fix(webview-ui): correct new-file diff line counting by ignoring trailing newline in unified diff; add test for ChatRow

Author: hannesrudolph

webview-ui/src/components/chat/__tests__/ChatRow.diff-actions.spec.tsx

@@ -111,4 +111,25 @@ describe("ChatRow - inline diff stats and actions", () => {
 		expect(screen.getByText("+3")).toBeInTheDocument()
 		expect(screen.getByText("-0")).toBeInTheDocument()
 	})
+
+	it("counts only added lines for newFileCreated with trailing newline", () => {
+		const content = "a\nb\nc\n"
+		const message: any = {
+			type: "ask",
+			ask: "tool",
+			ts: Date.now(),
+			partial: false,
+			text: JSON.stringify({
+				tool: "newFileCreated",
+				path: "src/new-file.ts",
+				content,
+			}),
+		}
+
+		renderChatRow(message)
+
+		// Trailing newline should not increase the added count
+		expect(screen.getByText("+3")).toBeInTheDocument()
+		expect(screen.getByText("-0")).toBeInTheDocument()
+	})
 })

webview-ui/src/utils/diffUtils.ts

@@ -125,20 +125,22 @@ export function convertSearchReplaceToUnifiedDiff(content: string, filePath?: st
 	return hasBlocks ? unified : content
 }
 
-/** Build a unified diff for a brand new file (all content lines are additions) */
+/** Build a unified diff for a brand new file (all content lines are additions).
+ * Trailing newline is ignored for line counting and emission.
+ */
 export function convertNewFileToUnifiedDiff(content: string, filePath?: string): string {
 	const fileName = filePath || "file"
 	// Normalize EOLs to keep counts consistent
 	const normalized = content.replace(/\r\n/g, "\n")
-	const lines = normalized.split("\n")
+	const parts = normalized.split("\n")
+	// Drop trailing empty item produced by a final newline so we count only real content lines
+	const contentLines = parts[parts.length - 1] === "" ? parts.slice(0, -1) : parts
 
 	let diff = `--- /dev/null\n`
 	diff += `+++ ${fileName}\n`
-	diff += `@@ -0,0 +1,${normalized === "" ? 0 : lines.length} @@\n`
+	diff += `@@ -0,0 +1,${contentLines.length} @@\n`
 
-	for (const line of lines) {
-		// Preserve final newline behavior: if content ended with newline, split will produce trailing ""
-		// which is still okay to emit as "+", it represents a blank line.
+	for (const line of contentLines) {
 		diff += `+${line}\n`
 	}