Fixes #91178: Use previous part when dealing with offsets with an after inline decoration

src/vs/editor/browser/viewParts/lines/rangeUtil.ts

@@ -121,6 +121,13 @@ export class RangeUtil {
 		startChildIndex = Math.min(max, Math.max(min, startChildIndex));
 		endChildIndex = Math.min(max, Math.max(min, endChildIndex));
 
+		if (startChildIndex === endChildIndex && startOffset === endOffset && startOffset === 0) {
+			// We must find the position at the beginning of a <span>
+			// To cover cases of empty <span>s, aboid using a range and use the <span>'s bounding box
+			const clientRects = domNode.children[startChildIndex].getClientRects();
+			return this._createHorizontalRangesFromClientRects(clientRects, clientRectDeltaLeft);
+		}
+
 		// If crossing over to a span only to select offset 0, then use the previous span's maximum offset
 		// Chrome is buggy and doesn't handle 0 offsets well sometimes.
 		if (startChildIndex !== endChildIndex) {

src/vs/editor/common/viewLayout/lineDecorations.ts

@@ -72,16 +72,25 @@ export class LineDecoration {
 		return result;
 	}
 
+	private static _typeCompare(a: InlineDecorationType, b: InlineDecorationType): number {
+		const ORDER = [2, 0, 1, 3];
+		return ORDER[a] - ORDER[b];
+	}
+
 	public static compare(a: LineDecoration, b: LineDecoration): number {
 		if (a.startColumn === b.startColumn) {
 			if (a.endColumn === b.endColumn) {
-				if (a.className < b.className) {
-					return -1;
-				}
-				if (a.className > b.className) {
-					return 1;
+				const typeCmp = LineDecoration._typeCompare(a.type, b.type);
+				if (typeCmp === 0) {
+					if (a.className < b.className) {
+						return -1;
+					}
+					if (a.className > b.className) {
+						return 1;
+					}
+					return 0;
 				}
-				return 0;
+				return typeCmp;
 			}
 			return a.endColumn - b.endColumn;
 		}

src/vs/editor/common/viewLayout/viewLineRenderer.ts

@@ -809,6 +809,7 @@ function _renderLine(input: ResolvedRenderLineInput, sb: IStringBuilder): Render
 	let visibleColumn = startVisibleColumn;
 	let charOffsetInPart = 0;
 
+	let partDisplacement = 0;
 	let prevPartContentCnt = 0;
 	let partAbsoluteOffset = 0;
 
@@ -822,6 +823,7 @@ function _renderLine(input: ResolvedRenderLineInput, sb: IStringBuilder): Render
 		const partType = part.type;
 		const partRendersWhitespace = (renderWhitespace !== RenderWhitespace.None && part.isWhitespace());
 		const partRendersWhitespaceWithWidth = partRendersWhitespace && !fontIsMonospace && (partType === 'mtkw'/*only whitespace*/ || !containsForeignElements);
+		const partIsEmptyAndHasPseudoAfter = (charIndex === partEndIndex && part.metadata === LinePartMetadata.PSEUDO_AFTER);
 		charOffsetInPart = 0;
 
 		sb.appendASCIIString('<span class="');
@@ -853,7 +855,8 @@ function _renderLine(input: ResolvedRenderLineInput, sb: IStringBuilder): Render
 			sb.appendASCII(CharCode.GreaterThan);
 
 			for (; charIndex < partEndIndex; charIndex++) {
-				characterMapping.setPartData(charIndex, partIndex, charOffsetInPart, partAbsoluteOffset);
+				characterMapping.setPartData(charIndex, partIndex - partDisplacement, charOffsetInPart, partAbsoluteOffset);
+				partDisplacement = 0;
 				const charCode = lineContent.charCodeAt(charIndex);
 				let charWidth: number;
 
@@ -893,7 +896,8 @@ function _renderLine(input: ResolvedRenderLineInput, sb: IStringBuilder): Render
 			sb.appendASCII(CharCode.GreaterThan);
 
 			for (; charIndex < partEndIndex; charIndex++) {
-				characterMapping.setPartData(charIndex, partIndex, charOffsetInPart, partAbsoluteOffset);
+				characterMapping.setPartData(charIndex, partIndex - partDisplacement, charOffsetInPart, partAbsoluteOffset);
+				partDisplacement = 0;
 				const charCode = lineContent.charCodeAt(charIndex);
 
 				let producedCharacters = 1;
@@ -954,6 +958,12 @@ function _renderLine(input: ResolvedRenderLineInput, sb: IStringBuilder): Render
 			prevPartContentCnt = partContentCnt;
 		}
 
+		if (partIsEmptyAndHasPseudoAfter) {
+			partDisplacement++;
+		} else {
+			partDisplacement = 0;
+		}
+
 		sb.appendASCIIString('</span>');
 
