Fixes #55818: Tweak indentation guessing code to accomodate for code alignment

src/vs/editor/common/model/indentationGuesser.ts

@@ -7,10 +7,18 @@
 import { CharCode } from 'vs/base/common/charCode';
 import { ITextBuffer } from 'vs/editor/common/model';
 
+class SpacesDiffResult {
+	public spacesDiff: number;
+	public looksLikeAlignment: boolean;
+}
+
 /**
  * Compute the diff in spaces between two line's indentation.
  */
-function spacesDiff(a: string, aLength: number, b: string, bLength: number): number {
+function spacesDiff(a: string, aLength: number, b: string, bLength: number, result: SpacesDiffResult): void {
+
+	result.spacesDiff = 0;
+	result.looksLikeAlignment = false;
 
 	// This can go both ways (e.g.):
 	//  - a: "\t"
@@ -49,22 +57,35 @@ function spacesDiff(a: string, aLength: number, b: string, bLength: number): num
 	}
 
 	if (aSpacesCnt > 0 && aTabsCount > 0) {
-		return 0;
+		return;
 	}
 	if (bSpacesCnt > 0 && bTabsCount > 0) {
-		return 0;
+		return;
 	}
 
 	let tabsDiff = Math.abs(aTabsCount - bTabsCount);
 	let spacesDiff = Math.abs(aSpacesCnt - bSpacesCnt);
 
 	if (tabsDiff === 0) {
-		return spacesDiff;
+		// check if the indentation difference might be caused by alignment reasons
+		// sometime folks like to align their code, but this should not be used as a hint
+		result.spacesDiff = spacesDiff;
+
+		if (spacesDiff > 0 && 0 <= bSpacesCnt - 1 && bSpacesCnt - 1 < a.length && bSpacesCnt < b.length) {
+			if (b.charCodeAt(bSpacesCnt) !== CharCode.Space && a.charCodeAt(bSpacesCnt - 1) === CharCode.Space) {
+				// This looks like an alignment desire: e.g.
+				// const a = b + c,
+				//       d = b - c;
+
+				result.looksLikeAlignment = true;
+			}
+		}
+		return;
 	}
 	if (spacesDiff % tabsDiff === 0) {
-		return spacesDiff / tabsDiff;
+		result.spacesDiff = spacesDiff / tabsDiff;
+		return;
 	}
-	return 0;
 }
 
 /**
@@ -95,6 +116,7 @@ export function guessIndentation(source: ITextBuffer, defaultTabSize: number, de
 	const MAX_ALLOWED_TAB_SIZE_GUESS = 8;			// max(2,4,6,8) = 8
 
 	let spacesDiffCount = [0, 0, 0, 0, 0, 0, 0, 0, 0];		// `tabSize` scores
+	let tmp = new SpacesDiffResult();
 
 	for (let lineNumber = 1; lineNumber <= linesCount; lineNumber++) {
 		let currentLineLength = source.getLineLength(lineNumber);
@@ -134,7 +156,14 @@ export function guessIndentation(source: ITextBuffer, defaultTabSize: number, de
 			linesIndentedWithSpacesCount++;
 		}
 
-		let currentSpacesDiff = spacesDiff(previousLineText, previousLineIndentation, currentLineText, currentLineIndentation);
+		spacesDiff(previousLineText, previousLineIndentation, currentLineText, currentLineIndentation, tmp);
+
+		if (tmp.looksLikeAlignment) {
+			// skip this line entirely
+			continue;
+		}
+
+		let currentSpacesDiff = tmp.spacesDiff;
 		if (currentSpacesDiff <= MAX_ALLOWED_TAB_SIZE_GUESS) {
 			spacesDiffCount[currentSpacesDiff]++;
 		}

src/vs/editor/test/common/model/textModel.test.ts

@@ -550,6 +550,32 @@ suite('Editor Model - TextModel', () => {
 		]);
 	});
 
+	test('issue #55818: Broken indentation detection', () => {
+		assertGuess(true, 2, [
+			'',
+			'/* REQUIRE */',
+			'',
+			'const foo = require ( \'foo\' ),',
+			'      bar = require ( \'bar\' );',
+			'',
+			'/* MY FN */',
+			'',
+			'function myFn () {',
+			'',
+			'  const asd = 1,',
+			'        dsa = 2;',
+			'',
+			'  return bar ( foo ( asd ) );',
+			'',
+			'}',
+			'',
+			'/* EXPORT */',
+			'',
+			'module.exports = myFn;',
+			'',
+		]);
+	});
+
 	test('validatePosition', () => {
 
 		let m = TextModel.createFromString('line one\nline two');