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Propagate actual error info when loading a TPA assembly fails with FileNotFoundException #126782

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7e896cd
Improve FileNotFoundException diagnostics in assembly loading
elinor-fung Apr 10, 2026
6503066
Wire diagnostic info through full bind chain to exception throw sites
elinor-fung Apr 10, 2026
1be58e3
Revert TryOpenFile ERROR_OPEN_FAILED change
elinor-fung Apr 10, 2026
cc0c5be
Switch diagnostic strings to Printf format and append mode
elinor-fung Apr 10, 2026
ec7a60c
Include HRESULT message in diagnostic info and update cached prefix
elinor-fung Apr 10, 2026
c6dc939
Add tests for TPA assembly load failures
elinor-fung Apr 10, 2026
7976c56
Change FusionLog back to get-only auto-property
elinor-fung Apr 11, 2026
96228a0
Simplify EEFileLoadException: delegating ctor and throw site
elinor-fung Apr 11, 2026
f4ce4b9
Add newline separators between diagnostic messages
elinor-fung Apr 11, 2026
bdc3496
Move Init failure diagnostic next to the Init call
elinor-fung Apr 11, 2026
42d636d
Fix test comments to match actual build mechanism
elinor-fung Apr 11, 2026
db4fdb2
Fix include ordering and use delegating constructor
elinor-fung Apr 15, 2026
a298c54
Address PR review feedback for tests
elinor-fung Apr 15, 2026
275d271
Fix test failures: ensure DLLs removed before test payload packaging
elinor-fung Apr 16, 2026
f8981fa
Move diagnostic info into BindResult struct
elinor-fung Apr 22, 2026
ca68101
Merge remote-tracking branch 'upstream/main' into copilot/improve-fnf…
elinor-fung Apr 24, 2026
c6eecd3
Take diagnostic info by const SString& in failure cache Add
elinor-fung Apr 24, 2026
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5 changes: 3 additions & 2 deletions src/coreclr/System.Private.CoreLib/src/System/IO/FileLoadException.CoreCLR.cs
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Expand Up @@ -47,16 +47,17 @@ internal enum FileLoadExceptionKind
}

[UnmanagedCallersOnly]
internal static unsafe void Create(FileLoadExceptionKind kind, char* pFileName, int hresult, object* pThrowable, Exception* pException)
internal static unsafe void Create(FileLoadExceptionKind kind, char* pFileName, int hresult, char* pDiagnosticInfo, object* pThrowable, Exception* pException)
{
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try
{
string? fileName = pFileName is not null ? new string(pFileName) : null;
string? diagnosticInfo = pDiagnosticInfo is not null ? new string(pDiagnosticInfo) : null;
Debug.Assert(Enum.IsDefined(kind));
*pThrowable = kind switch
{
FileLoadExceptionKind.BadImageFormat => new BadImageFormatException(fileName, hresult),
FileLoadExceptionKind.FileNotFound => new FileNotFoundException(fileName, hresult),
FileLoadExceptionKind.FileNotFound => new FileNotFoundException(fileName, hresult, diagnosticInfo),
FileLoadExceptionKind.OutOfMemory => new OutOfMemoryException(),
_ /* FileLoadExceptionKind.FileLoad */ => new FileLoadException(fileName, hresult),
};
Expand Down
6 changes: 6 additions & 0 deletions src/coreclr/System.Private.CoreLib/src/System/IO/FileNotFoundException.CoreCLR.cs
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Expand Up @@ -12,5 +12,11 @@ internal FileNotFoundException(string? fileName, int hResult)
FileName = fileName;
SetMessageField();
}

internal FileNotFoundException(string? fileName, int hResult, string? diagnosticInfo)
: this(fileName, hResult)
{
FusionLog = diagnosticInfo;
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}
}
}
44 changes: 35 additions & 9 deletions src/coreclr/binder/assemblybindercommon.cpp
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Expand Up @@ -37,7 +37,8 @@ extern HRESULT RuntimeInvokeHostAssemblyResolver(INT_PTR pAssemblyLoadContextToB

