Let CustomTypeMarshaller implementation use Span of unmanaged type for Value marshalling (#67172)

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Analyzers/CustomTypeMarshallerAnalyzer.cs

@@ -588,7 +588,7 @@ public void AnalyzeMarshallerType(SymbolAnalysisContext context)
                         inConstructor = ctor;
                     }
 
-                    if (callerAllocatedSpanConstructor is null && ManualTypeMarshallingHelper.IsCallerAllocatedSpanConstructor(ctor, type, _spanOfByte, marshallerData.Kind))
+                    if (callerAllocatedSpanConstructor is null && ManualTypeMarshallingHelper.IsCallerAllocatedSpanConstructor(ctor, type, _spanOfT, marshallerData.Kind, out _))
                     {
                         callerAllocatedSpanConstructor = ctor;
                     }

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/Strings.resx

@@ -354,10 +354,10 @@
     <value>The specified custom marshaller direction for '{0}' is invalid</value>
   </data>
   <data name="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription" xml:space="preserve">
-    <value>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</value>
+    <value>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</value>
   </data>
   <data name="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage" xml:space="preserve">
-    <value>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</value>
+    <value>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</value>
   </data>
   <data name="ValueInRequiresOneParameterConstructorDescription" xml:space="preserve">
     <value>A 'Value'-kind native type must provide a one-parameter constructor taking the managed type as a parameter</value>

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.cs.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.de.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.es.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.fr.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.it.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.ja.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.ko.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.pl.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.pt-BR.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.ru.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.tr.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.zh-Hans.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Resources/xlf/Strings.zh-Hant.xlf

@@ -505,13 +505,13 @@
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorDescription">
-        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span&lt;byte&gt;' as parameters</target>
+        <source>A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">A 'Value'-kind native type that supports the 'CallerAllocatedBuffer' feature must provide a two-parameter constructor taking the managed type and a 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
-        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</source>
-        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span&lt;byte&gt;' as parameters</target>
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
         <note />
       </trans-unit>
       <trans-unit id="ValueInRequiresOneParameterConstructorDescription">

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/ManagedTypeInfo.cs

@@ -51,6 +51,7 @@ public static ManagedTypeInfo CreateTypeInfoForTypeSymbol(ITypeSymbol type)
 
     public sealed record SpecialTypeInfo(string FullTypeName, string DiagnosticFormattedName, SpecialType SpecialType) : ManagedTypeInfo(FullTypeName, DiagnosticFormattedName)
     {
+        public static readonly SpecialTypeInfo Byte = new("byte", "byte", SpecialType.System_Void);
         public static readonly SpecialTypeInfo Int32 = new("int", "int", SpecialType.System_Int32);
         public static readonly SpecialTypeInfo Void = new("void", "void", SpecialType.System_Void);
 

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/ManualTypeMarshallingHelper.cs

@@ -194,19 +194,37 @@ public static bool HasToManagedMethod(ITypeSymbol nativeType, ITypeSymbol manage
         public static bool IsCallerAllocatedSpanConstructor(
             IMethodSymbol ctor,
             ITypeSymbol managedType,
-            ITypeSymbol spanOfByte,
-            CustomTypeMarshallerKind variant)
+            ITypeSymbol spanOfT,
+            CustomTypeMarshallerKind variant,
+            out ITypeSymbol? spanElementType)
         {
+            spanElementType = null;
             if (variant == CustomTypeMarshallerKind.LinearCollection)
             {
                 return ctor.Parameters.Length == 3
-                && SymbolEqualityComparer.Default.Equals(managedType, ctor.Parameters[0].Type)
-                && SymbolEqualityComparer.Default.Equals(spanOfByte, ctor.Parameters[1].Type)
-                && ctor.Parameters[2].Type.SpecialType == SpecialType.System_Int32;
+                    && SymbolEqualityComparer.Default.Equals(managedType, ctor.Parameters[0].Type)
+                    && IsSpanOfUnmanagedType(ctor.Parameters[1].Type, spanOfT, out spanElementType)
+                    && spanElementType.SpecialType == SpecialType.System_Byte
+                    && ctor.Parameters[2].Type.SpecialType == SpecialType.System_Int32;
             }
             return ctor.Parameters.Length == 2
                 && SymbolEqualityComparer.Default.Equals(managedType, ctor.Parameters[0].Type)
-                && SymbolEqualityComparer.Default.Equals(spanOfByte, ctor.Parameters[1].Type);
+                && IsSpanOfUnmanagedType(ctor.Parameters[1].Type, spanOfT, out spanElementType);
+
+            static bool IsSpanOfUnmanagedType(ITypeSymbol typeToCheck, ITypeSymbol spanOfT, out ITypeSymbol? typeArgument)
+            {
+                typeArgument = null;
+                if (typeToCheck is INamedTypeSymbol namedType
+                    && SymbolEqualityComparer.Default.Equals(spanOfT, namedType.ConstructedFrom)
+                    && namedType.TypeArguments.Length == 1
+                    && namedType.TypeArguments[0].IsUnmanagedType)
+                {
+                    typeArgument = namedType.TypeArguments[0];
+                    return true;
+                }
+
+                return false;
+            }
         }
 
