Copydotnet.d.ts to wwwroot on build/publish.

src/mono/browser/build/BrowserWasmApp.targets

@@ -27,6 +27,7 @@
       $(WasmGenerateAppBundleDependsOn);
       GenerateBuildRuntimeConfigurationFiles;
       _GetWasmGenerateAppBundleDependencies;
+      _CopyDotnetTypeScriptDefinitions;
       _WasmGenerateAppBundle;
       _WasmGenerateRunV8Script;
     </WasmGenerateAppBundleDependsOn>
@@ -609,4 +610,29 @@
 
     <Exec Condition="'$(OS)' != 'Windows_NT'" Command="chmod a+x &quot;$(WasmRunV8ScriptPath)&quot;" />
   </Target>
+
+  <!-- Copy dotnet.d.ts to wwwroot for TypeScript development experience -->
+  <Target Name="_CopyDotnetTypeScriptDefinitions" 
+          Condition="Exists('$(MSBuildProjectDirectory)\wwwroot') and Exists('$(MicrosoftNetCoreAppRuntimePackRidNativeDir)dotnet.d.ts')">
+
+    <PropertyGroup>
+      <_DotnetTypesSourcePath>$(MicrosoftNetCoreAppRuntimePackRidNativeDir)dotnet.d.ts</_DotnetTypesSourcePath>
+      <_DotnetTypesDestPath>$(MSBuildProjectDirectory)\wwwroot\dotnet.d.ts</_DotnetTypesDestPath>
+    </PropertyGroup>
+
+    <!-- Only copy if source exists and is newer than destination or destination doesn't exist -->
+    <Copy SourceFiles="$(_DotnetTypesSourcePath)"
+          DestinationFiles="$(_DotnetTypesDestPath)"
+          Condition="!Exists('$(_DotnetTypesDestPath)') Or '$([System.IO.File]::GetLastWriteTime($(_DotnetTypesSourcePath)))' &gt; '$([System.IO.File]::GetLastWriteTime($(_DotnetTypesDestPath)))'"
+          SkipUnchangedFiles="true" />
+
+    <Message Text="Copied dotnet.d.ts to wwwroot directory for TypeScript IntelliSense" 
+             Condition="Exists('$(_DotnetTypesSourcePath)')" 
+             Importance="low" />
+
+    <!-- Add the file as Content so it gets included in the project -->
+    <ItemGroup Condition="Exists('$(_DotnetTypesDestPath)')">
+      <Content Include="wwwroot\dotnet.d.ts" Condition="'@(Content)' == '' Or !(@(Content->AnyHaveMetadataValue('Identity', 'wwwroot\dotnet.d.ts')))" />
+    </ItemGroup>
+  </Target>
 </Project>

src/mono/browser/runtime/rollup.config.js

@@ -259,6 +259,14 @@ if (isDebug) {
     });
 }
 
+// Always copy to the wasmbrowser template so it stays in sync
+typesConfig.output.push({
+    format: "es",
+    file: "../../wasm/templates/templates/browser/wwwroot/dotnet.d.ts",
+    banner: banner_dts,
+    plugins: [alwaysLF(), writeOnChangePlugin()],
+});
+
 const allConfigs = [
     loaderConfig,
     runtimeConfig,

src/mono/wasm/Wasm.Build.Tests/Templates/WasmTemplateTests.cs

@@ -317,5 +317,64 @@
             }
 
         }
+
+        [Theory]
+        [InlineData(Configuration.Debug)]
+        [InlineData(Configuration.Release)]
+        public void TypeScriptDefinitionsCopiedToWwwroot(Configuration config)
+        {
+            ProjectInfo info = CreateWasmTemplateProject(Template.WasmBrowser, config, aot: false, "tsdefs");
+
+            // Build the project to trigger the _CopyDotnetTypeScriptDefinitions target
+            BuildProject(info, config, new BuildOptions());
+
+            // Verify that dotnet.d.ts exists in wwwroot
+            string projectDirectory = Path.GetDirectoryName(info.ProjectFilePath)!;
+            string dotnetDtsPath = Path.Combine(projectDirectory, "wwwroot", "dotnet.d.ts");
+
+            Assert.True(File.Exists(dotnetDtsPath), $"dotnet.d.ts should exist at {dotnetDtsPath}");
+
+            // Verify that the file contains expected TypeScript definitions
+            string content = File.ReadAllText(dotnetDtsPath);
+            Assert.Contains("interface DotnetHostBuilder", content);
+            Assert.Contains("RuntimeAPI", content);
+            Assert.Contains("Licensed to the .NET Foundation", content);
+        }
+
+        [Fact]
+        public void TypeScriptDefinitionsUpdatedWhenNewer()
+        {
+            Configuration config = Configuration.Debug;
+            ProjectInfo info = CreateWasmTemplateProject(Template.WasmBrowser, config, aot: false, "tsupdate");
+
+            string projectDirectory = Path.GetDirectoryName(info.ProjectFilePath)!;
+            string dotnetDtsPath = Path.Combine(projectDirectory, "wwwroot", "dotnet.d.ts");
+
+            // First build
+            BuildProject(info, config, new BuildOptions());
+            Assert.True(File.Exists(dotnetDtsPath), $"dotnet.d.ts should exist at {dotnetDtsPath}");
+
+            DateTime firstWriteTime = File.GetLastWriteTime(dotnetDtsPath);
+
+            // Wait a moment to ensure different timestamps
+            Thread.Sleep(1100);
+
+            // Modify the template file to simulate an older version
+            File.WriteAllText(dotnetDtsPath, "// Old version\ninterface OldAPI { }");
+            DateTime modifiedTime = File.GetLastWriteTime(dotnetDtsPath);
+
+            // Second build should update the file
+            BuildProject(info, config, new BuildOptions());
+            DateTime secondWriteTime = File.GetLastWriteTime(dotnetDtsPath);
+
+            // Verify the file was updated (should be newer than our manual modification)
+            Assert.True(secondWriteTime > modifiedTime, 
+                $"File should have been updated. First: {firstWriteTime}, Modified: {modifiedTime}, Second: {secondWriteTime}");
+
+            // Verify content was restored to proper TypeScript definitions
+            string content = File.ReadAllText(dotnetDtsPath);
+            Assert.Contains("interface DotnetHostBuilder", content);
+            Assert.DoesNotContain("Old version", content);
+        }
     }
 }