STDAPI BinderAcquirePEImage(LPCTSTR szAssemblyPath,
PEImage** ppPEImage,
ProbeExtensionResult probeExtensionResult);
ProbeExtensionResult probeExtensionResult,
SString *pDiagnosticInfo = NULL);

namespace BINDER_SPACE
{
Expand Down Expand Up @@ -193,7 +194,8 @@ namespace BINDER_SPACE
/* in */ AssemblyName *pAssemblyName,
/* in */ bool excludeAppPaths,
/* out */ Assembly **ppAssembly,
/* [out, optional] */ Assembly **ppExistingAssemblyOnFailure)
/* [out, optional] */ Assembly **ppExistingAssemblyOnFailure,
/* out */ SString *pDiagnosticInfo)
{
HRESULT hr = S_OK;
LONG kContextVersion = 0;
Expand Down Expand Up @@ -225,6 +227,11 @@ namespace BINDER_SPACE
Exit:
tracer.TraceBindResult(bindResult);

if (pDiagnosticInfo != NULL && !bindResult.GetDiagnosticInfo().IsEmpty())
{
pDiagnosticInfo->Append(bindResult.GetDiagnosticInfo());
}

if (bindResult.HaveResult())
{
BindResult hostBindResult;
Expand Down Expand Up @@ -405,7 +412,7 @@ namespace BINDER_SPACE
pAssemblyName->GetDisplayName(assemblyDisplayName,
AssemblyName::INCLUDE_VERSION);

hr = pApplicationContext->GetFailureCache()->Lookup(assemblyDisplayName);
hr = pApplicationContext->GetFailureCache()->Lookup(assemblyDisplayName, &pBindResult->GetDiagnosticInfo());
if (FAILED(hr))
{
if ((hr == HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND)) && skipFailureCaching)
Expand Down Expand Up @@ -459,7 +466,7 @@ namespace BINDER_SPACE
}
}

hr = pApplicationContext->AddToFailureCache(assemblyDisplayName, hr);
hr = pApplicationContext->AddToFailureCache(assemblyDisplayName, hr, pBindResult->GetDiagnosticInfo());
}

LogExit:
Expand Down Expand Up @@ -869,7 +876,8 @@ namespace BINDER_SPACE
hr = GetAssembly(assemblyFilePath,
TRUE, // fIsInTPA
&pTPAAssembly,
probeExtensionResult);
probeExtensionResult,
&pBindResult->GetDiagnosticInfo());

BinderTracing::PathProbed(assemblyFilePath, BinderTracing::PathSource::Bundle, hr);

Expand Down Expand Up @@ -899,7 +907,9 @@ namespace BINDER_SPACE

hr = GetAssembly(fileName,
TRUE, // fIsInTPA
&pTPAAssembly);
&pTPAAssembly,
ProbeExtensionResult::Invalid(),
&pBindResult->GetDiagnosticInfo());
BinderTracing::PathProbed(fileName, BinderTracing::PathSource::ApplicationAssemblies, hr);

pBindResult->SetAttemptResult(hr, pTPAAssembly);
Expand Down Expand Up @@ -985,7 +995,8 @@ namespace BINDER_SPACE
HRESULT AssemblyBinderCommon::GetAssembly(SString &assemblyPath,
BOOL fIsInTPA,
Assembly **ppAssembly,
ProbeExtensionResult probeExtensionResult)
ProbeExtensionResult probeExtensionResult,
SString *pDiagnosticInfo)
{
HRESULT hr = S_OK;

Expand All @@ -1001,12 +1012,27 @@ namespace BINDER_SPACE
{
LPCTSTR szAssemblyPath = const_cast<LPCTSTR>(assemblyPath.GetUnicode());

hr = BinderAcquirePEImage(szAssemblyPath, &pPEImage, probeExtensionResult);
hr = BinderAcquirePEImage(szAssemblyPath, &pPEImage, probeExtensionResult, pDiagnosticInfo);
IF_FAIL_GO(hr);
}

// Initialize assembly object
IF_FAIL_GO(pAssembly->Init(pPEImage, fIsInTPA));
hr = pAssembly->Init(pPEImage, fIsInTPA);
if (FAILED(hr))
{
if (pDiagnosticInfo != NULL)
{
if (!pDiagnosticInfo->IsEmpty())
pDiagnosticInfo->AppendUTF8("\n");

StackSString format;
format.LoadResource(IDS_BINDING_FAILED_TO_INIT_ASSEMBLY);
StackSString hrMsg;
GetHRMsg(hr, hrMsg);
pDiagnosticInfo->AppendPrintf(format.GetUTF8(), assemblyPath.GetUTF8(), hrMsg.GetUTF8());
}
goto Exit;
}