         public static IMethodSymbol? FindGetPinnableReference(ITypeSymbol type)

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Marshalling/AttributedMarshallingModelGeneratorFactory.cs

@@ -165,7 +165,7 @@ private IMarshallingGenerator CreateCustomNativeTypeMarshaller(TypePositionInfo
                 {
                     throw new MarshallingNotSupportedException(info, context);
                 }
-                marshallingStrategy = new StackallocOptimizationMarshalling(marshallingStrategy, marshalInfo.BufferSize.Value);
+                marshallingStrategy = new StackallocOptimizationMarshalling(marshallingStrategy, marshalInfo.BufferElementType.Syntax, marshalInfo.BufferSize.Value);
             }
 
             if ((marshalInfo.MarshallingFeatures & CustomTypeMarshallerFeatures.UnmanagedResources) != 0)

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Marshalling/ICustomNativeTypeMarshallingStrategy.cs

@@ -252,11 +252,13 @@ public IEnumerable<StatementSyntax> GeneratePinStatements(TypePositionInfo info,
     internal sealed class StackallocOptimizationMarshalling : ICustomNativeTypeMarshallingStrategy
     {
         private readonly ICustomNativeTypeMarshallingStrategy _innerMarshaller;
+        private readonly TypeSyntax _bufferElementType;
         private readonly int _bufferSize;
 
-        public StackallocOptimizationMarshalling(ICustomNativeTypeMarshallingStrategy innerMarshaller, int bufferSize)
+        public StackallocOptimizationMarshalling(ICustomNativeTypeMarshallingStrategy innerMarshaller, TypeSyntax bufferElementType, int bufferSize)
         {
             _innerMarshaller = innerMarshaller;
+            _bufferElementType = bufferElementType;
             _bufferSize = bufferSize;
         }
 
@@ -274,16 +276,16 @@ public IEnumerable<StatementSyntax> GenerateMarshalStatements(TypePositionInfo i
         {
             if (StackAllocOptimizationValid(info, context))
             {
-                // byte* <managedIdentifier>__stackptr = stackalloc byte[<_bufferSize>];
+                // <bufferElementType>* <managedIdentifier>__stackptr = stackalloc <bufferElementType>[<_bufferSize>];
                 yield return LocalDeclarationStatement(
                 VariableDeclaration(
-                    PointerType(PredefinedType(Token(SyntaxKind.ByteKeyword))),
+                    PointerType(_bufferElementType),
                     SingletonSeparatedList(
                         VariableDeclarator(GetStackAllocPointerIdentifier(info, context))
                             .WithInitializer(EqualsValueClause(
                                 StackAllocArrayCreationExpression(
                                         ArrayType(
-                                            PredefinedType(Token(SyntaxKind.ByteKeyword)),
+                                            _bufferElementType,
                                             SingletonList(ArrayRankSpecifier(SingletonSeparatedList<ExpressionSyntax>(
                                                 LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(_bufferSize))
                                             ))))))))));
@@ -332,7 +334,7 @@ public IEnumerable<ArgumentSyntax> GetNativeTypeConstructorArguments(TypePositio
                     ObjectCreationExpression(
                         GenericName(Identifier(TypeNames.System_Span),
                             TypeArgumentList(SingletonSeparatedList<TypeSyntax>(
-                                PredefinedType(Token(SyntaxKind.ByteKeyword))))))
+                                _bufferElementType))))
                     .WithArgumentList(
                         ArgumentList(SeparatedList(new ArgumentSyntax[]
                         {

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/MarshallingAttributeInfo.cs

