fix: Fix VB.NET indexing by implementing fallback chunking system

- Create fallback extensions system for languages without WASM parsers
- Add VB.NET (.vb) to fallback extensions list
- Remove broken VB.NET parser configuration that was using C# parser
- Add comprehensive tests for VB.NET indexing
- Make system extensible for future languages without parsers

Fixes #6420

Author: daniel-lxs

src/services/code-index/processors/__tests__/parser.vb.spec.ts

@@ -0,0 +1,260 @@
+import { describe, it, expect, beforeEach, vi } from "vitest"
+import { CodeParser } from "../parser"
+import * as path from "path"
+
+// Mock TelemetryService
+vi.mock("../../../../../packages/telemetry/src/TelemetryService", () => ({
+	TelemetryService: {
+		instance: {
+			captureEvent: vi.fn(),
+		},
+	},
+}))
+
+import { shouldUseFallbackChunking } from "../../shared/fallback-extensions"
+
+describe("CodeParser - VB.NET and Fallback Extensions Support", () => {
+	let parser: CodeParser
+
+	beforeEach(() => {
+		parser = new CodeParser()
+	})
+
+	it("should use fallback chunking for VB.NET files", async () => {
+		const vbContent = `
+Imports System
+Imports System.Collections.Generic
+Imports System.Linq
+
+Namespace MyApplication
+    Public Class Calculator
+        Private _history As New List(Of String)()
+
+        Public Function Add(a As Integer, b As Integer) As Integer
+            Dim result As Integer = a + b
+            _history.Add($"{a} + {b} = {result}")
+            Return result
+        End Function
+
+        Public Function Subtract(a As Integer, b As Integer) As Integer
+            Dim result As Integer = a - b
+            _history.Add($"{a} - {b} = {result}")
+            Return result
+        End Function
+
+        Public Function Multiply(a As Integer, b As Integer) As Integer
+            Dim result As Integer = a * b
+            _history.Add($"{a} * {b} = {result}")
+            Return result
+        End Function
+
+        Public Function Divide(a As Integer, b As Integer) As Double
+            If b = 0 Then
+                Throw New DivideByZeroException("Cannot divide by zero")
+            End If
+            Dim result As Double = CDbl(a) / CDbl(b)
+            _history.Add($"{a} / {b} = {result}")
+            Return result
+        End Function
+
+        Public Function GetHistory() As List(Of String)
+            Return New List(Of String)(_history)
+        End Function
+
+        Public Sub ClearHistory()
+            _history.Clear()
+        End Sub
+    End Class
+
+    Public Module Program
+        Sub Main(args As String())
+            Dim calc As New Calculator()
+            
+            Console.WriteLine("Calculator Demo")
+            Console.WriteLine("===============")
+            
+            Console.WriteLine($"10 + 5 = {calc.Add(10, 5)}")
+            Console.WriteLine($"10 - 5 = {calc.Subtract(10, 5)}")
+            Console.WriteLine($"10 * 5 = {calc.Multiply(10, 5)}")
+            Console.WriteLine($"10 / 5 = {calc.Divide(10, 5)}")
+            
+            Console.WriteLine()
+            Console.WriteLine("History:")
+            For Each entry In calc.GetHistory()
+                Console.WriteLine($"  {entry}")
+            Next
+        End Sub
+    End Module
+End Namespace
+`.trim()
+
+		const result = await parser.parseFile("test.vb", {
+			content: vbContent,
+			fileHash: "test-hash",
+		})
+
+		// Should have results from fallback chunking
+		expect(result.length).toBeGreaterThan(0)
+
+		// Check that all blocks are of type 'fallback_chunk'
+		result.forEach((block) => {
+			expect(block.type).toBe("fallback_chunk")
+		})
+
+		// Verify content is properly chunked
+		const totalContent = result.map((block) => block.content).join("\n")
+		expect(totalContent).toBe(vbContent)
+
+		// Verify file path is correct
+		expect(result[0].file_path).toBe("test.vb")
+	})
+
+	it("should handle large VB.NET files with proper chunking", async () => {
+		// Create a large VB.NET file content
+		const largeVbContent =
+			`
+Imports System
+Imports System.Collections.Generic
+
+Namespace LargeApplication
+` +
+			// Generate many classes to create a large file
+			Array.from(
+				{ length: 50 },
+				(_, i) => `
+    Public Class TestClass${i}
+        Private _id As Integer = ${i}
+        Private _name As String = "Class ${i}"
+        Private _data As New Dictionary(Of String, Object)()
+
+        Public Property Id As Integer
+            Get
+                Return _id
+            End Get
+            Set(value As Integer)
+                _id = value
+            End Set
+        End Property
+
+        Public Property Name As String
+            Get
+                Return _name
+            End Get
+            Set(value As String)
+                _name = value
+            End Set
+        End Property
+
+        Public Sub ProcessData()
+            For i As Integer = 0 To 100
+                _data.Add($"key_{i}", $"value_{i}")
+            Next
+        End Sub
+
+        Public Function GetData() As Dictionary(Of String, Object)
+            Return New Dictionary(Of String, Object)(_data)
+        End Function
+    End Class
+`,
+			).join("\n") +
+			`
+End Namespace
+`
+
+		const result = await parser.parseFile("large-test.vb", {
+			content: largeVbContent,
+			fileHash: "large-test-hash",
+		})
+
+		// Should have multiple chunks due to size
+		expect(result.length).toBeGreaterThan(1)
+
+		// All chunks should be fallback chunks
+		result.forEach((block) => {
+			expect(block.type).toBe("fallback_chunk")
+		})
+
+		// Verify chunks don't exceed max size
+		result.forEach((block) => {
+			expect(block.content.length).toBeLessThanOrEqual(150000) // MAX_BLOCK_CHARS * MAX_CHARS_TOLERANCE_FACTOR
+		})
+	})
+
+	it("should handle empty VB.NET files", async () => {
+		const emptyContent = ""
+
+		const result = await parser.parseFile("empty.vb", {
+			content: emptyContent,
+			fileHash: "empty-hash",
+		})
+
+		// Should return empty array for empty content
+		expect(result).toEqual([])
+	})
+
+	it("should handle small VB.NET files below minimum chunk size", async () => {
+		const smallContent = "Imports System"
+
+		const result = await parser.parseFile("small.vb", {
+			content: smallContent,
+			fileHash: "small-hash",
+		})
+
+		// Should return empty array for content below MIN_BLOCK_CHARS
+		expect(result).toEqual([])
+	})
+
+	it("should use fallback chunking for other configured fallback extensions", async () => {
+		// Test with Scala which is in our fallback list
+		const content = `object ScalaExample {
+			def main(args: Array[String]): Unit = {
+				println("This is a Scala file that should use fallback chunking")
+				val numbers = List(1, 2, 3, 4, 5)
+				val doubled = numbers.map(_ * 2)
+				println(s"Doubled numbers: $doubled")
+			}
+			
+			def factorial(n: Int): Int = {
+				if (n <= 1) 1
+				else n * factorial(n - 1)
+			}
+		}`
+
+		const result = await parser.parseFile("test.scala", {
+			content: content,
+			fileHash: "test-hash-scala",
+		})
+
+		// Should have results from fallback chunking
+		expect(result.length).toBeGreaterThan(0)
+
+		// Check that all blocks are of type 'fallback_chunk'
+		result.forEach((block) => {
+			expect(block.type).toBe("fallback_chunk")
+		})
+	})
+})
+
+describe("Fallback Extensions Configuration", () => {
+	it("should correctly identify extensions that need fallback chunking", () => {
+		// Extensions that should use fallback
+		expect(shouldUseFallbackChunking(".vb")).toBe(true)
+		expect(shouldUseFallbackChunking(".scala")).toBe(true)
+
+		// Extensions that should not use fallback (have working parsers)
+		expect(shouldUseFallbackChunking(".js")).toBe(false)
+		expect(shouldUseFallbackChunking(".ts")).toBe(false)
+		expect(shouldUseFallbackChunking(".py")).toBe(false)
+		expect(shouldUseFallbackChunking(".java")).toBe(false)
+		expect(shouldUseFallbackChunking(".cs")).toBe(false)
+		expect(shouldUseFallbackChunking(".go")).toBe(false)
+		expect(shouldUseFallbackChunking(".rs")).toBe(false)
+	})
+
+	it("should be case-insensitive", () => {
+		expect(shouldUseFallbackChunking(".VB")).toBe(true)
+		expect(shouldUseFallbackChunking(".Vb")).toBe(true)
+		expect(shouldUseFallbackChunking(".SCALA")).toBe(true)
+		expect(shouldUseFallbackChunking(".Scala")).toBe(true)
+	})
+})