// We're done
*ppAssembly = pAssembly.Extract();
Expand Down
12 changes: 8 additions & 4 deletions src/coreclr/binder/customassemblybinder.cpp
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Expand Up @@ -14,7 +14,8 @@ using namespace BINDER_SPACE;
// CustomAssemblyBinder implementation
// ============================================================================
HRESULT CustomAssemblyBinder::BindAssemblyByNameWorker(BINDER_SPACE::AssemblyName *pAssemblyName,
BINDER_SPACE::Assembly **ppCoreCLRFoundAssembly)
BINDER_SPACE::Assembly **ppCoreCLRFoundAssembly,
SString *pDiagnosticInfo)
{
VALIDATE_ARG_RET(pAssemblyName != nullptr && ppCoreCLRFoundAssembly != nullptr);
HRESULT hr = S_OK;
Expand All @@ -28,7 +29,9 @@ HRESULT CustomAssemblyBinder::BindAssemblyByNameWorker(BINDER_SPACE::AssemblyNam
hr = AssemblyBinderCommon::BindAssembly(this,
pAssemblyName,
false, //excludeAppPaths,
ppCoreCLRFoundAssembly);
ppCoreCLRFoundAssembly,
nullptr /* ppExistingAssemblyOnFailure */,
pDiagnosticInfo);
if (!FAILED(hr))
{
_ASSERTE(*ppCoreCLRFoundAssembly != NULL);
Expand All @@ -39,7 +42,8 @@ HRESULT CustomAssemblyBinder::BindAssemblyByNameWorker(BINDER_SPACE::AssemblyNam
}

HRESULT CustomAssemblyBinder::BindUsingAssemblyName(BINDER_SPACE::AssemblyName* pAssemblyName,
BINDER_SPACE::Assembly** ppAssembly)
BINDER_SPACE::Assembly** ppAssembly,
SString* pDiagnosticInfo)
{
// When LoadContext needs to resolve an assembly reference, it will go through the following lookup order:
//
Expand All @@ -58,7 +62,7 @@ HRESULT CustomAssemblyBinder::BindUsingAssemblyName(BINDER_SPACE::AssemblyName*

{
// Step 1 - Try to find the assembly within the LoadContext.
hr = BindAssemblyByNameWorker(pAssemblyName, &pCoreCLRFoundAssembly);
hr = BindAssemblyByNameWorker(pAssemblyName, &pCoreCLRFoundAssembly, pDiagnosticInfo);
if ((hr == HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND)) ||
(hr == FUSION_E_APP_DOMAIN_LOCKED) || (hr == FUSION_E_REF_DEF_MISMATCH))
{
Expand Down
11 changes: 7 additions & 4 deletions src/coreclr/binder/defaultassemblybinder.cpp
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Expand Up @@ -14,7 +14,8 @@ using namespace BINDER_SPACE;
HRESULT DefaultAssemblyBinder::BindAssemblyByNameWorker(BINDER_SPACE::AssemblyName *pAssemblyName,
BINDER_SPACE::Assembly **ppCoreCLRFoundAssembly,
bool excludeAppPaths,
BINDER_SPACE::Assembly **ppExistingAssemblyOnFailure)
BINDER_SPACE::Assembly **ppExistingAssemblyOnFailure,
SString *pDiagnosticInfo)
{
VALIDATE_ARG_RET(pAssemblyName != nullptr && ppCoreCLRFoundAssembly != nullptr);
HRESULT hr = S_OK;
Expand All @@ -28,7 +29,8 @@ HRESULT DefaultAssemblyBinder::BindAssemblyByNameWorker(BINDER_SPACE::AssemblyNa
pAssemblyName,
excludeAppPaths,
ppCoreCLRFoundAssembly,
ppExistingAssemblyOnFailure);
ppExistingAssemblyOnFailure,
pDiagnosticInfo);
if (!FAILED(hr))
{
(*ppCoreCLRFoundAssembly)->SetBinder(this);
Expand All @@ -46,7 +48,8 @@ HRESULT DefaultAssemblyBinder::BindAssemblyByNameWorker(BINDER_SPACE::AssemblyNa
// DefaultAssemblyBinder implementation
// ============================================================================
HRESULT DefaultAssemblyBinder::BindUsingAssemblyName(BINDER_SPACE::AssemblyName *pAssemblyName,
BINDER_SPACE::Assembly **ppAssembly)
BINDER_SPACE::Assembly **ppAssembly,
SString *pDiagnosticInfo)
{
HRESULT hr = S_OK;
VALIDATE_ARG_RET(pAssemblyName != nullptr && ppAssembly != nullptr);
Expand All @@ -55,7 +58,7 @@ HRESULT DefaultAssemblyBinder::BindUsingAssemblyName(BINDER_SPACE::AssemblyName

ReleaseHolder<BINDER_SPACE::Assembly> pCoreCLRFoundAssembly;

hr = BindAssemblyByNameWorker(pAssemblyName, &pCoreCLRFoundAssembly, false /* excludeAppPaths */);
hr = BindAssemblyByNameWorker(pAssemblyName, &pCoreCLRFoundAssembly, false /* excludeAppPaths */, nullptr /* ppExistingAssemblyOnFailure */, pDiagnosticInfo);