@@ -143,6 +143,7 @@ public enum CustomTypeMarshallerPinning
         CustomTypeMarshallerFeatures MarshallingFeatures,
         CustomTypeMarshallerPinning PinningFeatures,
         bool UseDefaultMarshalling,
+        ManagedTypeInfo? BufferElementType,
         int? BufferSize) : MarshallingInfo;
 
     /// <summary>
@@ -178,6 +179,7 @@ public enum CustomTypeMarshallerPinning
             MarshallingFeatures,
             PinningFeatures,
             UseDefaultMarshalling,
+            SpecialTypeInfo.Byte,
             BufferSize
         );
 
@@ -672,6 +674,26 @@ private CountInfo CreateCountInfo(AttributeData marshalUsingData, ImmutableHashS
                     GetMarshallingInfo(elementType, useSiteAttributes, indirectionLevel + 1, inspectedElements, ref maxIndirectionDepthUsed));
             }
 
+            ManagedTypeInfo? bufferElementTypeInfo = null;
+            if (customTypeMarshallerData.Value.Features.HasFlag(CustomTypeMarshallerFeatures.CallerAllocatedBuffer))
+            {
+                ITypeSymbol? bufferElementType = null;
+                INamedTypeSymbol spanOfT = _compilation.GetTypeByMetadataName(TypeNames.System_Span_Metadata)!;
+                foreach (IMethodSymbol ctor in nativeType.Constructors)
+                {
+                    if (ManualTypeMarshallingHelper.IsCallerAllocatedSpanConstructor(ctor, type, spanOfT, customTypeMarshallerData.Value.Kind, out bufferElementType))
+                        break;
+                }
+
+                if (bufferElementType is null)
+                {
+                    _diagnostics.ReportInvalidMarshallingAttributeInfo(attrData, nameof(SR.ValueInCallerAllocatedBufferRequiresSpanConstructorMessage), nativeType.ToDisplayString(), type.ToDisplayString());
+                    return NoMarshallingInfo.Instance;
+                }
+
+                bufferElementTypeInfo = ManagedTypeInfo.CreateTypeInfoForTypeSymbol(bufferElementType);
+            }
+
             return new NativeMarshallingAttributeInfo(
                 ManagedTypeInfo.CreateTypeInfoForTypeSymbol(nativeType),
                 toNativeValueMethod is not null ? ManagedTypeInfo.CreateTypeInfoForTypeSymbol(toNativeValueMethod.ReturnType) : null,
@@ -679,6 +701,7 @@ private CountInfo CreateCountInfo(AttributeData marshalUsingData, ImmutableHashS
                 customTypeMarshallerData.Value.Features,
                 pinning,
                 UseDefaultMarshalling: !isMarshalUsingAttribute,
+                bufferElementTypeInfo,
                 customTypeMarshallerData.Value.BufferSize);
         }
 

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/Strings.resx

 <?xml version="1.0" encoding="utf-8"?>
 <root>
-  <!--
-    Microsoft ResX Schema
-
+  <!-- 
+    Microsoft ResX Schema 
+    
     Version 2.0
-
-    The primary goals of this format is to allow a simple XML format
-    that is mostly human readable. The generation and parsing of the
-    various data types are done through the TypeConverter classes
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
     associated with the data types.
-
+    
     Example:
-
+    
     ... ado.net/XML headers & schema ...
     <resheader name="resmimetype">text/microsoft-resx</resheader>
     <resheader name="version">2.0</resheader>
@@ -26,36 +26,36 @@
         <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
         <comment>This is a comment</comment>
     </data>
-
-    There are any number of "resheader" rows that contain simple
+                
+    There are any number of "resheader" rows that contain simple 
     name/value pairs.
-
-    Each data row contains a name, and value. The row also contains a
-    type or mimetype. Type corresponds to a .NET class that support
-    text/value conversion through the TypeConverter architecture.
-    Classes that don't support this are serialized and stored with the
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
     mimetype set.
-
-    The mimetype is used for serialized objects, and tells the
-    ResXResourceReader how to depersist the object. This is currently not
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
     extensible. For a given mimetype the value must be set accordingly:
-
-    Note - application/x-microsoft.net.object.binary.base64 is the format
-    that the ResXResourceWriter will generate, however the reader can
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
     read any of the formats listed below.
-
+    
     mimetype: application/x-microsoft.net.object.binary.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
             : and then encoded with base64 encoding.
-
+    
     mimetype: application/x-microsoft.net.object.soap.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
             : and then encoded with base64 encoding.
 
