fix: change diagnostic limiting from size-based to count-based

- Modified diagnosticsToProblemsString() to limit by message count instead of content size
- Updated UI description to accurately reflect count-based limiting
- Updated tests to verify count-based limiting works correctly
- When maxDiagnosticMessages is set to 1, it now shows exactly 1 diagnostic message

Author: hannesrudolph

src/integrations/diagnostics/__tests__/diagnostics.spec.ts

@@ -423,7 +423,7 @@ describe("diagnosticsToProblemsString", () => {
 		expect(vscode.workspace.openTextDocument).not.toHaveBeenCalled()
 	})
 
-	it("should limit diagnostics based on content size when maxDiagnostics is specified", async () => {
+	it("should limit diagnostics based on count when maxDiagnostics is specified", async () => {
 		// Mock file URI
 		const fileUri = vscode.Uri.file("/path/to/file.ts")
 
@@ -450,28 +450,28 @@ describe("diagnosticsToProblemsString", () => {
 		}
 		vscode.workspace.openTextDocument = vitest.fn().mockResolvedValue(mockDocument)
 
-		// Test with maxDiagnostics set to 3 (which translates to ~3000 character limit)
+		// Test with maxDiagnostics set to 3 (should include exactly 3 diagnostics)
 		const result = await diagnosticsToProblemsString(
 			[[fileUri, diagnostics]],
 			[vscode.DiagnosticSeverity.Error, vscode.DiagnosticSeverity.Warning],
 			"/path/to",
 			true, // includeDiagnostics
-			3, // maxDiagnostics (will be converted to character limit)
+			3, // maxDiagnostics (count limit)
 		)
 
-		// Verify that diagnostics are included based on size limit, prioritizing errors
+		// Verify that exactly 3 diagnostics are included, prioritizing errors
 		expect(result).toContain("Error 1")
 		expect(result).toContain("Error 2")
 		expect(result).toContain("Error 3")
-		// Warnings may or may not be included depending on the size calculation
+		// Warnings should not be included since we have 3 errors and limit is 3
+		expect(result).not.toContain("Warning 1")
+		expect(result).not.toContain("Warning 2")
 
-		// Verify the limit message is included if some diagnostics were omitted
-		if (!result.includes("Warning 1") || !result.includes("Warning 2")) {
-			expect(result).toContain("more problems omitted to prevent context overflow")
-		}
+		// Verify the limit message is included
+		expect(result).toContain("2 more problems omitted to prevent context overflow")
 	})
 
-	it("should prioritize errors over warnings when limiting diagnostics by size", async () => {
+	it("should prioritize errors over warnings when limiting diagnostics by count", async () => {
 		// Mock file URIs
 		const fileUri1 = vscode.Uri.file("/path/to/file1.ts")
 		const fileUri2 = vscode.Uri.file("/path/to/file2.ts")
@@ -506,7 +506,7 @@ describe("diagnosticsToProblemsString", () => {
 		}
 		vscode.workspace.openTextDocument = vitest.fn().mockResolvedValue(mockDocument)
 
-		// Test with maxDiagnostics set to 2 (which translates to ~2000 character limit)
+		// Test with maxDiagnostics set to 2 (should include exactly 2 diagnostics)
 		const result = await diagnosticsToProblemsString(
 			[
 				[fileUri1, diagnostics1],
@@ -515,22 +515,19 @@ describe("diagnosticsToProblemsString", () => {
 			[vscode.DiagnosticSeverity.Error, vscode.DiagnosticSeverity.Warning, vscode.DiagnosticSeverity.Information],
 			"/path/to",
 			true, // includeDiagnostics
-			2, // maxDiagnostics (will be converted to character limit)
+			2, // maxDiagnostics (count limit)
 		)
 
-		// Verify errors are prioritized over warnings
+		// Verify exactly 2 errors are included (prioritized over warnings)
 		expect(result).toContain("Error in file1")
 		expect(result).toContain("Error in file2")
-		// Warnings and info may not be included due to size limit
-
-		// Verify the limit message is included if diagnostics were omitted
-		if (
-			!result.includes("Warning in file1") ||
-			!result.includes("Warning in file2") ||
-			!result.includes("Info in file2")
-		) {
-			expect(result).toContain("more problems omitted to prevent context overflow")
-		}
+		// Warnings and info should not be included
+		expect(result).not.toContain("Warning in file1")
+		expect(result).not.toContain("Warning in file2")
+		expect(result).not.toContain("Info in file2")
+
+		// Verify the limit message is included
+		expect(result).toContain("3 more problems omitted to prevent context overflow")
 	})
 
 	it("should handle maxDiagnostics with no limit when undefined", async () => {

src/integrations/diagnostics/index.ts

@@ -86,12 +86,8 @@ export async function diagnosticsToProblemsString(
 	const fileStats = new Map<vscode.Uri, vscode.FileStat>()
 	let result = ""
 
-	// If we have a limit, we need to use size-based limiting instead of count-based
+	// If we have a limit, use count-based limiting
 	if (maxDiagnosticMessages && maxDiagnosticMessages > 0) {
-		// Convert maxDiagnosticMessages to a character limit
-		// Assuming average diagnostic message is ~1000 characters, multiply by the count
-		const MAX_PROBLEMS_CONTENT_SIZE = maxDiagnosticMessages * 1000
-		let currentSize = 0
 		let includedCount = 0
 		let totalCount = 0
 
@@ -112,10 +108,15 @@ export async function diagnosticsToProblemsString(
 			return a.diagnostic.range.start.line - b.diagnostic.range.start.line
 		})
 
-		// Process diagnostics and track size
+		// Process diagnostics up to the count limit
 		const includedDiagnostics: typeof allDiagnostics = []
 		for (const item of allDiagnostics) {
-			// Format the diagnostic to calculate its size
+			// Stop if we've reached the count limit
+			if (includedCount >= maxDiagnosticMessages) {
+				break
+			}
+
+			// Format the diagnostic
 			let label: string
 			switch (item.diagnostic.severity) {
 				case vscode.DiagnosticSeverity.Error:
@@ -156,15 +157,8 @@ export async function diagnosticsToProblemsString(
 				diagnosticText = `\n- [${source}${label}] ${line} | (unavailable) : ${item.diagnostic.message}`
 			}
 
-			// Check if adding this diagnostic would exceed the size limit
-			const diagnosticSize = diagnosticText.length + path.relative(cwd, item.uri.fsPath).toPosix().length + 2 // +2 for newlines
-			if (currentSize + diagnosticSize > MAX_PROBLEMS_CONTENT_SIZE && includedCount > 0) {
-				break // Stop before exceeding limit
-			}
-
 			item.formattedText = diagnosticText
 			includedDiagnostics.push(item)
-			currentSize += diagnosticSize
 			includedCount++
 		}
 

webview-ui/src/i18n/locales/en/settings.json

@@ -495,7 +495,7 @@
 			},
 			"maxMessages": {
 				"label": "Maximum diagnostic messages",
-				"description": "Controls the approximate size limit for diagnostic messages. The value represents a multiplier for content size (each unit ≈ 1KB). This prevents context overflow by limiting total diagnostic content rather than count. Higher values allow more diagnostic information but increase token usage.",
+				"description": "Limits the number of diagnostic messages (errors, warnings) included in the context. When set, only this many diagnostics will be shown, prioritizing errors over warnings. Set to 0 for unlimited diagnostics.",
 				"resetTooltip": "Reset to default value (50)",
 				"unlimitedLabel": "Unlimited"
 			}