Nathan Totten <nate@zuplo.com>

Author: Copilot

CHANGELOG.md

@@ -14,6 +14,7 @@ All notable changes to the "prettier-vscode" extension will be documented in thi
 - Fixed parser detection fallback when using plugins with Prettier v3
 - Added new Prettier v3 options: `objectWrap`, `experimentalOperatorPosition`
 - Added support for TypeScript config files (`.prettierrc.ts`, `.prettierrc.cts`, `.prettierrc.mts`, `prettier.config.ts`, etc.) introduced in Prettier 3.5.0 - Thanks to [@dr2009](https://github.com/dr2009)
+- Fixed issue where unnecessary TextEdits were applied when document was already formatted, which could cause spurious changes or cursor positioning issues (#3232)
 
 ## [11.0.0]
 

src/PrettierEditService.ts

@@ -202,7 +202,12 @@ export default class PrettierEditService implements Disposable {
       );
 
       const edits = await this.provideEdits(editor.document, { force: true });
-      if (edits.length !== 1) {
+      if (edits.length === 0) {
+        this.loggingService.logInfo("Document is already formatted.");
+        return;
+      }
+      if (edits.length > 1) {
+        this.loggingService.logWarning(`Unexpected multiple edits (${edits.length}), expected 0 or 1`);
         return;
       }
 
@@ -446,11 +451,22 @@ export default class PrettierEditService implements Disposable {
     const duration = new Date().getTime() - startTime;
     this.loggingService.logInfo(`Formatting completed in ${duration}ms.`);
     const edit = this.minimalEdit(document, result);
+    if (!edit) {
+      // Document is already formatted, no changes needed
+      this.loggingService.logDebug("Document is already formatted, no changes needed.");
+      return [];
+    }
     return [edit];
   };
 
-  private minimalEdit(document: TextDocument, string1: string) {
+  private minimalEdit(document: TextDocument, string1: string): TextEdit | null {
     const string0 = document.getText();
+    
+    // Quick check: if strings are identical, no edit needed
+    if (string0 === string1) {
+      return null;
+    }
+    
     // length of common prefix
     let i = 0;
     while (

src/test/suite/format.test.ts

@@ -51,4 +51,33 @@ describe("Test format Document", () => {
     formatSameAsPrettier("formatTest/htmlWithLiterals.html"));
   it("formats Vue", () => formatSameAsPrettier("formatTest/ugly.vue"));
   it("formats HBS", () => formatSameAsPrettier("formatTest/ugly.hbs"));
+  it("formats Markdown", () => formatSameAsPrettier("formatTest/ugly.md"));
+
+  it("formats Markdown without adding extra empty lines", async () => {
+    // This test checks for the issue where formatting MD files multiple times
+    // would add empty lines at the end (up to 2 empty lines)
+    const { actual: firstFormat } = await format("project", "formatTest/ugly.md");
+    
+    // Count trailing newlines
+    const countTrailingNewlines = (str: string) => {
+      let count = 0;
+      for (let i = str.length - 1; i >= 0; i--) {
+        if (str[i] === '\n') count++;
+        else if (str[i] === '\r') continue; // Skip \r in CRLF
+        else break;
+      }
+      return count;
+    };
+    
+    const firstCount = countTrailingNewlines(firstFormat);
+    
+    // Format a second time via the extension to verify idempotency
+    const { actual: secondFormat } = await format("project", "formatTest/ugly.md");
+    const secondCount = countTrailingNewlines(secondFormat);
+    
+    // Should have exactly 1 trailing newline after both formats
+    assert.equal(firstCount, 1, "First format should have exactly 1 trailing newline");
+    assert.equal(secondCount, 1, "Second format should have exactly 1 trailing newline");
+    assert.equal(firstFormat, secondFormat, "Formatting via extension should be idempotent");
+  });
 });

test-fixtures/project/formatTest/ugly.md

@@ -0,0 +1,3 @@
+# Hello
+
+This is a test.