Support disabling the task result caching, do not write the cache file if up to date or no assets

Author: javiercn

src/StaticWebAssetsSdk/Targets/Microsoft.NET.Sdk.StaticWebAssets.Compression.targets

@@ -223,7 +223,7 @@ Copyright (c) .NET Foundation. All rights reserved.
   <Target Name="ResolveBuildCompressedStaticWebAssets" DependsOnTargets="$(ResolveBuildCompressedStaticWebAssetsDependsOn)">
 
     <PropertyGroup>
-      <_ResolveBuildCompressedStaticWebAssetsCachePath>$(_StaticWebAssetsManifestBase)rbcswa.dswa.cache.json</_ResolveBuildCompressedStaticWebAssetsCachePath>
+      <_ResolveBuildCompressedStaticWebAssetsCachePath Condition="'$(StaticWebAssetsCacheDefineStaticWebAssetsEnabled)' == 'true'">$(_StaticWebAssetsManifestBase)rbcswa.dswa.cache.json</_ResolveBuildCompressedStaticWebAssetsCachePath>
     </PropertyGroup>
 
     <DefineStaticWebAssets

src/StaticWebAssetsSdk/Targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets

@@ -100,7 +100,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     -->
 
     <PropertyGroup>
-      <_ResolveJsInitializerModuleStaticWebAssetsCachePath>$(_StaticWebAssetsManifestBase)rjimswa.dswa.cache.json</_ResolveJsInitializerModuleStaticWebAssetsCachePath>
+      <_ResolveJsInitializerModuleStaticWebAssetsCachePath Condition="'$(StaticWebAssetsCacheDefineStaticWebAssetsEnabled)' == 'true'">$(_StaticWebAssetsManifestBase)rjimswa.dswa.cache.json</_ResolveJsInitializerModuleStaticWebAssetsCachePath>
     </PropertyGroup>
 
     <DefineStaticWebAssets Condition="@(_JSModuleCandidates) != ''"
@@ -417,10 +417,10 @@ Copyright (c) .NET Foundation. All rights reserved.
     </ItemGroup>
 
     <PropertyGroup>
-      <_ResolveJSModuleStaticWebAssetsRazorCachePath>$(_StaticWebAssetsManifestBase)rjsmrazor.dswa.cache.json</_ResolveJSModuleStaticWebAssetsRazorCachePath>
+      <_ResolveJSModuleStaticWebAssetsRazorCachePath Condition="'$(StaticWebAssetsCacheDefineStaticWebAssetsEnabled)' == 'true'">$(_StaticWebAssetsManifestBase)rjsmrazor.dswa.cache.json</_ResolveJSModuleStaticWebAssetsRazorCachePath>
     </PropertyGroup>
     <PropertyGroup>
-      <_ResolveJSModuleStaticWebAssetsCshtmlCachePath>$(_StaticWebAssetsManifestBase)rjsmcshtml.dswa.cache.json</_ResolveJSModuleStaticWebAssetsCshtmlCachePath>
+      <_ResolveJSModuleStaticWebAssetsCshtmlCachePath Condition="'$(StaticWebAssetsCacheDefineStaticWebAssetsEnabled)' == 'true'">$(_StaticWebAssetsManifestBase)rjsmcshtml.dswa.cache.json</_ResolveJSModuleStaticWebAssetsCshtmlCachePath>
     </PropertyGroup>
 
     <!-- Find JS module files -->

src/StaticWebAssetsSdk/Targets/Microsoft.NET.Sdk.StaticWebAssets.targets

@@ -433,6 +433,7 @@ Copyright (c) .NET Foundation. All rights reserved.
       <StaticWebAssetFingerprintingEnabled Condition="'$(StaticWebAssetFingerprintingEnabled)' == ''">true</StaticWebAssetFingerprintingEnabled>
       <StaticWebAssetMergeTarget Condition="'$(TargetFrameworks)' != '' and '$(TargetPlatformIdentifier)' == 'browser'">Browser</StaticWebAssetMergeTarget>
       <StaticWebAssetMergeTarget Condition="'$(TargetFrameworks)' != '' and '$(TargetPlatformIdentifier)' == ''">Server</StaticWebAssetMergeTarget>
+      <StaticWebAssetsCacheDefineStaticWebAssetsEnabled Condition="'$(StaticWebAssetsCacheDefineStaticWebAssetsEnabled)' == ''">true</StaticWebAssetsCacheDefineStaticWebAssetsEnabled>
 
       <!-- Manifest paths -->
       <_StaticWebAssetsManifestBase Condition="'$(_StaticWebAssetsManifestBase)' == ''">$(IntermediateOutputPath)</_StaticWebAssetsManifestBase>
@@ -672,7 +673,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     DependsOnTargets="ResolveStaticWebAssetsConfiguration;UpdateExistingPackageStaticWebAssets">
 
     <PropertyGroup>
-      <_ResolveProjectStaticWebAssetsCachePath>$(_StaticWebAssetsManifestBase)rpswa.dswa.cache.json</_ResolveProjectStaticWebAssetsCachePath>
+      <_ResolveProjectStaticWebAssetsCachePath Condition="'$(StaticWebAssetsCacheDefineStaticWebAssetsEnabled)' == 'true'">$(_StaticWebAssetsManifestBase)rpswa.dswa.cache.json</_ResolveProjectStaticWebAssetsCachePath>
     </PropertyGroup>
 
     <DefineStaticWebAssets

src/StaticWebAssetsSdk/Tasks/DefineStaticWebAssets.Cache.cs

@@ -113,7 +113,7 @@ internal static DefineStaticWebAssetsCache ReadOrCreateCache(TaskLoggingHelper l
 
         internal void WriteCacheManifest()
         {
-            if (_manifestPath != null)
+            if (_manifestPath != null && !_cacheUpToDate && InputHashes.Count > 0)
             {
                 using var manifestFile = File.OpenWrite(_manifestPath);
                 manifestFile.SetLength(0);