From 83b3dfb9420f748125205de355c86a87e2f7c3ec Mon Sep 17 00:00:00 2001
From: Andrew Arnott <andrew.arnott@microsoft.com>
Date: Thu, 13 Oct 2022 06:28:00 -0600
Subject: [PATCH] Add `BSTR.Length` property

Closes #717
---
 src/Microsoft.Windows.CsWin32/Generator.cs    |  1 +
 .../templates/BSTR.cs                         |  7 ++++++
 test/GenerationSandbox.Tests/BasicTests.cs    | 23 +++++++++++++++++++
 3 files changed, 31 insertions(+)
 create mode 100644 src/Microsoft.Windows.CsWin32/templates/BSTR.cs

diff --git a/src/Microsoft.Windows.CsWin32/Generator.cs b/src/Microsoft.Windows.CsWin32/Generator.cs
index 5f62fafb..69de9f5f 100644
--- a/src/Microsoft.Windows.CsWin32/Generator.cs
+++ b/src/Microsoft.Windows.CsWin32/Generator.cs
@@ -4157,6 +4157,7 @@ private StructDeclarationSyntax DeclareTypeDefStruct(TypeDefinition typeDef, Typ
         {
             case "BSTR":
                 members = members.AddRange(this.CreateAdditionalTypeDefBSTRMembers());
+                members = members.AddRange(this.ExtractMembersFromTemplate(name.Identifier.ValueText));
                 break;
             case "PWSTR":
                 members = members.AddRange(this.CreateAdditionalTypeDefPWSTRMembers());
diff --git a/src/Microsoft.Windows.CsWin32/templates/BSTR.cs b/src/Microsoft.Windows.CsWin32/templates/BSTR.cs
new file mode 100644
index 00000000..e65b0ea8
--- /dev/null
+++ b/src/Microsoft.Windows.CsWin32/templates/BSTR.cs
@@ -0,0 +1,7 @@
+internal partial struct BSTR
+{
+	/// <summary>
+	/// Gets the length of the BSTR in characters.
+	/// </summary>
+	internal unsafe int Length => this.Value is null ? 0 : checked((int)(*(((uint*)this.Value) - 1) / sizeof(char)));
+}
diff --git a/test/GenerationSandbox.Tests/BasicTests.cs b/test/GenerationSandbox.Tests/BasicTests.cs
index 906d8691..1855f2a9 100644
--- a/test/GenerationSandbox.Tests/BasicTests.cs
+++ b/test/GenerationSandbox.Tests/BasicTests.cs
@@ -80,6 +80,29 @@ public void BSTR_ToString_Null()
         Assert.Null(bstr.ToString());
     }
 
+    [Theory]
+    [InlineData("")]
+    [InlineData("h")]
+    [InlineData("hello")]
+    public void BSTR_Length(string value)
+    {
+        BSTR bstr = (BSTR)Marshal.StringToBSTR(value);
+        try
+        {
+            Assert.Equal(value.Length, bstr.Length);
+        }
+        finally
+        {
+            Marshal.FreeBSTR(bstr);
+        }
+    }
+
+    [Fact]
+    public void BSTR_Length_Null()
+    {
+        Assert.Equal(0, default(BSTR).Length);
+    }
+
     [Fact]
     public unsafe void BSTR_ImplicitConversionTo_ReadOnlySpan()
     {