     mimetype: application/x-microsoft.net.object.bytearray.base64
-    value   : The object must be serialized into a byte array
+    value   : The object must be serialized into a byte array 
             : using a System.ComponentModel.TypeConverter
             : and then encoded with base64 encoding.
     -->
@@ -198,4 +198,7 @@
   <data name="RuntimeMarshallingMustBeDisabled" xml:space="preserve">
     <value>Runtime marshalling must be disabled in this project by applying the 'System.Runtime.InteropServices.DisableRuntimeMarshallingAttribute' to the assembly to enable marshalling this type.</value>
   </data>
+  <data name="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage" xml:space="preserve">
+    <value>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</value>
+  </data>
 </root>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.cs.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.de.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.es.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.fr.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.it.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.ja.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.ko.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.pl.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.pt-BR.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.ru.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.tr.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.zh-Hans.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Resources/xlf/Strings.zh-Hant.xlf

@@ -137,6 +137,11 @@
         <target state="new">Specified type is not supported by source-generated P/Invokes</target>
         <note />
       </trans-unit>
+      <trans-unit id="ValueInCallerAllocatedBufferRequiresSpanConstructorMessage">
+        <source>The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</source>
+        <target state="new">The type '{0}' specifies that it supports 'In' marshalling with the 'CallerAllocatedBuffer' feature for '{1}' but does not provide a one-parameter constructor that takes a '{1}' and 'Span' of an 'unmanaged' type as parameters</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomTypeMarshallerFixerTests.cs

@@ -983,6 +983,53 @@ struct Native
             await VerifyCS.VerifyCodeFixAsync(source, source);
         }
 
+        [Fact]
+        public async Task NativeTypeWithIncorrectStackallocConstructor_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x100)]
+struct {|#0:Native|}
+{
+    public Native(S managed) {}
+    public Native(S s, int i) {}
+    public Native(S s, Span<object> buffer) {}
+}";
+            string fixedSource = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[CustomTypeMarshaller(typeof(S), Direction = CustomTypeMarshallerDirection.In, Features = CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x100)]
+struct Native
+{
+    public Native(S managed) {}
+    public Native(S s, int i) {}
+    public Native(S s, Span<object> buffer) {}
+
+    public Native(S managed, Span<byte> buffer)
+    {
+        throw new NotImplementedException();
+    }
+}";
+            await VerifyCS.VerifyCodeFixAsync(source,
+                fixedSource,
+                VerifyCS.Diagnostic(ValueInCallerAllocatedBufferRequiresSpanConstructorRule).WithLocation(0).WithArguments("Native", "S"));
+        }
+
         [Fact]
         public async Task NativeTypeWithOnlyStackallocConstructor_ReportsDiagnostic()
         {

src/libraries/System.Runtime.InteropServices/tests/TestAssets/SharedTypes/NonBlittable.cs

@@ -132,11 +132,11 @@ public void FreeNative()
         private bool isNullString;
 
         public Utf16StringMarshaller(string str)
-            : this(str, default(Span<byte>))
+            : this(str, default(Span<ushort>))
         {
         }
 
-        public Utf16StringMarshaller(string str, Span<byte> buffer)
+        public Utf16StringMarshaller(string str, Span<ushort> buffer)
         {
             isNullString = false;
             if (str is null)
@@ -147,8 +147,8 @@ public Utf16StringMarshaller(string str, Span<byte> buffer)
             }
             else if ((str.Length + 1) < buffer.Length)
             {
-                span = MemoryMarshal.Cast<byte, ushort>(buffer);
-                str.AsSpan().CopyTo(MemoryMarshal.Cast<byte, char>(buffer));
+                span = buffer;
+                str.AsSpan().CopyTo(MemoryMarshal.Cast<ushort, char>(buffer));
                 // Supplied memory is in an undefined state so ensure
                 // there is a trailing null in the buffer.
                 span[str.Length] = '\0';
@@ -192,7 +192,7 @@ public void FreeNative()
             Marshal.FreeCoTaskMem((IntPtr)allocated);
         }
     }
-    
+
     [CustomTypeMarshaller(typeof(string), Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer, BufferSize = 0x100)]
     public unsafe ref struct Utf8StringMarshaller
     {

src/samples/LibraryImportGeneratorSample/LibraryImportGeneratorSample.csproj

@@ -6,6 +6,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <LangVersion>preview</LangVersion>
     <Nullable>enable</Nullable>
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
 
     <!-- Indicate to the compiler to output generated files to disk. Source addded
          by the LibraryImportGenerator can be found in the intermediate directory. -->