From cb166eb5359639c59f54d4547767a91404fb63da Mon Sep 17 00:00:00 2001
From: lewing <lewing@microsoft.com>
Date: Thu, 18 Jun 2026 14:12:29 -0500
Subject: [PATCH 1/2] [browser] Wasm boot JSON: touch a stamp, not the boot
 JSON itself
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The build and publish boot JSON targets used <Touch Files="$(_WasmBuildBootJsonPath)" />
to give MSBuild's Inputs/Outputs check a current output timestamp despite
GenerateWasmBootJson's content-preservation behavior (PR #125367). However the
boot JSON ($(_WasmBuildBootJsonPath), typically obj/.../dotnet.js, and the
publish equivalent) is also a source for the StaticWebAssets compression
pipeline and the PreserveNewest copy target. Bumping its mtime on every
successful build defeats their incrementality checks and breaks
`dotnet build -question`:

  Building target "_BuildCopyStaticWebAssetsPreserveNewest" partially, because
  some output files are out of date with respect to their input files.
  [_BuildStaticWebAssetsPreserveNewest:
    Input  = obj/.../compressed/{hash}-{0}-{fp}-{fp}.gz,
    Output = bin/.../wwwroot/_framework/dotnet.{fp}.js.gz]
  Input file is newer than output file.

This is the same regression that PR #118637 (Aug 2025) originally fixed by
introducing ArtifactWriter.PersistFileIfChanged. PR #125367's <Touch> on the
boot JSON re-broke it by bumping the file's mtime unconditionally after every
successful run.

Replace the <Touch> on the boot JSON with a <Touch> on a separate
`wasm-bootjson-{build,publish}.complete.stamp` file, and use that stamp as the
target's Outputs=. MSBuild now sees a current output timestamp for its own
incrementality check on the boot-JSON target, without touching the boot JSON
itself — preserving content-mtime semantics for downstream consumers.

Fixes dotnet/runtime#129280
Fixes the downstream cascade observed on PR dotnet/runtime#129454 (WBT
`TypeScriptDefinitionsCopiedToWwwrootOnBuild(Debug, emitTypeScriptDts:True)`).

Same fix applied to both the build (`_WriteBuildWasmBootJsonFile`) and
publish (`GeneratePublishWasmBootJson`) paths since both have identical
shape and the same downstream consumers.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 ...rosoft.NET.Sdk.WebAssembly.Browser.targets | 29 ++++++++++++-------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
index ab8d6606aba35e..923058fb7f95a3 100644
--- a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
+++ b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
@@ -708,7 +708,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     DependsOnTargets="_WriteWasmBootJsonBuildPropertyStamp"
     Condition="'$(WasmBuildingForNestedPublish)' != 'true'"
     Inputs="@(IntermediateAssembly);@(WasmStaticWebAsset);@(_WasmJsModuleCandidatesForBuild);@(_WasmFilesToIncludeInFileSystemStaticWebAsset);@(_WasmJsConfigStaticWebAsset);@(_WasmDotnetJsForBuild);@(WasmBootConfigExtension);$(ProjectRuntimeConfigFilePath);$(MSBuildProjectFullPath);$(MSBuildThisFileFullPath);$(_WebAssemblySdkTasksAssembly);$(IntermediateOutputPath)wasm-bootjson-build.stamp"
-    Outputs="$(_WasmBuildBootJsonPath)">
+    Outputs="$(IntermediateOutputPath)wasm-bootjson-build.complete.stamp">
 
     <GenerateWasmBootJson
       AssemblyPath="@(IntermediateAssembly)"
@@ -748,12 +748,20 @@ Copyright (c) .NET Foundation. All rights reserved.
 
     <ItemGroup>
       <FileWrites Include="$(_WasmBuildBootJsonPath)" />
+      <FileWrites Include="$(IntermediateOutputPath)wasm-bootjson-build.complete.stamp" />
     </ItemGroup>
 
-    <!-- The GenerateWasmBootJson task uses content comparison and preserves old timestamps when
-         the output content is unchanged. Touch the output so MSBuild's Inputs/Outputs check
-         sees a current timestamp and can correctly skip this target on subsequent builds. -->
-    <Touch Files="$(_WasmBuildBootJsonPath)" />
+    <!-- The GenerateWasmBootJson task uses content comparison and preserves old timestamps
+         when the output content is unchanged. We need a current timestamp on something for
+         MSBuild's Inputs/Outputs check to correctly skip this target on subsequent builds,
+         but we must NOT touch $(_WasmBuildBootJsonPath) itself: that file is a source for the
+         StaticWebAssets compression pipeline (GZipCompress/BrotliCompress) and the copy-to-
+         output target (_BuildCopyStaticWebAssetsPreserveNewest). Bumping its timestamp on every
+         build defeats their incrementality checks and breaks `dotnet build -question` (see
+         dotnet/runtime#129280, dotnet/runtime#124729, dotnet/aspnetcore#63207).
+         Touch a separate stamp file that is the target's Outputs= so MSBuild sees a current
+         output timestamp without affecting downstream consumers of the boot JSON. -->
+    <Touch Files="$(IntermediateOutputPath)wasm-bootjson-build.complete.stamp" AlwaysCreate="true" />
   </Target>
 
