src/vs/editor/contrib/comment/lineCommentCommand.ts/LineCommentCommand/_analyzeLines
class LineCommentCommand:	public static _analyzeLines(type: Type, insertSpace: boolean, model: ISimpleModel, lines: ILinePreflightData[], startLineNumber: number, ignoreEmptyLines: boolean, ignoreFirstLine: boolean): IPreflightData {
		let onlyWhitespaceLines = true;

		let shouldRemoveComments: boolean;
		if (type === Type.Toggle) {
			shouldRemoveComments = true;
		} else if (type === Type.ForceAdd) {
			shouldRemoveComments = false;
		} else {
			shouldRemoveComments = true;
		}

		for (let i = 0, lineCount = lines.length; i < lineCount; i++) {
			const lineData = lines[i];
			const lineNumber = startLineNumber + i;

			if (lineNumber === startLineNumber && ignoreFirstLine) {
				// first line ignored
				lineData.ignore = true;
				continue;
			}

			const lineContent = model.getLineContent(lineNumber);
			const lineContentStartOffset = strings.firstNonWhitespaceIndex(lineContent);

			if (lineContentStartOffset === -1) {
				// Empty or whitespace only line
				lineData.ignore = ignoreEmptyLines;
				lineData.commentStrOffset = lineContent.length;
				continue;
			}

			onlyWhitespaceLines = false;
			lineData.ignore = false;
			lineData.commentStrOffset = lineContentStartOffset;

			if (shouldRemoveComments && !BlockCommentCommand._haystackHasNeedleAtOffset(lineContent, lineData.commentStr, lineContentStartOffset)) {
				if (type === Type.Toggle) {
					// Every line so far has been a line comment, but this one is not
					shouldRemoveComments = false;
				} else if (type === Type.ForceAdd) {
					// Will not happen
				} else {
					lineData.ignore = true;
				}
			}

			if (shouldRemoveComments && insertSpace) {
				// Remove a following space if present
				const commentStrEndOffset = lineContentStartOffset + lineData.commentStrLength;
				if (commentStrEndOffset < lineContent.length && lineContent.charCodeAt(commentStrEndOffset) === CharCode.Space) {
					lineData.commentStrLength += 1;
				}
			}
		}

		if (type === Type.Toggle && onlyWhitespaceLines) {
			// For only whitespace lines, we insert comments
			shouldRemoveComments = false;

			// Also, no longer ignore them
			for (let i = 0, lineCount = lines.length; i < lineCount; i++) {
				lines[i].ignore = false;
			}
		}

		return {
			supported: true,
			shouldRemoveComments: shouldRemoveComments,
			lines: lines
		};
	}