make EmccInitialHeapSize dynamic based on size of the assemblies

src/mono/wasm/build/WasmApp.Native.targets

@@ -149,6 +149,10 @@
     <Error Condition="'$(_IsEMSDKMissing)' == 'true'"
            Text="$(_EMSDKMissingErrorMessage) Emscripten SDK is required for building native files." />
 
+    <AssembliesTotalSize Assemblies="@(WasmAssembliesToBundle)">
+      <Output TaskParameter="TotalSize" PropertyName="_WasmAssembliesTotalSize" />
+    </AssembliesTotalSize>
+
     <PropertyGroup>
       <_MonoAotCrossCompilerPath>@(MonoAotCrossCompiler->WithMetadataValue('RuntimeIdentifier','browser-wasm'))</_MonoAotCrossCompilerPath>
       <_EmccDefaultFlagsRsp>$([MSBuild]::NormalizePath($(_WasmRuntimePackSrcDir), 'emcc-default.rsp'))</_EmccDefaultFlagsRsp>
@@ -188,6 +192,7 @@
       <_EmccLinkRsp>$(_WasmIntermediateOutputPath)emcc-link.rsp</_EmccLinkRsp>
 
       <EmccInitialHeapSize Condition="'$(EmccInitialHeapSize)' == ''">$(EmccTotalMemory)</EmccInitialHeapSize>
+      <EmccInitialHeapSize Condition="'$(EmccInitialHeapSize)' == '' and '$(_WasmAssembliesTotalSize)' != '' and $(_WasmAssembliesTotalSize) > 16777216">$(_WasmAssembliesTotalSize)</EmccInitialHeapSize>
       <EmccInitialHeapSize Condition="'$(EmccInitialHeapSize)' == ''">16777216</EmccInitialHeapSize>
     </PropertyGroup>
 

src/mono/wasm/build/WasmApp.targets

@@ -1,6 +1,7 @@
 <Project>
   <UsingTask TaskName="WasmAppBuilder" AssemblyFile="$(WasmAppBuilderTasksAssemblyPath)" />
   <UsingTask TaskName="WasmLoadAssembliesAndReferences" AssemblyFile="$(WasmAppBuilderTasksAssemblyPath)" />
+  <UsingTask TaskName="AssembliesTotalSize" AssemblyFile="$(WasmAppBuilderTasksAssemblyPath)" />
 
   <!--
       Required public items/properties:
@@ -51,7 +52,7 @@
       - $(EmccFlags)                        - Emcc flags used for both compiling native files, and linking
       - $(EmccExtraLDFlags)                 - Extra emcc flags for linking
       - $(EmccExtraCFlags)                  - Extra emcc flags for compiling native files
-      - $(EmccInitialHeapSize)              - Initial heap size specified with `emcc`. Default value: 16777216
+      - $(EmccInitialHeapSize)              - Initial heap size specified with `emcc`. Default value: 16777216 or size of the DLLs.
                                               Corresponds to `INITIAL_MEMORY` arg for emcc.
                                               (previously named EmccTotalMemory, which is still kept as an alias)
 
@@ -203,6 +204,10 @@
       <WasmAssembliesToBundle Include="$(PublishDir)\**\*.dll" />
     </ItemGroup>
 
+    <AssembliesTotalSize Assemblies="@(WasmAssembliesToBundle)">
+      <Output TaskParameter="TotalSize" PropertyName="_WasmAssembliesTotalSize" />
+    </AssembliesTotalSize>
+
     <PropertyGroup Condition="'$(_WasmRuntimeConfigFilePath)' == ''">
       <_WasmRuntimeConfigFilePath Condition="$([System.String]::new(%(PublishItemsOutputGroupOutputs.Identity)).EndsWith('$(AssemblyName).runtimeconfig.json'))">@(PublishItemsOutputGroupOutputs)</_WasmRuntimeConfigFilePath>
     </PropertyGroup>

src/tasks/WasmAppBuilder/AssembliesTotalSize.cs

@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+// estimate the total size of the assemblies we are going to load and round it up to 64K
+public class AssembliesTotalSize : Task
+{
+    [Required]
+    [NotNull]
+    public string[]? Assemblies { get; set; }
+
+    [Output]
+    public long? TotalSize { get; private set; }
+
+    public override bool Execute ()
+    {
+        long totalSize=0;
+        foreach (var asm in Assemblies)
+        {
+            var info = new FileInfo(asm);
+            if (!info.Exists)
+            {
+                Log.LogError($"Could not find assembly '{asm}'");
+                return false;
+            }
+            totalSize += info.Length;
+        }
+        totalSize += 0x10000;
+        totalSize &= 0xFFFF0000;
+
+        TotalSize = totalSize;
+
+        return true;
+    }
+}