Make more of the HSTRING methods const (#2078)

.github/workflows/build.yml

@@ -64,7 +64,7 @@ jobs:
     name: Check windows
     strategy:
       matrix:
-        rust: [1.59.0, stable, nightly]
+        rust: [1.64.0, stable, nightly]
         runs-on:
           - windows-2019
           - ubuntu-latest

crates/libs/implement/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2018"
 license = "MIT OR Apache-2.0"
 description = "The implement macro for the windows crate"
 repository = "https://github.com/microsoft/windows-rs"
-rust-version = "1.61"
+rust-version = "1.64"
 
 [package.metadata.docs.rs]
 default-target = "x86_64-pc-windows-msvc"

crates/libs/interface/Cargo.toml

@@ -6,7 +6,7 @@ authors = ["Microsoft"]
 license = "MIT OR Apache-2.0"
 description = "The interface macro for the windows crate"
 repository = "https://github.com/microsoft/windows-rs"
-rust-version = "1.61"
+rust-version = "1.64"
 
 [package.metadata.docs.rs]
 default-target = "x86_64-pc-windows-msvc"

crates/libs/windows/Cargo.toml

@@ -9,7 +9,7 @@ description = "Rust for Windows"
 repository = "https://github.com/microsoft/windows-rs"
 documentation = "https://microsoft.github.io/windows-docs-rs/"
 readme = "../../../docs/readme.md"
-rust-version = "1.59"
+rust-version = "1.64"
 
 [package.metadata.docs.rs]
 default-target = "x86_64-pc-windows-msvc"

crates/libs/windows/src/core/strings/hstring.rs

@@ -3,44 +3,43 @@ use super::*;
 /// A WinRT string ([HSTRING](https://docs.microsoft.com/en-us/windows/win32/winrt/hstring))
 /// is reference-counted and immutable.
 #[repr(transparent)]
-pub struct HSTRING(*mut Header);
+pub struct HSTRING(Option<std::ptr::NonNull<Header>>);
 
 impl HSTRING {
     /// Create an empty `HSTRING`.
     ///
     /// This function does not allocate memory.
     pub const fn new() -> Self {
-        Self(std::ptr::null_mut())
+        Self(None)
     }
 
     /// Returns `true` if the string is empty.
-    pub fn is_empty(&self) -> bool {
+    pub const fn is_empty(&self) -> bool {
         // An empty HSTRING is represented by a null pointer.
-        self.0.is_null()
+        self.0.is_none()
     }
 
     /// Returns the length of the string.
-    pub fn len(&self) -> usize {
-        if self.is_empty() {
-            return 0;
+    pub const fn len(&self) -> usize {
+        if let Some(header) = self.get_header() {
+            header.len as usize
+        } else {
+            0
         }
-
-        unsafe { (*self.0).len as usize }
     }
 
     /// Get the string as 16-bit wide characters (wchars).
-    pub fn as_wide(&self) -> &[u16] {
+    pub const fn as_wide(&self) -> &[u16] {
         unsafe { std::slice::from_raw_parts(self.as_ptr(), self.len()) }
     }
 
     /// Returns a raw pointer to the `HSTRING` buffer.
-    pub fn as_ptr(&self) -> *const u16 {
-        if self.is_empty() {
+    pub const fn as_ptr(&self) -> *const u16 {
+        if let Some(header) = self.get_header() {
+            header.data
+        } else {
             const EMPTY: [u16; 1] = [0];
             EMPTY.as_ptr()
-        } else {
-            let header = self.0;
-            unsafe { (*header).data }
         }
     }
 
@@ -80,7 +79,16 @@ impl HSTRING {
 
         // Write a 0 byte to the end of the buffer.
         std::ptr::write((*ptr).data.offset((*ptr).len as isize), 0);
-        Self(ptr)
+        Self(std::ptr::NonNull::new(ptr))
+    }
+
+    const fn get_header(&self) -> Option<&Header> {
+        if let Some(header) = &self.0 {
+            // TODO: this can be replaced with `as_ref` in future: https://github.com/rust-lang/rust/issues/91822
+            unsafe { Some(&*(header.as_ptr() as *const Header)) }
+        } else {
+            None
+        }
     }
 }
 
