SqlPersistenceTask: An unhandled exception occurred: Could not find assembly 'NServiceBus.Persistence.Sql, Version=9.0.0.0

[danielmarbach]

The issue was that the MetadataLoadContext needed to resolve referenced assemblies (like NServiceBus.Persistence.Sql) when reading custom attributes, but the MSBuild task runs AfterTargets="AfterCompile" using the intermediate assembly from the obj/ folder, where dependencies might not be copied yet.

The fix passes the @(ReferencePath) item group from MSBuild to the script generator, which contains the full paths to all referenced assemblies. These are then included in the PathAssemblyResolver so the MetadataLoadContext can resolve them.

2>: Error  : SqlPersistenceTask: An unhandled exception occurred:
Exception:
Could not find assembly 'NServiceBus.Persistence.Sql, Version=9.0.0.0, Culture=neutral, PublicKeyToken=9fc386479f8a226c'. Either explicitly load this assembly using a method such as LoadFromAssemblyPath() or use a MetadataAssemblyResolver that returns a valid assembly.
StackTrace:
   at System.Reflection.TypeLoading.Ecma.EcmaResolver.ResolveAssembly(AssemblyReferenceHandle handle, EcmaModule module)
   at System.Reflection.TypeLoading.Ecma.EcmaResolver.ComputeTypeRefResolution(TypeReferenceHandle handle, EcmaModule module)
   at System.Reflection.TypeLoading.Ecma.EcmaResolver.<>c.<.cctor>b__15_1(EntityHandle h, EcmaModule m)
   at System.Reflection.TypeLoading.Ecma.MetadataTable`2.GetOrAdd(EntityHandle handle, C context, Func`3 factory)
   at System.Reflection.TypeLoading.Ecma.EcmaResolver.ResolveTypeRef(TypeReferenceHandle handle, EcmaModule module)
   at System.Reflection.TypeLoading.Ecma.EcmaResolver.ResolveTypeDefRefOrSpec(EntityHandle handle, EcmaModule module, TypeContext& typeContext)
   at System.Reflection.TypeLoading.Ecma.EcmaCustomAttributeData.ComputeAttributeType()
   at System.Reflection.TypeLoading.RoCustomAttributeData.get_AttributeType()
   at SettingsAttributeReader.<>c.<Read>b__0_0(CustomAttributeData x) in /_/src/ScriptBuilder/AttributeReading/SettingsAttributeReader.cs:line 14
   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Func`2 predicate, Boolean& found)
   at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
   at SettingsAttributeReader.Read(Assembly assembly) in /_/src/ScriptBuilder/AttributeReading/SettingsAttributeReader.cs:line 13
   at ScriptGenerator.Generate() in /_/src/ScriptBuilder/ScriptGenerator.cs:line 49
   at ScriptGenerator.Generate(String assemblyPath, String targetDirectory, Action`2 logError, Func`2 promotionPathFinder) in /_/src/ScriptBuilder/ScriptGenerator.cs:line 24
   at InnerTask.Execute() in /_/src/ScriptBuilderTask/InnerTask.cs:line 24
   at NServiceBus.Persistence.Sql.SqlPersistenceScriptBuilderTask.Execute() in /_/src/ScriptBuilderTask/SqlPersistenceScriptBuilderTask.cs:line 42
Source:
System.Reflection.MetadataLoadContext

[danielmarbach]

Local build verification of latest commit

[danielmarbach]

@bording Given this is not an area I'm super knowledgeable in, I'd appreciate your review

[Copilot]

Pull request overview

This PR fixes an issue where the MSBuild task failed to resolve referenced assemblies when using MetadataLoadContext to read custom attributes. The task runs after compilation using the intermediate assembly from the obj/ folder, where dependencies aren't yet copied. The solution passes the @(ReferencePath) item group from MSBuild, which contains full paths to all referenced assemblies, ensuring the MetadataLoadContext can resolve them properly.

Changes:

• Added ReferencePath parameter to the MSBuild task and targets file to pass referenced assembly paths
• Modified ScriptGenerator to accept and use reference paths when creating the PathAssemblyResolver
• Added comprehensive tests to verify the fix works in isolated assembly scenarios

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
SqlPersistenceScriptBuilderTask.cs	Added ReferencePath property and passes it to InnerTask
NServiceBus.Persistence.Sql.targets	Passes @(ReferencePath) from MSBuild to the task
InnerTask.cs	Accepts referencePaths parameter and forwards to ScriptGenerator
ScriptGenerator.cs	Implements CollectAssemblyFiles method to include reference paths in assembly resolution
SettingsAttributeReader.cs	Minor code style modernization (collection expressions)
InnerTaskTests.cs	Added tests for isolated assembly scenarios with and without reference paths
InnerTaskTests approval file	Renamed to match updated test name
APIApprovals.Approve.approved.txt	Updated to reflect new public API surface

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[DavidBoike]

• Would have worked, but we went with Use PEReader instead of reflection in script generator #1900 for fewer dependencies and lighter memory footprint during builds.