   <!-- Define the boot config file as a static web asset and create endpoints.
@@ -1180,7 +1188,7 @@ Copyright (c) .NET Foundation. All rights reserved.
   <Target Name="GeneratePublishWasmBootJson"
     DependsOnTargets="_WriteWasmPublishBootJsonPropertyStamp"
     Inputs="@(IntermediateAssembly);@(_WasmPublishAsset);@(_WasmJsModuleCandidatesForPublish);@(_WasmPublishConfigFile);@(_WasmDotnetJsForPublish);@(WasmBootConfigExtension);$(ProjectRuntimeConfigFilePath);$(MSBuildProjectFullPath);$(MSBuildThisFileFullPath);$(_WebAssemblySdkTasksAssembly);$(IntermediateOutputPath)wasm-bootjson-publish.stamp"
-    Outputs="$(IntermediateOutputPath)$(_WasmPublishBootConfigFileName)">
+    Outputs="$(IntermediateOutputPath)wasm-bootjson-publish.complete.stamp">
 
     <GenerateWasmBootJson
       AssemblyPath="@(IntermediateAssembly)"
@@ -1220,12 +1228,13 @@ Copyright (c) .NET Foundation. All rights reserved.
 
     <ItemGroup>
       <FileWrites Include="$([MSBuild]::NormalizePath($(IntermediateOutputPath), $(_WasmPublishBootConfigFileName)))" />
+      <FileWrites Include="$(IntermediateOutputPath)wasm-bootjson-publish.complete.stamp" />
     </ItemGroup>
 
-    <!-- The GenerateWasmBootJson task uses content comparison and preserves old timestamps when
-         the output content is unchanged. Touch the output so MSBuild's Inputs/Outputs check
-         sees a current timestamp and can correctly skip this target on subsequent builds. -->
-    <Touch Files="$(IntermediateOutputPath)$(_WasmPublishBootConfigFileName)" />
+    <!-- See _WriteBuildWasmBootJsonFile for rationale: touch a separate stamp file rather than
+         the boot JSON itself to avoid cascading mtime bumps into downstream StaticWebAssets
+         compression / copy targets. -->
+    <Touch Files="$(IntermediateOutputPath)wasm-bootjson-publish.complete.stamp" AlwaysCreate="true" />
 
   </Target>
 

From 97a975c2cd9a8c5b57252bf09865286c6c4fbee9 Mon Sep 17 00:00:00 2001
From: lewing <lewing@microsoft.com>
Date: Thu, 18 Jun 2026 14:20:38 -0500
Subject: [PATCH 2/2] Track .complete.stamp in always-run wrapper FileWrites

Addresses Copilot review feedback on dotnet/runtime#129591: the
.complete.stamp files added in the prior commit are only listed in
FileWrites inside the incremental targets (_WriteBuildWasmBootJsonFile,
GeneratePublishWasmBootJson). When those targets are skipped on
incremental builds, the in-body <ItemGroup> entries are not populated,
so `dotnet clean` would leave the stamps behind.

Mirror the existing pattern from PR #125367: also add the stamp paths
to FileWrites in the always-run wrapper targets
(_GenerateBuildWasmBootJson and _AddPublishWasmBootJsonToStaticWebAssets)
that track the boot JSON itself for the same reason.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../build/Microsoft.NET.Sdk.WebAssembly.Browser.targets    | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
index 923058fb7f95a3..d586a4d6c80452 100644
--- a/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
+++ b/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
@@ -773,6 +773,11 @@ Copyright (c) .NET Foundation. All rights reserved.
     <ItemGroup>
       <!-- Track boot JSON for clean operations even when _WriteBuildWasmBootJsonFile was skipped -->
       <FileWrites Include="$(_WasmBuildBootJsonPath)" />
+      <!-- Track the completion stamp here too: when _WriteBuildWasmBootJsonFile is skipped on
+           incremental builds, its in-body FileWrites entries aren't populated. Without this,
+           `dotnet clean` would leave the stamp behind and the next build would (correctly)
+           see it as up-to-date even though the boot JSON was just cleaned. -->
+      <FileWrites Include="$(IntermediateOutputPath)wasm-bootjson-build.complete.stamp" />
       <_WasmBuildBootConfigCandidate
         Include="$(_WasmBuildBootJsonPath)"
         RelativePath="_framework/$(_WasmBootConfigFileName)" />
@@ -1092,6 +1097,8 @@ Copyright (c) .NET Foundation. All rights reserved.
     <ItemGroup>
       <!-- Track boot JSON for clean operations even when GeneratePublishWasmBootJson was skipped -->
       <FileWrites Include="$(IntermediateOutputPath)$(_WasmPublishBootConfigFileName)" />
+      <!-- Track the completion stamp here too: see _GenerateBuildWasmBootJson for rationale. -->
+      <FileWrites Include="$(IntermediateOutputPath)wasm-bootjson-publish.complete.stamp" />
       <_WasmPublishBootConfigCandidate
         Include="$([MSBuild]::NormalizePath($(IntermediateOutputPath), $(_WasmPublishBootConfigFileName)))"
         RelativePath="_framework/$(_WasmBootConfigFileName)" />