Allow Error and Result<()> to be the same size as HRESULT

.github/workflows/msrv-windows-result.yml

@@ -27,3 +27,5 @@ jobs:
         run: rustup update --no-self-update ${{ matrix.rust }} && rustup default ${{ matrix.rust }}
       - name: Check
         run: cargo check -p windows-result --all-features
+      - name: Check Default Features
+        run: cargo check -p windows-result

crates/libs/core/Cargo.toml

@@ -36,3 +36,4 @@ windows-interface = { path = "../interface",  version = "0.57.0" }
 [features]
 default = ["std"]
 std = []
+slim-errors = ["windows-result/slim-errors"]

crates/libs/result/Cargo.toml

@@ -13,6 +13,8 @@ categories = ["os::windows-apis"]
 [features]
 default = ["std"]
 std = []
+# slim-errors reduces the size of Error (and Result<()>) to that of a single HRESULT
+slim-errors = []
 
 [lints]
 workspace = true
@@ -21,6 +23,9 @@ workspace = true
 default-target = "x86_64-pc-windows-msvc"
 targets = []
 
+[dependencies]
+static_assertions = "1.0"
+
 [dependencies.windows-targets]
 version = "0.52.5"
 path = "../targets"

crates/libs/result/src/bstr.rs

@@ -0,0 +1,50 @@
+use super::*;
+
+#[repr(transparent)]
+pub struct BasicString(*const u16);
+
+impl BasicString {
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    pub fn len(&self) -> usize {
+        if self.0.is_null() {
+            0
+        } else {
+            unsafe { SysStringLen(self.0) as usize }
+        }
+    }
+
+    pub fn as_wide(&self) -> &[u16] {
+        let len = self.len();
+        if len != 0 {
+            unsafe { core::slice::from_raw_parts(self.as_ptr(), len) }
+        } else {
+            &[]
+        }
+    }
+
+    pub fn as_ptr(&self) -> *const u16 {
+        if !self.is_empty() {
+            self.0
+        } else {
+            const EMPTY: [u16; 1] = [0];
+            EMPTY.as_ptr()
+        }
+    }
+}
+
+impl Default for BasicString {
+    fn default() -> Self {
+        Self(core::ptr::null_mut())
+    }
+}
+
+impl Drop for BasicString {
+    fn drop(&mut self) {
+        if !self.0.is_null() {
+            unsafe { SysFreeString(self.0) }
+        }
+    }
+}