chore: introduce string.IsNullOrEmpty helper (#3179)

Author: mxschmitt

src/Playwright/Core/APIRequest.cs

@@ -63,7 +63,7 @@ async Task<IAPIRequestContext> IAPIRequest.NewContextAsync(APIRequestNewContextO
 
             storageState = File.ReadAllText(options?.StorageStatePath);
         }
-        if (!string.IsNullOrEmpty(storageState) && storageState != null)
+        if (!storageState.IsNullOrEmpty())
         {
             args.Add("storageState", JsonSerializer.Deserialize<object>(storageState, Helpers.JsonExtensions.DefaultJsonSerializerOptions));
         }

src/Playwright/Core/APIRequestContext.cs

@@ -95,7 +95,7 @@ internal async Task<IAPIResponse> InnerFetchAsync(IRequest request, string? urlO
     [MethodImpl(MethodImplOptions.NoInlining)]
     public async Task<IAPIResponse> FetchAsync(string url, APIRequestContextOptions? options = null)
     {
-        if (!string.IsNullOrEmpty(_closeReason) && _closeReason != null)
+        if (!_closeReason.IsNullOrEmpty())
         {
             throw new PlaywrightException(_closeReason);
         }

src/Playwright/Core/Browser.cs

@@ -154,7 +154,7 @@ public async Task<IBrowserContext> NewContextAsync(BrowserNewContextOptions? opt
             storageState = File.ReadAllText(options.StorageStatePath);
         }
 
-        if (!string.IsNullOrEmpty(storageState) && storageState != null)
+        if (!storageState.IsNullOrEmpty())
         {
             args.Add("storageState", JsonSerializer.Deserialize<object>(storageState, Helpers.JsonExtensions.DefaultJsonSerializerOptions));
         }

src/Playwright/Core/HarRouter.cs

@@ -50,7 +50,7 @@ private HarRouter(LocalUtils localUtils, string harId, HarNotFound notFoundActio
     internal static async Task<HarRouter> CreateAsync(LocalUtils localUtils, string file, HarNotFound notFoundAction, HarRouterOptions options)
     {
         var (harId, error) = await localUtils.HarOpenAsync(file).ConfigureAwait(false);
-        if (!string.IsNullOrEmpty(error) && error != null)
+        if (!error.IsNullOrEmpty())
         {
             throw new PlaywrightException(error);
         }

src/Playwright/Core/Route.cs

@@ -196,7 +196,7 @@ private async Task RaceWithTargetCloseAsync(Task task)
             isBase64 = true;
             length = resultBody.Length;
         }
-        else if (!string.IsNullOrEmpty(body) && body != null)
+        else if (!body.IsNullOrEmpty())
         {
             resultBody = body;
             isBase64 = false;
@@ -219,15 +219,15 @@ private async Task RaceWithTargetCloseAsync(Task task)
             }
         }
 
-        if (!string.IsNullOrEmpty(contentType) && contentType != null)
+        if (!contentType.IsNullOrEmpty())
         {
             resultHeaders["content-type"] = contentType;
         }
         else if (json != null)
         {
             resultHeaders["content-type"] = "application/json";
         }
-        else if (!string.IsNullOrEmpty(path) && path != null)
+        else if (!path.IsNullOrEmpty())
         {
             resultHeaders["content-type"] = path.GetContentType();
         }

src/Playwright/Core/ScriptsHelper.cs

@@ -28,6 +28,7 @@
 using System.Linq;
 using System.Reflection;
 using System.Text.Json;
+using Microsoft.Playwright.Helpers;
 using Microsoft.Playwright.Transport.Converters;
 
 namespace Microsoft.Playwright.Core;
@@ -75,11 +76,11 @@ internal static object SerializedArgument(object? arg)
 
     internal static string EvaluationScript(string? content, string? path, bool addSourceUrl)
     {
-        if (!string.IsNullOrEmpty(content) && content != null)
+        if (!content.IsNullOrEmpty())
         {
             return content;
         }
-        else if (!string.IsNullOrEmpty(path) && path != null)
+        else if (!path.IsNullOrEmpty())
         {
             var source = File.ReadAllText(path);
             return addSourceUrl ? AddSourceUrlToScript(source, path) : source;

src/Playwright/Core/Tracing.cs

@@ -108,7 +108,7 @@ private async Task DoStopChunkAsync(string? filePath)
         {
             // Not interested in artifacts.
             await _TracingStopChunkAsync("discard").ConfigureAwait(false);
-            if (!string.IsNullOrEmpty(_stacksId) && _stacksId != null)
+            if (!_stacksId.IsNullOrEmpty())
             {
                 if (_connection.LocalUtils != null)
                 {
@@ -135,7 +135,7 @@ private async Task DoStopChunkAsync(string? filePath)
         // The artifact may be missing if the browser closed while stopping tracing.
         if (artifact == null)
         {
-            if (!string.IsNullOrEmpty(_stacksId) && _stacksId != null)
+            if (!_stacksId.IsNullOrEmpty())
             {
                 if (_connection.LocalUtils != null)
                 {

src/Playwright/Core/Waiter.cs

@@ -78,7 +78,7 @@ public void Dispose()
                 ["waitId"] = _waitId,
                 ["phase"] = "after",
             };
-            if (!string.IsNullOrEmpty(_error) && _error != null)
+            if (!_error.IsNullOrEmpty())
             {
                 info["error"] = _error;
             }

src/Playwright/Helpers/NotNullWhenAttribute.cs

@@ -0,0 +1,8 @@
+namespace System.Diagnostics.CodeAnalysis;
+
+// This can be dropped when we drop netstandard2.0
+[AttributeUsage(AttributeTargets.Parameter)]
+internal sealed class NotNullWhenAttribute(bool returnValue) : Attribute
+{
+    public bool ReturnValue { get; } = returnValue;
+}

src/Playwright/Helpers/StringExtensions.cs

@@ -24,6 +24,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 
@@ -603,7 +604,7 @@ internal static class StringExtensions
     /// </summary>
     /// <param name="query">Query string.</param>
     /// <returns>A <see cref="Dictionary{TKey, TValue}"/> containing the parsed QueryString.</returns>
-    public static Dictionary<string, string> ParseQueryString(this string query)
+    internal static Dictionary<string, string> ParseQueryString(this string query)
     {
         if (query is null)
         {
@@ -656,4 +657,14 @@ internal static string MimeType(this string file)
 
         return path.Substring(index);
     }
+
+    /// <summary>
+    /// Checks if the string is null or empty. This should be used instead of string.IsNullOrEmpty to avoid nullability warnings.
+    /// If we drop netstandard2.0 support, we can migrate to string.IsNullOrEmpty().
+    /// Relates https://stackoverflow.com/a/64066801.
+    /// </summary>
+    internal static bool IsNullOrEmpty([NotNullWhen(false)] this string? data)
+    {
+        return string.IsNullOrEmpty(data);
+    }
 }