 	}

src/vs/editor/test/common/viewLayout/viewLineRenderer.test.ts

@@ -388,6 +388,66 @@ suite('viewLineRenderer.renderLine', () => {
 		assertCharacterMapping(_actual.characterMapping, expectedOffsetsArr, [12, 12, 24, 1, 21, 2, 1, 20, 1, 1]);
 	});
 
+	test('issue #91178: after decoration type shown before cursor', () => {
+		const lineText = '//just a comment';
+		const lineParts = createViewLineTokens([
+			createPart(16, 1)
+		]);
+		const expectedOutput = [
+			'<span class="mtk1">//just\u00a0a\u00a0com</span>',
+			'<span class="mtk1 dec2"></span>',
+			'<span class="mtk1 dec1"></span>',
+			'<span class="mtk1">ment</span>',
+		].join('');
+
+		const expectedCharacterMapping = new CharacterMapping(17, 4);
+		expectedCharacterMapping.setPartData(0, 0, 0, 0);
+		expectedCharacterMapping.setPartData(1, 0, 1, 0);
+		expectedCharacterMapping.setPartData(2, 0, 2, 0);
+		expectedCharacterMapping.setPartData(3, 0, 3, 0);
+		expectedCharacterMapping.setPartData(4, 0, 4, 0);
+		expectedCharacterMapping.setPartData(5, 0, 5, 0);
+		expectedCharacterMapping.setPartData(6, 0, 6, 0);
+		expectedCharacterMapping.setPartData(7, 0, 7, 0);
+		expectedCharacterMapping.setPartData(8, 0, 8, 0);
+		expectedCharacterMapping.setPartData(9, 0, 9, 0);
+		expectedCharacterMapping.setPartData(10, 0, 10, 0);
+		expectedCharacterMapping.setPartData(11, 0, 11, 0);
+		expectedCharacterMapping.setPartData(12, 2, 0, 12);
+		expectedCharacterMapping.setPartData(13, 3, 1, 12);
+		expectedCharacterMapping.setPartData(14, 3, 2, 12);
+		expectedCharacterMapping.setPartData(15, 3, 3, 12);
+		expectedCharacterMapping.setPartData(16, 3, 4, 12);
+
+		const actual = renderViewLine(new RenderLineInput(
+			true,
+			false,
+			lineText,
+			false,
+			true,
+			false,
+			0,
+			lineParts,
+			[
+				new LineDecoration(13, 13, 'dec1', InlineDecorationType.After),
+				new LineDecoration(13, 13, 'dec2', InlineDecorationType.Before),
+			],
+			4,
+			0,
+			10,
+			10,
+			10,
+			-1,
+			'none',
+			false,
+			false,
+			null
+		));
+
+		assert.equal(actual.html, '<span>' + expectedOutput + '</span>');
+		assertCharacterMapping2(actual.characterMapping, expectedCharacterMapping);
+	});
+
 	test('issue Microsoft/monaco-editor#280: Improved source code rendering for RTL languages', () => {
 		let lineText = 'var קודמות = \"מיותר קודמות צ\'ט של, אם לשון העברית שינויים ויש, אם\";';
 
@@ -693,6 +753,33 @@ suite('viewLineRenderer.renderLine', () => {
 		assert.equal(_actual.html, '<span>' + expectedOutput + '</span>');
 	});
 
+	interface ICharMappingData {
+		charOffset: number;
+		partIndex: number;
+		charIndex: number;
+	}
+
+	function decodeCharacterMapping(source: CharacterMapping) {
+		const mapping: ICharMappingData[] = [];
+		for (let charOffset = 0; charOffset < source.length; charOffset++) {
+			const partData = source.charOffsetToPartData(charOffset);
+			const partIndex = CharacterMapping.getPartIndex(partData);
+			const charIndex = CharacterMapping.getCharIndex(partData);
+			mapping.push({ charOffset, partIndex, charIndex });
+		}
+		const absoluteOffsets: number[] = [];
+		for (const absoluteOffset of source.getAbsoluteOffsets()) {
+			absoluteOffsets.push(absoluteOffset);
+		}
+		return { mapping, absoluteOffsets };
+	}
+
+	function assertCharacterMapping2(actual: CharacterMapping, expected: CharacterMapping): void {
+		const _actual = decodeCharacterMapping(actual);
+		const _expected = decodeCharacterMapping(expected);
+		assert.deepEqual(_actual, _expected);
+	}
+
 	function assertCharacterMapping(actual: CharacterMapping, expectedCharPartOffsets: number[][], expectedPartLengths: number[]): void {
 
 		assertCharPartOffsets(actual, expectedCharPartOffsets);