Allow Error and Result<()> to be the same size as HRESULT (#3126)

Author: sivadeilra

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

@@ -27,3 +27,15 @@ 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
+      - name: Check Slim Errors
+        shell: pwsh
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $env:RUSTFLAGS = '--cfg=windows_slim_errors'
+
+          # This will show the size of Error, which lets us confirm that RUSTFLAGS was set.
+          cargo test -p windows-result --lib -- --nocapture --test-threads=1
+
+          cargo check -p windows-result

Cargo.toml

@@ -16,4 +16,4 @@ exclude = [
 [workspace.lints.rust]
 rust_2018_idioms = { level = "warn", priority = -1 }
 missing_docs = "warn"
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(windows_raw_dylib, windows_debugger_visualizer)'] }
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(windows_raw_dylib, windows_debugger_visualizer, windows_slim_errors)'] }

crates/libs/result/.natvis

@@ -1,13 +1,21 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
   <Type Name="windows_result::error::Error">
     <Expand>
-      <ExpandedItem>code</ExpandedItem>
-      <Item Name="[info]">info</Item>
+      <ExpandedItem>(HRESULT)code.__0.__0,hr</ExpandedItem>
+      <Item Name="[code]">(HRESULT)code.__0.__0</Item>
+      <Item Name="[info]">info.ptr</Item>
     </Expand>
   </Type>
 
   <Type Name="windows_result::hresult::HRESULT">
     <DisplayString>{(HRESULT)__0}</DisplayString>
   </Type>
+
+  <Type Name="windows_result::error::error_info::ErrorInfo">
+    <DisplayString>ErrorInfo</DisplayString>
+    <Expand>
+      <Item Name="[object]">*(void**)&amp;ptr</Item>
+    </Expand>
+  </Type>
 </AutoVisualizer>

crates/libs/result/Cargo.toml

@@ -21,6 +21,9 @@ 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) }
+        }
+    }
+}