#if !defined(DACCESS_COMPILE)
if ((hr == HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND)) ||
Expand Down
20 changes: 18 additions & 2 deletions src/coreclr/binder/failurecache.cpp
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Expand Up @@ -11,6 +11,7 @@
//
// ============================================================

#include "common.h"
#include "failurecache.hpp"

namespace BINDER_SPACE
Expand All @@ -32,7 +33,8 @@ namespace BINDER_SPACE
}

HRESULT FailureCache::Add(SString &assemblyNameorPath,
HRESULT hrBindingResult)
HRESULT hrBindingResult,
const SString &diagnosticInfo)
{
HRESULT hr = S_OK;

Expand All @@ -44,6 +46,10 @@ namespace BINDER_SPACE

pFailureCacheEntry->GetAssemblyNameOrPath().Set(assemblyNameorPath);
pFailureCacheEntry->SetBindingResult(hrBindingResult);
if (!diagnosticInfo.IsEmpty())
{
pFailureCacheEntry->SetDiagnosticInfo(diagnosticInfo);
}

Hash::Add(pFailureCacheEntry);
pFailureCacheEntry.SuppressRelease();
Expand All @@ -52,14 +58,24 @@ namespace BINDER_SPACE
return hr;
}

HRESULT FailureCache::Lookup(SString &assemblyNameorPath)
HRESULT FailureCache::Lookup(SString &assemblyNameorPath,
SString *pDiagnosticInfo)
{
HRESULT hr = S_OK;
FailureCacheEntry *pFailureCachEntry = Hash::Lookup(assemblyNameorPath);

if (pFailureCachEntry != NULL)
{
hr = pFailureCachEntry->GetBindingResult();
if (pDiagnosticInfo != NULL && !pFailureCachEntry->GetDiagnosticInfo().IsEmpty())
{
if (!pDiagnosticInfo->IsEmpty())
pDiagnosticInfo->AppendUTF8("\n");

StackSString format;
format.LoadResource(IDS_BINDING_CACHED_FAILURE_PREFIX);
pDiagnosticInfo->AppendPrintf(format.GetUTF8(), pFailureCachEntry->GetDiagnosticInfo().GetUTF8());
}
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}

return hr;
Expand Down
3 changes: 2 additions & 1 deletion src/coreclr/binder/inc/applicationcontext.hpp
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Expand Up @@ -95,7 +95,8 @@ namespace BINDER_SPACE
inline ExecutionContext *GetExecutionContext();
inline FailureCache *GetFailureCache();
inline HRESULT AddToFailureCache(SString &assemblyNameOrPath,
HRESULT hrBindResult);
HRESULT hrBindResult,
const SString &diagnosticInfo);
inline StringArrayList *GetAppPaths();
inline SimpleNameToFileNameMap *GetTpaList();
inline StringArrayList *GetPlatformResourceRoots();
Expand Down
5 changes: 3 additions & 2 deletions src/coreclr/binder/inc/applicationcontext.inl
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Expand Up @@ -41,9 +41,10 @@ FailureCache *ApplicationContext::GetFailureCache()
}

HRESULT ApplicationContext::AddToFailureCache(SString &assemblyNameOrPath,
HRESULT hrBindResult)
HRESULT hrBindResult,
const SString &diagnosticInfo)
{
HRESULT hr = GetFailureCache()->Add(assemblyNameOrPath, hrBindResult);
HRESULT hr = GetFailureCache()->Add(assemblyNameOrPath, hrBindResult, diagnosticInfo);
IncrementVersion();
return hr;
}
Expand Down
6 changes: 4 additions & 2 deletions src/coreclr/binder/inc/assemblybindercommon.hpp
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Expand Up @@ -32,7 +32,8 @@ namespace BINDER_SPACE
/* in */ AssemblyName *pAssemblyName,
/* in */ bool excludeAppPaths,
/* out */ Assembly **ppAssembly,
/* [out, optional] */ Assembly **ppExistingAssemblyOnFailure = nullptr);
/* [out, optional] */ Assembly **ppExistingAssemblyOnFailure = nullptr,
/* out */ SString *pDiagnosticInfo = NULL);

static HRESULT BindToSystem(/* in */ SString &systemDirectory,
/* out */ Assembly **ppSystemAssembly);
Expand All @@ -45,7 +46,8 @@ namespace BINDER_SPACE
static HRESULT GetAssembly(/* in */ SString &assemblyPath,
/* in */ BOOL fIsInTPA,
/* out */ Assembly **ppAssembly,
/* in */ ProbeExtensionResult probeExtensionResult = ProbeExtensionResult::Invalid());
/* in */ ProbeExtensionResult probeExtensionResult = ProbeExtensionResult::Invalid(),
/* out */ SString *pDiagnosticInfo = NULL);

