// Returns null if an assembly of an equivalent identity has not been added previously, otherwise returns the reference that added it.
// - Both assembly names are strong (have keys) and are either equal or FX unified
// - Both assembly names are weak (no keys) and have the same simple name.
private MetadataReference TryAddAssembly(AssemblyIdentity identity, MetadataReference boundReference, DiagnosticBag diagnostics, CommonLocation location,
ref Dictionary <string, List <ReferencedAssemblyIdentity> > referencesBySimpleName)
{
if (referencesBySimpleName == null)
{
referencesBySimpleName = new Dictionary <string, List <ReferencedAssemblyIdentity> >(StringComparer.OrdinalIgnoreCase);
}
List <ReferencedAssemblyIdentity> sameSimpleNameIdentities;
string simpleName = identity.Name;
if (!referencesBySimpleName.TryGetValue(simpleName, out sameSimpleNameIdentities))
{
referencesBySimpleName.Add(simpleName, new List <ReferencedAssemblyIdentity> {
new ReferencedAssemblyIdentity(identity, boundReference)
});
return(null);
}
ReferencedAssemblyIdentity equivalent = default(ReferencedAssemblyIdentity);
if (identity.IsStrongName)
{
foreach (var other in sameSimpleNameIdentities)
{
// only compare strong with strong (weak is never equivalent to strong and vice versa)
if (other.Identity.IsStrongName && identity.IsEquivalent(other.Identity))
{
equivalent = other;
break;
}
}
}
else
{
foreach (var other in sameSimpleNameIdentities)
{
// only compare weak with weak
if (!other.Identity.IsStrongName && WeakIdentityPropertiesEquivalent(identity, other.Identity))
{
equivalent = other;
break;
}
}
}
if (equivalent.Identity == null)
{
sameSimpleNameIdentities.Add(new ReferencedAssemblyIdentity(identity, boundReference));
return(null);
}
// equivalent found - ignore and/or report an error:
if (identity.IsStrongName)
{
Debug.Assert(equivalent.Identity.IsStrongName);
// versions migth have been unified for a Framework assembly:
if (identity != equivalent.Identity)
{
// Dev11 C# reports an error
// Dev11 VB keeps both references in the compilation and reports an ambiguity error when a symbol is used.
// BREAKING CHANGE in VB: we report an error for both languages
// Multiple assemblies with equivalent identity have been imported: '{0}' and '{1}'. Remove one of the duplicate references.
MessageProvider.ReportDuplicateMetadataReferenceStrong(diagnostics, location, boundReference, identity, equivalent.MetadataReference, equivalent.Identity);
}
// If the versions match exactly we ignore duplicates w/o reporting errors while
// Dev11 C# reports:
// error CS1703: An assembly with the same identity '{0}' has already been imported. Try removing one of the duplicate references.
// Dev11 VB reports:
// Fatal error BC2000 : compiler initialization failed unexpectedly: Project already has a reference to assembly System.
// A second reference to 'D:\Temp\System.dll' cannot be added.
}
else
{
MessageProvider.ReportDuplicateMetadataReferenceWeak(diagnostics, location, boundReference, identity, equivalent.MetadataReference, equivalent.Identity);
}
Debug.Assert(equivalent.MetadataReference != null);
return(equivalent.MetadataReference);
}