Write selection text to hidden textarea on macOS (microsoft#156717)

* Write selection text to hidden textarea on macOS

Fixes microsoft#27799

* use `getValueLengthInRange` to avoid large allocations

Co-authored-by: Benjamin Pasero <benjamin.pasero@gmail.com>

Author: pingren

src/vs/editor/browser/controller/textAreaHandler.ts

@@ -195,6 +195,9 @@ export class TextAreaHandler extends ViewPart {
 			},
 			getValueInRange: (range: Range, eol: EndOfLinePreference): string => {
 				return this._context.viewModel.getValueInRange(range, eol);
+			},
+			getValueLengthInRange: (range: Range): number => {
+				return this._context.viewModel.model.getValueLengthInRange(range);
 			}
 		};
 
@@ -242,6 +245,15 @@ export class TextAreaHandler extends ViewPart {
 							return new TextAreaState(textBefore, textBefore.length, textBefore.length, position, position);
 						}
 					}
+					// on macOS, write current selection into textarea will allow system text services pick selected text,
+					// but we still want to limit the amount of text given Chromium handles very poorly text even of a few
+					// thousand chars
+					// (https://github.com/microsoft/vscode/issues/27799)
+					const LIMIT_CHARS = 500;
+					if (platform.isMacintosh && !selection.isEmpty() && simpleModel.getValueLengthInRange(selection) < LIMIT_CHARS) {
+						const text = simpleModel.getValueInRange(selection, EndOfLinePreference.TextDefined);
+						return new TextAreaState(text, 0, text.length, selection.getStartPosition(), selection.getEndPosition());
+					}
 
 					// on Safari, document.execCommand('cut') and document.execCommand('copy') will just not work
 					// if the textarea has no content selected. So if there is an editor selection, ensure something

src/vs/editor/browser/controller/textAreaState.ts

@@ -23,6 +23,7 @@ export interface ISimpleModel {
 	getLineCount(): number;
 	getLineMaxColumn(lineNumber: number): number;
 	getValueInRange(range: Range, eol: EndOfLinePreference): string;
+	getValueLengthInRange(range: Range): number;
 }
 
 export interface ITypeData {

src/vs/editor/test/browser/controller/imeTester.ts

@@ -34,6 +34,10 @@ class SingleLineTestModel implements ISimpleModel {
 		return this._line.substring(range.startColumn - 1, range.endColumn - 1);
 	}
 
+	getValueLengthInRange(range: Range): number {
+		return this.getValueInRange(range, EndOfLinePreference.TextDefined).length;
+	}
+
 	getModelLineContent(lineNumber: number): string {
 		return this._line;
 	}