src/services/code-index/processors/parser.ts

@@ -6,6 +6,7 @@ import { LanguageParser, loadRequiredLanguageParsers } from "../../tree-sitter/l
 import { parseMarkdown } from "../../tree-sitter/markdownParser"
 import { ICodeParser, CodeBlock } from "../interfaces"
 import { scannerExtensions } from "../shared/supported-extensions"
+import { shouldUseFallbackChunking } from "../shared/fallback-extensions"
 import { MAX_BLOCK_CHARS, MIN_BLOCK_CHARS, MIN_CHUNK_REMAINDER_CHARS, MAX_CHARS_TOLERANCE_FACTOR } from "../constants"
 import { TelemetryService } from "@roo-code/telemetry"
 import { TelemetryEventName } from "@roo-code/types"
@@ -101,6 +102,11 @@ export class CodeParser implements ICodeParser {
 			return this.parseMarkdownContent(filePath, content, fileHash, seenSegmentHashes)
 		}
 
+		// Check if this extension should use fallback chunking
+		if (shouldUseFallbackChunking(`.${ext}`)) {
+			return this._performFallbackChunking(filePath, content, fileHash, seenSegmentHashes)
+		}
+
 		// Check if we already have the parser loaded
 		if (!this.loadedParsers[ext]) {
 			const pendingLoad = this.pendingLoads.get(ext)

src/services/code-index/shared/fallback-extensions.ts

@@ -0,0 +1,27 @@
+/**
+ * Extensions that should always use fallback chunking instead of tree-sitter parsing.
+ * These are typically languages that don't have a proper WASM parser available
+ * or where the parser doesn't work correctly.
+ *
+ * NOTE: Only extensions that are already in the supported extensions list can be added here.
+ * To add support for new file types, they must first be added to the tree-sitter extensions list.
+ *
+ * HOW TO ADD A NEW FALLBACK EXTENSION:
+ * 1. First ensure the extension is in src/services/tree-sitter/index.ts extensions array
+ * 2. Add the extension to the fallbackExtensions array below
+ * 3. Remove any parser case for this extension from src/services/tree-sitter/languageParser.ts
+ * 4. The file will automatically use length-based chunking for indexing
+ */
+export const fallbackExtensions = [
+	".vb", // Visual Basic .NET - no dedicated WASM parser
+	".scala", // Scala - removed from parser, uses fallback chunking
+]
+
+/**
+ * Check if a file extension should use fallback chunking
+ * @param extension File extension (including the dot)
+ * @returns true if the extension should use fallback chunking
+ */
+export function shouldUseFallbackChunking(extension: string): boolean {
+	return fallbackExtensions.includes(extension.toLowerCase())
+}