#if !defined(DACCESS_COMPILE)
static HRESULT BindUsingHostAssemblyResolver (/* in */ INT_PTR pAssemblyLoadContextToBindWithin,
Expand Down
4 changes: 4 additions & 0 deletions src/coreclr/binder/inc/bindresult.hpp
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Expand Up @@ -56,12 +56,16 @@ namespace BINDER_SPACE

const AttemptResult* GetAttempt(bool foundInContext) const;

SString& GetDiagnosticInfo() { return m_diagnosticInfo; }
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@AaronRobinsonMSFT AaronRobinsonMSFT Apr 28, 2026

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Can we avoid this abstract? I'd imagine a method to return a LPCWSTR and then one to set the current SString. Sharing out a private SString field is a long standing bad thing.


protected:
bool m_isContextBound;
ReleaseHolder<Assembly> m_pAssembly;

AttemptResult m_inContextAttempt;
AttemptResult m_applicationAssembliesAttempt;

SString m_diagnosticInfo;
};
};

Expand Down
4 changes: 2 additions & 2 deletions src/coreclr/binder/inc/customassemblybinder.h
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Expand Up @@ -23,7 +23,7 @@ class CustomAssemblyBinder final : public AssemblyBinder
BINDER_SPACE::Assembly** ppExistingAssemblyOnConflict = nullptr) override;

HRESULT BindUsingAssemblyName(BINDER_SPACE::AssemblyName* pAssemblyName,
BINDER_SPACE::Assembly** ppAssembly) override;
BINDER_SPACE::Assembly** ppAssembly, SString* pDiagnosticInfo = NULL) override;

AssemblyLoaderAllocator* GetLoaderAllocator() override;

Expand All @@ -49,7 +49,7 @@ class CustomAssemblyBinder final : public AssemblyBinder
void ReleaseLoadContext();

private:
HRESULT BindAssemblyByNameWorker(BINDER_SPACE::AssemblyName *pAssemblyName, BINDER_SPACE::Assembly **ppCoreCLRFoundAssembly);
HRESULT BindAssemblyByNameWorker(BINDER_SPACE::AssemblyName *pAssemblyName, BINDER_SPACE::Assembly **ppCoreCLRFoundAssembly, SString *pDiagnosticInfo = NULL);

DefaultAssemblyBinder *m_pDefaultBinder;

Expand Down
5 changes: 3 additions & 2 deletions src/coreclr/binder/inc/defaultassemblybinder.h
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Expand Up @@ -21,7 +21,7 @@ class DefaultAssemblyBinder final : public AssemblyBinder
BINDER_SPACE::Assembly** ppExistingAssemblyOnConflict = nullptr) override;

HRESULT BindUsingAssemblyName(BINDER_SPACE::AssemblyName* pAssemblyName,
BINDER_SPACE::Assembly** ppAssembly) override;
BINDER_SPACE::Assembly** ppAssembly, SString* pDiagnosticInfo = NULL) override;

AssemblyLoaderAllocator* GetLoaderAllocator() override
{
Expand All @@ -48,7 +48,8 @@ class DefaultAssemblyBinder final : public AssemblyBinder
BINDER_SPACE::AssemblyName *pAssemblyName,
BINDER_SPACE::Assembly **ppCoreCLRFoundAssembly,
bool excludeAppPaths,
BINDER_SPACE::Assembly **ppExistingAssemblyOnFailure = nullptr);
BINDER_SPACE::Assembly **ppExistingAssemblyOnFailure = nullptr,
SString *pDiagnosticInfo = NULL);
};

#endif // __DEFAULT_ASSEMBLY_BINDER_H__
6 changes: 4 additions & 2 deletions src/coreclr/binder/inc/failurecache.hpp
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Expand Up @@ -28,8 +28,10 @@ namespace BINDER_SPACE
~FailureCache();

HRESULT Add(/* in */ SString &assemblyNameorPath,
/* in */ HRESULT hrBindResult);
HRESULT Lookup(/* in */ SString &assemblyNameorPath);
/* in */ HRESULT hrBindResult,
/* in */ const SString &diagnosticInfo);
HRESULT Lookup(/* in */ SString &assemblyNameorPath,
/* out */ SString *pDiagnosticInfo = NULL);
void Remove(/* in */ SString &assemblyName);
};
};
Expand Down
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