@@ -104,11 +112,11 @@ impl Default for HSTRING {
 
 impl Clone for HSTRING {
     fn clone(&self) -> Self {
-        if self.is_empty() {
-            return Self::new();
+        if let Some(header) = self.get_header() {
+            Self(std::ptr::NonNull::new(header.duplicate()))
+        } else {
+            Self::new()
         }
-
-        unsafe { Self((*self.0).duplicate()) }
     }
 }
 
@@ -118,12 +126,14 @@ impl Drop for HSTRING {
             return;
         }
 
-        unsafe {
-            let header = std::mem::replace(&mut self.0, std::ptr::null_mut());
+        if let Some(header) = self.0.take() {
             // REFERENCE_FLAG indicates a string backed by static or stack memory that is
             // thus not reference-counted and does not need to be freed.
-            if (*header).flags & REFERENCE_FLAG == 0 && (*header).count.release() == 0 {
-                heap_free(header as *mut std::ffi::c_void);
+            unsafe {
+                let header = header.as_ref();
+                if header.flags & REFERENCE_FLAG == 0 && header.count.release() == 0 {
+                    heap_free(header as *const _ as *mut _);
+                }
             }
         }
     }

crates/libs/windows/src/core/weak_ref_count.rs

@@ -13,11 +13,11 @@ impl WeakRefCount {
     }
 
     pub fn add_ref(&self) -> u32 {
-        self.0.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |count_or_pointer| (!is_weak_ref(count_or_pointer)).then(|| count_or_pointer + 1)).map(|u| u as u32 + 1).unwrap_or_else(|pointer| unsafe { TearOff::decode(pointer).strong_count.add_ref() })
+        self.0.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |count_or_pointer| (!is_weak_ref(count_or_pointer)).then_some(count_or_pointer + 1)).map(|u| u as u32 + 1).unwrap_or_else(|pointer| unsafe { TearOff::decode(pointer).strong_count.add_ref() })
     }
 
     pub fn release(&self) -> u32 {
-        self.0.fetch_update(Ordering::Release, Ordering::Relaxed, |count_or_pointer| (!is_weak_ref(count_or_pointer)).then(|| count_or_pointer - 1)).map(|u| u as u32 - 1).unwrap_or_else(|pointer| unsafe {
+        self.0.fetch_update(Ordering::Release, Ordering::Relaxed, |count_or_pointer| (!is_weak_ref(count_or_pointer)).then_some(count_or_pointer - 1)).map(|u| u as u32 - 1).unwrap_or_else(|pointer| unsafe {
             let tear_off = TearOff::decode(pointer);
             let remaining = tear_off.strong_count.release();
 
@@ -214,7 +214,7 @@ impl TearOff {
             .fetch_update(Ordering::Acquire, Ordering::Relaxed, |count| {
                 // Attempt to acquire a strong reference count to stabilize the object for the duration
                 // of the `QueryInterface` call.
-                (count != 0).then(|| count + 1)
+                (count != 0).then_some(count + 1)
             })
             .map(|_| {
                 // Let the object respond to the upgrade query.

crates/tests/core/tests/hstring.rs

@@ -3,6 +3,7 @@ use windows::core::*;
 
 #[test]
 fn hstring_works() {
+    assert_eq!(std::mem::size_of::<HSTRING>(), std::mem::size_of::<usize>());
     let empty = HSTRING::new();
     assert!(empty.is_empty());
     assert!(empty.is_empty());

crates/tools/windows/src/main.rs

@@ -47,7 +47,7 @@ description = "Rust for Windows"
 repository = "https://github.com/microsoft/windows-rs"
 documentation = "https://microsoft.github.io/windows-docs-rs/"
 readme = "../../../docs/readme.md"
-rust-version = "1.59"
+rust-version = "1.64"
 
 [package.metadata.docs.rs]
 default-target = "x86_64-pc-windows-msvc"

crates/tools/yml/src/main.rs

@@ -215,7 +215,7 @@ jobs:
     name: Check windows
     strategy:
       matrix:
-        rust: [1.59.0, stable, nightly]
+        rust: [1.64.0, stable, nightly]
         runs-on:
           - windows-2019
           - ubuntu-latest