nes: support <NO_EDIT> response and update post-script in user message

Author: ulugbekna

src/extension/xtab/common/promptCrafting.ts

@@ -130,7 +130,7 @@ function getPostScript(strategy: PromptingStrategy | undefined, currentFilePath:
 			postScript = `<|aggressive|>${aggressivenessLevel}<|/aggressive|>`;
 			break;
 		case PromptingStrategy.PatchBased:
-			postScript = `Output a modified diff style format with the changes you want. Each change patch must start with \`<filename>:<line number>\` and then include some non empty "anchor lines" preceded by \`-\` and the new lines meant to replace them preceded by \`+\`. Put your changes in the order that makes the most sense, for example edits inside the code_to_edit region and near the user's <|cursor|> should always be prioritized.`;
+			postScript = `Output a modified diff style format with the changes you want. Each change patch must start with \`<filename>:<line number>\` and then include some non empty "anchor lines" preceded by \`-\` and the new lines meant to replace them preceded by \`+\`. Put your changes in the order that makes the most sense, for example edits inside the code_to_edit region and near the user's <|cursor|> should always be prioritized. Output "<NO_EDIT>" if you don't have a good edit candidate.`;
 			break;
 		case PromptingStrategy.SimplifiedSystemPrompt:
 		case PromptingStrategy.CopilotNesXtab:

src/extension/xtab/common/tags.ts

@@ -36,6 +36,8 @@ export namespace PromptTags {
 }
 
 export namespace ResponseTags {
+	export const NO_EDIT = '<NO_EDIT>';
+
 	export const NO_CHANGE = {
 		start: '<NO_CHANGE>'
 	};

src/extension/xtab/node/xtabCustomDiffPatchResponseHandler.ts

@@ -10,6 +10,7 @@ import { LineReplacement } from '../../../util/vs/editor/common/core/edits/lineE
 import { LineRange } from '../../../util/vs/editor/common/core/ranges/lineRange';
 import { OffsetRange } from '../../../util/vs/editor/common/core/ranges/offsetRange';
 import { StringText } from '../../../util/vs/editor/common/core/text/abstractText';
+import { ResponseTags } from '../common/tags';
 
 
 class Patch {
@@ -83,6 +84,9 @@ export class XtabCustomDiffPatchResponseHandler {
 		let currentPatch: Patch | null = null;
 		for await (const line of linesStream) {
 			// if no current patch, try to parse a new one
+			if (line.trim() === ResponseTags.NO_EDIT) {
+				break;
+			}
 			if (currentPatch === null) {
 				currentPatch = Patch.ofLine(line);
 				continue;